linux-kernel - Re: [PATCH] sendfile removal

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Message-ID: <20070531190339.GF32105@kernel.dk>
Date:	Thu, 31 May 2007 21:03:39 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	linux-kernel@...r.kernel.org, cotte@...ibm.com, neilb@...e.de,
	zanussi@...ibm.com, Linus Torvalds <torvalds@...l.org>,
	hch@...radead.org
Subject: Re: [PATCH] sendfile removal

On Thu, May 31 2007, Hugh Dickins wrote:
> On Thu, 31 May 2007, Jens Axboe wrote:
> > 
> > This patch removes the ->sendfile() hook from the file_operations
> > structure, and replaces the sys_sendfile() mechanism to be based on
> > ->splice_read() instead. There should be no functional changes.
> > 
> > Work to be done:
> > 
> > - The ext2 xip support needs a splice_read() implementation, currently I
> >   just if 0'ed out the send xip_file_sendfile(). CC'ed Carsten, who
> >   seems to be the author of this code.
> > 
> > - shmem needs a splice_read() implementation. Optimistically CC'ed Hugh.
> 
> I'll take that "Optimistically" as a special compliment,
> rather than as a particular insult ;)

It's a compliment for sure, the "optimistically" was just mentioned
because there are lots of people mentioned in that file, but I mostly
remember you doing some heavy lifting there :-)

> Yes, thanks, please leave shmem_file_splice_read() to me, I'll give
> it priority now.  Not deep enough in yet, but I'll probably aim for
> something simple-minded (correct but slow once it hits swap).

Super, thanks!!

> > - nfds: The ->rq_sendfile_ok optimization is gone for now. I can't
> >   determine the value of it, but I'm assuming it's there for a reason.
> >   Any chance this can be converted to splice, or use something else than
> >   ->sendfile()? CC'ed Neil.
> > 
> > - relay: needs a splice_read() implementation. I think Tom already has
> >   one, CC'ed him.
> > 
> > Apart from that, it was mostly straight forward. Almost everybody uses
> > generic_file_sendfile(), which makes the conversion easy. I changed loop
> > to use do_generic_file_read() instead of sendfile, it works for me...
> 
> Christoph already picked up on that, and it's of interest to shmem too:
> loop over tmpfs in 2.6 was relying on shmem_file_sendfile, for which
> the generic route is not good enough.
> 
> If we're giving a .splice_read to everything which used to have a
> .sendfile, then I think you just need to make do_lo_read() use
> ->splice_read now?

Yes, I will make that change myself. I can do that, as I seem to have
sucessfully pushed out the remaining work to others :-)

-- 
Jens Axboe

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