linux-kernel - Re: Re: question about splice

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Date:	Fri, 26 Jul 2013 15:53:54 +0800
From:	majianpeng <majianpeng@...il.com>
To:	"Gu Zheng" <guz.fnst@...fujitsu.com>
Cc:	"Al Viro" <viro@...iv.linux.org.uk>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Re: question about splice

>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.
>
If it use some method like COW, i think it can avoid this problem.
>Thanks,
>Gu
>
>> Maybe this is not a problem or am i missing something?
>
>> 
>> Thanks!
>> Jianpeng MaN�Р骒r��y����b�X�肚�v�^?)藓{.n?+�伐�{��赙zXФ.�≤�}��财�z?&j:+v��?.��赙zZ+�?+zf＂�h���~����i?��z?.�wア??�ㄨ�?&?)撷.f��^j谦y�m��@A�a囤?
>0鹅h?.��i
>
>
Thanks!
Jianpeng Ma
>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!
>> Jianpeng MaN�Р骒r��y����b�X�肚�v�^?)藓{.n?+�伐�{��赙zXФ.�≤�}��财�z?&j:+v��?.��赙zZ+�?+zf＂�h���~����i?��z?.�wア??�ㄨ�?&?)撷.f��^j谦y�m��@A�a囤?
>0鹅h?.��i
>
>