[PATCH] tgtd: protect socket for management IPC with lockf(3)

[Hitoshi Mitake <mitake.hitoshi@xxxxxxxxxxxxx>]

If two or more tgtds are launched with same control port (a number
specified with -C option), tgtadm cannot communicate with tgtds
because the latest tgtd cominates the socket. This behavior is
confusing.

This patch lets tgtd lock the socket with lockf(3). With this change,
tgtd will exits when the socket of its control port is already locked.

Signed-off-by: Hitoshi Mitake <mitake.hitoshi@xxxxxxxxxxxxx>
---
 usr/mgmt.c |   36 +++++++++++++++++++++++++++++-------
 usr/tgtd.c |    6 +++---
 2 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/usr/mgmt.c b/usr/mgmt.c
index c0bf7be..e795555 100644
--- a/usr/mgmt.c
+++ b/usr/mgmt.c
@@ -62,8 +62,9 @@ struct mgmt_task {
 
 #define MAX_MGT_BUFSIZE	(8*1024) /* limit incoming mgmt request data size */
 
-static int ipc_fd;
+static int ipc_fd, ipc_lock_fd;
 char mgmt_path[256];
+char mgmt_lock_path[256];
 
 static struct mgmt_task *mtask_alloc(void);
 static void mtask_free(struct mgmt_task *mtask);
@@ -760,13 +761,30 @@ out:
 int ipc_init(void)
 {
 	extern short control_port;
-	int fd, err;
+	int fd = 0, err;
 	struct sockaddr_un addr;
 
+	sprintf(mgmt_lock_path, "%s.%d.lock", TGT_IPC_NAMESPACE, control_port);
+	ipc_lock_fd = open(mgmt_lock_path, O_WRONLY | O_CREAT,
+			   S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
+	if (ipc_lock_fd < 0) {
+		eprintf("failed to open lock file for management IPC\n");
+		return -1;
+	}
+
+	if (lockf(ipc_lock_fd, F_TLOCK, 1) < 0) {
+		if (errno == EACCES || errno == EAGAIN)
+			eprintf("another tgtd is using %s\n", mgmt_lock_path);
+		else
+			eprintf("unable to get lock of management IPC: %s"\
+				" (errno: %m)\n", mgmt_lock_path);
+		goto close_lock_fd;
+	}
+
 	fd = socket(AF_LOCAL, SOCK_STREAM, 0);
 	if (fd < 0) {
 		eprintf("can't open a socket, %m\n");
-		return -1;
+		goto close_lock_fd;
 	}
 
 	sprintf(mgmt_path, "%s.%d", TGT_IPC_NAMESPACE, control_port);
@@ -778,24 +796,27 @@ int ipc_init(void)
 	err = bind(fd, (struct sockaddr *) &addr, sizeof(addr));
 	if (err) {
 		eprintf("can't bind a socket, %m\n");
-		goto out;
+		goto close_ipc_fd;
 	}
 
 	err = listen(fd, 32);
 	if (err) {
 		eprintf("can't listen a socket, %m\n");
-		goto out;
+		goto close_ipc_fd;
 	}
 
 	err = tgt_event_add(fd, EPOLLIN, mgmt_event_handler, NULL);
 	if (err)
-		goto out;
+		goto close_ipc_fd;
 
 	ipc_fd = fd;
 
 	return 0;
-out:
+
+close_ipc_fd:
 	close(fd);
+close_lock_fd:
+	close(ipc_lock_fd);
 	return -1;
 }
 
@@ -803,4 +824,5 @@ void ipc_exit(void)
 {
 	tgt_event_del(ipc_fd);
 	close(ipc_fd);
+	close(ipc_lock_fd);
 }
diff --git a/usr/tgtd.c b/usr/tgtd.c
index f985510..64eff32 100644
--- a/usr/tgtd.c
+++ b/usr/tgtd.c
@@ -577,11 +577,11 @@ int main(int argc, char **argv)
 
 	spare_args = optind < argc ? argv[optind] : NULL;
 
-	err = ipc_init();
-	if (err)
+	if (is_daemon && daemon(0, 0))
 		exit(1);
 
-	if (is_daemon && daemon(0, 0))
+	err = ipc_init();
+	if (err)
 		exit(1);
 
 	err = log_init(program_name, LOG_SPACE_SIZE, is_daemon, is_debug);
-- 
1.7.10.4

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