lib: Ensure FRR detects running of the second instance of a FRR daemon, doesnot allow...

Solution :
The following procedures would be performed :

1. Verify if the pid file for each daemon is present or not. If the file is not present, that means the
   daemon is getting instantiated for the first time. So let it go ahead.
   If the file is present proceed to point ‘2’.

2. Try fetching the properties of the pid file.

3. If it has RW lock, that means one instance of this the daemon is already running.
   So stop moving ahead and do exit() else let it go ahead.
Please note all above procedure happen at
   the initial state of daemon’s instantiation, much before it starts any session with other
   process/allocates resources etc.. and this verification do not have any impact of any
   operations done later, if the verification succeeds.

Signed-off-by: bisdhdh sadhub@vmware.com

diff --git a/lib/libfrr.c b/lib/libfrr.c
index 821c57f37b2d1a9c4e7c09ae2d2bc23dd53d082c..115c70f7c9981cc61560e00a38773d426c82b62b 100644 (file)
--- a/lib/libfrr.c
+++ b/lib/libfrr.c
@@ -262,12 +262,39 @@ bool frr_zclient_addr(struct sockaddr_storage *sa, socklen_t *sa_len,
 
 static struct frr_daemon_info *di = NULL;
 
+static void frr_guard_daemon(void)
+{
+       int fd;
+       struct flock lock;
+
+       const char *path = di->pid_file;
+       fd = open(path, O_RDWR);
+       if (fd != -1) {
+               memset(&lock, 0, sizeof(lock));
+               lock.l_type = F_WRLCK;
+               lock.l_whence = SEEK_SET;
+               if (fcntl(fd, F_GETLK, &lock) < 0) {
+                       flog_err_sys(LIB_ERR_SYSTEM_CALL,
+                               "Could not do F_GETLK pid_file %s (%s), exiting",
+                               path, safe_strerror(errno));
+                       exit(1);
+               } else if (lock.l_type == F_WRLCK) {
+                       flog_err_sys(LIB_ERR_SYSTEM_CALL,
+                               "Process %d has a write lock on file %s already! Error : ( %s)",
+                               lock.l_pid, path, safe_strerror(errno));
+                       exit(1);
+               }
+               close(fd);
+       }
+}
+
 void frr_preinit(struct frr_daemon_info *daemon, int argc, char **argv)
 {
        di = daemon;
 
        /* basename(), opencoded. */
        char *p = strrchr(argv[0], '/');
+
        di->progname = p ? p + 1 : argv[0];
 
        umask(0027);
@@ -589,6 +616,9 @@ struct thread_master *frr_init(void)
 
        zprivs_init(di->privs);
 
+       /* Guard to prevent a second instance of this daemon */
+       frr_guard_daemon();
+
        master = thread_master_create(NULL);
        signal_init(master, di->n_signals, di->signals);