Re: [Qemu-block] [Qemu-devel] [PATCH] qemu-img: simplify img_convert

[Peter Lieven]

Am 20.04.2017 um 16:18 schrieb Eric Blake:
> On 04/20/2017 09:11 AM, Eric Blake wrote:
> > On 04/20/2017 09:05 AM, Fam Zheng wrote:
> > > On Tue, 02/28 14:35, Peter Lieven wrote:
> > > > img_convert has been around before there was an ImgConvertState or
> > > > a block backend, but it has never been modified to directly use
> > > > these structs. Change this by parsing parameters directly into
> > > > the ImgConvertState and directly use BlockBackend where possible.
> > > > Futhermore variable initalization has been reworked and sorted.
> > > >
> > > > Signed-off-by: Peter Lieven <address@hidden>
> > > I see an iotest failure with this patch, in Kevin's block-next tree:
> > >
> > > 019 1s ... - output mismatch (see 019.out.bad)
> > > --- /stor/work/qemu/tests/qemu-iotests/019.out  2017-04-17 16:19:56.523968474 
> > > +0800
> > > +++ 019.out.bad 2017-04-20 22:03:29.868216955 +0800
> > > @@ -1086,8 +1086,8 @@
> > >   
> > >   Checking if backing clusters are allocated when they shouldn't
> > >   
> > > -0/128 sectors allocated at offset 1 MiB
> > > -0/128 sectors allocated at offset 4.001 GiB
> > > +128/128 sectors allocated at offset 1 MiB
> > > +128/128 sectors allocated at offset 4.001 GiB
> > Hmm - I wonder if my patch to make 'zero with unmap' on an image with no
> > backing file prefer pure unallocated clusters over a reads-as-zero would
> > make a difference.
> > https://lists.gnu.org/archive/html/qemu-devel/2017-04/msg01728.html
> >
> > Testing now...
> Nope, did not make a difference, although it's certainly related; per my
> comment in that thread that:
>
>      Note that technically, we _could_ write a cluster as unallocated
>      rather than zero if a backing file exists but the backing file
>      also reads as zero, but that's more expensive to determine, so
>      this optimization is limited to qcow2 without a backing file.

I will look into this tomorrow.


Peter

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Peter Lieven

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