linux-kernel - Re: [PATCH] splice: fix wrong __splice_from

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Date:	Mon, 16 Jul 2007 19:53:01 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] splice: fix wrong __splice_from_pipe() usage

Jens Axboe <jens.axboe@...cle.com> writes:

> On Mon, Jul 16 2007, OGAWA Hirofumi wrote:
>> Hi,
>> 
>> I've noticed the nfsd read corruption by recent change. And this patch
>> fixes the problem for me, is this right fix?
>> -- 
>> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
>> 
>> 
>> __splice_from_pipe() is updating the sd->pos for the actor, but those
>> functions are passing the sd of reader side directory. So, splice
>> updates sd->pos twice.
>> 
>> This fixes usage of __splice_from_pipe().
>
> For sendfile() usage, or the nfsd path that uses splice to send?

nfsd_vfs_read() path.

nfsd_vfs_read()
    splice_direct_to_actor()
        while(len) {
            do_splice_to()                     [update sd->pos]
                -> generic_file_splice_read()  [read from sd->pos]
            nfsd_direct_splice_actor()
                -> __splice_from_pipe()        [update sd->pos]
        }

do_splice_to() updates sd->pos for read, and pass updated sd to
__splice_from_pipe(), and __splice_from_pipe() updates sd->pos for
write. So, next do_splice_to() read from wrong position.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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