Issue 19 - patch by tilman2: Fix PID-file support again

diff --git a/src/main.c b/src/main.c
index 36c5f88db63232928ba607e91518c4292a21aacc..cef4f605a4d2e88877d7e488dbb83302e378f962 100644 (file)
--- a/src/main.c
+++ b/src/main.c
@@ -59,17 +59,50 @@ char *bindaddr;
 
 void lockfile(const char *pidfile)
 {
-       int lfp;
+       int lfp, flags;
        char str[16];
-       
-       lfp = open(pidfile, O_RDWR|O_CREAT|O_EXCL, 0640);
+
+       /* Don't use O_TRUNC here -- we want to leave the PID file
+        * unmodified if we cannot lock it.
+        */
+       lfp = open(pidfile, O_WRONLY|O_CREAT, 0640);
        
        if (lfp < 0)
                Log_fatal("Cannot open PID-file %s for writing", pidfile);
+
+       /* Try to lock the file. */
+       if (lockf(lfp, F_TLOCK, 0) < 0) {
+               close(lfp);
+
+               if (errno == EACCES || errno == EAGAIN)
+                       Log_fatal("PID file is locked -- uMurmur already running?");
+
+               Log_fatal("Cannot lock PID file: %s", strerror(errno));
+       }
+
+       /* Now that we locked the file, erase its contents. */
+       if (ftruncate(lfp, 0) < 0) {
+               close(lfp);
+               Log_fatal("Cannot truncate PID file: %s", strerror(errno));
+       }
+
        snprintf(str,16,"%d\n", getpid());
        write(lfp, str, strlen(str)); /* record pid to lockfile */
-       close(lfp);
        Log_info("PID-file: %s", pidfile);
+
+       /* If uMurmur ever starts to fork()+exec(), we don't want it to
+        * leak the fd to the forked process though. Set the close-on-exec
+        * flag to prevent leakage.
+        */
+       flags = fcntl(lfp, F_GETFD, 0);
+       flags |= FD_CLOEXEC;
+       fcntl(lfp, F_SETFD, (long) flags);
+
+       /* Don't close(lfp) here!
+        * We want the fd to remain opened so the lock is held until the
+        * process exits.
+        */
+       lfp = -1;
 }
 
 /* Drops privileges (if configured to do so). */