linux-kernel - Re: [PATCH v2 4/4] splice: fix updating sd->pos wrongly

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Message-ID: <AANLkTikycDykLRPnRZFAbdIszTOMDVFoX4DGiLcCvSqd@mail.gmail.com>
Date:	Sat, 29 May 2010 22:22:54 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Jamie Lokier <jamie@...reable.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>, axboe@...nel.dk,
	viro@...iv.linux.org.uk, mszeredi@...e.cz,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] splice: fix updating sd->pos wrongly

On Sat, May 29, 2010 at 10:09 PM, Jamie Lokier <jamie@...reable.org> wrote:
>
> Not true if the "file" is /dev/mem or /dev/kmem.  The starting offset
> can be negative, so can end at zero.
>
> It's an obscure case and I don't know if you can sendfile from
> /dev/{,k}mem anyway :-) but illustrates why sd->pos != 0 is dubious.
>

So the safe way is checking if splice_read() updates pos or not, isn't it?

if (sd->pos != prev_pos)
    sd->pos = prev_pos + ret;


-- 
Regards，
Changli Gao(xiaosuo@...il.com)
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