linux-kernel - Re: [patch 0/3] [RFC] kernel/glibc mismatch of "readlink" syscall?

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Message-ID: <20081027204509.GA27111@ub>
Date:	Tue, 28 Oct 2008 10:11:48 +0100
From:	"Andries E. Brouwer" <Andries.Brouwer@....nl>
To:	mtk.manpages@...il.com
Cc:	Daniel Gollub <dgollub@...e.de>, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org, linux-man@...r.kernel.org,
	ltp-list@...ts.sourceforge.net, "A.E. Brouwer" <aeb@....tue.nl>
Subject: Re: [patch 0/3] [RFC] kernel/glibc mismatch of "readlink" syscall?

On Fri, Oct 24, 2008 at 05:53:25PM -0500, Michael Kerrisk wrote:

> Hi Daniel,
> 
> On Thu, Oct 23, 2008 at 9:50 AM, Daniel Gollub <dgollub@...e.de> wrote:
>>
>> found something which looks for me like a kernel/glibc syscall mismatch.
>>
>> The standard and the manpages and glibc have
>> ssize_t readlink(..., size_t bufsize);
>>
>> But the kernel has
>>
>> linux-2.6/include/linux/syscalls.h:
>> asmlinkage long sys_readlink(..., int bufsiz);
>>
>> All readlink prototypes, expect the one in the kernel, have an unsigned
>> buffer size.
> 
> I agree; the inconsistency is strange.

Hmm. I am inclined not to agree. There is no reason to expect
any particular relation between the kernel prototype of sys_foo
(if such a function exists)
and the user space prototype of the foo() C-library function.

The POSIX standard, man-pages, libc include files document the
userspace / libc interface, not the system call interface.
The system call interface is mostly undocumented.

The kernel prototype is chosen for kernel-internal or historical reasons.

Andries

sys_ppc32.c:
/* Note: it is necessary to treat bufsiz as an unsigned int ... */
asmlinkage long compat_sys_readlink(..., u32 bufsiz)

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