linux-kernel - Re: [net-next PATCH v4 1/3] sysctl: refactor integer handling proc code

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Message-ID: <4B7C19F1.9090106@redhat.com>
Date:	Thu, 18 Feb 2010 00:31:45 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Octavian Purdila <opurdila@...acom.com>
CC:	David Miller <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Linux Kernel Developers <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [net-next PATCH v4 1/3] sysctl: refactor integer handling proc
 code

Octavian Purdila wrote:
> On Tuesday 16 February 2010 15:08:23 you wrote:
>> Octavian Purdila wrote:
>>> On Tuesday 16 February 2010 10:41:07 you wrote:
>>>>> +
>>>>> +     if (!write && !first && left && !err)
>>>>> +             err = proc_put_newline(&buffer, &left);
>>>>> +     if (write && !err)
>>>>> +             err = proc_skip_wspace(&buffer, &left);
>>>>> +     if (err == -EFAULT /* do we really need to check for -EFAULT? */
>>>>> || +         (write && first))
>>>>> +             return err ? : -EINVAL;
>>>> The logic here seems messy, adding one or two goto's may help?
>>> OK, I'll give it a try.
>>>
>>> What about the EFAULT check, is that really required?
>> I think so, it means to keep the errno to user-space when it is EFAULT,
>> right? This seems reasonable.
>>
> 
> The problem I see is that this way we don't actually acknowledge some of the 
> set values, e.g. say that we have buffer="1 2 3" and length = 100. Although we 
> do accept values 1, 2 and 3 we don't acknowledge that to the user (as we would 
> do for, say "1 2 3 4a"), but return -EFAULT.
> 
> I think it would be better to skip this check. That means that the user will 
> get the ack for the 1, 2 and 3 values and next time it continues the write it 
> will get -EFAULT.
> 
> This will of course change the userspace ABI, albeit in a minor way, and it is 
> not clear to me if doing this is allowed (even if this new approach would be 
> the correct one).
> 

I think the right behavior is accept "1 2 3" and return the number of
bytes that we accept.
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