linux-kernel - Re: splice question

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Message-ID: <20070812205614.GA29485@hardeman.nu>
Date:	Sun, 12 Aug 2007 22:56:14 +0200
From:	David Härdeman <david@...deman.nu>
To:	linux-kernel@...r.kernel.org
Subject: Re: splice question

On Sun, Aug 12, 2007 at 12:41:54PM -0700, Linus Torvalds wrote:
>On Sun, 12 Aug 2007, David H?rdeman wrote:
>> Otherwise I guess I'd have to add a second pipe, then (in a loop)
>> tee() from the first to the second pipe and then splice from the second pipe
>> to a socket. Doesn't sound very elegant and would need quite a lot of extra
>> syscalls.
>
>You really should think of this as a memcpy(), and you'll be in the right 
>mindframe. The system calls themselves are cheap.

Ok, I've implemented it using two pipes, and it works. But it does seem 
a bit wasteful...in case one client is not keeping up, the data will 
have to be tee():ed first from pipe1 to pipe2, only to then find out 
that the splice() from pipe2 to socket only does a partial transfer 
after which the data in pipe2 has to be thrown away and then the loop 
starts over with the next client.

A tee() from pipe1 to the socket could (I imagine) realize immediately 
that the socket does not have enough buffer space and return EWOULDBLOCK 
and avoid at least one copy?

-- 
David Härdeman
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