Merge branch 'pr2983'

1 files changed, 29 insertions, 0 deletions

diff --git a/lib/libfrr.c b/lib/libfrr.c
index 821c57f37b..61f5fa7081 100644
--- a/lib/libfrr.c
+++ b/lib/libfrr.c
@@ -262,6 +262,32 @@ 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;
@@ -589,6 +615,9 @@ 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);