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 13:44:08 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	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>,
	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 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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