Re: [Qemu-discuss] qemu-img convert stuck

[Fam Zheng]

On Wed, 04/18 15:58, Fam Zheng wrote:
> On Wed, 04/18 15:42, David Lee wrote:
> > On Thu, Apr 12, 2018 at 11:57 PM, David Lee <address@hidden> wrote:
> > >>>
> > >>> We tested qemu-kvm-ev-2.9.0-16.el7_4.14.1 - where from the source RPM we
> > >>> verified it does contain ef6dada8b44e1e7c4bec5c1115903af9af415b50
> > >>>
> > >>> But the issue still exists.  The convert got stuck if one of the old
> > >>> active overlay
> > >>> had been 'vol-resize'd  with qemu monitor command to a larger size.  
> > >>> This looks
> > >>> like a prerequisite but not sufficient condition to trigger this 
> > >>> badness.
> > >>
> > >> So it is a separate issue. Did you try upstream master as well?
> > >>
> > >> Fam
> > >
> > > Not yet.
> > 
> > Stefan & FAM,
> > 
> > Here are the steps to reproduce this issue reliably:
> > 
> > # qemu-img create -f qcow2 test.qcow2 100m
> > ... omitted
> > # qemu-img create -F qcow2 -f qcow2 -b test.qcow2 overlay.qcow2
> > ... omitted
> > # qemu-img resize overlay.qcow2 +20m
> > Image resized.
> > # qemu-img create -F qcow2 -f qcow2 -b overlay.qcow2 overlay2.qcow2
> > ... omitted
> > # qemu-img convert overlay2.qcow2 -f qcow2 -O qcow2 combined.qcow2
> > [hang]
> > 
> > 
> > # qemu-img --version
> > qemu-img version 2.9.0(qemu-kvm-ev-2.9.0-16.el7_4.14.1)
> 
> Thanks, I can reproduce this but not on master. I will take a look.

qemu-img hangs because the convert_iteration_sectors loop cannot make any
progress when it reaches the end of the base image. It is a bug (implicitly?)
fixed by Eric Blake (Cc'ed) 's BDRV_BLOCK_EOF patches on upstream, backporting
them to the above downstream version fixes the problem for me:

commit c61e684e44272f2acb2bef34cf2aa234582a73a9
Author: Eric Blake <address@hidden>

    block: Exploit BDRV_BLOCK_EOF for larger zero blocks

commit fb0d8654ffc3ea1494067327fc4c4da5d0872724
Author: Eric Blake <address@hidden>

    block: Add BDRV_BLOCK_EOF to bdrv_get_block_status()

Fam