linux-kernel - Re: New copyfile system call

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Message-ID: <20130222002901.GA22670@dcvr.yhbt.net>
Date:	Fri, 22 Feb 2013 00:29:01 +0000
From:	Eric Wong <normalperson@...t.net>
To:	Jeremy Allison <jra@...ba.org>
Cc:	"Myklebust, Trond" <Trond.Myklebust@...app.com>,
	Ric Wheeler <rwheeler@...hat.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Chris L. Mason" <clmason@...ionio.com>,
	Christoph Hellwig <hch@...radead.org>,
	Alexander Viro <aviro@...hat.com>,
	"Martin K. Petersen" <mkp@....net>, Hannes Reinecke <hare@...e.de>
Subject: Re: New copyfile system call - discuss before LSF?

Jeremy Allison <jra@...ba.org> wrote:
> On Thu, Feb 21, 2013 at 01:51:53PM +0000, Myklebust, Trond wrote:
> > On Thu, 2013-02-21 at 12:37 +0100, Ric Wheeler wrote:
> > > We have debated the need to have a system call to allow for offloading copy 
> > > operations, for example to an NFS server (part to the new NFS 4.2 
> > > specification), SCSI target device (two different SCSI commands do this), local 
> > > file systems (reflink, etc) and I suspect many other possible parts of the stack 
> > > could implement this.
> > 
> > sendfile64() pretty much already has the right arguments for a
> > "copyfile", however it would be nice to add a 'flags' parameter: the
> > NFSv4.2 version would use that to specify whether or not to copy file
> > metadata.
> 
> What would be really nice is if sendfile allowed zero-copy
> from network socket to a file descriptor. That would help
> a *lot* of my small system OEMs (and no splice() just doesn't
> cut it :-).

I've often wish the pipe requirement of splice() could be dropped,
to allow copying between arbitrary FDs.  Perhaps this can be done?
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