Message-ID: <51F22287.8050204@cn.fujitsu.com>
Date: Fri, 26 Jul 2013 15:17:27 +0800
From: Gu Zheng <guz.fnst@cn.fujitsu.com>
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To: majianpeng <majianpeng@gmail.com>
CC: viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: question about splice
References: <201307261507562231224@gmail.com>
In-Reply-To: <201307261507562231224@gmail.com>
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Hi Jianpeng,

On 07/26/2013 03:08 PM, majianpeng wrote:

> Hi all,
> 	I used splice and found a prolem(at least i call).
> The demo is:
> A:splice(regularfileA--->pipe);
> B:splice(pipe--->regularfileB)
> Before do B, we modify the data of regA which now in pipe. The data to regularfileB willbe change.
> If we used the buff
> A:read(regA, buff);
> B: write(buff, regB);
> After A, the contend of regA can't effect the buff.
> Review the code of splice,I know the pipe share the pagecache of regA.

Right. And also this is the splice's original design intention, using share mmap rather
than copy_to_user/copy_from_user in order to achieve zero-copy.

Thanks,
Gu

> Maybe this is not a problem or am i missing something?

> 
> Thanks!
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