linux-kernel - Re: [PATCH v3 0/3] preadv & pwritev syscalls.

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Date:	Mon, 15 Dec 2008 16:03:11 +0000
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Gerd Hoffmann <kraxel@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v3 0/3] preadv & pwritev syscalls.

On Mon, Dec 15, 2008 at 12:36:14PM +0100, Gerd Hoffmann wrote:

> Next revision of the patch series, with the alignment issue fixed by
> swapping the last two arguments as suggested by arch maintainers.
> 
> I've dropped the now-obsolete wrappers for mips.  Ralf, please
> double-check.

It fixes the alignment issue but still won't work; on MIPS 32-bit userspace
will pass the 64-bit argument in two registers but the 64-bit kernel code
will assume it to be passed in a single registers.  It'd be ugly but passing
a pointer to a 64-bit argument would solve the issue; something like this:

sys_preadv(unsigned long fd, const struct iovec __user *vec,
                  unsigned long vlen, loff_t __user *pos);
compat_sys_preadv(unsigned long fd, const struct compat_iovec __user *vec,
                  unsigned long vlen, loff_t __user *pos);

sys_splice uses loff_t __user * arguments as well and that's why it's
doesn't need any compat wrapper.

I'm surprised this works for x86; does x86-64 code really expect 64-bit
arguments as 2 32-bit arguments?

Patch 1/3 looks like it's a bug fix and you may want to submit this
separate from the remainder of the series for 2.6.28?

  Ralf
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