linux-kernel - Re: splice blocks indefinitely when len

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Message-ID: <20061030195426.GO14055@kernel.dk>
Date:	Mon, 30 Oct 2006 20:54:27 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Daniel Drake <ddrake@...ntes3d.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: splice blocks indefinitely when len > 64k?

On Mon, Oct 30 2006, Daniel Drake wrote:
> Hi,
> 
> I'm experimenting with splice and have run into some unusual behaviour.
> 
> I am using the utilities in git://brick.kernel.dk/data/git/splice.git
> 
> In splice.h, when changing SPLICE_SIZE from:
> 
> #define SPLICE_SIZE (64*1024)
> 
> to
> 
> #define SPLICE_SIZE ((64*1024)+1)
> 
> splice-cp hangs indefinitely when copying files sized 65537 bytes or
> more. It hangs on the first splice() call.
> 
> Is this a bug? I'd like to be able to copy much more than 64kb on a
> single splice call.

You can't, internally splice is using a pipe which is currently confined
to 16 pages. The SPLICE_SIZE define isn't a suggestion in the code, it
reflects that. You could fix splice-cp to not stall on changing that,
however that still doesn't change the fact that you can only move chunks
of 64kb (on your arch) right now.

-- 
Jens Axboe

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