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

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

[Nicolas Dichtel]

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().

Signed-off-by: JunweiZhang <junwei.zhang@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---
 ip/ipnetns.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index fa2b681..a4a68a7 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");
@@ -185,10 +186,17 @@ 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)
+	pid = fork();
+	if (pid < 0)
+		return EXIT_FAILURE;
+	else if (pid > 0)
+		waitpid(pid, &status, 0);
+	else if (execvp(cmd, argv + 1)  < 0) {
 		fprintf(stderr, "exec of \"%s\" failed: %s\n",
 			cmd, strerror(errno));
-	return EXIT_FAILURE;
+		return EXIT_FAILURE;
+	}
+	return WIFEXITED(status) ? EXIT_SUCCESS : EXIT_FAILURE;
 }
 
 static int is_pid(const char *str)
-- 
1.8.2.1

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

[Ben Hutchings]

On Fri, 2013-07-05 at 18:05 +0200, Nicolas Dichtel wrote:
> 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().

A Unix shell forks every command it runs, so why should ip do this too?

[...]
> +       return WIFEXITED(status) ? EXIT_SUCCESS : EXIT_FAILURE;
[...]

So you throw away the original exit code of the child process.

I suspect your actual problem has to do with the exit code of the child,
and your shell script contains 'set -e'.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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

[Nicolas Dichtel]

Le 05/07/2013 22:49, Ben Hutchings a écrit :
> On Fri, 2013-07-05 at 18:05 +0200, Nicolas Dichtel wrote:
>> 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().
>
> A Unix shell forks every command it runs, so why should ip do this too?
Just to show the problem:

$ 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.

>
> [...]
>> +       return WIFEXITED(status) ? EXIT_SUCCESS : EXIT_FAILURE;
> [...]
>
> So you throw away the original exit code of the child process.
Right, should use WEXITSTATUS(). I will send a v2.

>
> I suspect your actual problem has to do with the exit code of the child,
> and your shell script contains 'set -e'.
Maybe I miss something, but man execvp says:
"The exec() functions only return if an error has have occurred."

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

[Ben Hutchings]

On Mon, 2013-07-08 at 11:41 +0200, Nicolas Dichtel wrote:
> Le 05/07/2013 22:49, Ben Hutchings a écrit :
> > On Fri, 2013-07-05 at 18:05 +0200, Nicolas Dichtel wrote:
> >> 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().
> >
> > A Unix shell forks every command it runs, so why should ip do this too?
> Just to show the problem:
> 
> $ cat test.batch
> netns add netns1
> netns exec netns1 ip l
> netns
> $ ip -b test.batch
[...]

Sorry, I totally missed that there is this 'batch' sub-command in ip.  I
think you are right that it should fork in this case.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.