netdev - Re: [PATCH -next] xen-netback: fix some error return code

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Message-ID: <CAPgLHd_yD=s0xKXop8T47hvxw2MZD9PHZ9tKKB+45Y5uOHNUVQ@mail.gmail.com>
Date:	Mon, 16 Dec 2013 21:57:43 +0800
From:	Wei Yongjun <weiyj.lk@...il.com>
To:	Ian.Campbell@...rix.com
Cc:	wei.liu2@...rix.com, yongjun_wei@...ndmicro.com.cn,
	xen-devel@...ts.xenproject.org, netdev@...r.kernel.org
Subject: Re: [PATCH -next] xen-netback: fix some error return code

On 12/16/2013 09:40 PM, Ian Campbell wrote:
> On Mon, 2013-12-16 at 13:13 +0000, Wei Liu wrote:
>> On Mon, Dec 16, 2013 at 01:49:29PM +0800, Wei Yongjun wrote:
>>> From: Wei Yongjun <yongjun_wei@...ndmicro.com.cn>
>>>
>>> Fix to return -EPROTO error code instead of 0(overwrite by maybe_pull_tail())
>>> if skb_partial_csum_set() return false.
>>>
>>> Signed-off-by: Wei Yongjun <yongjun_wei@...ndmicro.com.cn>
>>> ---
>>>  drivers/net/xen-netback/netback.c | 16 ++++++++++++----
>>>  1 file changed, 12 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
>>> index 800496b..b16daa7 100644
>>> --- a/drivers/net/xen-netback/netback.c
>>> +++ b/drivers/net/xen-netback/netback.c
>>> @@ -1108,8 +1108,10 @@ static int checksum_setup_ip(struct xenvif *vif, struct sk_buff *skb,
>>>  			goto out;
>>>  
>>>  		if (!skb_partial_csum_set(skb, off,
>>> -					  offsetof(struct tcphdr, check)))
>>> +					  offsetof(struct tcphdr, check))) {
>>> +			err = -EPROTO;
>> Why is this needed? It is set to -EPROTO before the 'switch'.
> Agreed.

As I said in the description, err is overwrited to 0 by the above
'err = maybe_pull_tail(...)' call in the same 'case XXX'.
Refer to the source code:

1104                 err = maybe_pull_tail(skb,
1105                                       off + sizeof(struct tcphdr),
1106                                       MAX_IP_HDR_LEN);
1107                 if (err < 0)
1108                         goto out;
1109 
1110                 if (!skb_partial_csum_set(skb, off,
1111                                           offsetof(struct tcphdr, check)))
1112                         goto out;



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