[PATCH iproute2 v3] ipbatch: fix use of 'ip netns exec'

[Nicolas Dichtel <nicolas.dichtel@6wind.com>]

From: JunweiZhang <junwei.zhang@6wind.com>

execvp() does not return when the command succeed, hence all commands in the
batch file after the line 'ip netns exec' are not executed.

Let's fork before calling execvp().

Example:
$ cat test.batch
netns add netns1
netns exec netns1 ip l
netns
$ ip -b test.batch
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN mode DEFAULT
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: sit0: <NOARP> mtu 1480 qdisc noop state DOWN mode DEFAULT
    link/sit 0.0.0.0 brd 0.0.0.0

All command after 'netns exec' are never executed.

With the patch:
$ ip -b test.batch
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN mode DEFAULT
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: sit0: <NOARP> mtu 1480 qdisc noop state DOWN mode DEFAULT
    link/sit 0.0.0.0 brd 0.0.0.0
netns1

Now, existing netns are displayed.

Signed-off-by: JunweiZhang <junwei.zhang@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---

v3: be more verbose on error (fork(), waitpid())
    when child fails, just exit to avoid double cleanning
    check WIFEXITED() and waitpid() before using WEXITSTATUS()

v2: keep exit status of the child
    add an example in the commit log

 ip/ipnetns.c | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index fa2b681..474a296 100644
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -138,6 +138,7 @@ static int netns_exec(int argc, char **argv)
 	const char *name, *cmd;
 	char net_path[MAXPATHLEN];
 	int netns;
+	int pid, status;
 
 	if (argc < 1) {
 		fprintf(stderr, "No netns name specified\n");
@@ -185,9 +186,32 @@ static int netns_exec(int argc, char **argv)
 	/* Setup bind mounts for config files in /etc */
 	bind_etc(name);
 
-	if (execvp(cmd, argv + 1)  < 0)
-		fprintf(stderr, "exec of \"%s\" failed: %s\n",
-			cmd, strerror(errno));
+	pid = fork();
+	if (pid < 0) {
+		perror("fork");
+		return EXIT_FAILURE;
+	} else if (pid == 0) {
+		/* Child */
+		if (execvp(cmd, argv + 1)  < 0)
+			fprintf(stderr, "exec of \"%s\" failed: %s\n",
+				cmd, strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	/* Parent */
+	if (waitpid(pid, &status, 0) < 0) {
+		perror("waitpid");
+		return EXIT_FAILURE;
+	}
+
+	if (WIFEXITED(status)) {
+		/* ip must returns the status of the child, but do_cmd() will
+		 * add a minus to this returned value, so let's add another one
+		 * here to cancel it.
+		 */
+		return -WEXITSTATUS(status);
+	}
+
 	return EXIT_FAILURE;
 }
 
-- 
1.8.2.1