linux-kernel - Re: [PATCH 1/15] block copy: initial XCOPY offload support

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Date:	Tue, 5 Aug 2014 18:45:47 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Pavel Machek <pavel@....cz>
cc:	"Alasdair G. Kergon" <agk@...hat.com>,
	Mike Snitzer <msnitzer@...hat.com>,
	Jonathan Brassow <jbrassow@...hat.com>,
	Edward Thornber <thornber@...hat.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>, dm-devel@...hat.com,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH 1/15] block copy: initial XCOPY offload support



On Mon, 4 Aug 2014, Pavel Machek wrote:

> On Tue 2014-07-15 15:34:47, Mikulas Patocka wrote:
> > This is Martin Petersen's xcopy patch
> > (https://git.kernel.org/cgit/linux/kernel/git/mkp/linux.git/commit/?h=xcopy&id=0bdeed274e16b3038a851552188512071974eea8)
> > with some bug fixes, ported to the current kernel.
> > 
> > This patch makes it possible to use the SCSI XCOPY command.
> > 
> > We create a bio that has REQ_COPY flag in bi_rw and a bi_copy structure
> > that defines the source device. The target device is defined in the
> > bi_bdev and bi_iter.bi_sector.
> > 
> > There is a new BLKCOPY ioctl that makes it possible to use XCOPY from
> > userspace. The ioctl argument is a pointer to an array of four uint64_t
> > values.
> 
> But it is there only for block devices, right?
> 
> Is there plan to enable tools such as /bin/cp to use XCOPY?
> 
> 									Pavel

It is interesting idea, but it would be far from simple. You could make 
sendfile (or maybe splice) use XCOPY, but it needs to interact with page 
cache.

Mikulas
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