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

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Date:	Tue, 16 Feb 2010 16:00:54 +0200
From:	Octavian Purdila <opurdila@...acom.com>
To:	Cong Wang <amwang@...hat.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

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).

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