xserver: Detect an clean up stale lock file

diff --git a/compositor/xserver-launcher.c b/compositor/xserver-launcher.c
index 61ffc09..c11f410 100644 (file)
--- a/compositor/xserver-launcher.c
+++ b/compositor/xserver-launcher.c
@@ -30,6 +30,7 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <unistd.h>
+#include <signal.h>
 
 #include <xcb/xcb.h>
 
@@ -551,8 +552,9 @@ int
 wlsc_xserver_init(struct wl_display *display)
 {
        struct wlsc_xserver *mxs;
-       char lockfile[256], pid[16];
+       char lockfile[256], pid[16], *end;
        socklen_t size, name_size;
+       pid_t other;
        int fd;
 
        mxs = malloc(sizeof *mxs);
@@ -574,15 +576,44 @@ wlsc_xserver_init(struct wl_display *display)
                fd = open(lockfile,
                          O_WRONLY | O_CLOEXEC | O_CREAT | O_EXCL, 0444);
                if (fd < 0 && errno == EEXIST) {
-                       fprintf(stderr, "server %d exists\n", mxs->display);
+                       fd = open(lockfile, O_CLOEXEC, O_RDONLY);
+                       if (fd < 0 || read(fd, pid, 11) != 11) {
+                               fprintf(stderr,
+                                       "can't read lock file %s: %s\n",
+                                       lockfile, strerror(errno));
+                               mxs->display++;
+                               continue;
+                       }
+
+                       other = strtol(pid, &end, 0);
+                       if (end != pid + 10) {
+                               fprintf(stderr, "can't parse lock file %s\n",
+                                       lockfile);
+                               mxs->display++;
+                               continue;
+                       }
+
+                       if (kill(other, 0) < 0 && errno == ESRCH) {
+                               /* stale lock file; unlink and try again */
+                               fprintf(stderr,
+                                       "unlinking stale lock file %s\n",
+                                       lockfile);
+                               unlink(lockfile);
+                               continue;
+                       }
+
                        mxs->display++;
                        continue;
                } else if (fd < 0) {
+                       fprintf(stderr, "failed to create lock file %s: %s\n",
+                               lockfile, strerror(errno));
                        close(mxs->fd);
                        free(mxs);
                        return -1;
                }
 
+               /* Subtle detail: we use the pid of the wayland
+                * compositor, not the xserver in the lock file. */
                size = snprintf(pid, sizeof pid, "%10d\n", getpid());
                write(fd, pid, size);
                close(fd);
@@ -591,9 +622,10 @@ wlsc_xserver_init(struct wl_display *display)
                                     sizeof mxs->addr.sun_path,
                                     "/tmp/.X11-unix/X%d", mxs->display) + 1;
                size = offsetof(struct sockaddr_un, sun_path) + name_size;
+               unlink(mxs->addr.sun_path);
                if (bind(mxs->fd, (struct sockaddr *) &mxs->addr, size) < 0) {
-                       fprintf(stderr, "failed to bind to %s (%m)\n",
-                               mxs->addr.sun_path);
+                       fprintf(stderr, "failed to bind to %s (%s)\n",
+                               mxs->addr.sun_path, strerror(errno));
                        unlink(lockfile);
                        close(mxs->fd);
                        free(mxs);
@@ -602,7 +634,7 @@ wlsc_xserver_init(struct wl_display *display)
                break;
        } while (errno != 0);
 
-       fprintf(stderr, "listening on display %d\n", mxs->display);
+       fprintf(stderr, "xserver listening on display :%d\n", mxs->display);
 
        if (listen(mxs->fd, 1) < 0) {
                unlink(mxs->addr.sun_path);