Re: New copyfile system call - discuss before LSF?

From: Eric Wong
Date: Thu Feb 21 2013 - 19:29:19 EST

Jeremy Allison <jra@xxxxxxxxx> 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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