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| -rw-r--r-- | doc/info/mds.texinfo | 111 |
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diff --git a/doc/info/mds.texinfo b/doc/info/mds.texinfo index d0befae..b275952 100644 --- a/doc/info/mds.texinfo +++ b/doc/info/mds.texinfo @@ -53,6 +53,7 @@ Texts. A copy of the license is included in the section entitled @menu * Overview:: Brief overview of @command{mds}. * Architecture:: Architectural overview of @command{mds}. +* Protocol:: The @command{mds} procotol. * GNU Free Documentation License:: Copying and sharing this manual. @end menu @@ -285,6 +286,116 @@ 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 +@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 + + + @node GNU Free Documentation License @appendix GNU Free Documentation License @include fdl.texinfo |