add sigdanger support

Signed-off-by: Mattias Andrée <maandree@operamail.com>

9 files changed, 82 insertions, 9 deletions

diff --git a/src/libmdsserver/macros.h b/src/libmdsserver/macros.h
index 2d3f7a3..215c51a 100644
--- a/src/libmdsserver/macros.h
+++ b/src/libmdsserver/macros.h
@@ -24,6 +24,7 @@
 
 #include <stdio.h>
 #include <errno.h>
+#include <signal.h>
 
 /*
 #include <unistd.h>
@@ -363,5 +364,14 @@
 #define exit_if(CONDITION, INSTRUCTIONS)  if (CONDITION)  { INSTRUCTIONS return 1; }
 
 
+/**
+ * The system is running out of memory.
+ * Quick, free up all your unused memory or kill yourself!
+ */
+#ifndef SIGDANGER
+# define SIGDANGER  SIGRTMAX
+#endif
+
+
 #endif
 
diff --git a/src/mds-base.c b/src/mds-base.c
index be4efbb..429632e 100644
--- a/src/mds-base.c
+++ b/src/mds-base.c
@@ -192,8 +192,9 @@ int __attribute__((weak)) connect_to_display(void)
  */
 static int server_initialised_fork_for_safety(void)
 {
-  unsigned pending_alarm = alarm(0);
+  unsigned pending_alarm = alarm(0); /* Disable the alarm. */
   pid_t pid = fork();
+  int status;
   
   if (pid == (pid_t)-1)
     {
@@ -202,17 +203,29 @@ static int server_initialised_fork_for_safety(void)
       return -1;
     }
   else if (pid == 0)
+    /* Reinstate the alarm for the child. */
     alarm(pending_alarm);
   else
     {
-      int status;
+      /* SIGDANGER cannot hurt the parent process. */
+      if (xsigaction(SIGDANGER, SIG_IGN) < 0)
+	{
+	  xperror(*argv);
+	  eprint("WARNING! parent process failed to sig up ignoring of SIGDANGER.");
+	}
+      
+      /* Wait for the child process to die. */
       if (uninterruptable_waitpid(pid, &status, 0) == (pid_t)-1)
 	{
 	  xperror(*argv);
 	  kill(pid, SIGABRT);
 	  sleep(5);
 	}
+      
+      /* Clean up after us. */
       fork_cleanup(status);
+      
+      /* Die like the child. */
       if      (WIFEXITED(status))    exit(WEXITSTATUS(status));
       else if (WIFSIGNALED(status))  raise(WTERMSIG(status));
       exit(1);
@@ -541,6 +554,32 @@ int main(int argc_, char** argv_)
 
 
 /**
+ * This function is called when `SIGDANGER` is received
+ * of `server_characteristics.danger_is_deadly` is non-zero
+ * unless the signal handler for `SIGDANGER` has been
+ * modified by the server implementation.
+ * 
+ * This function will abruptly kill the process
+ * 
+ * @param  signo  The signal that has been received
+ */
+static void commit_suicide(int signo)
+{
+  (void) signo;
+  
+  eprint("SIGDANGER received, process is killing itself to free memory.");
+  
+  /* abort(), but on the process rather than the thread. */
+  xsigaction(SIGABRT, SIG_DFL);
+  kill(getpid(), SIGABRT);
+  
+  /* Just in case. */
+  xperror(*argv);
+  _exit(1);
+}
+
+
+/**
  * Set up signal traps for all especially handled signals
  * 
  * @return  Non-zero on error
@@ -556,9 +595,15 @@ int trap_signals(void)
   /* Implement clean exit on SIGINT. */
   fail_if (xsigaction(SIGINT, received_terminate) < 0);
   
-  /* Implement clean exit on SIGRTMIN. */
+  /* Implement silent interruption on SIGRTMIN. */
   fail_if (xsigaction(SIGRTMIN, received_noop) < 0);
   
+  /* Implement silent interruption on SIGDANGER. */
+  if (server_characteristics.danger_is_deadly)
+    { fail_if (xsigaction(SIGDANGER, commit_suicide) < 0); }
+  else
+    { fail_if (xsigaction(SIGDANGER, SIG_IGN) < 0); }
+  
   return 0;
  pfail:
   xperror(*argv);
diff --git a/src/mds-base.h b/src/mds-base.h
index 2dac449..c3c6c9c 100644
--- a/src/mds-base.h
+++ b/src/mds-base.h
@@ -64,6 +64,18 @@ typedef struct server_characteristics
    */
   unsigned fork_for_safety : 1;
   
+  /**
+   * Seting this to non-zero without setting a signal action
+   * for `SIGDANGER` will cause the server to die if `SIGDANGER`
+   * is received. It is safe to set both `danger_is_deadly` and
+   * `fork_for_safety` to non-zero, during the call of
+   * `server_initialised` the signal handler for `SIGDANGER`
+   * in the parent process will be set to `SIG_IGN` independently
+   * of the value of `danger_is_deadly` if `fork_for_safety`
+   * is set to non-zero.
+   */
+  unsigned danger_is_deadly : 1;
+  
 } __attribute__((packed)) server_characteristics_t;
 
 
diff --git a/src/mds-clipboard.c b/src/mds-clipboard.c
index 7ed2508..6ad068b 100644
--- a/src/mds-clipboard.c
+++ b/src/mds-clipboard.c
@@ -46,7 +46,8 @@ server_characteristics_t server_characteristics =
     .require_display = 1,
     .require_respawn_info = 1,
     .sanity_check_argc = 1,
-    .fork_for_safety = 0
+    .fork_for_safety = 0,
+    .danger_is_deadly = 0
   };
 
 
diff --git a/src/mds-echo.c b/src/mds-echo.c
index 01f8e97..2b20387 100644
--- a/src/mds-echo.c
+++ b/src/mds-echo.c
@@ -46,7 +46,8 @@ server_characteristics_t server_characteristics =
     .require_display = 1,
     .require_respawn_info = 0,
     .sanity_check_argc = 1,
-    .fork_for_safety = 0
+    .fork_for_safety = 0,
+    .danger_is_deadly = 0
   };
 
 
diff --git a/src/mds-kkbd.c b/src/mds-kkbd.c
index 11d33b1..db12746 100644
--- a/src/mds-kkbd.c
+++ b/src/mds-kkbd.c
@@ -88,7 +88,8 @@ server_characteristics_t server_characteristics =
     .require_display = 1,
     .require_respawn_info = 0,
     .sanity_check_argc = 1,
-    .fork_for_safety = 1
+    .fork_for_safety = 1,
+    .danger_is_deadly = 0
   };
 
 
diff --git a/src/mds-registry/mds-registry.c b/src/mds-registry/mds-registry.c
index baefee7..1676cf6 100644
--- a/src/mds-registry/mds-registry.c
+++ b/src/mds-registry/mds-registry.c
@@ -43,7 +43,8 @@ server_characteristics_t server_characteristics =
     .require_display = 1,
     .require_respawn_info = 0,
     .sanity_check_argc = 1,
-    .fork_for_safety = 0
+    .fork_for_safety = 0,
+    .danger_is_deadly = 0
   };
 
 
diff --git a/src/mds-respawn.c b/src/mds-respawn.c
index 02b466c..6072ad9 100644
--- a/src/mds-respawn.c
+++ b/src/mds-respawn.c
@@ -47,7 +47,8 @@ server_characteristics_t server_characteristics =
     .require_display = 0,
     .require_respawn_info = 1,
     .sanity_check_argc = 0,
-    .fork_for_safety = 0
+    .fork_for_safety = 0,
+    .danger_is_deadly = 0
   };
 
 
diff --git a/src/mds-server/mds-server.c b/src/mds-server/mds-server.c
index 85e7c5c..a77fadb 100644
--- a/src/mds-server/mds-server.c
+++ b/src/mds-server/mds-server.c
@@ -57,7 +57,8 @@ server_characteristics_t server_characteristics =
     .require_display = 0, /* We will service one ourself. */
     .require_respawn_info = 1,
     .sanity_check_argc = 1,
-    .fork_for_safety = 0
+    .fork_for_safety = 0,
+    .danger_is_deadly = 0
   };