netdev - Re: [PATCH] tuntap: fix error return code in tun_set

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Date:	Tue, 23 Apr 2013 15:39:08 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	Jerry Chu <hkchu@...gle.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 04/23/2013 02:59 PM, Jerry Chu wrote:
> 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?

As far as I can see, it can't return 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!

Yes, have added a comment.

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