To: linux-kernel@vger.kernel.org
From: Stephen Hemminger <shemminger@osdl.org>
Subject: Re: splice blocks indefinitely when len > 64k?
Date: Mon, 30 Oct 2006 13:08:13 -0800
Organization: OSDL
Message-ID: <20061030130813.12b3adc1@freekitty>
References: <1162226390.7280.18.camel@systems03.lan.brontes3d.com>
	<20061030195426.GO14055@kernel.dk>
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On Mon, 30 Oct 2006 20:54:27 +0100
Jens Axboe <jens.axboe@oracle.com> wrote:

> 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.
> 

It could accept larger values but only move SPLICE_SIZE, assuming
caller checked for partial completions.

-- 
Stephen Hemminger <shemminger@osdl.org>
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