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:	Mon, 24 Aug 2015 23:24:37 +0200
From:	Heinrich Schuchardt <xypron.glpk@....de>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Sean Fu <fxinrong@...il.com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Eric B Munson <emunson@...mai.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Don Zickus <dzickus@...hat.com>,
	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.

This seems to be the relevant patch:

https://lkml.org/lkml/2010/5/5/104
Amerigo Wang <amwang@...hat.com>  2010-05-05 02:26:45
00b7c3395aec3df43de5bd02a3c5a099ca51169f
+static const char proc_wspace_sep[] = { ' ', '\t', '\n' };

So since 2010 we have the current behavior.

Best regards

Heinrich Schuchardt

On 24.08.2015 22:44, Andrew Morton wrote:
> On Mon, 24 Aug 2015 23:33:58 +0800 Sean Fu <fxinrong@...il.com> wrote:
> 
>> On Mon, Aug 24, 2015 at 8:27 PM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>>>
>>>
>>> On August 24, 2015 1:56:13 AM PDT, Sean Fu <fxinrong@...il.com> wrote:
>>>> when the input argument "count" including the terminating byte "\0",
>>>> The write system call return EINVAL on proc file.
>>>> But it return success on regular file.
>>>
>>> Nonsense.  It will write the '\0' to a regular file because it is just data.
>>>
>>> Integers in proc are more than data.
>>>
>>> So I see no justification for this change.
>> In fact, "write(fd, "1\0", 2)" on Integers proc file return success on
>> 2.6 kernel. I already tested it on 2.6.6.60 kernel.
>>
>> So, The latest behavior of "write(fd, "1\0", 2)" is different from old
>> kernel(2.6).
>> This maybe impact the compatibility of some user space program.
> 
> 2.6 was a long time ago.  If this behaviour change has happened in the
> last 1-2 kernel releases then there would be a case to consider making
> changes.  But if the kernel has been this way for two years then it's
> too late to bother switching back to the old (and strange) behaviour.
> 
> 
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