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Date: Fri, 26 May 2017 12:08:34 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 3/7] qcow2: Make perform_cow() call
 do_perform_cow() twice
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To: Alberto Garcia <berto@igalia.com>
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Max Reitz <mreitz@redhat.com>, Eric Blake <eblake@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, "Denis V . Lunev" <den@openvz.org>

Am 26.05.2017 um 11:10 hat Alberto Garcia geschrieben:
> On Fri 26 May 2017 10:11:29 AM CEST, Kevin Wolf <kwolf@redhat.com> wrote:
> >> --- a/block/qcow2-cluster.c
> >> +++ b/block/qcow2-cluster.c
> >> @@ -414,6 +414,10 @@ static int coroutine_fn do_perform_cow(BlockDriverState *bs,
> >>      struct iovec iov;
> >>      int ret;
> >>  
> >> +    if (bytes == 0) {
> >> +        return 0;
> >> +    }
> >> +
> 
>    [...]
> 
> >> +static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
> >>  {
> >>      BDRVQcow2State *s = bs->opaque;
> >> +    Qcow2COWRegion *start = &m->cow_start;
> >> +    Qcow2COWRegion *end = &m->cow_end;
> >>      int ret;
> >>  
> >> -    if (r->nb_bytes == 0) {
> >> +    if (start->nb_bytes == 0 && end->nb_bytes == 0) {
> >>          return 0;
> >>      }
> >
> > With this change, it can now happen that we call do_perform_cow() with
> > bytes == 0.
> 
> Yes, but see the change I made to do_perform_cow() in the same patch
> (quoted above).

Wait... How did you manage to hack my email account and insert this
retroactively? :-)

Sorry for the noise then, I must have been looking at the source code of
the wrong commit.

Kevin