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Date:	Mon, 22 Apr 2013 23:59:57 -0700
From:	Jerry Chu <hkchu@...gle.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	Wei Yongjun <weiyj.lk@...il.com>,
	David Miller <davem@...emloft.net>, mst@...hat.com,
	Eric Dumazet <edumazet@...gle.com>, nhorman@...driver.com,
	yongjun_wei@...ndmicro.com.cn,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] tuntap: fix error return code in tun_set_iff()

On Mon, Apr 22, 2013 at 11:19 PM, Jason Wang <jasowang@...hat.com> wrote:
>
> On 04/23/2013 01:37 PM, Jerry Chu wrote:
> > On Fri, Apr 12, 2013 at 6:17 AM, Wei Yongjun <weiyj.lk@...il.com> wrote:
> >> From: Wei Yongjun <yongjun_wei@...ndmicro.com.cn>
> >>
> >> Fix to return a negative error code from the error handling
> >> case instead of 0, as returned elsewhere in this function.
> >>
> >> Signed-off-by: Wei Yongjun <yongjun_wei@...ndmicro.com.cn>
> >> ---
> >>  drivers/net/tun.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> >> index b7c457a..729ed53 100644
> >> --- a/drivers/net/tun.c
> >> +++ b/drivers/net/tun.c
> >> @@ -1594,7 +1594,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
> >>
> >>                 if (tun->flags & TUN_TAP_MQ &&
> >>                     (tun->numqueues + tun->numdisabled > 1))
> >> -                       return err;
> >> +                       return -EBUSY;
> > I don't understand - yes it was a brainless bug to return err without
> > setting it!
>
> err was in fact set by tun_attach, so it was always zero here. The code
> works by chance w/o this patch :)

What if tun_attach() returns something > 0?

> > But won't the fix pretty much disable multi-q because only the the creation of
> > the 1st queue will succeed? I thought the intent of "tuntap: fix ambigious
> > multiqueue API" was to "Only allow TUNSETIFF to create queues.".
>
> Yes this patch will break the creation of more than 1 queues.
> >
> > The code is very confusing. (Or am I the one who is confused? Sigh.)
>
> -EBUSY is wrong here, we need return 0 for succeed here. The logic is,
> if we have more than 1 queues attached, no need to re-initialize the net
> device again. Will send patch to correct this.

A comment there will be useful!

Thanks,

Jerry

>
> Thanks.
>
> >
> > Jerry
> >
> >>         }
> >>         else {
> >>                 char *name;
> >>
> >> --
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