linux-kernel - Re: [PATCH] kernel/sysctl.c: If "count" including the terminating byte '\0' the write system call should retrun success.

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Date:	Wed, 26 Aug 2015 00:44:46 +0800
From:	Sean Fu <fxinrong@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Eric B Munson <emunson@...mai.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Don Zickus <dzickus@...hat.com>,
	Heinrich Schuchardt <xypron.glpk@....de>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/sysctl.c: If "count" including the terminating
 byte '\0' the write system call should retrun success.

On Tue, Aug 25, 2015 at 10:15 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Tue, 25 Aug 2015 15:50:18 +0800
> Sean Fu <fxinrong@...il.com> wrote:
>
>> On Tue, Aug 25, 2015 at 10:24 AM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>> >
>> >
>> > On August 24, 2015 6:57:57 PM MDT, Sean Fu <fxinrong@...il.com> wrote:
>> >>An application from HuaWei which works fine on 2.6 encounters this
>> >>issue on 3.0 or later kernel.
>> >
>> > My sympathies.  Being stuck with a 3rd party application you can barely talk about that has been broken for 5years and no one reported it.
>> >
>> > Ordinarily we would fix a regression like this. As it has been 5years the challenge now is how do we tell if there are applications that depend on the current behavior.
>> >
>> > Before we can change the behavior back we need a convincing argument that we won't cause a regression in another application by making the change.
>> >
>> > I do not see how such an argument can be made.  So you have my sympathies but I do not see how we can help you.
>> We should consider this patch basing on my following arguments.
>> 1 Different version kernel should keep consistent on this behavior.
>
> The thing is, the above argument is against the patch. The behavior
> changed 2 years ago, and nobody noticed. Changing it back only causes
> more inconsistent behavior.
It is impossible to cause more inconsistent behavior.
it just enhance compatibility(support "xx...x\0").
This patch just modify "proc_wspace_sep" array. and "proc_wspace_sep" is static.
Only "proc_get_long" used this array, "proc_get_long" is also static.
There are only 4 place to call "proc_get_long" in kernel/sysctl.c.
I will prove that these 4 callers have no bad impact later.

>
>
>> 2 This writting behavior on proc file should be same with writting on
>> regular file as possible as we can.
>
> Writing to a proc file causes kernel actions. Writing to a regular file
> just saves data. That's not an argument here.
>
>> 3 This patch does not have any potential compatibility risk with 3rd
>> party application.
>
> How do you know that?
I will prove that all other write usage is not impacted later.

Thanks for all reply.

Sean
>
> -- Steve
>
>> 4 Support writting "1...\0" to proc file.
>>
>> >
>> > Eric
>> >
>
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