linux-kernel - Re: splice() on two pipes

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Message-ID: <20090430062151.GU4593@kernel.dk>
Date:	Thu, 30 Apr 2009 08:21:51 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Max Kellermann <max@...mpel.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: splice() on two pipes

On Wed, Apr 29 2009, Max Kellermann wrote:
> Hi,
> 
> when I read about the splice() system call, I thought it was obvious
> that it could copy data between two pipes.  I was surprised that this
> assumption is wrong, it's not possible on 2.6.29, I get EINVAL.  Can
> anybody please explain this limitation?
> 
> Background: I want to forward data between two subprocesses, which are
> connected to me with a pipe().
> 
> I have attached a small test program which prints a table of supported
> splice operations.  Here's the output on 2.6.29.1:
> 
>  in\out  pipe    sock    reg     chr
>  pipe    no      yes     yes     yes
>  sock    no      no      no      no
>  reg     yes     no      no      no
>  chr     no      no      no      no

See sys_tee().

-- 
Jens Axboe

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