netdev - RE: Splice status

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Date:	Tue, 6 Jul 2010 05:36:16 +0300
From:	Ofer Heifetz <oferh@...vell.com>
To:	Changli Gao <xiaosuo@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>
CC:	Jens Axboe <axboe@...nel.dk>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: Splice status

Regarding your remark of replacing sendfile with recvfile, I have two questions:
1) what will be used if both are enabled in smb.conf
2) from your experience, which is faster for reading files?
________________________________________
From: Changli Gao [xiaosuo@...il.com]
Sent: Tuesday, July 06, 2010 5:01 AM
To: Eric Dumazet
Cc: Jens Axboe; Ofer Heifetz; netdev@...r.kernel.org
Subject: Re: Splice status

On Mon, Jul 5, 2010 at 8:50 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le lundi 05 juillet 2010 à 13:52 +0300, Ofer Heifetz a écrit :
>> I am using Samba, so from my understanding of the source code, it
> loops and performs splice(sock, pipe) and splice(pipe, fd). There is no
> flush of any sort in between.
>>
>> When you say drain you mean to flush all data to pipe?
>>
>
> Draining pipe before splice() call would only trigger the bug less
> often.

If we don't drain the pipe before calling splice(2), the data spliced
from pipe maybe not be what we expect. Then data corruption occurs.

>
> splice(sock, pipe) can block if caller dont use appropriate "non
> blocking pipe' splice() mode, even if pipe is empty before a splice()
> call.

I don't think it is expected. The code of sys_recvfile is much like
the sendfile(2) implementation in kernel. If sys_recvfile may block
without non_block flag, sendfile(2) may block too.

BTW: Samba can use sendfile(2) instead in sys_recvfile.

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