Message-ID: <55DB8B95.7050005@gmx.de>
Date: Mon, 24 Aug 2015 23:24:37 +0200
From: Heinrich Schuchardt <xypron.glpk@gmx.de>
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To: Andrew Morton <akpm@linux-foundation.org>, Sean Fu <fxinrong@gmail.com>
CC: "Eric W. Biederman" <ebiederm@xmission.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Ulrich Obergfell <uobergfe@redhat.com>,
        "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>,
        Prarit Bhargava <prarit@redhat.com>,
        Eric B Munson <emunson@akamai.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Thomas Gleixner <tglx@linutronix.de>, Don Zickus <dzickus@redhat.com>,
        David Rientjes <rientjes@google.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kernel/sysctl.c: If "count" including the terminating
 byte '\0' the write system call should retrun success.
References: <CAGk-QBt147T_A-BuPn1M2rHkQaCn0_RXgZvx3Zbf9L3_7CDQtQ@mail.gmail.com>	<FBEE5CF8-6B74-4060-9553-1D42BDAD15FA@xmission.com>	<CAGk-QBuwieG3ymXstdLTewAOONPKorpQFD_5QqjJ2BkkLQb2-g@mail.gmail.com> <20150824134408.be0ffaa654f7d26802119b81@linux-foundation.org>
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This seems to be the relevant patch:

https://lkml.org/lkml/2010/5/5/104
Amerigo Wang <amwang@redhat.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@gmail.com> wrote:
> 
>> On Mon, Aug 24, 2015 at 8:27 PM, Eric W. Biederman
>> <ebiederm@xmission.com> wrote:
>>>
>>>
>>> On August 24, 2015 1:56:13 AM PDT, Sean Fu <fxinrong@gmail.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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