Add handler for fatal X server conditions

Unless X server failures are caught, these can cause a premature
exit of chansrv, giving it no chance to clean up. This is currently a
particular problem for fuser mounts.

sesman/chansrv/chansrv.c

@@ -1278,6 +1278,16 @@ segfault_signal_handler(int sig)
     exit(0);
 }
 
+/*****************************************************************************/
+static void
+x_server_fatal_handler(void)
+{
+    LOGM((LOG_LEVEL_INFO, "xserver_fatal_handler: entered......."));
+    /* At this point the X server has gone away. Dont make any X calls. */
+    xfuse_deinit();
+    exit(0);
+}
+
 /*****************************************************************************/
 static int
 get_display_num_from_display(char *display_text)
@@ -1576,6 +1586,9 @@ main(int argc, char **argv)
     g_signal_child_stop(child_signal_handler); /* SIGCHLD */
     g_signal_segfault(segfault_signal_handler);
 
+    /* Cater for the X server exiting unexpectedly */
+    xcommon_set_x_server_fatal_handler(x_server_fatal_handler);
+
     LOGM((LOG_LEVEL_INFO, "main: DISPLAY env var set to %s", display_text));
 
     if (g_display_num == 0)

sesman/chansrv/xcommon.c

@@ -28,6 +28,7 @@
 #include "log.h"
 #include "clipboard.h"
 #include "rail.h"
+#include "xcommon.h"
 
 /*
 #undef LOG_LEVEL
@@ -50,6 +51,9 @@ Atom g_utf8_string = 0;
 Atom g_net_wm_name = 0;
 Atom g_wm_state = 0;
 
+static x_server_fatal_cb_type x_server_fatal_handler = 0;
+
+
 /*****************************************************************************/
 static int
 xcommon_error_handler(Display *dis, XErrorEvent *xer)
@@ -64,16 +68,27 @@ xcommon_error_handler(Display *dis, XErrorEvent *xer)
 }
 
 /*****************************************************************************/
-/* The X server had an internal error.  This is the last function called.
-   Do any cleanup that needs to be done on exit, like removing temporary files.
+/* Allow the caller to be notified on X server failure
+   Specified callback can do any cleanup that needs to be done on exit,
+   like removing temporary files. This is the last function called.
    Don't worry about memory leaks */
-#if 0
+void
+xcommon_set_x_server_fatal_handler(x_server_fatal_cb_type handler)
+{
+    x_server_fatal_handler = handler;
+}
+
+/*****************************************************************************/
+/* The X server had an internal error */
 static int
 xcommon_fatal_handler(Display *dis)
 {
+    if (x_server_fatal_handler)
+    {
+        x_server_fatal_handler();
+    }
     return 0;
 }
-#endif
 
 /*****************************************************************************/
 /* returns time in milliseconds
@@ -110,7 +125,7 @@ xcommon_init(void)
     /* setting the error handlers can cause problem when shutting down
        chansrv on some xlibs */
     XSetErrorHandler(xcommon_error_handler);
-    //XSetIOErrorHandler(xcommon_fatal_handler);
+    XSetIOErrorHandler(xcommon_fatal_handler);
 
     g_x_socket = XConnectionNumber(g_display);
 

sesman/chansrv/xcommon.h

@@ -26,6 +26,8 @@
 #define FORMAT_TO_BYTES(_format) \
     (_format) == 32 ? sizeof(long) : (_format) / 8
 
+typedef void (*x_server_fatal_cb_type)(void);
+
 int
 xcommon_get_local_time(void);
 int
@@ -34,5 +36,7 @@ int
 xcommon_get_wait_objs(tbus* objs, int* count, int* timeout);
 int
 xcommon_check_wait_objs(void);
+void
+xcommon_set_x_server_fatal_handler(x_server_fatal_cb_type handler);
 
 #endif