aboutsummaryrefslogtreecommitdiffstats
path: root/doc/info/mds.texinfo
blob: 18c1b9d3bfef02eb26e02f5a1a910bc29e3af1c8 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
\input texinfo   @c -*-texinfo-*-

@c %**start of header
@setfilename mds.info
@settitle mds
@afourpaper
@documentencoding UTF-8
@documentlanguage en
@finalout
@c %**end of header


@dircategory Graphics environment
@direntry
* mds: (mds).                        The micro-display server
@end direntry


@copying
Copyright @copyright{} 2014 Mattias Andrée

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled
``GNU Free Documentation License''.
@end quotation
@end copying

@ifnottex
@node Top
@top mds -- The micro-display server
@insertcopying
@end ifnottex

@titlepage
@title mds
@subtitle The micro-display server
@author by Mattias Andrée (maandree)

@page
@c @center `'
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents



@menu
* Overview::                        Brief overview of @command{mds}.
* Architecture::                    Architectural overview of @command{mds}.
* Protocol::                        The @command{mds} procotol.
* Utilities::                       About @command{mds} utilities.
* Servers::                         About @command{mds} servers.
* Protocols::                       @command{mds} procotols.
* libmdsserver::                    Overview of @command{libmdsserver}.
* mds-base::                        Overview of @command{mds-base}.
* Keyboard Codes::                  Scancodes and keycodes.
* GNU Free Documentation License::  Copying and sharing this manual.
@end menu



@node Overview
@chapter Overview

@command{mds}@footnote{mds stands for micro-display server.}
is a display server protocol and an implementation of said
protocol. What makes @command{mds} stand out is its core
design choice: it is desigend just like a microkernel.
Rather than one, possibly modular, process --- a monolithic
process --- mds is comprised of many small servers, each
exchangable and responsible for one thing.

@command{mds} goal is neither security, performance nor
a perfect graphical experience. @command{mds} is all
about flexibility and freedom 0@footnote{The freedom to run
the program as you wish, for any purpose.}.

The reason for having a display server architectured as a
microkernel is so that components can be added, remove
and replaced online. Additionally, the message passing
between the servers makes it easy to design a system that
lets you make clients that can listen on messages between
the servers and perhaps modify them. This enables you to
do so much more with your display server. Moreover, if
a single part of the system crashes it does not bring down
the whole system, and the crashed server can be respawned
with minor side effects. @command{mds} is architectured
in three layers: a microkernel, a master server and a
collection of servers. And clients are actually located
on the same layer as the servers, because there is no
actual difference, the only thing that separates a server
from a client is for what purpose you run it. @command{mds}'s
kernel is a minimal program that do initialisation of the
display, such as giving it an index and create runtime
files and directories for servers and other programs
to use. Then the kernel creates a domain socket for the
master server and spawns the master server and respawns
it if it crashes. Because of this, if the master server
crashes it will not lose its socket when it is respawned.
The master server than, on its initial spawn, starts
the all servers and other programs that the user have
choosen and then starts accepting connections to it and
coordinates messages between servers and clients. Further,
separating all components into separate processes enables
us to only give the servers the privileges they actually
need, rather than having one program with root privileges
that takes care of everything even things that do not do
require any privileges.

All @command{mds}'s servers, that is all running parts of
@command{mds} except the kernel, are designed so that they
can re-execute themself so that they can be updated online
without any side effects. Servers serialises their state,
saves it to RAM (in a directory created by the kernel),
re-execute themself and loads their serialised state. The
kernel cannot do this because when it has spawned the
master server it has no reason to re-execute, its only mission
is to respawn the master server it if would happen to crash.
It would technically be possible to enable the kernel to
re-execute but it is not worth it as it as no reason to
re-execute, and doing so puts the display server at risk
of crashing.



@node Architecture
@chapter Architecture

@menu
* Layers::                          The layers of the display server.
* Interprocess Communication::      How servers and clients communicate.
@end menu



@node Layers
@section Layers

The @command{mds} display server in architectured in
three layers. The first layer is called the kernel.
The kernel is responsible for acquiring a display
server index@footnote{As with any display server,
the system can have multiple instances of
@command{mds} running at the same time.}, set up
environment variables to indicate which display
server and display server instance is being used,
create a domain socket for the display server and
start the master server and restart it if it crashes,
and then clean up the system when the display server
closes. The kernel only responsible for creating
the domain socket for communication with the display
server, it is not responsible for using it, that
mission falls to the master server.

The second layer is the master server. The master
server has two responsibilities: coordinating
message passing between other servers and clients
@footnote{In @command{mds} their is no functional
distinction between servers and clients, the
distinction is purely semantic.} and starting
other servers.

The third layer is the other servers and clients.
protocolwise there is no specification on how
they are started. But in the reference
implementation of the master server, this is
done by starting a shell script with the
pathname @file{$@{XDG_CONFIG_HOME@}/mdsinitrc}
and the user is responsible for providing the
logic in that shell script.@footnote{Moonstruck
users are allowed to implement this in C
or any other language of their choosing.}
@c Which is better: cray-cray users, lunatic users,
@c moonstruck users, insane users, ballers, madmen,
@c loony tunes?
These servers implements the actual functionality
of the display server.



@node Interprocess Communication
@section Interprocess Communication

Intrinsic to @command{mds} is a powerful
interprocess communication mechanism. Servers
and clients connect to the display server by
connecting to a domain socket served by the
master server. A server or client that has
connected to the display server can do three
things:

@itemize
@item
Request assignment of a unique ID.

@item
Multicast a message.

@item
Join or leave a multicast groups.
@end itemize

Upon assignment of an ID the master server
will automatically place the client in a
multicast group for that specific client.
This automatically multicast group assignment
is done by the master server simply so you
as a debugger do not forget to do so. When
a client is disconnected it will and out a
message to a specific multicast group that
the client, refered to by it's ID, have closed.

A message in the @command{mds} protocol is
comprised of two parts: headers and a payload.
When a client joins a multicast group it is
actually say that it is interested and receiving
broadcasts containing a specific header or a
specific header--value pair, or that it is
interesting in all messages@footnote{This
could be used for logging, possibly spying and
networking.}. Thus a message is automatically
multicasted to groups indicated by its headers.

The multicast groups and receiving of groups
is called interceptions. The interesting
property of interceptions is that they may
be modifying. When a server registers for
message interception it can say that it wants
to be able to modify messages. If this is done
and the server receives a message for which it
has said it want to be able to modify it,
the master server will wait for that server
to respond before it send the message to
the next server in the interception list.
The server can choose to do three things
with a message that it has opted in for
modification of: leave the message as-is,
modify the message, or consume the message.
A message consumption is done by modify
the message to make it empty. A consumed
message will not be send to any further
clients or servers in the interception list.

To make this mechanism sensible, a server or
client can set a priority when it registers
for interception (does not need to be
modifying.) When a message is broadcasted it
will be received by all servers in the
interception except the original sender,
unless it gets consumes. The order in which
the master server sends the message to the
recipients is determined by priority the
servers registed with. The message first sent
to the recipients with highest priority and
last to the recipients with lowestr priority,
and orderd by the priority between those
priorities. Of two or more servers have the
same priority the order in which they will
receive the message, of those recipients,
is arbitrary.

An interesting property of this machanism
is demonstrated in the @command{mds-vt}
server. Unlike most servers @command{mds-vt}
maintains two concurrent connections to
the display. Once @command{mds-vt} receives
a signal from the OS kernel requesting to
switch virtual terminal, @command{mds-vt}
will from one of its connections send
out a message and wait for it to be
received in its other connection and the
let the OS kernel switch virtual terminal.
The secondary connection to the display
has registered interception with lower
priority of the message that the primary
connection broadcasts. This message will
be received by other servers that will
let the message continue to the next
server in the interception list once that
server is ready for the OS kernel to switch
virtual terminal. All of these server has
registered modifying interception of the
message but none will actually modify or
consume the message; it is only used a
mechanism for letting @command{mds-vt} know
when all servers are ready for the switch
without having to know how many they are
and wait for a reply from all of them.



@node Protocol
@chapter Protocol

@menu
* Environment Variables::           Identifying the active display server
* Signals::                         Signalling individual servers
* Filesystem::                      The display server's footprint on the filesystem
* Message Passing::                 Sending messages between servers and clients
* Interception::                    Implementing protocols and writing unanticipated clients
@end menu



@node Environment Variables
@section Environment Variables

A crucial of any display server is letting child
processes know which display server they should
connect to. @command{X.org} does by setting the
environment variable @env{DISPLAY} to
@code{<host>:<display index>}, where @code{<host>}
is empty if the display is one the local machine.
In this tradition @command{mds} does the same thing
with the environment variable @env{MDS_DISPLAY}.

@command{mds} also creates a new process group and
export the new process group ID to the environment
variable @command{MDS_PGROUP}. This process group
can be used to send signals to all @command{mds}
servers collectively.



@node Signals
@section Signals

@command{mds} servers can re-execute into an
updated version of their binary. This can be
used to update display server online after
a new version has been installed. To do this
send the signal @command{SIGUSR1} to the server
you want update. If a server does not support
online updating it will ignore this signal.
If the operating system defines a signal named
@command{SIGUPDATE}, this signal is used
instead of @command{SIGUSR1}.

If you need servers to free up allocated
memory that they do not use, send the signal
@command{SIGDANGER}, or if not defined
@command{SIGRTMAX}. Unimportant servers may
choose to die on @command{SIGDANGER}.



@node Filesystem
@section Filesystem

The @command{mds} kernel creates two directories
for the @command{mds} servers to use: one for
runtime data and one for temporary data.
These directories are named by
@code{MDS_RUNTIME_ROOT_DIRECTORY} and
@code{MDS_STORAGE_ROOT_DIRECTORY}, respectively,
by the header file @file{<libmdsserver/config.h>}.
If the systems runtime data directory is @file{/run}
and transient temporary data directory is @file{/tmp},
and the package name of @command{mds} is @command{mds},
these directories will be @file{/run/mds} and
@file{/tmp/.@{system-directory@}.mds}, respectively.
In @file{/tmp/.@{system-directory@}.mds} the kernel
will create a directory for the display server instance
named @file{.data} prefixed by the display server index.
For example if the display server index is zero,
temporary data may be stored in
@file{/tmp/.@{system-directory@}.mds/0.data}

As defined by @code{SHM_PATH_PATTERN} by
@file{<libmdsserver/config.h>}, when a server
re-executes itself it will marshal its state to
the POSIX shared memory unit named
@file{/.proc-pid-%ji}, where @file{%ji}
@footnote{@code{%ji} is the pattern in @code{*printf}
functions for the data type @code{intmax_t}.} is
replaced with the process ID of the server. This
file will be bound to the pathname
@file{/dev/shm/.proc-pid-%ji} if POSIX shared
memory is stored in @file{/dev/shm} by the
operating system.

In @code{MDS_RUNTIME_ROOT_DIRECTORY} the kernel
will create two files. @file{.pid} and @file{.socket},
both prefixed with the display server index
@footnote{@file{0.pid} and @file{0.socket} if
the display server index is 0.}. The @file{.pid}
file contains the process ID of the display server
and is used by the kernel to figure out whether
an display server index is still in use or just
not properly cleaned up. Of course it can be used
by any program to find the process ID of the
kernel process of a display server instance.
The @file{.socket} is the domain socket used
for communication with the display server and
its servers and clients.



@node Message Passing
@section Message Passing

Message passing over domain sockets is the
underlaying technique for communicating with
the display server. To communicate with the
display server in the local machine a process
must connect to the domain socket created by
the display server kernel as named in
@ref{Filesystem}.

Clients should request a unique ID when it
connects to the display server.@footnote{There
is seldom a reason for servers to do this.}
To do this the client sends

@example
Command: assign-id\n
Message ID: 0\n
\n
@end example

where @code{\n} is an LF-line break.
The value on the @code{Message ID} line
does not need to be 0, but servers and
clients often start with 0 and count
upwards. The value is however bound to
an unsigned 32-bit integer. All message
must contain this @code{Message ID} header,
otherwise the message is considered corrupt
and is ignored.

The empty line signifies the end of the
header list, and in this case the end of
the message. But a message may contain
payload beneath this empty line. To
include a payload, add the header
@code{Length} that says how many bytes
the payload is comprised of.

A header must contain a header name and
header value without any trailing or
leading spaces, and `: ' (colon, one
regular blank space) exactly delimits
the name and the value.

When the master server receives this
@code{Command: assign-id} message it
will assign the client a unique ID
and send it to the client.@footnote{The
master server is the only server than
can address the client uniquely before
it has an ID, so this part can only
be implement in the master server.}
If the client already has an ID, it
will send back that ID to the client.
This response consists of two headers
@code{ID assignment} and @code{In
response to}, containing the client's
new (or possibly already assigned) ID
and the value that was in the
@code{Message ID} header, respectively.
For example:

@example
ID assignment: 0:1\n
In response to: 0\n
\n
@end example

Notice that the master server never
includes @code{Message ID} in message
originating from it.

As seen in this example, the client ID
consists of two integers delimited by
a colon (`:'). Both of these integers
are unsigned 32-bit integers. This is
done this way because unsigned 64-bit
integers are forbidden because it is
not supportable natively be some
programming languages.

Before a has gotten a unique client ID
assigned to it, it will be `0:0'.

If a client gets disconnected from the
master server, the master server will
sends out a signal header message.
This header will be @code{Client closed}
and contain ID of the client that closed.
For example:

@example
Client closed: 0:1\n
\n
@end example

Be aware that if a server or client
closes and does not have a unique client
ID, this message will be:

@example
Client closed: 0:0\n
\n
@end example

Once a client has an unique client ID
assigned to it, it should always include
the header @code{Client ID} in its
messages. The value of @code{Client ID}
should be the client's ID. If a server
wants to address this client, it should
include the header @code{To} with the
value set to the recipient's client ID.
Be aware that such message may not be
sent to that recipient uniquely, any
server or client is free to sign up
for receive of such message, any messages
or message contain any other header or
header--value pair that may also be
included in the header.



@node Interception
@section Interception

As discussed in @ref{Interprocess Communication},
interception in the primary feature of
@command{mds}'s message passing system.
Not only does it enable servers to select
which message it wants to receive in order
to provide it's service. It also enables
clients to do anything, things that was
never anticipated. As an exaple of its
power, @command{mds} does not provide any
protocol for taking screenshots or recording
a session. Instead, a screenshot application
signs up for messages pass between the
compositor and presentation servers, and
simply requests that the compositor resends
the screen, a feature intended for the
presentation servers. A screen recoding
application would do the same and just
hang on and record all message passed
between the servers.

If you want your server or client to
receive all messages passed around in
the display server, simply sign up for
all messages:

@example
Command: intercept\n
Message ID: 0\n
\n
@end example

But if you only want messages contain
the header @code{Command}, include
that header in the payload of the message:

@example
Command: intercept\n
Message ID: 0\n
Length: 8\n
\n
Command\n
@end example

It is allowed to include multiple headers.
You can also be more strict, and require
a specific value for a header, for example:

@example
Command: intercept\n
Message ID: 0\n
Length: 16\n
\n
Command: get-vt\n
@end example

You may mix these two types of requirements
freely. Your client will receive any message
that satisfies at least one of the requirements,
these requirements may be split into multiple
message or coalesced into one message; but
you cannot request to include receive a message
if multiple requirements are satisfied.

Alternatively you can choose to stop receiving
message that satisfies requirements. For example:

@example
Command: intercept\n
Stop: yes\n
Message ID: 1\n
Length: 16\n
\n
Command: get-vt\n
@end example

Or stop receiving all messages:

@example
Command: intercept\n
Stop: yes\n
Message ID: 1\n
\n
@end example

Note that this will stop you from receiving
messages contain the @code{To} header addressed
to you until you request to receiving such
messages again.

When you sign up for message you may request
to be able to modify them before that are
send to the next client in the list of client
that should receive them. To do this include
the header--value pair @code{Modifying: yes}:

@example
Command: intercept\n
Modifying: yes\n
Message ID: 0\n
Length: 30\n
\n
Command: keyboard-enumeration\n
@end example

It is up to the client to keep track of
which message that it may modify. When
you receive a message that you can modify
you must respond when you are done with
the message.

For example, if you have signed up
for @code{Command: keyboard-enumeration}
with the ability to modify such messages
and the message

@example
Command: keyboard-enumeration\n
To: 0:1\n
In response to: 2\n
Message ID: 1\n
Length: 7\n
\n
kernel\n
@end example

is send from a server, you may receive
it as

@example
Command: keyboard-enumeration\n
To: 0:1\n
In response to: 2\n
Message ID: 1\n
Length: 7\n
Modify ID: 4\n
\n
kernel\n
@end example

Be aware that the @code{Modify ID} may
be included even if you have not signed
up to be able to modify the message,
it is enough that one client before you
has or it was originally included
@footnote{You may however not include
this header when you send out an
orginal message.}.

If you receive the message as such
and want to add the line
@code{on-screen-keyboard-20376} to
the payload should send out:
@footnote{The first line containing
starting with @code{Message ID} is an
example, it should be whatever is
appropriate for your client.}

@example
Modify ID: 4\n
Message ID: 2\n
Modify: yes\n
Length: 127\n
\n
Command: keyboard-enumeration\n
To: 0:1\n
In response to: 2\n
Message ID: 1\n
Length: 32\n
Modify ID: 4\n
\n
kernel\n
on-screen-keyboard-20376\n
@end example

If you however decide not to modify
the message send out

@example
Modify ID: 4\n
Message ID: 2\n
Modify: no\n
\n
@end example

There is also a third option:
to consume to the message. This
stops any further clients from
receiving the message. This is
done by modifying the message
into an empty message:

@example
Modify ID: 4\n
Message ID: 2\n
Modify: yes\n
\n
@end example

You may choose to include the
header--value pair @code{Length: 0},
it is however redundant and
discouraged.

This mechanism of being able to
modify message does not make much
sense unless you can control in
the order the clients receive
messages. This is done with what
is called priority. The higher
priority you have, the earlier
you will receive the message. The
default priority is zero, and the
priority is bound to a signed
64-bit integer. If you want to
be able to list yourself in
@code{Command: keyboard-enumeration}
message, you should sign up
with a positive priority since
the final recipient or requested
the enumeration will receive it
with priority zero. Therefore
you should sign up for such message
with a message like:
@footnote{4611686018427387904 is
halfway to the maximium value.}

@example
Command: intercept\n
Modifying: yes\n
Priority: 4611686018427387904\n
Message ID: 0\n
Length: 30\n
\n
Command: keyboard-enumeration\n
@end example



@node Utilities
@chapter Utilities

@menu
* mds-respawn::                     The server immortality protocol.
* mds-reg::                         The registry control command.
* mds-clip::                        The clipboard control command.
* mds-screenshot::                  The screenshot utility.
* mds-slay::                        The process killing utility.
* External Utilities::              Suggestion on utilities you can utilise.
@end menu



@node mds-respawn
@section @command{mds-respawn}

@command{mds-respawn} is a utility intended to be used
in @file{$@{XDG_CONFIG_HOME@}/mdsinitrc}. It will spawn
a selected set of servers. If a server it spawns exits
with a bad status, @command{mds-respawn} will respawn it.
@command{mds-respawn} supports two options in the command
line:

@table @option
@item --alarm=SECONDS
Schedule @command{mds-respawn} to die in @var{SECONDS}
seconds. At most 1 minute.

@item --interval=SECONDS
Spawned servers that die twice with @var{SECONDS}
seconds should stop respawning until the signal
@code{SIGUSR2} is send to @command{mds-respawn}.
At most 1 minute.
@end table

Commands for servers to spawn are specified within
curly braces. Each of the braces must be alone its
its own argument. For example:

@example
mds-respawn --interval=5       \
  @{ mds-foo --initial-spawn @}  \
  @{ mds-bar --initial-spawn @}  &
@end example

will spawn and supervise the servers @command{mds-foo}
and @command{mds-bar}. Both spawned with the
argument @option{--initial-spawn}. When a server is
respawed by @command{mds-respawn}, @option{--initial-spawn}
in its argument list will be replaced by
@option{--respawn} to let the server know it is being
respawned.

A server is considered to exit with a failure status
unless it exits with the return value 0 or is terminated
by the signal @code{SIGTERM}.



@node mds-reg
@section @command{mds-reg}

@command{mds-reg} is a utility that can be used to list,
available protocols provided by running servers. It can
also wait for a set of protocols to become available. To
list all available protocols run @command{mds-reg --list}.
And to wait for the protocol @code{foo} run
@command{mds-reg --wait=foo}. To also wait for the protocol
@code{bar} run @command{mds-reg --wait=foo,bar} or
@command{mds-reg --wait=foo --wait=bar}. Both of these
styles can be mixed if you want to wait for even more
protocols.



@node mds-clip
@section @command{mds-clip}

@command{mds-clip} is a utility that can be used to
review the clipboards on the display and manipulate them.
@command{mds-clip} recognises the following options:

@table @option
@item --push
Push non-option arguments from the command line into
the clipboard.

@item --expire=SECONDS
Can be used with @option{--push}. The clip will not
removed after @var{SECONDS} seconds.

@item --pop
Pop items from the clipboard whose indices are listed
in the command line as non-option arguments. The first
index is 1.

@item --clear
Pop all items in the clipboard.

@item --list
List items in the clipboard whose indices are listed
in the command line as non-option arguments. The first
index is 1. If no indicies are specified, all clips
will be listed.

@item --size
Print the size of the clipboard, the number of clips
in the clipboard.

@item --capacity
Print the capacity of the clipboard, the number of
clips the clipboard can hold. If both @option{--size}
and @option{--capacity} is used, the size will be
printed on the first line and the capacity will be
printed on the second line.

@item --resize=CAPACITY
Change the capaciy of the clipboard to @var{CAPACITY}
clips.

@item --stdin
Can be used with @option{--push}. If used, the clip
that should be placed on the top of the clipboard
stack should be read from stdin.

@item --delimiter=DELIMITER
Can be used with @option{--stdin} or @option{--list}.
If used with @option{--stdin}, an line containing
only @var{DELIMITER} will delimit two values that
should be placed in the clipboard. If used with
@option{--list}, a line containing only @var{DELIMITER}
will delimit two values in the output. The default
delimiter for @option{--list} is an empty line.

@item -1
Use the primary clipboard, that is, the text copy
clipboard. This is the default clipboard.

@item -2
Use the secondary clipboard, that is, the text
selection clipboard.

@item -3
Use the tertiary clipboard, that is, the non-text
copy clipboard.
@end table



@node mds-screenshot
@section @command{mds-screenshot}

@command{mds-screenshot} is a simple utility, and
reference implementation there of, that can take a
screeenshot of either the display, a monitor, or a
window with or without its decorating window. It can
also include or exclude the rat cursor or gamma
ramps. @command{mds-screenshot} recognises the
following options:

@table @option
@item --monitor
Take screenshot of the monitor. The rat will
be used to select monitor.

@item --monitor=WINDOW_ID
Take screenshot of the monitor whose root window's
window ID is @var{WINDOW_ID} or has another window
in it whose window ID is @var{WINDOW_ID}.

@item --embed
Take a screenshot of an embedded window.
The rat will be used to select window.

@item --embed=WINDOW_ID
Take a screenshot of an embedded window whose
window ID is @var{WINDOW_ID}.

@item --window
Take a screenshot a window.
The rat will be used to select window.

@item --window=WINDOW_ID
Take a screenshot of a window whose
window ID is @var{WINDOW_ID}.

@item --decoration
Include the window's decoration, if used together
with @option{--window}. Ignored if used without
@option{--window}.

@item --cursor
Include the rat cursor in the screenshot.

@item --gamma
Include the effects of gamma ramps in the screenshot.

@item --low-gamma=LOW_PRIORITY
Include the effects of gamma ramps with a priority
above @var{LOW_PRIORITY} in the screenshot.

@item --high-gamma=HIGH_PRIORITY
Include the effects of gamma ramps with a priority
below @var{HIGH_PRIORITY} in the screenshot. If used
together with @option{--low-gamma=LOW_PRIORITY},
the range [@var{LOW_PRIORITY}, @var{HIGH_PRIORITY}]
will be used.
@end table

Optionally, you can add a non-option argument that
specifies the pathname of the saved file.

If neither @option{--monitor}, @option{--embed} or
@option{--window} is used, a screenshot will be
taked of the display. That is, all monitors.

In case of mirrored outputs, one of the potential
outputs will be selected arbitrarily if
@option{--gamma}, @option{--low-gamma} or
@option{--high-gamma} is used. If neither is used,
the screenshot will be identical for all mirrored
outputs.



@node mds-slay
@section @command{mds-slay}

@command{mds-slay} a utility that can be used to
kill a process by it window or identify the window
ID of a window. @command{mds-slay} recognises the
following options:

@table @option
@item --embed
Kill an embedded window.
The rat will be used to select window.

@item --embed=WINDOW_ID
Kill an embedded window whose
window ID is @var{WINDOW_ID}.

@item --window
Kill a window.
The rat will be used to select window.

@item --window=WINDOW_ID
Kill a window whose
window ID is @var{WINDOW_ID}.

@item --signal=SIGNAL
Send the signal @var{SIGNAL} to the
process owning the selected window.

@item --no-signal
Do not send a signal; only identify the
window.

@item --keep-cursor
Do not change the cursor to a kill cursor.

@item --print
The the ID of the selected window.
@end table



@node External Utilities
@section External Utilities

Servers let you use the option @command{--on-init-fork}
to put the process in the background when it has been
initialised. This can used to spawn that depend on each
other in linear order. For example, if @command{mds-bar}
requires that @command{mds-foo} is initialised before it
can be initialised, you can in
@file{$@{XDG_CONFIG_HOME@}/mdsinitrc} write:

@example
mds-foo --on-init-fork
mds-bar &
@end example

This will start @command{mds-bar} when @command{mds-foo}
has been initialised. However if one of them crashes,
that server will not respawn; to fix this @command{mds-respawn}
can be used, but use of @command{mds-respawn} hinders
the use of @option{--on-init-fork}. Instead you can use
@option{--on-init-sh} and global semaphores. The packages,
and commands, @command{cmdipc} and @command{ipcmd} can be
used for this purpose. We will use @command{cmdipc} in an
example:

@example
S=$(cmdipc -Scx set 1 | cut -d ' ' -f 2)
# Create a System V semaphore with the value 1.

mds-respawn @{ mds-foo --on-init-sh="cmdipc -Sk $S p" @} &
# Spawn `mds-foo` and decrease the semaphore with 1 when initialised.

cmdipc -Sk $S z            # Wait for the semaphore's value to become 0.
cmdipc -Srk $S             # Remove the semaphore.
mds-respawn @{ mds-bar @} &  # Spawn `mds-bar`.
@end example

This is however seldom necessary as @command{mds-reg} can
often be used instead, with more abstraction as you would
only need to specify what servers need to wait for, not
what they provide.

Another useful command (and package) is @command{setpgrp}.
@command{mds} puts itself an all its children in a new
process group. However you may want to put processes that
are not @command{mds} servers or @command{mds} utilities
in a separate process group. @command{setpgrp} can be used
to starta process in a new process group.



@node Servers
@chapter Servers

An @command{mds} display server instance is comprised of
multiple small servers that each implements a small part
of the display server's functionallity. This chapter will
include all servers but the master sever, @command{mds-server}
and the kernel, @command{mds}, the latter of which is not
actually a server.

@menu
* mds-echo::                        The @command{mds-echo} server.
* mds-registry::                    The @command{mds-registry} server.
* mds-vt::                          The @command{mds-vt} server.
* mds-clipboard::                   The @command{mds-clipboard} server.
* mds-iclipboard::                  The @command{mds-iclipboard} server.
* mds-drag::                        The @command{mds-drag} server.
* mds-idrag::                       The @command{mds-idrag} server.
* mds-kkbd::                        The @command{mds-kkbd} server.
* mds-kkbdrate::                    The @command{mds-kkbdrate} server.
* mds-kbd::                         The @command{mds-kbd} server.
* mds-keytrans::                    The @command{mds-keytrans} server.
* mds-keystick::                    The @command{mds-keystick} server.
* mds-kbdbind::                     The @command{mds-kbdbind} server.
* mds-multikey::                    The @command{mds-multikey} server.
* mds-rat::                         The @command{mds-rat} server.
* mds-ratbind::                     The @command{mds-ratbind} server.
* mds-gestures::                    The @command{mds-gestures} server.
* mds-kbd2rat::                     The @command{mds-kbd2rat} server.
* mds-hwcursor::                    The @command{mds-hwcursor} server.
* mds-swcursor::                    The @command{mds-swcursor} server.
* mds-cursorshadow::                The @command{mds-cursorshadow} server.
* mds-cursorgamma::                 The @command{mds-cursorgamma} server.
* mds-hwgamma::                     The @command{mds-hwgamma} server.
* mds-swgamma::                     The @command{mds-swgamma} server.
* mds-coopgamma::                   The @command{mds-coopgamma} server.
* mds-dcvs::                        The @command{mds-dcvs} server.
* mds-colour::                      The @command{mds-colour} server.
* mds-retro-crt::                   The @command{mds-retro-crt} server.
* mds-state::                       The @command{mds-state} server.
* mds-focus::                       The @command{mds-focus} server.
* mds-kill::                        The @command{mds-kill} server.
* mds-screensaver::                 The @command{mds-screensaver} server.
* mds-compositor::                  The @command{mds-compositor} server.
* mds-crtc::                        The @command{mds-crtc} server.
* mds-dri::                         The @command{mds-dri} server.
* mds-fb::                          The @command{mds-fb} server.
* mds-seat::                        The @command{mds-seat} server.
* mds-host::                        The @command{mds-host} server.
* mds-remote::                      The @command{mds-remote} server.
* mds-xmds::                        The @command{mds-xmds} server.
* mds-wmds::                        The @command{mds-wmds} server.
* mds-mmds::                        The @command{mds-mmds} server.
* mds-mdsx::                        The @command{mds-mdsx} server.
* mds-mdsw::                        The @command{mds-mdsw} server.
* mds-mdsm::                        The @command{mds-mdsm} server.
* mds-decorator::                   The @command{mds-decorator} server.
* mds-tile::                        The @command{mds-tile} server.
* mds-stack::                       The @command{mds-stack} server.
* mds-workspace::                   The @command{mds-workspace} server.
* mds-tray::                        The @command{mds-tray} server.
@end menu



@node mds-echo
@section @command{mds-echo}

@command{mds-echo} is a server that echos message that
contain the header--value pair @command{Command: echo}.
This server can be used for debugging and testing as
well as to enable network heartbeats.



@node mds-registry
@section @command{mds-registry}

@command{mds-registry} is a server that keeps a registry
of all protocols that are supported they the sum of all
active servers. It can also be used by other servers to
wait until a protocol has become available.



@node mds-vt
@section @command{mds-vt}

@command{mds-vt} is the server that acquires a virtual
terminal for the display, manages virtual terminal
switches and enables other servers to get access to
the virtual terminal's TTY and informs them of which
virtual terminal the display is located on. It also
enables other servers to switch the virtual terminals
mode to graphical mode or text mode.



@node mds-clipboard
@section @command{mds-clipboard}

@command{mds} has three clipboards, one for copied
text, one for selected text, and one for non-textual
data. Each of these clipboards are stacks, just
like in GNU Emacs. @command{mds-clipboard} implements
these clipboards and automatic removal of outdated
clips. Clips can be configured to expire based on
time or when its originator closes.



@node mds-iclipboard
@section @command{mds-iclipboard}

@command{mds-iclipboard} is an alternative to
@command{mds-clipboard} that can be used to share
clipboard between multiple display servers
instances.



@node mds-drag
@section @command{mds-drag}

@command{mds-drag} is the server that implements
drag-and-drop support.



@node mds-idrag
@section @command{mds-idrag}

@command{mds-idrag} is an alternative to
@command{mds-drag} that lets you drag and drop
between display server instances.



@node mds-kkbd
@section @command{mds-kkbd}

@command{mds-kkbd} implements access to the kernel-based
keyboard. It does not however implement delay and rate
configurations for the kernel-based keyboard as that
requires root privileges. The kernel-based keyboard is
a keyboard that can be accessed by reconfiguring
stdin in a TTY using @code{ioctl} and then read from
stdin. @command{mds-kkbd} does not implement any keyboard
layout, rather it broadcasts scancodes and keycode.
However it can remap keycodes, but not scancodes.



@node mds-kkbdrate
@section @command{mds-kkbdrate}

@command{mds-kkbdrate} is a complemental server to
@command{mds-kkbd}, it implements rate and delay
control for the kernel-based keyboard.



@node mds-kbd
@section @command{mds-kbd}

@command{mds-kbd} is an alternative to
@command{mds-kkbd} and @command{mds-kkbdrate}.
In contrast to @command{mds-kkbd}, @command{mds-kbd}
implements control over individual keybroads rather
than utilising the kernels keyboard drivers to
treats all keyboards a one keyboard. This server
is only useful for multiseat sessions and if you
otherwise actually want to handle the keyboards
individually.



@node mds-keytrans
@section @command{mds-keytrans}

@command{mds-keytrans} is the server than translates
keycodes from @command{mds-kkbd} and @command{mds-kbd},
and third-party alternatives, to characters and other
attributes. It implements the keyboard's layouts including
modifiers, letters, other symbols, dead keys and compose.



@node mds-keystick
@section @command{mds-keystick}

@command{mds-keystick} is a server that can be used
to enable sticky keys.



@node mds-kbdbind
@section @command{mds-kbdbind}

@command{mds-kbdbind} is a server similar to
@command{xbindkeys}. It can be used to run commands
upon selected key combinations, for example starting
@code{dmenu} or change keyboard layout.
@command{mds-kbdbind} can distinguish keyboards
from eachother.



@node mds-multikey
@section @command{mds-multikey}

@command{mds-multikey} is a server that can
bind a key, key combination, or sequence their
of to a sequence of keys or key combinations.
For example, you could bind `<super>x, y' to
simulate that a key `Faux1' is pressed, a key
that does not exist, this key press could be
picked up by @command{mds-kbdbind} to enable
@command{mds-kbdbind} to respond to squences
rather than single keys and single key
combinations. alternatively you could bind
`<super>x' to press `x' a selected number of
times with a short selectable delay between
them; or `<super>x, 5' to press `x' five times.



@node mds-rat
@section @command{mds-rat}

@command{mds-rat} is a server that implements
support of rat (also known as mouse) devices.



@node mds-ratbind
@section @command{mds-ratbind}

@command{mds-ratbind} is a server similar to
@command{mds-kbdbind}. However, @command{mds-ratbind}
respons to rat and rat cursor actions rather
than keyboard actions. It can for example be
used to implement hotcorners.



@node mds-gestures
@section @command{mds-gestures}

@command{mds-gestures} is a server similar to
@command{mds-ratbind}. However it is specialised
to respond to gestures.



@node mds-kbd2rat
@section @command{mds-kbd2rat}

If you do not have a rat or rather use your keyboard,
the server @command{mds-kbd2rat} can be used to
bind keyboard actions to simulate rat actions.
This server is a specialisation of @code{mds-kbdbind},
rather than spawning generic commands it broadcasts
messages without the display server to move the
rat cursor and click on rat buttons. @code{mds-kbdbind}
could be used to do this, but @command{mds-kbd2rat}
will not spawn a new process for each action.



@node mds-hwcursor
@section @command{mds-hwcursor}

@command{mds-hwcursor} is a server that draws
the rat cursor to the monitor on a plane
separate from all other content on the display.
Is less esoteric terms, it implements a hardware
cursor.



@node mds-swcursor
@section @command{mds-swcursor}

@command{mds-swcursor} is a server that draws
the rat cursor to the monitor on the same plane
as all other content on the display. Is less
esoteric terms, it implements a software cursor.



@node mds-cursorshadow
@section @command{mds-cursorshadow}

@command{mds-cursorshadow} is a server that
can be used to decorate the rat cursor with
a configurable shadow.



@node mds-cursorgamma
@section @command{mds-cursorgamma}

@command{mds-cursorgamma} is a server you can
use if you use @command{mds-hwcursor} to, if
not done by the graphics driver, correct the
gamma correction on the hardware cursor using
software gamma ramps. This of courses works
whether you are using hardware or software
gamma ramps for your monitor's gamma correction.
If can even be used if you do not use gamma
correction, in such case, only the cursor
will have its gamma corrected.



@node mds-hwgamma
@section @command{mds-hwgamma}

To enable gamma correction, use the server
@command{mds-hwgamma}. It implements hardware
gamma ramps, that is, gamma ramps assisted
by hardware acceleration.



@node mds-swgamma
@section @command{mds-swgamma}

If your graphics driver does not support
@command{mds-hwgamma}, you can instead use
@command{mds-swgamma}. It implements software
gamma ramps, that is, it will modify each
pixel according to the selected gamma
correction before it is send to the presentation
sever. To accelerate this process,
@command{mds-swgamma} can tell programs how
to modify its colours before sending it; the
programs can then tell @command{mds-swgamma}
not to apply its correction. Programs such
as video players can also use this to tell
the server not to apply gamma correction as
that may cause the video to be played back
to slowly.



@node mds-coopgamma
@section @command{mds-coopgamma}

@command{mds-coopgamma} is a server that
can be used to enable multiple clients to
manipulate the gamma ramps without stepping
on eachothers toes. It does this by letting
clients tell which priority their corrections
has and use this data to chain together there
modifications. For example if one program
wants to apply a red filter to the display
and another program wants to correct the
monitors' gamma, the red filter program will
send lookup tables for the gamma with high
priority and the correction program will
send its lookup tables with low priority.
@command{mds-coopgamma} will then apply the
latter lookup tables on top of the red filter.
The clients can tell @command{mds-coopgamma}
whether it should remove their changes when
they close, or even keep them and wait for
the client to restart.



@node mds-dcvs
@section @command{mds-dcvs}

@command{mds-dcvs} is a server than can be
used to simulate defective colour vision.
That is, it can for example turn the display
greyscale (colour blindness) or add a filter
the simulates deuteranopia or deuteranomaly.
This server is intended for testing that
interfaces are suitable for people with
defective colour vision.



@node mds-colour
@section @command{mds-colour}

@command{mds-colour} is a server that implements
colour names, such as system colours and generic
names, for example `red', whose exact colour can
be configured by the user. A terminal written for
@command{mds} whould look up colours such as `red'
and `light red' and get the colours the terminal
should use by default. Nothing is to be assumed
for such colours, not even that `light red' is in
fact lighter than `dark red', or that `red' is in
fact `red', only that it is the colour the user
wants to see when a colour is supposed to be `red'.
@command{mds-colour} will notify clients when a
colour has been reconfigured, added or removed.

@command{mds-colour} is also responsible for
informing clients on which two colours clients
should use and how to dither them (by percent, not
by pattern). This is useful if only 16-bit colours
can be used, or if only 24-colour can used but
gradients between for example sRGB(255, 255, 255)
and sRGB(254, 254, 254) is to be drawn.



@node mds-retro-crt
@section @command{mds-retro-crt}

@command{mds-retro-crt} is a server that applies
filters used in the terminal emulator
@command{cool-retro-term} to the whole display.



@node mds-state
@section @command{mds-state}

@command{mds-state} is the server that keeps tracks
of the windows' state.



@node mds-focus
@section @command{mds-focus}

@command{mds-focus} is the server focuses windows
and windows' components.



@node mds-kill
@section @command{mds-kill}

@command{mds-kill} is a server that can be used to
send signals to processes by identifying them by
their windows. This server can also be used to
simply identify the process that owns a window.



@node mds-screensaver
@section @command{mds-screensaver}

@command{mds-screensaver} is a server that can be
used to start a screensaver or deactive monitors when
the input devices has not be used for a period of
time provided that no client has disabled this. It
is capable of deactiving single monitors or start
a screensaver on single monitors rather than all
monitors.



@node mds-compositor
@section @command{mds-compositor}

@command{mds-compositor} is the server that composes
the output. It takes output of all windows and arranges
it to one image per monitor and sends it to the presentation
servers, such as @command{mds-dri} and @command{mds-fb}.



@node mds-crtc
@section @command{mds-crtc}

@command{mds-crtc} is the server that identifies
CRTC:s and provide access to them.



@node mds-dri
@section @command{mds-dri}

@command{mds-dri} is a server that displays
content using the Direct Rendering Infrastructure.



@node mds-fb
@section @command{mds-fb}

@command{mds-fd} is a server that displays
content using frame buffers.



@node mds-seat
@section @command{mds-seat}

@command{mds-seat} is a server that enables
seat-sandboxing. It can be used to place
two users on the same machine without them
interfering with each others monitors and
input devices. Servers started below
@command{mds-seat} become shared and servers
started above @command{mds-seat} become
seat-private. @command{mds-seat} can filter
messages from shared servers so only the
appropriate seat receives them.



@node mds-host
@section @command{mds-host}

@command{mds-host} is a server that enables
servers like @command{mds-remote} running
on remote machines to connect to the local
machine and its display server.



@node mds-remote
@section @command{mds-remote}

@command{mds-remote} is a server that enables
you to connect extend a remote @command{mds}
with your local machine. This can be used to
make a display server instance span multiple
computers including its monitors and input
devices.



@node mds-xmds
@section @command{mds-xmds}

@command{mds-xmds} is a server that translates
X.org calls to @command{mds} calls. It can be used
to run X.org-only programs inside @command{mds}.


@node mds-wmds
@section @command{mds-wmds}

@command{mds-wmds} is a server that translates
Wayland calls to @command{mds} calls. It can be used
to run Wayland-only programs inside @command{mds}.


@node mds-mmds
@section @command{mds-mmds}

@command{mds-mmds} is a server that translates
Mir calls to @command{mds} calls. It can be used
to run Mir-only programs inside @command{mds}.



@node mds-mdsx
@section @command{mds-mdsx}

@command{mds-mdsx} is a server that translates
@command{mds} calls to X.org calls. It can be used
to enable @command{mds} specific programs to run
inside the X.org display servers.



@node mds-mdsw
@section @command{mds-mdsw}

@command{mds-mdsw} is a server that translates
@command{mds} calls to Wayland calls. It can be used
to enable @command{mds} specific programs to run
inside the Wayland display servers.



@node mds-mdsm
@section @command{mds-mdsm}

@command{mds-mdsm} is a server that translates
@command{mds} calls to Mir calls. It can be used
to enable @command{mds} specific programs to run
inside the display server Mir.



@node mds-decorator
@section @command{mds-decorator}

@command{mds-decorator} is a server that provides a
simple, reference implementation of a, window decorator.



@node mds-tile
@section @command{mds-tile}

@command{mds-tile} is a server that provides a
simple, reference implementation of a, tiling window manager.



@node mds-stack
@section @command{mds-stack}

@command{mds-stack} is a server that provides a
simple, reference implementation of a, stack window manager.



@node mds-workspace
@section @command{mds-workspace}

@command{mds-workspace} is a server that provides
simple, reference implementation of, workspaces.



@node mds-tray
@section @command{mds-tray}

@command{mds-tray} is a server that provides a
simple, reference implementation of a, status icon tray.



@node Protocols
@chapter Protocols

@menu
* Infrastructure Protocols::        Infrastructure protocols.
* Virtual Terminal Protocols::      Virtual terminal protocols.
* Keyboard Protocols::              Keyboard protocols.
* Clipboard Protocols::             Clipboard protocols.
* Status Icon Protocols::           Status icon protocols.
* Miscellaneous Protocols::         Miscellaneous protocols.
@end menu



@node Infrastructure Protocols
@section Infrastructure Protocols

@menu
* assign-id::                       Assign new ID to client, or fetch current ID.
* intercept::                       Sign up for reception of message.
* register::                        Register availability of a command for which you implement a service.
* reregister::                      Request for reregistration for available commands.
* error::                           Notify a client about a request failure.
@end menu



@node assign-id
@subsection assign-id

@table @asis
@item Identifying header:
@code{Command: assign-id}

@item Action:
Assign new ID to client, or fetch current ID.

@item Purpose:
Assigning ID to clients so server can respond to that client.

@item Compulsivity:
Manditory, part of the core infrastructure.

@item Reference implementation:
@command{mds-server}
@end table



@node intercept
@subsection intercept

@table @asis
@item Identifying header:
@code{Command: intercept}

@item Action:
Sign up for reception of message.

@item Optional header: @code{Stop}
Stop reception of messages if the value for
the header @code{Stop} is @code{yes}.

@item Optional header: @code{Priority}
Signed 64-bit integer of reception priority
(reversed of order).

@item Optional header: @code{Modifying}
Send message asynchronously and await
modification if the value for the header
@code{Modifying} is @code{yes}.

@item Optional header: @code{Length}
Length of the message.

@item Message:
List of headers and header--value-pairs that
qualifies a message for reception, all messages
qualifies if this list is empty.

@item Purpose:
Filter received message for clients and servers.

@item Purpose:
Assigned interception order for modification of messages.

@item Compulsivity:
Manditory, part of the core infrastructure.

@item Reference implementation:
@command{mds-server}
@end table



@node register
@subsection register

@table @asis
@item Identifying header:
@code{Command: register}

@item Action:
Register availability of a command for which you implement a service.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment} header
in response to a @code{Command: assign-id} header.

@item Conditionally required header: @code{Length}
Length of the message.
Required if @code{Action: list} is included in the headers.

@item Optional header: @code{Action}
@table @code
@item remove
Remove availability from registry if the value
of the header @code{Action} is @code{remove}.
@item wait
Wait until listed commands are available if the
value of the header @code{Action} is @code{wait}.
However if a protocol becomes unavailable during this
wait period it will still be counted as available for
this wait action.
@item list
Send a list of availability commands if the value
of the header @code{Action} is @code{list}.
@end table

@item Conditionally optional header: @code{Time to live}
The maximum number of seconds to wait.
Available and optional if @code{Action: wait}
is included in the headers.

@item Message:
List of values for the header @code{Command}
that you implement.

@item Purpose:
Identify supported display server operations.

@item Purpose:
Initialisation process synchronisation.

@item Compulsivity:
Highly recommended, programs may stall a bit from
time to time without it, or at initialisation
depending on the program's implementation.

@item Reference implementation:
@command{mds-registry}
@end table



@node reregister
@subsection reregister

@table @asis
@item Identifying header:
@code{Command: reregister}

@item Action:
Request that all servers resends @code{Command: register}
with either @code{Action: add} or without the @code{Action}
header (does the same thing.)

@item Purpose:
Rebuild registry created with @code{Command: register}
if the registry server crashes.

@item Compulsivity:
Highly recommended, programs may think a protocol is not
supported of the registry server crashes if you do not
implement this in your server.

@item Reference implementation:
@command{mds-registry}.
@end table



@node error
@subsection error

@table @asis
@item Identifying header:
@code{Command: error}

@item Action:
Notify a client about a request failure.

@item Required header: @code{To}
The ID of the client that send a request that failed.

@item Required header: @code{In response to}
The ID of the message whose request failed.

@item Required header: @code{Error}
The errno number of the error, 0 on success if the
message was not an information query. The string
``custom'' can be used if there is not errno number,
optionally followed by a blank space and a number
that identifies the error, this number must be
positive (not zero).

@item Conditionally optional header: @code{Length}
The length of the message.
Available and optional if ``custom'' is used in
the header @code{Error}.

@item Message:
Description of the error, single line, mid-sentence case,
no punctuation in the end, must not be question but rather
it must be a statement.

@item Purpose:
Enable keyboard layout servers to automatically set active
locks when the server starts based on currently active LED:s.

@item Compulsivity:
Optional.
@end table



@node Virtual Terminal Protocols
@section Virtual Terminal Protocols

@menu
* get-vt::                          Get the index of the virtual terminal the server is display on.
* configure-vt::                    Reconfigure the virtual terminal the server is display on.
* switching-vt::                    Notify servers about an ongoing virtual terminal switch.
@end menu



@node get-vt
@subsection get-vt

@table @asis
@item Identifying header:
@code{Command: get-vt}

@item Action:
Get the index of the virtual terminal the server is display on.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment} header
in response to a @code{Command: assign-id} header.

@item Response:
The server will response with the header @code{VT index}
and the index of the virtual terminal the server is
display on in decimal format. Additionally the server
will respond with the header @code{Active} with the value
@code{yes} if the VT is in the foreground or the value
@code{no} if the VT is in the background.

@item Purpose:
Allow programs to be aware of whether the display is in the
foreground or the background.

@item Purpose:
Allow programs to be aware of which VT the server is running on.

@item Purpose:
Allow programs to gain access of the TTY associated with the
VT such that they can use ioctl and similar calls on that TTY.

@item Compulsivity:
Required.

@item Reference implementation:
@code{mds-vt}
@end table



@node configure-vt
@subsection configure-vt

@table @asis
@item Identifying header:
@code{configure-vt}

@item Action:
Reconfigure the virtual terminal the server is display on.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment} header
in response to a @code{Command: assign-id} header.

@item Optional header: @code{graphical}
@table @code
@item yes
Set the TTY graphical mode if the value of the header
@code{graphical} is @code{yes}.
@item no
Set the TTY text mode if the value of the header
@code{graphical} is @code{no}.
@end table
The server implementing this protocol should not set the
TTY to  text mode temporarily when switching TTY. It is
up the the server that set the request for graphical mode
to temporarily switch to text mode when switching TTY.

@item Optional header: @code{exclusive}
@table @code
@item yes
The server may block other process from opening the TTY
if the value of the header @code{exclusive} is @code{yes}.
@item no
The server may not block other process from opening the TTY
if the value of the header @code{exclusive} is @code{no}.
@end table

@item Response:
The server will response with a @code{Command: error}.

@item Purpose:
Allow presentation servers to enter and leave graphical mode.

@item Purpose:
Allow programs to gain access of the TTY associated with the
VT such that they can use ioctl and similar calls on that TTY.

@item Compulsivity:
Required.

@item Reference implementation:
@code{mds-vt}
@end table



@node switching-vt
@subsection switching-vt

@table @asis
@item Identifying header:
@code{Command: switching-vt}

@item Action:
Notify servers about an ongoing virtual terminal switch.

@item Required header: @code{Status}
@table @code
@item deactivating
The kernel wants to place the display in the background
if the value of the header @code{Status} is @code{deactivating}.
@item activating
The kernel wants to place the display in the foreground
if the value of the header @code{Status} is @code{activating}.
@end table

@item Instructions:
When a virtual terminal switch is requested the
server implementing control VT switching involving
the display's virtual terminal will get signaled by
the kernel. Upon this signal the server should
broadcast this command. All servers that need to
release or acquire resouces should intercept this
message with the possibility of modifying it. Once
a server is ready for the VT to switch it should
let the message pass to the next server by telling
the master server that it is no modification to do.
Once all servers are read for the switch the server
that emitted this message should signal the kernel
that it may switch VT. The server should detect
this by setting up secondary contection to the
display that intercepts this message. This connection
should intercept this message with priority @math{-2^{62}},
all servers that need to perform actions before the
switch takes place must have a priority higher than
@math{-2^{62}}, preferably 0.

@item Purpose:
Allow servers to release resources when the user switch
virtual terminal before the terminal actually changes and
to reacquire resources when the virtual terminal become
active again.

@item Compulsivity:
Required.

@item Reference implementation:
@code{mds-vt} and @code{mds-kkbd}
@end table



@node Keyboard Protocols
@section Keyboard Protocols

@menu
* key-sent::                        Announce a keyboard input event.
* enumerate-keyboards::             List available keyboards.
* keyboard-enumeration::            Response to @code{Command: enumerate-keyboards}.
* set-keyboard-leds::               Activate and deactivate LED:s on a keyboard.
* get-keyboard-leds::               List exisiting LED:s on a keyboard and their state.
* keycode-map::                     Remap keyboard keycodes and query current mapping.
* new-keyboard::                    Announce the existance of a new keyboard.
* old-keyboard::                    Announce the removal of an old keyboard.
@end menu



@node key-sent
@subsection key-sent

@table @asis
@item Identifying header:
@command{Command: key-sent}

@item Action:
Announce a keyboard input event.

@item Required header: @code{Keyboard}
Any string that uniquely identifies the keyboard.
@table @asis
@item Purpose:
Enable multi-keyboard aware programs and give at
least on keyboard per seat in a multi-seat environment.
@item Note:
mds-kkbd uses @code{kernel} to indicate that it uses
the kernel and thus lumps together all keyboards.
@end table

@item Required header: @code{Released}
@table @code
@item yes
The value of the header @code{Released} will
be @code{yes} if the key was released.
@item no
The value of the header @code{Released} will be
@code{no} otherwise, that is, held down or pressed.
@end table
Note: pause/break is automatically released directly after
it has been pressed. This is feature built into keyboards
and servers should not try to circumvent this.

@item Required header: @code{Keycode}
An unsigned 14-bit integer identifying the key, may be remapped.

@item Optional header: @code{Scancode}
Either an unsigned 7-bit integer or a single blank space
separated trio of unsigned 7-bit integers, identifying the key.
This is the scancode sent from the keyboard and optionally
unified by the keyboard driver, however with the typed/released
bit zeroed out. This may not be remapped.

@item Optional header: @code{Modifiers}
Single blank space separated list of active modifiers:
@table @code
@item shift
Shift (level 2)
@item ctrl
Control
@item alt
Alternative/Option
@item altgr
Alternative Graphic (level 3)
@item lvl*
@code{*} may be any @math{2^n + 1} integer with
@math{1 < n < 20}.
@item super
Super
@item hyper
Hyper
@item ultra
Ultra
@item caps
Caps (usually a lock key)
@item num
Num (usually a lock key)
@item scrl
Scroll (usually a lock key)
@item top
Top (historical)
@item front
Front (historical)
@item greek
Greek (historical)
@item compose
Compose (rare, it is usally a dead key)
@end table
Any key that has been locked should be prefix with
@code{+}, if the key has been locked by nullified
with non-lock modifier it should be prefixed with
a @code{-}. If no modifier is active or has been
nullified, @code{none} should be used.

@item Optional header: @code{Key}
A textual representation of the key that has been typed or
released, as mapped by the keyboard layout.
@table @code
@item esc
Escape
@item f*
F@code{*} where @code{*} is any integer.
@item sysrq
System Request/Print Screen
@item scrl
Scroll (lock)
@item break
Break/Pause
@item backspace
Backspace
@item tab
Tab
@item return
Return/Enter
@item space
Blank Space
@item menu
Application Menu
@item ins
Insert
@item home
Home
@item pgup
Page Up
@item del
Delete
@item end
End
@item pgdown
Page Down
@item up
Up Arrow
@item left
Left Arrow
@item down
Down Arrow
@item right
Right Arrow
@item shift
Shift (level 2)
@item begin
Begin (keypad 5 in nagivation mode)
@item ctrl
Control
@item alt
Alternative/Option
@item altgr
Alternative Graphic (level 3)
@item lvl*
@code{*} may be any @math{2^n + 1} integer
@math{with 1 < n < 20}.
@item super
Super
@item hyper
Hyper
@item ultra
Ultra
@item caps
Caps (usually a lock key)
@item num
Num (usually a lock key)
@item scrl
Scroll (usually a lock key)
@item top
Top (historical)
@item front
Front (historical)
@item greek
Greek (historical)
@item compose
Compose (usally a dead key)
@item hexcompose
Hex-Compose (usally a dead key)
(Use to create aribitrary characters.)
@item longhexcompose
Long Hex-Compose (usally a dead key)
(Variant of hexcompose for longer codepoints.)
@item modelock
Mode Lock
@item letter *
@code{*} may be any UTF-8 encoded letter.
@end table
Keys that lock/unlock a modifer should be suffixed with a
blank space and a @code{lock}. If the key is a dead key
(even the compose key) should use @code{dead} instead. A
position, either @code{left}, @code{right}, @code{keypad}
or an index, followed by a blank space, should prefix any
key that occurs on multiple position on the keyboard,
unless it only appears on the keypad once and once not on
the keypad. Keys without any meaning should be identified
as @code{unknown}. Modifiers and dead keys should not
affect the value.

@item Optional header: @code{Characters}
UTF-8 encoded string that has been written.

@item Purpose:
Enable the user to use a keyboard, physical or on-screen.

@item Purpose:
Enable programs to send keys as part of a
script or a reply of a recorded session.

@item Compulsivity:
Highly-recommended, a computer is as good
as useless without a keyboard.

@item Reference implementation:
@command{mds-kkbd}, @command{mds-kbd} and @command{mds-keytrans}
@end table



@node enumerate-keyboards
@subsection enumerate-keyboards

@table @asis
@item Identifying header:
@command{Command: enumerate-keyboards}

@item Action:
List available keyboards.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment} header
in response to a @code{Command: assign-id} header.

@item Instructions:
This message must be consumed by the first server that
receives it and implements support for it, and then send
out a @code{Command: keyboard-enumeration} populated with
the keyboard it provide as named in the @code{Keyboard}
header for protocols such as @code{Command: key-sent}.

@item Purpose:
Make it possible for clients to list all available
keyboards so that can be configured individually.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-kkbd} and @command{mds-kbd}
@end table



@node keyboard-enumeration
@subsection keyboard-enumeration

@table @asis
@item Identifying header:
@command{Command: keyboard-enumeration}

@item Action:
Response to @code{Command: enumerate-keyboards}.

@item Required header: @code{To}
The ID received under @code{Client ID} header in
the @code{Command: enumerate-keyboards} message
that triggered this message to be broadcasted

@item Required header: @code{In response to}
The ID received under the @code{Message ID} header
in the @code{Command: enumerate-keyboards} message
that triggered this message to be broadcasted.

@item Required header: @code{Length}
Length of the message.

@item Message:
New line separated list of available keyboards.

@item Instructions:
All keyboard servers should listen for this message
and append all keyboards it implement to the message
once recieved.

@item Purpose:
Make it possible for clients to list all available
keyboards so that can be configured individually

@item Compulsivity:
Required if you implement @command{Command: enumerate-keyboards}.

@item Reference implementation:
@command{mds-kkbd} and @command{mds-kbd}
@end table



@node set-keyboard-leds
@subsection set-keyboard-leds

@table @asis
@item Identifying header:
@command{Command: set-keyboard-leds}

@item Action:
Activate and deactivate LED:s on a keyboard.

@item Required header: @code{Active}
LED:s that should be turned on. If a LED is listed here
but not in @code{Mask} that LED should be turned on if
it is off, and turned off if it is on.

The value is a single blank space separated list of LED:s:
@table @code
@item num
Num lock
@item caps
Caps lock
@item scroll
Scroll lock
@item compose
Compose
@end table
Unsupported LED:s should be silently ignored.

@item Required header: @code{Mask}
LED:s listed here that do not appear in @code{Active}
should be turned off. The value of this header follows
the same rules as for @code{Active}.

@item Optional header: @code{Keyboard}
A string that identifies the keyboard that should be
affected. If omitted all keyboard are affected.

@item Purpose:
Enable keyboard layout servers to activate and deactive
LED:s on the keyboard to indicate active locks.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-kkbd}, @command{mds-kbd} and @command{mds-keytrans}
@end table



@node get-keyboard-leds
@subsection get-keyboard-leds

@table @asis
@item Identifying header:
@command{Command: get-keyboard-leds}

@item Action:
List exisiting LED:s on a keyboard and their state.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment} header
in response to a @code{Command: assign-id} header.

@item Required header: @code{Keyboard}
A string that identifies the keyboard that
should be affected.

@item Response:
The server implementing support for
@code{Command: get-keyboard-leds} for the keyboard
indicated by @code{Keyboard} should send a message
back to the client indicated by rge @code{Client ID}
header (using the @code{To} header) with the headers:
@table @code
@item Active
List of currently turned on LED:s.
@item Present
List of LED:s that the server believes
to be present on the keyboards.
@end table
Both of these headers followes the rules of the
@code{Active} header under @code{Command: set-keyboard-leds}.

@item Purpose:
Enable keyboard layout servers to automatically
set active locks when the server starts based on
currently active LED:s

@item Compulsivity:
Recommended. Required if you implement support for
@code{Command: set-keyboard-leds}. If you do not
support this protocol servers and clients and stall
when they try to get the active LED:s

@item Reference implementation:
@command{mds-kkbd}, @command{mds-kbd} and @command{mds-keytrans}
@end table



@node keycode-map
@subsection keycode-map

@table @asis
@item Identifying header:
@command{Command: keycode-map}

@item Action:
Remap keyboard keycodes and query current mapping.

@item Required header: @code{Action}
@table @code
@item remap
Remap keys if the value of the header @code{Action}
is @code{remap}.
@item reset
Reset all mappings to identity mapping if the value
of the header @code{Action} is @code{reset}.
@item query
Query mapping if the value of the header @code{Action}
is @code{query}.
@end table
Each affected server will send a message format
like that of @code{Action: remap} with current
mapping that are not identity mappings.

@item Optional header: @code{Keyboard}
A string that identifies the keyboard that should be
affected. If omitted all keyboard are affected.

@item Conditionally required header: @code{Client ID}
Your ID, provided by the @code{ID assignment} header
in response to a @code{Command: assign-id} header.
Required if @code{Action: query} is included in the headers.

@item Conditionally optional header: @code{Length}
The length of the message.
Available and optional if @code{Action: remap}
is included in the headers.

@item Message:
Each line contains contains two single space delimited numbers,
the first number is the keycode as determined by the scancode,
the second number is keycode that scancode should generate.
For example, @code{1 1} resets Escape to be mapped to Escape,
and @code{1 59} remaps Escape to F1, while
@example
1 59
59 1
@end example
swaps Escape and F1.

@item Purpose:
Enable the user to swap or replace keys on the keyboard.

@item Purpose:
Enable the user manually correct an incorrectly mapped keyboard.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-kbd} and @command{mds-kkbd}
@end table



@node new-keyboard
@subsection new-keyboard

@table @asis
@item Identifying header:
@command{Command: new-keyboard}

@item Action:
Announce the existance of a new keyboard.

@item Required header: @code{Length}
The length of the message.

@item Message:
List of strings that identifies the keyboards
that have been added.

@item Purpose:
Enable servers and clients to detect new keyboards.

@item Compulsivity:
Recommended.

@item Reference implementation:
@command{mds-kbd} and @command{mds-kkbd}
@end table



@node old-keyboard
@subsection old-keyboard

@table @asis
@item Identifying header:
@command{Command: old-keyboard}

@item Action:
Announce the removal of an old keyboard.

@item Required header: @command{Length}
The length of the message.

@item Message:
List of strings that identifies the keyboards
that have been removed.

@item Purpose:
Enable servers and clients to detect removal of keyboards.

@item Compulsivity:
Recommended.

@item Reference implementation:
@command{mds-kbd}
@end table



@node Clipboard Protocols
@section Clipboard Protocols

@menu
* clipboard::                       Read or manipulate a clipboard.
* clipboard-info::                  Clipboard event announcements.
@end menu



@node clipboard
@subsection clipboard

@table @asis
@item Identifying header:
@command{Command: clipboard}

@item Action:
Read or manipulate a clipboard.

@item Required header: @code{Level}
The clipboard level, an [1, 3] integer:
@table @code
@item 1
Text copied/pasted using the keyboard or a menu item.
(This level is called `primary'.)
@item 2
Text copied/pasted using the rat.
(This level is called `secondary'.)
@item 3
Data to begin with a line describing the data type.
(This level is called `tertiary'.)
@end table

@item Required header: @code{Action}
What to do with the clipboard:
    add)  Write the message to the clipboard
    read)  Read the clipboard
    clear)  Clear all entries on the selected level on the clipboard
    set-size)  Shrink/grow the clipstack
    get-size)  Read the size of the clipstack
      In the reply, the server will send:
        Size: <configured maximum size of the clipstack>
        Used: <number of elements currently in the clipstack>

@item Conditionally required header: @code{Length}
Length of the message.
Required if @code{Action: add} is included in the headers.

@item Conditionally required header: @code{Size}
The maximum number of elements in the clipstack.
Required if @code{Action: set-size} is included in the headers.

@item Conditionally required header: @code{Client ID}
Your ID, provided by the @code{ID assignment} header
in response to a @code{Command: assign-id} header.
Required if @code{Action: read} or @code{Action: read} is
included in the headers, or if @code{Action: add} is
included in the headers and if the header @code{Time to live}
is included and has a value starting with @code{until-death}.

@item Conditionally optional header: @code{Index}
The index of the item in the clipstack, starting at 0.
Available and optional if the @code{Action: read} is
included in the headers.

@item Conditionally optional header: @code{Time to live}
The number of seconds the entry should be available before
it is removed by the server, or:
@table @code
@item until-death
Remove entry when the client closes.
@item until-death #
Remove entry when the client closes,
or @code{#} seconds have elapsed.
@item forever:
Never remove it. (This is the default.)
@end table
The server will always remove the entry when either:
@enumerate 1
@item
it is at the bottom of the clipstack and a new
entry is added to the clipstack, or
@item
@code{Action: clear} is issued for the clipstack.
@end enumerate
The entry will also be removed, unless
@code{Time to live: forever} is used, if the server
crashes or is re-executed.

It is up to the implementation to choose when the
removal actually takes place. For example, the reference
implementation will pop entries that have timed out when
a new entry is added, the reading on the clipstack is
requested or the server is reexecuted, but another
implement may choose to pop entires asynchronously using
another thread or an alarm an pop when @code{SIGARLM} is
received.

Available and optional if the @code{Action: add} is
included in the headers.

@item Message:
The content to add to the clipboard.

@item Purpose:
Enable the user to duplicate content from one process
into another process without requiring those processes
to be aware of eathother to any extent.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-clipboard}
@end table



@node clipboard-info
@subsection clipboard-info

@table @asis
@item Identifying header:
@command{Command: clipboard-info}

@item Action:
The clipboard server sends out some information about
what it is doing, such as automatically removing entires.

@item Included header: @code{Event}
@table @code
@item pop
The value of the header @code{Event} is @code{pop}
when an item in the clipstack has been removed.
If the value header--value-pair is used the following
headers will also be included in the message:
@table @code
@item Level
The clipboard level that has been affected.
@item Popped
The index of the item in the clipstack that has been removed.
@item Size
Configured maximum size of the clipstack.
@item Used
Number of elements currently in the clipstack.
@end table
@item crash
The value of the header @code{Event} is @code{crash} when
the clipboard has been reset because of a software crash.
@end table

@item Purpose:
Enable clients to get notification about changes
to the clipboard, that cannot trivially derived
from @command{Command: clipboard}

@item Compulsivity:
Optional add-on to the clipboard's functionallity.

@item Reference implementation:
@command{mds-clipboard}
@end table



@node Status Icon Protocols
@section Status Icon Protocols

@menu
* add-tray-icon::                   Add a status icons to the status icon tray.
* update-tray-icon::                Change the status of a status icon.
* tray-update::                     Send updates about the status tray to the status icon.
* new-tray::                        Announce the existence of a new status icon trays.
@end menu



@node add-tray-icon
@subsection add-tray-icon

@table @asis
@item Identifying header:
@command{Command: add-tray-icon}

@item Action:
Add a status icons to the status icon tray.

The client should keep in mind that there can be any number of
trays available on the system: zero, one, two or three, ...,
and that it will get a response once from every tray.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment} header
in response to a @code{Command: assign-id} header.

@item Required header: @code{Package}
The name of the package to which the program announced the icon
belongs.

@item Required header: @code{Icon ID}
An ID of the icon that can be used identify the icon, icon ID:s
are not unique, but the combination of a package and a icon ID
should be unque and can be used to ignore already added icons
and hide icons that the user has been configured to be hidden.

@item Required header: @code{Title}
A title describing the icon for the user, used to configured
when icons should be hidden and shown among other configuration.

@item Required header: @code{Icon}
The name or pathname of an icon to use together with the title.

@item Response:
Recipients will respond with a message containing the headers:
@table @code
@item To
Will contain the value of the @code{Client ID} from the
message that triggered this response.
@item In response to
Will contain the value of the @code{Message ID} from the
message that triggered this response.
@item Message ID
Will contain a value as described in @ref{Message Passing}.
@item Socket
Will contain an ID to where the icon should be embeded.
@item Will send update
The value of this header will be @code{yes} if this
message will be followed by a @code{Command: tray-update}
message. Otherwise the value will be @code{no}.
@end table

@item Purpose:
Enable clients to add a small icon that displays the status
of programs, particularly minimised programs and services.

@item Compulsivity:
Optional.
@end table



@node update-tray-icon
@subsection update-tray-icon

@table @asis
@item Identifying header:
@command{Command: update-tray-icon}

@item Action:
Change the status of a status icon.

@item Required header: @code{Status}
@table @code
@item hide
Hide the icon if the value of the
@code{Status} header is @code{hide}.
@item show
Show the icon if the value of the
@code{Status} header is @code{show}.
@item active
The icon is active if the value of
the @code{Status} header is @code{active}.
@item inactive
The icon is inactive if the value of
the @code{Status} header is @code{inactive}.
@end table

@item Purpose:
Enable status trays to automatically hide inactive icons.

@item Purpose:
Hide icons without actually removing them.

@item Compulsivity:
Required if supporting @code{Command: add-tray-icon},
only @code{Status: hide} and @code{Status show} is required.
@end table



@node tray-update
@subsection tray-update

@table @asis
@item Identifying header:
@command{Command: tray-update}

@item Action:
Send updates about the status tray to the status icon.

@item Required header: @code{Socket}
Where the icon is embedded, used to identify the
affected tray.

@item Conditionally required header: @code{Max colour}
The maximum colour component value, for example, if using 24-bit
colour, which component will be 8-bit and the maximum value will
be 255, this also applies to the alpha component.
Required if either for the @code{Colour}-, @code{Foreground}-
or @code{Alpha}-header are used.

@item Conditionally required header: @code{Size}
The width and height, in pixels, the icon should have.
Required if the @code{Length}-header is used,
otherwise this header is optional.

@item Conditionally required header: @code{Has alpha}
@table @code
@item yes
The message contains an alpha channel if the
value of the @code{Has alpha} header is @code{yes}.
@item no
The message does not contain an alpha channel if the
value of the @code{Has alpha} header is @code{no}.
@end table
Required if the @code{Length}-header is used.

@item Conditionally required header: @code{Bytes}
The number of bytes the subpixels used, for example,
24-bit colours will have this set to 1 because each
subpixel has 8 bits, 48-bit colours will have this
set to 2 because each subpixel has 16 bits
Allowed values are: 1, 2, 4 and 8. These values are
used used so that CPU:s with any endianness can be
trivially used as the words sizes are guaranteed to
be supported in C, and mixed/middle-endiannes gets
complicated if we go outside this.
Required if the @code{Length}-header is used.

@item Conditionally optional/required header: @code{Colour}
Single blank space-separated [0, @code{<Max colour>}]
sRGB 3-tuple.
Available and optional if the @code{Length}-header
is not used.
Required if the @code{Foreground}-header but not
@code{Length}-header is used.

@item Conditionally optional header: @code{Foreground}
Single blank space-separated [0, @code{<Max colour>}] sRGB 3-tuple.

@item Optional header: @code{Alpha}
The opacity of the tray.

@item Optional header: @code{Length}
Length of the message.

@item Optional header: @code{Use urgency}
@table @code
@item yes
The icon tray may blink if the value of the
@code{Use urgency} header is @code{yes}.
@item no
The icon tray may not blink if the value of
the @code{Use urgency} header is @code{no}.
@end table

@item Message:
Raw binary encoding of the background image, bytes
are orders: row, pixel, channel (alpha, red, green,
blue), subpixel value (native CPU encoding). The
Alpha channel should be included but ignored if
@code{Has alpha: no}, in such as it is best to set
it to full.

Example image with @code{Bytes: 2},
@code{Has alpha: no} and @code{Size: 3}:
@example
sRGB(x0102, 0, 0), sRGB(0, x0304, 0), sRGB(0, 0, x0506)
sRGB(x0708, 0, 0), sRGB(0, x090A, 0), sRGB(0, 0, x0B0C)
sRGB(x0D0E, 0, 0), sRGB(0, x0F10, 0), sRGB(0, 0, x1112)
@end example

Encoding of example image in hexadecimal representation:
@example
FFFF 0102 0000 0000 FFFF 0000 0304 0000 FFFF 0000 0000 0506
FFFF 0708 0000 0000 FFFF 0000 090A 0000 FFFF 0000 0000 0B0C
FFFF 0D0E 0000 0000 FFFF 0000 0F10 0000 FFFF 0000 0000 1112
@end example

Note that on a big-endian system this would be:
@footnote{x86_64 computers are big-endian.}
@example
FF FF 02 01 0 0 0 0 FF FF 0 0 04 03 0 0 FF FF 0 0 0 0 06 05
FF FF 08 07 0 0 0 0 FF FF 0 0 0A 09 0 0 FF FF 0 0 0 0 0C 0B
FF FF 0E 0D 0 0 0 0 FF FF 0 0 10 0F 0 0 FF FF 0 0 0 0 12 11
@end example

It is up to the networking servers to translate
the encoding between machines.@footnote{The host
translates to big-endian unless they can confirm
that they have the same endianness.}

@item Purpose:
Enable clients to be aware of the appearance of the tray,
such as colours, transparency and background image.

@item Purpose:
Enable clients to be aware of how the user wants
status icons to behave.

@item Compulsivity:
Optional.
@end table



@node new-tray
@subsection new-tray

@table @asis
@item Identifying header:
@command{Command: new-tray}

@item Action:
Announce the existence of a new status icon trays.

@item Purpose:
Allow clients to add their status icons to status icon
trays that have been added to the display after those
programs have started and attempted to add their icons.

@item Compulsivity:
Required if supporting @code{Command: add-tray-icon}.
@end table



@node Miscellaneous Protocols
@section Miscellaneous Protocols

@menu
* echo::                            Echo back a message.
@end menu



@node echo
@subsection echo

@table @asis
@item Identifying header:
@command{Command: echo}

@item Action:
Echo back a message.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment} header
in response to a @code{Command: assign-id} header.

@item Optional header: @code{Length}
Length of the message.

@item Message:
Message to echo.

@item Purpose:
Debugging and testing.

@item Purpose:
Network heartbeat.

@item Compulsivity:
Recommended for network enabled servers.

@item Reference implementation:
@command{mds-echo}
@end table




@node libmdsserver
@chapter libmdsserver

libmdsserver is library written for the reference
implementation of the @command{mds} servers.
llibmdsserver does not contain support or any
protocols, rather it contains auxiliary functions,
macros, data structures such as linked lists and
hash tables, and support the basics of the message
passing protocol: receiving message and decode it
into headers and payloads.

@menu
* Macros::                          Writing macroscopic systems.
* Auxiliary Functions::             Auxiliary functions for servers.
* Data Structures::                 Data structures available in libmdsserver.
@end menu



@node Macros
@section Macros

The header file @file{<libmdsserver/macros.h>}
contains macros for readability and code reduction,
it also contains macros and definitions for portability;
they may either provide portability by nature, or
provide one place to do modifications to port the
system.

@table @asis
@item @code{xsnprintf} [(@code{char buffer[], char* format, ...}) @arrow{} @code{int}]
This is a wrapper for @code{snprintf} that allows you
to forget about the buffer size. When you know how long
a string can be, you should use @code{sprintf}. But when
you cannot know for sure you should use @code{xsnprintf}.
@code{xsnprintf} works exactly as @code{sprintf}, but
it will require that the first argument is defined
using @code{[]} rather than @code{*} because it will use
this to find out how large the buffer is so it can call
@code{snprintf} with that size.

@item @code{eprint} [(@code{const char* format}) @arrow{} @code{int}]
A wrapper for @code{fprintf} that prints a string prefixed
with the value value of @code{*argv} to @code{stderr}.
Because @code{eprintf} naïvely wraps @code{fprintf}, all
`%':s in the string must be duplicated.

@item @code{eprintf} [(@code{const char* format, ...}) @arrow{} @code{int}]
@code{eprint} extends @code{eprint} with variadic arguments
that can be used to insert values into the format string
just like you can do in @code{fprintf}.

@item @code{with_mutex} [(@code{pthread_mutex_t mutex, instructions})]
Wraps @code{instructions} with @code{errno = pthread_mutex_lock(mutex);}
and @code{errno = pthread_mutex_unlock(mutex);}, so a set of
instructions can be invoked inside mutex protection.

@item @code{with_mutex_if} [(@code{pthread_mutex_t mutex, condition, instructions})]
An alternative to @code{with_mutex} where @code{instructions}
is wrapped around @code{if (condition)} which in turn is
wrapped inside the mutex protection.

@item @code{max} [(@code{a, b})]
Returns the higher value of @code{a} and @code{b}.

@item @code{min} [(@code{a, b})]
Returns the lower value of @code{a} and @code{b}.

@item @code{buf_cast} [(@code{char* buffer, type, size_t index})]
Casts @code{buffer} to a @code{type} buffer and
subscripts to the @code{index}:th element. You
can either use this function as a getter or a
setter.

@item @code{buf_set} [(@code{char* buffer, type, size_t index, type variable}) @arrow{} @code{type}]
Wrapper for @code{buf_cast} that sets the addressed
element to the value of @code{variable}.

@item @code{buf_get} [(@code{const char* buffer, type, size_t index, type variable}) @arrow{} @code{type}]
Wrapper for @code{buf_cast} that sets the value of
@code{variable} to the value of the addressed element.

@item @code{buf_next} [(@code{char* buffer, type, size_t count}) @arrow{} @code{char*}]
Increases the pointer @code{buffer} by the size of
@code{type} @code{count} types.

@item @code{buf_prev} [(@code{char* buffer, type, size_t count}) @arrow{} @code{char*}]
Decreases the pointer @code{buffer} by the size of
@code{type} @code{count} types.

@item @code{buf_set_next} [(@code{char* buffer, type, type variable}) @arrow{} @code{type}]
@example
buf_set(buffer, type, 0, variable),
buf_next(buffer, type, 1);
@end example

@item @code{buf_get_next} [(@code{char* buffer, type, type variable}) @arrow{} @code{type}]
@example
buf_get(buffer, type, 0, variable),
buf_next(buffer, type, 1);
@end example

@item @code{strequals} [(@code{const char* a, const char* b}) @arrow{} @code{int}]
Evaluates whether the strings @code{a} and @code{b}
are equals, neither may be @code{NULL}.

@item @code{startswith} [(@code{const char* haystack, const char* needle}) @arrow{} @code{int}]
Evaluates whether the string @code{haystack}
starts with the string @code{needle}, neither
may be @code{NULL}.

@item @code{drop_privileges} [(void) @arrow{} @code{int}]
Sets the effective user to the real user and the
effective group to the real group. This is used
by most servers and ensure that they are not
running with unnecessary privileges. Returns zero
on and only on success.

@item @code{monotone} [(@code{struct timespec* time_slot}) @arrow{} @code{int}]
Stores the time of an unspecified monotonic clock
into @code{time_slot}. Returns zero on and only on
success.

@item @code{close_files} [(@code{condition}) @arrow{} @code{void}]
Closes all file descriptors named by a variable
@code{fd} for which @code{condition} evalutes
to non-zero.

@item @code{xfree} [(@code{void** array, size_t elements}) @arrow{} @code{void}]
Calls @code{free} on the first @code{elements}
elements in @code{array}, and than calls
@code{free} on @code{array}. This macro
requires @code{size_t i} is declared.

@item @code{xmalloc} [(@code{type* var, size_t elements, type}) @arrow{} @code{int}]
Allocates a @code{type*} with @code{elements}
elements and store the allocated pointer to
@code{var}. Returns zero on and only on success.

@item @code{xcalloc} [(@code{type* var, size_t elements, type}) @arrow{} @code{int}]
Allocates a zero-initialised @code{type*} with
@code{elements} elements and store the allocated
pointer to @code{var}. Returns zero on and only
on success.

@item @code{xrealloc} [(@code{type* var, size_t elements, type}) @arrow{} @code{int}]
Reallocates @code{var} and updates the variable
@code{var} accordingly. @code{var} will be
allocated to have @code{elements} elements
of the type @code{type}. If @code{var} is
@code{NULL} a new allocation is created. If
@code{elements} is zero, @code{var} will
be deallocated. Returns zero on and only
on success. On failure, @code{var} will be
@code{NULL}, so you must store the @code{var}
into another variable in case this macro
fails.

@item @code{growalloc} [(@code{type* old, type* var, size_t elements, type}) @arrow{} @code{int}]
When using this macro @code{var} should
be a @code{type*} pointer allocated for
@code{elements} elements of the type
@code{type}. This macro will reallocate
@code{var} to contain twice as many elements
and update @code{elements} accordingly.
On failure nothing changes. You must specify
an auxiliary @code{type*} variable and
specify it in as the @code{old} parameter.
Returns zero on and only on success.

@item @code{xperror} [(@code{const char* str}) @arrow{} @code{void}]
Invokes @code{perror(str)} if and only if
@code{errno} is non-zero and then sets
@code{errno} to zero. @code{str} should
unless you have a specific reason be
@code{*argv}.

@item @code{fail_if} [(@code{condition}) @arrow{} @code{void}]
If @code{condition} is satisfied, a jump
is made to the label @code{pfail}.
@code{pfail:} should be used for calling
@code{xperror} and return @code{-1}.

@item @code{exit_if} [(@code{condition, instructions}) @arrow{} @code{void}]
If @code{condition} is satisfied,
@code{instructions} is invoked and
@code{1} is @code{return}:ed.
@end table

Additionally, @file{<libmdsserver/macros.h>}
defines any missing signal name:
currenly @code{SIGDANGER} and
@code{SIGUPDATE}, and by inclusion of
@file{<libmdsserver/macro-bits.h>}, variants
of @code{atoi} for portability and
convenience:

@table @code
@item atoz
Parse a human readable @code{const char*}
10-radix integer to a @code{size_t}.

@item atosz
Parse a human readable @code{const char*}
10-radix integer to a @code{ssize_t}.

@item atoh
Parse a human readable @code{const char*}
10-radix integer to a @code{short int}.

@item atouh
Parse a human readable @code{const char*}
10-radix integer to an @code{unsigned short int}.

@item atou
Parse a human readable @code{const char*}
10-radix integer to an @code{unsigned int}.

@item atoul
Parse a human readable @code{const char*}
10-radix integer to an @code{unsigned long int}.

@item atoull
Parse a human readable @code{const char*}
10-radix integer to an @code{unsigned long long int}.

@item ato8
Parse a human readable @code{const char*}
10-radix integer to an @code{int8_t}.

@item atou8
Parse a human readable @code{const char*}
10-radix integer to an @code{uint8_t}.

@item ato16
Parse a human readable @code{const char*}
10-radix integer to an @code{int16_t}.

@item atou16
Parse a human readable @code{const char*}
10-radix integer to an @code{uint16_t}.

@item ato32
Parse a human readable @code{const char*}
10-radix integer to an @code{int32_t}.

@item atou32
Parse a human readable @code{const char*}
10-radix integer to an @code{uint32_t}.

@item ato64
Parse a human readable @code{const char*}
10-radix integer to an @code{int64_t}.

@item atou64
Parse a human readable @code{const char*}
10-radix integer to an @code{uint64_t}.

@item atoj
Parse a human readable @code{const char*}
10-radix integer to an @code{intmax_t}.

@item atouj
Parse a human readable @code{const char*}
10-radix integer to an @code{uintmax_t}.
@end table



@node Auxiliary Functions
@section Auxiliary Functions

In the header file @file{<libmdsserver/util.h>},
libmdsserver defines common functions to help
write servers more concisely.

@table @asis
@item @code{parse_client_id} [(@code{const char* str}) @arrow{} @code{uint64_t}]
Convert a client ID string into a client ID integer.

@item @code{getenv_nonempty} [(@code{const char* var}) @arrow{} @code{char*}]
Read an environment variable, return @code{NULL} if
the variable's value is an empty string.

@item @code{prepare_reexec} [(@code{void}) @arrow{} @code{int}]
Prepare the server so that it can re-execute into
a newer version of the executed file.

This is required for two reasons:

@enumerate 1
@item
We cannot use @code{argv[0]} as @env{PATH}-resolution
may cause it to reexec into another pathname, and
maybe to wrong program. Additionally @code{argv[0]}
may not even refer to the program, and @code{chdir}
could also hinter its use.

@item
The kernel appends ` (deleted)' to
@file{/proc/self/exe} once it has been removed,
so it cannot be replaced.
@end enumerate

The function will should be called immediately, it
will store the content of @file{/proc/self/exe}.
Return zero on success and @code{-1} on error.

@item @code{reexec_server} [(@code{int argc, char** argv, int reexeced}) @arrow{} @code{void}]
Re-execute the server. If @code{prepare_reexec}
failed or has not been called, @code{argv[0]}
will be used as a fallback. This functions
has three input parameters:

@table @code
@item argc
The number of elements in @code{argv}.
@item argv
The command line arguments.
@item reexeced
Whether the server has previously been re-executed
@end table

This function only returns on failure.

@item @code{xsigaction} [(@code{int signo, void (*function)(int signo)}) @arrow{} @code{int}]
@code{sigaction} with the same parameters as @code{signal}.
This function should only be used for common @command{mds}
signals and signals that does not require any special settings.
This function may choose to add additional behaviour depending
on the signal, such as blocking other signals. Returns zero
on success and @code{-1} on error.

@item @code{send_message} [(@code{int socket, const char* message, size_t length}) @arrow{} @code{size_t}]
Send the message @code{messsage}, of length @code{length}
over the socket that is access with the file descriptor
@code{socket}. Returns the number of bytes that have been
sent, even on error.

@item @code{strict_atoi} [(@code{const char* str, int* value, int min, int max}) @arrow{} @code{int}]
A version of @code{atoi} that is strict about the syntax
and bounds. Parses the string @code{str} into an @code{int}
and stores it in @code{*value}. If the string is not a
10-radix integer or has a value outside [@code{min},
@code{max}], @code{-1} is returned, otherwise zero is
returned.

@item @code{full_write} [(@code{int fd, const char* buffer, size_t length}) @arrow{} @code{int}]
Send the buffer @code{buffer}, with the length @code{length},
into the file whose file descriptor is @code{fd} and ignores
interruptions. Returns zero on success and @code{-1} on error.

@item @code{full_read} [(@code{int fd, size_t* length}) @arrow{} @code{char*}]
Read the file whose file descriptor is @code{fd} completely
and ignore interruptions. If @code{length} if not @code{NULL},
the length of the read file is stored in @code{*length}.
On success, the read content is retured, on error @code{NULL}
is returned.

@item @code{startswith_n} [(@code{const char*, const char*, size_t, size_t}) @arrow{} @code{int}]
Check whether a string begins with a specific string,
where neither of the strings are necessarily NUL-terminated.
The parameters are:

@table @code
@item const char* haystack
The string that should start with the other string.
@item const char* needle
The string the first string should start with.
@item size_t haystack_n
The length of @code{haystack}.
@item size_t needle_n
The length of @code{needle}.
@end table

Returns 1 if @code{haystack} beings with @code{needle},
otherwise zero is returned.

@item @code{uninterruptable_waitpid} [(@code{pid_t pid, int* restrict status, int options}) @arrow{} @code{pid_t}]
Wrapper around @code{waitpid} that never returns on an
interruption unless it is interrupted one hundred times
within the same clock second. The parameters and return
value are exactly those of @code{waitpid}.
@end table



@node Data Structures
@section Data Structures

libmdsserver provides a small set of datastructures
that are used by the @command{mds} servers. All of
these are written with marshal-functionallity.

@table @asis
@item @code{client_list_t} @{also known as @code{struct client_list}@}
In the header file @file{<libmdsserver/client-list.h>},
libmdsserver defines a dynamic list for storing
client ID:s.

@item @code{linked_list_t} @{also known as @code{struct linked_list}@}
In the header file @file{<libmdsserver/linked-list.h>},
libmdsserver defines a linear array sentinel doubly
linked list.

@item @code{hash_table_t} @{also known as @code{struct hash_table}@}
In the header file @file{<libmdsserver/hash-table.h>},
libmdsserver defines a hash table.

@item @code{fd_table_t} @{also known as @code{struct fd_table}@}
In the header file @file{<libmdsserver/fd-table.h>},
libmdsserver defines a lookup table for small
positive integer keys, intended as an alternative
to hash tables for file descriptors as keys.

@item @code{mds_message_t} @{also known as @code{struct mds_message}@}
In the header file @file{<libmdsserver/mds-message.h>},
libmdsserver defines a data structure for message
between the server or client and the master server,
with the capability of reading for a socket.
@end table

These data structures share a common set of associated
function. However, they do not use the same functions;
they are identical except they are are named with the
associated data structure. We will use @code{X_t}
as an example.

@table @asis
@item @code{X_destroy} [(@code{X_t* restrict this}) @arrow{} @code{void}]
Releases all resouces in @code{*this},
@code{this} itself is however not @code{free}:d.

However, @code{hash_table_destory} and
@code{fd_table_destory} have another signature.

@item @code{X_clone} [(@code{const X_t* restrict this, X_t* restrict out}) @arrow{} @code{int}]
Create a deep duplicate of @code{*this} and store
it in @code{*out}.

@item @code{X_marshal_size} [(@code{const X_t* restrict this}) @arrow{} @code{size_t}]
Calculates the exact allocate size needed for
the parameter @code{data} in the function
@code{X_marshal} if called with the same
@code{this} parameter.

@item @code{X_marshal} [(@code{const X_t* restrict this, char* restrict data}) @arrow{} @code{void}]
Marshal the state of @code{*this} into
@code{data}. The number of bytes that
will be stored (contiguously) in @code{data}
can be calculated with @code{X_marshal_size}.

@item @code{X_unmarshal} [(@code{X_t* restrict this, char* restrict data)}) @arrow{} @code{int}]
Unmarshal a @code{X_t} from
@code{data} into @code{*this}. Returns
zero on success and @code{-1} on error.
The number of bytes read from @code{data}
should, if required, have been precalculated
with @code{X_marshal_size} and stored in an
earlier location of @code{data}.

However, @code{hash_table_unmarshal} and
@code{fd_table_unmarshal} have another signature.
@end table

@menu
* Client List::                     The @code{client_list_t} data structure.
* Linked List::                     The @code{linked_list_t} data structure.
* Tables::                          The @code{fd_table_t} and @code{hash_table_t} data structures.
* Message Structure::               The @code{mds_message_t} data structure.
@end menu



@page
@node Client List
@subsection Client List

To create a client list, allocate a
@code{client_list_t*} or otherwise obtain
a @code{client_list_t*}, and call
@code{client_list_create} with that
pointer as the first argument, and
the @code{0} as the second argument,
unless you want to tune the initialisation.
@code{client_list_create} will return
zero on and only on successful initialisation.
@code{client_list_create}'s second parameter
--- @code{size_t capacity} --- can be used
to specify how many element the list should
initially fit. It will grow when needed, but
it is a good idea to tell it how many elements
you are planning to populate it with.

@code{client_list_t} has two associated
functions for manipulating its content:

@table @asis
@item @code{client_list_add} [(@code{client_list_t* restrict this, uint64_t client}) @arrow{} @code{int}]
This function will add the element @code{client}
to the list @code{*this}, and return zero on
and only on success.

@item @code{client_list_remove} [(@code{client_list_t* restrict this, uint64_t client}) @arrow{} @code{void}]
This function will remove exactly one occurrence,
provided that there is at least on occurrence,
of the element @code{client} for the list @code{*this}.
@end table

The retrieve the number elements stored in
a list, reads its variable @code{size_t size}.
The variable @code{uint64_t* clients} is
used to retrieve stored elements.

@example
void print_elements(client_list_t* this)
@{
  size_t i;
  for (i = 0; i < this->size; i++)
    printf("Element #%zu: %" PRIu64 "\n", i, this->elements[i]);
@}
@end example



@node Linked List
@subsection Linked List

@code{linked_list_t} is a linear array sentinel
doubly linked list. This means that is implemented
using arrays rather than node references. More
specifically, since it is doubly linked@footnote{And
not using XOR-linking.}, it is implemented using
three arrays:

@table @asis
@item @code{values} [@code{size_t*}]
The value stored in each node.

@item @code{next} [@code{ssize_t*}]
The next node for each node, @code{edge} if the current
node is the last node, and @code{LINKED_LIST_UNUSED} if
there is no node on this position.

@item @code{previous} [@code{ssize_t*}]
The previous node for each node, @code{edge} if the current
node is the first node, and @code{LINKED_LIST_UNUSED} if
there is no node on this position.
@end table

The linked list has a sentinel node that joins
boths ends of the list. The index of this node
is stored in the variable @code{edge}.

Because the list is implemented using arrays, if the
number of elements in it shinks considerably, it will
not be able to automatically free unused space. Instead
you must call @code{linked_list_pack}:

@table @asis
@item @code{linked_list_pack} [(@code{linked_list_t* restrict this}) @arrow{} @code{int}]
Pack the list so that there are no reusable positions,
and reduce the capacity to the smallest capacity that
can be used. Note that values (nodes) returned by the
list's methods will become invalid. Additionally (to
reduce the complexity) the list will be defragment so
that the nodes' indices are continuous. This method has
linear time complexity and linear memory complexity.
@end table

To create a linked list list, allocate a
@code{linked_list_t*} or otherwise obtain
a @code{linked_list_t*}, and call
@code{linked_list_create} with that
pointer as the first argument, and
the @code{0} as the second argument,
unless you want to tune the initialisation.
@code{linked_list_create} will return
zero on and only on successful initialisation.
@code{linked_list_create}'s second parameter
--- @code{size_t capacity} --- can be used
to specify how many element the list should
initially fit. It will grow when needed, but
it is a good idea to tell it how many elements
you are planning to populate it with.

There are five functions adding and removing
items to and from a linked list:

@table @asis
@item @code{linked_list_insert_after} [(@code{this, size_t value, ssize_t predecessor}) @arrow{} @code{ssize_t}]
Create a new node with the value @code{value} and add it
to the list @code{*this} after the node @code{predecessor}.
On success, the new node is returned, on failure
@code{LINKED_LIST_UNUSED} is returned.

@item @code{linked_list_insert_before} [(@code{this, size_t value, ssize_t successor}) @arrow{} @code{ssize_t}]
Create a new node with the value @code{value} and add it
to the list @code{*this} before the node @code{successor}.
On success, the new node is returned, on failure
@code{LINKED_LIST_UNUSED} is returned.

@item @code{linked_list_remove_after} [(@code{this, ssize_t predecessor}) @arrow{} @code{ssize_t}]
Remove and return the node in the list @code{*this}
directly after the node @code{predecessor}.

@item @code{linked_list_remove_before} [(@code{this, ssize_t successor}) @arrow{} @code{ssize_t}]
Remove and return the node in the list @code{*this}
directly before the node @code{predecessor}.

@item @code{linked_list_remove} [(@code{this, ssize_t node}) @arrow{} @code{void}]
Remove the node @code{node} from the list @code{*this}.
@end table

The data type for @code{this} is @code{linked_list_t*}
with the @code{restrict} modifier for these and all
other @code{linked_list_t} functions.

Note that if the node @code{this->edge} is removed,
the list become circularly linked and the sentinel
will become missing which renders invokation of all
macros undefined in behaviour. Further note that
removing the sentinel while it is the only node in
the list invokes undefined behaviour. Also note that
addressing non-existing nodes invokes undefined
behaviour.

@file{<libmdsserver/linked_list.h>} defines two
macros for inserting nodes at the edges of a linked
list and two macros for removing nodes from the
edges of a linked list:

@table @asis
@item @code{linked_list_insert_beginning} [(@code{linked_list_t* this, size_t value}) @arrow{} @code{ssize_t}]
Create a new node with the value @code{value} in
insert it to the beginning of the list @code{*this}.
On success, the new node is returned, on failure
@code{LINKED_LIST_UNUSED} is returned.

@item @code{linked_list_insert_end} [(@code{linked_list_t* this, size_t value}) @arrow{} @code{ssize_t}]
Create a new node with the value @code{value} in
insert it to the end of the list @code{*this}.
On success, the new node is returned, on failure
@code{LINKED_LIST_UNUSED} is returned.

@item @code{linked_list_remove_beginning} [(@code{linked_list_t* this}) @arrow{} @code{ssize_t}]
Remove and return the first node in the
list @code{*this}.

@item @code{linked_list_remove_end} [(@code{linked_list_t* this}) @arrow{} @code{ssize_t}]
Remove and return the node node in the
list @code{*this}.
@end table

Additionally the library defines a macro that
wrappes the @code{for} keyword to iterate over
all nodes (except the sentinel node) the a
linked list:

@table @asis
@item @code{foreach_linked_list_node} [(@code{linked_list_t this, ssize_t node})]
Wrapper for `for` keyword that iterates over each
element in the list @code{this}, and store the
current node to the variable named by the parameter
@code{node} for each iterations.

@example
void print_linked_list_values(linked_list_t* list)
@{
  ssize_t node;
  foreach_linked_list_node (*list, node)
    printf("%zi\n", list->values[node]);
@}
@end example

Note that the data type for @code{this} in the
macro is not a pointer.
@end table

There is also a function intended for debugging:

@table @asis
@item @code{linked_list_dump} [(@code{linked_list_t* restrict this, FILE* restrict output}) @arrow{} @code{void}]
The all internal data of the list @code{*this}
into the stream @code{output}.
@end table



@node Tables
@subsection Tables

libmdsserver defines two similar data structures:
@code{fd_table_t} and @code{hash_table_t}. Whenever
a function exists for both data structures we will
write @code{X_table} instead of @code{fd_table} and
@code{hash_table}. Additionally, unless otherwise
stated, a function's parameter named @code{this}
will be of the type @code{hash_table_t*} if the
function's name start with @code{hash_table} and
@code{fd_table_t*} if the function's name start
with @code{fd_table}, with the @code{restrict}
modifier.

@table @asis
@item @code{X_table_create} [(@code{this}) @arrow{} @code{int}]
Initialises @code{*this} so it can be used as a
table. Returns zero on and only on success.

These functions are defined as macros.

@item @code{X_table_create_tuned} [(@code{this, size_t initial_capacity}) @arrow{} @code{int}]
Initialises @code{*this} so it can be used as a
table, and makes its initial capacity at least
@code{initial_capacity}. Returns zero on and only
on success.

@code{hash_table_create_tuned} is defined as a macro.

@item @code{hash_table_create_tuned} [(@code{this, size_t initial_capacity, float load_factor}) @arrow{} @code{int}]
Initialises @code{*this} so it can be used as a
table, and makes its initial capacity at least
@code{initial_capacity} and its load factor
@code{load_factor}. Returns zero on and only
on success.

@item @code{X_table_destroy} [(@code{this, free_func* key_freer, free_func* value_freer}) @arrow{} @code{void}]
Release all resources in the table @code{*this},
but do not @code{free} @code{this} itself.
Should be called even if construction fails.
If @code{keys_freer} is not @code{NULL}, this
function will be called for each key.
If @code{values_freer} is not @code{NULL}, this
function will be called for each value.

@item @code{X_table_contains_value} [(@code{const this, size_t value}) @arrow{} @code{int}]
Check whether the value @code{value} is stored
in the table @code{*this}.

@item @code{X_table_contains_key} [(@code{const this, key}) @arrow{} @code{int}]
Check whether the key @code{code} is used in the
table @code{*this}.

The data type for the parameter @code{key} is
@code{size_t} for @code{hash_table} and @code{int}
for @code{fd_table}.

@item @code{X_table_get} [(@code{const this, key}) @arrow{} @code{size_t}]
Look up a value by its key @code{key} in the
table @code{*this}. Zero will be returned if
the key was not used.

@item @code{hash_table_get_entry} [(@code{const this, size_t key}) @arrow{} @code{hash_entry_t*}]
Look up an entry by its key @code{key} in the
table @code{*this}. @code{NULL} will be returned
if the key was not used.

@item @code{X_table_put} [(@code{this, key, size_t value}) @arrow{} @code{size_t}]
Map the value @code{value} to the key @code{key}
in the talbe @code{*this}. If a value was already
mapped to the key, that value will be returned,
otherwise zero will be returned. Zero will also
be returned on error. @code{errno} will be set to
zero on and only on success.

The data type for the parameter @code{key} is
@code{size_t} for @code{hash_table} and @code{int}
for @code{fd_table}.

@item @code{X_table_remove} [(@code{this, key}) @arrow{} @code{size_t}]
Unmaps the key @code{key} for the table @code{*this}.
If a value was mapped to the key, that value will
be returned, otherwise zero will be returned.

The data type for the parameter @code{key} is
@code{size_t} for @code{hash_table} and @code{int}
for @code{fd_table}.

@item @code{X_table_clear} [(@code{this}) @arrow{} @code{void}]
Unmaps all keys in the table @code{*this}.

@item @code{X_table_unmarshal} [(@code{this, char* restrict data, remap_func* remapper}) @arrow{} @code{int}]
As described in @ref{Data Structures} but with one
additional parameter: @code{remapper}. If this
parameter is not @code{NULL} this function is used
to edit values. It will be called once for each
value and the output of the function will be used
inplace of the input value.
@end table

@file{<libmdsserver/hash-table.h>} also defines
as wrapper macro for the @code{for} keyword:

@table @asis
@item @code{foreach_hash_table_entry} [(@code{hash_table_t this, size_t i, hash_entry_t* entry})]
Iterates over entry element in the hash table
@code{*this}. On each iteration, the entry will
be stored to the variable @code{entry} and the
bucket index will be stored to the variable
@code{i}.

@example
void print_hash_table(hash_table_t* table)
@{
  hash_entry_t* entry;
  size_t i;
  foreach_hash_table_entry (*table, i, entry)
    printf("%zu --> %zu\n", entry->key, entry->value);
@}
@end example

Note the the data type for the parameter @code{this}
is not a popinter.
@end table

The structures @code{hash_table_t} and @code{fd_table_t}
contain the variable @code{value_comparator} which by
default is @code{NULL}. If this variable is set to @code{NULL},
two values will be considered equal if and only if they are
numerically identical; otherwise two values will be considered
equal if and only if @code{value_comparator} returned a
non-zero value if those two values are used for the function's
arguments. The data type for @code{value_comparator} is
@code{compare_func*}.

@code{hash_table_t} also contains two other variables:

@table @asis
@item @code{key_comparator} [@code{compare_func*}]
Identical to @code{value_comparator}, except it is used for
keys rather the values.

@item @code{hasher} [@code{hash_func*}]
By default, the hash value for key is identical to the key
itself. However, if this variable is not @code{NULL}, it
will be used to calculate the hash value for keys.
@end table

There is a secondary data structure defined for hash tables:
@code{hash_entry_t} @{also known as @code{struct hash_entry}@}.
It is the data structure used for entries in a hash table.
@code{hash_entry_t} contain three variables you may be interested in:

@table @asis
@item @code{key} [@code{size_t}]
The key.

@item @code{value} [@code{size_t}]
The value associated with the key.

@item @code{hash} [@code{size_t}]
The hash value of the key.
@end table

By inclusion of @file{<libmdsserver/table-common.h>},
@file{<libmdsserver/hash-table.h>} and @file{<libmdsserver/fd-table.h>}
defines four @code{typedef}:s for function signatures:

@table @asis
@item @code{compare_func} [(@code{size_t a, size_t b}) @arrow{} @code{int}]
A function that performs a comparison of two objects.
Should return non-zero if and only if @code{a} and
@code{b} are to be considered equal in the given
context.

@item @code{hash_func} [(@code{size_t value}) @arrow{} @code{size_t}]
A function that hashes an object or a value.
Should return the hash value for @code{value}.

@item @code{free_func} [(@code{size_t obj}) @arrow{} @code{void}]
A function that, to the extent that is appropriate,
releases the object @code{obj}'s resources and
@code{free}:s it.

@item @code{remap_func} [(@code{size_t obj}) @arrow{} @code{size_t}]
A function that translates a object into a new object.
The function should return new object that should replace
the object @code{obj}.
@end table

If you are working with strings, you may consider
including the header file @file{<libmdsserver/hash-help.h>}.
It defines to useful functions:

@table @asis
@item @code{string_hash} [(@code{const char* str}) @arrow{} @code{size_t}]
Calculate and returns the hash value of the string @code{str}.

@item @code{string_comparator} [(@code{char* str_a, char* str_b}) @arrow{} @code{int}]
Returns non-zero if either both @code{str_a} and @code{str_b}
are @code{NULL} or neither are @code{NULL} but are identical
strings by content upto their first NUL characters (or by address).
@end table

These functions are defined as pure and @code{static inline}.



@node Message Structure
@subsection Message Structure

Apart from internal data @code{mds_message_t} contains four
variables:

@table @asis
@item @code{headers} [@code{char**}]
The headers in the message, each element in this list
as an unparsed header, it consists of both the header
name and its associated value, joined by `: '. A header
cannot be @code{NULL} (unless its memory allocation failed,)
but @code{headers} itself is @code{NULL} if there are
no headers. The `Length' header should be included in
this list.

@item @code{header_count} [@code{size_t}]
The number of headers in the message.

@item @code{payload} [@code{char*}]
The payload of the message, @code{NULL} if
none (of zero-length).

@item @code{payload_size} [@code{size_t}]
The length of the message's payload.
This value will be the same as the value
of the `Length' header.
@end table

There are six functions specific to @code{mds_message_t}.
The @code{this}-parameter's data type for this functions
are @code{mds_message_t*} with the @code{restrict} modifier.

@table @asis
@item @code{mds_message_initialise} [(@code{this}) @arrow{} @code{int}]
Initialises @code{*this} so that it can be used by
@code{mds_message_read}. Returns zero on and only on
success. On failure you should destroy @code{*this}
using @code{mds_message_destroy}.

@item @code{mds_message_zero_initialise} [(@code{this}) @arrow{} @code{void}]
This function is similar to @code{mds_message_initialise},
however it cannot fail and thus have no return value.
The difference it is action is that it will not allocate
an internal buffer.

@item @code{mds_message_extend_headers} [(@code{this, size_t extent}) @arrow{} @code{int}]
Ensures that @code{extent} additional headers can
be stored in the @code{*this}. Returns zero on
and only on success.

@item @code{mds_message_read} [(@code{this, int fd}) @arrow{} @code{int}]
Reads the next message from the socket file descriptor
@code{fd} and stores it in @code{*this}. Returns zero
on success and non-zero on error or interruption. @code{*this}
should be destroyed using @code{mds_message_destroy} on
error but not on interruption. If @code{-2} is returned
@code{errno} will not have been set; @code{-2} indicates
that the message is malformated, which is a state that
cannot be recovered from.

@item @code{mds_message_compose_size} [(@code{const this}) @arrow{} @code{size_t}]
This function is to @code{mds_message_compose} as
@code{mds_message_marshal_size} is to
@code{mds_message_marshal}.

@item @code{mds_message_compose} [(@code{const this, char* restrict data}) @arrow{} @code{void}]
This function is similar to @code{mds_message_marshal}.
The only difference is that it will not store internal
data and instead create a message that can be broadcasted
in the display server message passing system.
@end table



@node mds-base
@chapter @file{mds-base}

@file{mds-base.c} and @file{mds-base.h} as an object
filepair whose purpose is similar to libmdsserver.
@file{mds-base} is compiled into all @command{mds}
servers and implements common procedures including
@code{main}. It also complements procedures that are
weakly defined, that is, if the server implementation
also defines them, the server implementations procedure
replaces @file{mds-base}'s implementation at
compile-time.

@file{mds-base} defines one function that you can
call from threads you create and functions that should
be implement depending on specified conditions:

@table @asis
@item @code{trap_signals} [(@code{void}) @arrow{} @code{int}]
Set up signal traps for all especially handled signals.
Returns zero on and only on success.
@end table

@file{mds-base} weakly defines functions that you can
replace if they do not suit your needs:

@table @asis
@item @code{parse_cmdline} [(@code{void}) @arrow{} @code{int}]
Parses command line arguments.
Returns zero on and only on success.

This function will parse the following options:

@table @option
@item --initial-spawn
It is the first time the server is spawn by its
spawner process.

@item --respawn
The server was respawned.

@item --re-exec
The server is re-executing.

@item --alarm=SECONDS
Kill the process after @var{SECONDS} seconds.
At most one minute.

@item --on-init-fork
Fork the process to detach it from its parent when
the server has been initialised.

@item --on-init-sh=COMMAND
When the server has been initialised, run the
command @var{COMMAND}.

@item --immortal
The server should to its best not to die. For example
do not die if @code{SIGDANGER} is received even if that
is the server's default action.
@end table

@item @code{connect_to_display} [(@code{void}) @arrow{} @code{int}]
Connects to the display.
Returns zero on and only on success.

@item @code{server_initialised} [(@code{void}) @arrow{} @code{int}]
This function should be called when the server has
been properly initialised but before initialisation
of anything that is removed at forking is initialised.
Returns zero on and only on success.

@item @code{signal_all} [(@code{int signo}) @arrow{} @code{void}]
This function should be implemented by the actual server
implementation if the server is multi-threaded. It sends
the singal @code{signo} to all threads except the current
thread.

@item @code{received_danger} [(@code{int signo}) @arrow{} @code{void}]
This function is called when a signal that signals the
system is running out of memory has been received. The exact
received signal is specified by the parameter @code{signo}.
When this function is invoked, the server should free up
all memory it can spare. When this function is invoked, it
should set the variable @code{danger} to a non-zero value.
If @code{server_characteristics.danger_is_deadly} is set,
this function will never be called.

@item @code{received_reexec} [(@code{int signo}) @arrow{} @code{void}]
This function is called when a signal that signals the
server to re-execute has been received. The exact
received signal is specified by the parameter @code{signo}.
When this function is invoked, it should set the variables
@code{reexecing} and @code{terminating} to a non-zero value.

@item @code{received_terminate} [(@code{int signo}) @arrow{} @code{void}]
This function is called when a signal that signals the
server to terminate has been received. The exact received
signal is specified by the parameter @code{signo}. When
this function is invoked, it should set the variable
@code{terminating} to a non-zero value.

@item @code{fork_cleanup} [(@code{int status}) @arrow{} @code{void}]
This function should be implemented by the actual server
implementation if the server has set
@code{server_characteristics.fork_for_safety} to be a
non-zero value. This function is called by the parent server
process when the child server process exits, if the server
has completed its initialisation. The parameter @code{status}
specifies the child process exit status as returned by
@code{waitpid}.
@end table

Additionally, @file{mds-base} expects the server implementation
to define and implement a set of functions:

@table @asis
@item @code{preinitialise_server} [(@code{void}) @arrow{} @code{int}]
This function will be invoked before @code{initialise_server}
(if not re-executing) or before @code{unmarshal_server}
(if not re-executing). Returns zero on and only on success.

@item @code{initialise_server} [(@code{void}) @arrow{} @code{int}]
This function should initialise the server. It not invoked
after a re-execution. Returns zero on and only on success.

@item @code{postinitialise_server} [(@code{void}) @arrow{} @code{int}]
This function will be invoked after @code{initialise_server}
(if not re-executing) or after @code{unmarshal_server} (if
re-executing). Returns zero on and only on success.

@item @code{marshal_server_size} [(@code{void}) @arrow{} @code{size_t}, pure]
Calculate and returns the number of bytes that will be stored
by @code{marshal_server}. On failure the server should call
@code{abort} or exit with failure status by other means.
However it should not be possible for this function to fail.
@code{marshal_server_size} must be pure.@footnote{That is,
define with and conforming to @code{__attribute__((pure))}.}.

@item @code{marshal_server} [(@code{char* state_buf}) @arrow{} @code{int}]
Marshal server implementation specific data into the buffer
@code{state_buf}. Returns zero on and only on success.

@item @code{unmarshal_server} [(@code{char* state_buf}) @arrow{} @code{int}]
Unmarshal server implementation specific data from the
buffer @code{state_buf} and update the servers state
accordingly. Returns zero on and only on success.

On critical failure the program should call @code{abort}
or exit with failure status by other means. That is, do not
let @code{reexec_failure_recover} run successfully, if it
unrecoverable error has occurred or one severe enough that
it is better to simply respawn.

@item @code{reexec_failure_recover} [(@code{void}) @arrow{} @code{int}]
Attempt to recover from a re-execution failure that has been
detected after the server successfully updated it execution
image. Returns zero on and only on success.

@item @code{master_loop} [(@code{void}) @arrow{} @code{int}]
Perform the server's mission. Returns zero on and only on success.
@end table

@file{mds-base} also defines a number of global variables.

@table @asis
@item @code{argc} [@code{int}]
Number of elements in @code{argv}.

@item @code{argv} [@code{char**}]
Command line arguments.

@item @code{is_respawn} [@code{int}]
Whether the server has been respawn rather than this
being the initial spawn. This will be at least as true
as @code{is_reexec}.

@item @code{is_reexec} [@code{int}]
Whether the server is continuing from a self-reexecution.

@item @code{is_immortal} [@code{int}]
Whether the server should do its best to resist event
triggered death.

@item @code{on_init_fork} [@code{int}]
Whether to fork the process when the server has been
properly initialised.

@item @code{on_init_sh} [@code{char*}]
Command the run (@code{NULL} for none) when the server
has been properly initialised.

@item @code{master_thread} [@code{pthread_t}]
The thread that runs the master loop.

@item @code{terminating} [@code{volatile sig_atomic_t}]
Whether the server has been signaled to terminate.

@item @code{reexecing} [@code{volatile sig_atomic_t}]
Whether the server has been signaled to re-execute.

@item @code{danger} [@code{volatile sig_atomic_t}]
Whether the server has been signaled to free unneeded memory.

@item @code{socket_fd} [@code{int}]
The file descriptor of the socket that is connected
to the server.
@end table

@file{mds-base} expects the server implementation to define
a variable that specifies how @file{mds-base} should behave:

@table @asis
@item @code{server_characteristics} [@code{server_characteristics_t}]
This variable should declared by the actual server
implementation. It must be configured before @code{main}
is invoked. That is, it should be configured by a
constructor. If it is configured at its definition,
it is configured by a constructor; that is normally
how you want to configured it.
@end table

@code{server_characteristics_t} @{also known as
@code{struct server_characteristics}@} is a packed
@footnote{That is, define with @code{__attribute__((packed))}.}
with the following fields:

@table @asis
@item @code{require_privileges} [@code{unsigned : 1}]
Setting this to zero will cause the server to drop
privileges as a security precaution.

@item @code{require_display} [@code{unsigned : 1}]
Setting this to non-zero will cause the server to connect
to the display.

@item @code{require_respawn_info} [@code{unsigned : 1}]
Setting this to non-zero will cause the server to refuse
to start unless either @option{--initial-spawn} or
@option{--respawn} is used.

@item @code{sanity_check_argc} [@code{unsigned : 1}]
Setting this to non-zero will cause the server to refuse to
start if there are too many command line arguments.

@item @code{fork_for_safety} [@code{unsigned : 1}]
Setting this to non-zero will cause the server to place
itself in a fork of itself when initialised. This can be
used to let the server clean up fatal stuff after itself
if it crashes. When the child exits, no matter how it
exits, the parent will call @code{fork_cleanup} and then
die it the same manner as the child.

@item @code{danger_is_deadly} [@code{unsigned : 1}]
Setting this to non-zero without setting a signal action
for @code{SIGDANGER} will cause the server to die if
@code{SIGDANGER} is received. It is safe to set both
@code{danger_is_deadly} and @code{fork_for_safety} to
non-zero, during the call of @code{server_initialised}
the signal handler for @code{SIGDANGER} in the parent
process will be set to @code{SIG_IGN} independently of
the value of @code{danger_is_deadly} if
@code{fork_for_safety} is set to non-zero.

This setting will be treated as set to zero if
@option{--immortal} is used.
@end table



@node Keyboard Codes
@chapter Keyboard Codes

Keyboard servers receive scancodes from keyboard
drivers. A scancode can either be comprised of
one byte or three bytes. In each byte, the most
significant bit (assuming unsigned bytes) is
ignore, however for it first byte in the scancode
it signifies whether the key was released: it is
set of the key is released, and not set if the key
was pressed or is being held down.

A scancode is comprised of three bytes if the lower
7-bits of the first byte is are all cleared, and the
highest bit in the two following bytes are set.

Ignoring the most significant bit in all bytes, the
keycode is the value of the byte if the scancode
is a single byte scancode. If the scancode is comprised
of three bytes, the first byte is ignored and the
keycode is @math{a \cdot 128 + b} where @math{a} is the
value of the second byte and @math{b} is the value
of the third byte.

@menu
* 105-keys Keycodes::               List of keycodes for 105-keys keyboards.
@end menu



@node 105-keys Keycodes
@section 105-keys Keycodes

This is a list of keyboards for the
105-keys keyboards, using QWERTY-layout
for reference.

@table @asis
@item @code{1}
@kbd{Escape} key
@item @code{2}--@code{11}
Keys: @kbd{1}, @kbd{2}, @kbd{3}, @kbd{4}, @kbd{5}, @kbd{6}, @kbd{7}, @kbd{8}, @kbd{9}, @kbd{0}
@item @code{12}
Key right of @kbd{0}.
@item @code{13}
Key left of @kbd{backspace}
@item @code{14}
@kbd{Backspace} key
@item @code{15}
@kbd{Tab} key
@item @code{16}--@code{25}
Keys: @kbd{q}, @kbd{w}, @kbd{e}, @kbd{r}, @kbd{t}, @kbd{y}, @kbd{u}, @kbd{i}, @kbd{o}, @kbd{p}
@item @code{26}
Key right of @kbd{p}, once removed
@item @code{27}
Key right of @kbd{p}, twice removed
@item @code{28}
@kbd{Return} key
@item @code{29}
Left @kbd{control} key
@item @code{30}--@code{38}
Keys: @kbd{a}, @kbd{s}, @kbd{d}, @kbd{f}, @kbd{g}, @kbd{h}, @kbd{j}, @kbd{k}, @kbd{l}
@item @code{39}
Key right of @kbd{l}, once removed
@item @code{40}
Key right of @kbd{l}, twice removed
@item @code{41}
Key left of @kbd{1}
@item @code{42}
Left @kbd{shift} key
@item @code{43}
Key right of @kbd{l}, three times removed
@item @code{44}--@code{50}
Keys: @kbd{z}, @kbd{x}, @kbd{c}, @kbd{v}, @kbd{b}, @kbd{n}, @kbd{m}
@item @code{51}
Key right of @kbd{m}, once removed
@item @code{52}
Key right of @kbd{m}, twice removed
@item @code{53}
Key right of @kbd{m}, three times removed
@item @code{54}
Right @kbd{shift} key
@item @code{55}
@kbd{Multiply} key on the keypad
@item @code{56}
@kbd{Alternative} key
@item @code{57}
@kbd{Space} key
@item @code{58}
@kbd{Caps lock} key
@item @code{59}--@code{68}
Keys: @kbd{F1} through @kbd{F10}
@item @code{69}
@kbd{Num lock} key
@item @code{70}
@kbd{Scroll lock} key
@item @code{71}--@code{73}
@kbd{7}, @kbd{8}, @kbd{9} keys on the keypad
@item @code{74}
@kbd{Minus} key on the keypad
@item @code{75}--@code{77}
@kbd{4}, @kbd{5}, @kbd{6} keys on the keypad
@item @code{78}
@kbd{Plus} key on the keypad
@item @code{79}--@code{82}
@kbd{1}, @kbd{2}, @kbd{3}, @kbd{0} keys on the keypad
@item @code{83}
@kbd{Comma} key on the keypad
@item @code{86}
Key left of @kbd{z}
@item @code{87}
@kbd{F11} key
@item @code{88}
@kbd{F12} key
@item @code{96}
@kbd{Return} key on the keypad
@item @code{97}
Right @kbd{control} key
@item @code{98}
@kbd{Divide} key on the keypad
@item @code{99}
@kbd{System Request/Print Screen} key
@item @code{100}
@kbd{Alternative graphic} key
@item @code{102}
@kbd{Home} key
@item @code{103}
@kbd{Up} arrow key
@item @code{104}
@kbd{Page up} key
@item @code{105}
@kbd{Left} arrow key
@item @code{106}
@kbd{Right} arrow key
@item @code{107}
@kbd{End} key
@item @code{108}
@kbd{Down} arrow key
@item @code{109}
@kbd{Page down} down
@item @code{110}
@kbd{Insert} key
@item @code{111}
@kbd{Delete} key
@item @code{119}
@kbd{Pause/Break} key
@item @code{125}
Left @kbd{super} key
@item @code{126}
Right @kbd{super} key
@item @code{127}
@kbd{Application menu} key
@end table



@node GNU Free Documentation License
@appendix GNU Free Documentation License
@include fdl.texinfo

@bye