netdev - [PATCH iproute2 v4] ipbatch: fix use of 'ip netns exec'

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Message-Id: <1373385312-4899-1-git-send-email-nicolas.dichtel@6wind.com>
Date:	Tue,  9 Jul 2013 17:55:12 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	eric.dumazet@...il.com, shemminger@...tta.com
Cc:	netdev@...r.kernel.org, junwei.zhang@...nd.com,
	bhutchings@...arflare.com,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: [PATCH iproute2 v4] ipbatch: fix use of 'ip netns exec'

From: JunweiZhang <junwei.zhang@...nd.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() if batch mode is used..

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@...nd.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
---

v4: use pid_t type for pid
    use _exit() instead of exit()
    fork only if batch is used

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 | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index fa2b681..cdc3101 100644
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -42,6 +42,7 @@
 #define MS_SHARED	(1 << 20)
 #endif
 
+extern char *batch_file;
 
 #ifndef HAVE_SETNS
 static int setns(int fd, int nstype)
@@ -185,6 +186,42 @@ static int netns_exec(int argc, char **argv)
 	/* Setup bind mounts for config files in /etc */
 	bind_etc(name);
 
+	if (batch_file) {
+		int status;
+		pid_t pid;
+
+		pid = fork();
+		if (pid < 0) {
+			perror("fork");
+			return EXIT_FAILURE;
+		}
+
+		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;
+	}
+
 	if (execvp(cmd, argv + 1)  < 0)
 		fprintf(stderr, "exec of \"%s\" failed: %s\n",
 			cmd, strerror(errno));
-- 
1.8.2.1

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