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

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Message-ID: <51DA893C.8070002@6wind.com>
Date:	Mon, 08 Jul 2013 11:41:16 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	shemminger@...tta.com, netdev@...r.kernel.org,
	junwei.zhang@...nd.com
Subject: Re: [PATCH iproute2] ipbatch: fix use of 'ip netns exec'

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@...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().
>
> 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."
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