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Date: Fri, 27 Apr 2018 14:28:05 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [Qemu-block] [RFC PATCH v2 3/7] qcow2: Implement
 copy offloading
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: qemu-devel@nongnu.org, Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, qemu-block@nongnu.org, Peter Lieven <pl@kamp.de>, Max Reitz <mreitz@redhat.com>, Ronnie Sahlberg <ronniesahlberg@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>

On Thu, 04/26 16:34, Stefan Hajnoczi wrote:
> On Wed, Apr 18, 2018 at 11:04:20AM +0800, Fam Zheng wrote:
> > +static int qcow2_co_copy_range_to(BlockDriverState *bs,
> > +                                  BdrvChild *src, uint64_t src_offset,
> > +                                  BdrvChild *dst, uint64_t dst_offset,
> > +                                  uint64_t bytes, BdrvRequestFlags flags)
> > +{
> 
> In theory this could increment the refcount if src == dst.  It's not
> necessary to go down to leaf nodes if the sharing can be handled at the
> qcow2 L2 table level.

Yes, this is a good optimization to have.

Fam