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From: Ralf Baechle <ralf@linux-mips.org>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH v2] Add preadv and pwritev system calls.
Date: Fri, 12 Dec 2008 15:40:24 +0000	[thread overview]
Message-ID: <20081212154024.GA31555@linux-mips.org> (raw)
In-Reply-To: <1229090440-32120-1-git-send-email-kraxel@redhat.com>

On Fri, Dec 12, 2008 at 03:00:40PM +0100, Gerd Hoffmann wrote:

> This patch adds preadv and pwritev system calls.  These syscalls are a
> pretty straightforward combination of pread and readv (same for write).
> They are quite useful for doing vectored I/O in threaded applications.
> Using lseek+readv instead opens race windows you'll have to plug with
> locking.
> 
> Other systems have such system calls too, for example NetBSD, check
> here: http://www.daemon-systems.org/man/preadv.2.html
> 
> The patch sports the actual system call implementation and the windup in
> the x86 system call tables.  Other archs are TBD.

> +asmlinkage ssize_t sys_preadv(unsigned long fd, const struct iovec __user *vec,
> +                              unsigned long vlen, loff_t pos)

> +asmlinkage ssize_t sys_pwritev(unsigned long fd, const struct iovec __user *vec,
> +                               unsigned long vlen, loff_t pos)

As so often before the devil is in the function prototype.  On some
architectures - 32-bit MIPS and PARISC, maybe others - 64-bit arguments
such as loff_t need to be passed in an _aligned_ pair of 32-bit
arguments which effectivly requires another wrapper like this around
your compat wrapper:

asmlinkage int sys32_preadv(unsigned long fd,
       const struct compat_iovec __user *vec,
       unsigned long vlen, int dummy, unsigned a5, unsigned a6)
{
	return compat_sys_preadv(fd, vec, vlen, merge_64(a5, a6));
}

merge_64() takes two 32-bit halves of a 64-bit argument and combines them
into a 64-bit argument again.

I wonder, does that merging happen magically on x86 or?

  Ralf

  parent reply	other threads:[~2008-12-12 15:43 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-12-12 14:00 Gerd Hoffmann
2008-12-12 15:29 ` Matthew Wilcox
2008-12-12 15:48   ` Gerd Hoffmann
2008-12-12 15:51     ` Matthew Wilcox
2008-12-12 16:02       ` Gerd Hoffmann
2008-12-12 17:03         ` Matthew Wilcox
2008-12-12 18:21           ` Alan Cox
2008-12-12 19:02             ` Russell King
2008-12-12 18:29         ` Scott Lurndal
2008-12-12 19:07           ` Russell King
2008-12-12 19:56             ` Gerd Hoffmann
2008-12-12 19:56               ` Gerd Hoffmann
2008-12-12 20:12               ` Russell King
2008-12-12 20:39                 ` Gerd Hoffmann
2008-12-12 20:39                   ` Gerd Hoffmann
2008-12-14 18:19               ` Pavel Machek
2008-12-15 16:37         ` Jennifer Pioch
2008-12-15 20:43           ` Gerd Hoffmann
2008-12-16  9:57             ` Arnd Bergmann
2008-12-17  1:45               ` [osol-code] " Dan Mick
2008-12-17  1:45                 ` Dan Mick
2008-12-12 19:47   ` Arnd Bergmann
2008-12-12 20:02     ` Gerd Hoffmann
2008-12-14 11:49   ` Heiko Carstens
2008-12-15  4:14   ` Paul Mackerras
2008-12-15  6:20     ` David Miller
2008-12-12 15:40 ` Ralf Baechle [this message]
2008-12-12 16:59 ` Russell King
2008-12-13  1:18 ` Michael Kerrisk

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