Re: [Qemu-devel] committing qcow2 to raw backing file

[Kevin Wolf]

Am 29.01.2014 um 14:50 hat Murali Balcha geschrieben:
> Thanks for the quick reply. The scenario I have is little different. The
> backing file is only 40 MB where as the virtual size of qcow2 is 1GB.
> 
> address@hidden:/tmp/20bcb425-d3c5-4c0f-819c-7c9b1a16fde3$ qemu-img
> info 2e94bd45-7e4e-4e04-a8b4-74d579cad892_vda.qcow2
> image: 2e94bd45-7e4e-4e04-a8b4-74d579cad892_vda.qcow2
> file format: raw
> virtual size: 39M (41126400 bytes)
> disk size: 39M
> address@hidden:/tmp/20bcb425-d3c5-4c0f-819c-7c9b1a16fde3$ qemu-img
> info 2bc87796-60e8-4024-8a40-fae817e094da_vda.qcow2
> image: 2bc87796-60e8-4024-8a40-fae817e094da_vda.qcow2
> file format: qcow2
> virtual size: 1.0G (1073741824 bytes)
> disk size: 3.3M
> cluster_size: 65536
> backing file: 
> /tmp/20bcb425-d3c5-4c0f-819c-7c9b1a16fde3/2e94bd45-7e4e-4e04-a8b4-74d579cad
> 892_vda.qcow2
> Format specific information:
>     compat: 0.10
> address@hidden:/tmp/20bcb425-d3c5-4c0f-819c-7c9b1a16fde3$ qemu-img
> commit 2bc87796-60e8-4024-8a40-fae817e094da_vda.qcow2
> qemu-img: Error while committing image
> 
> The qemu-img is bailing out when it detected that commit is happening
> beyond raw backing image.
> 
> 
> Is this a valid commit operation. This is how openstack sets up vms.

This is completely unrelated to the patch that you mentioned then.

The problem is that qemu-img would have to increase the image size of
the backing file first before it can commit all the data to it. I
believe there was a patch by Jeff (CC'ed) that would do exactly this.

Kevin

> On 1/29/14, 4:24 AM, "Kevin Wolf" <address@hidden> wrote:
> 
> >Am 29.01.2014 um 03:09 hat Murali Balcha geschrieben:
> >> Hi,
> >> My apologies for reaching out directly on your email. However I am new
> >>qemu and
> >> don¹t know the active mailing list for qemu related issues.
> >
> >The qemu mailing list is address@hidden You should generally
> >direct your questions there, though keeping individual persons in the CC
> >list is fine.
> >
> >> I have seen your
> >> name in one of the patches related to this
> >>issue.https://github.com/gooselinux/
> >> qemu-kvm/blob/master/kvm-block-Fix-image-re-open-in-bdrv_commit.patch
> >> 
> >>  We are using 1.6.90 and 1.7 of qemu. the qemu-img errors out with
> >>exact same
> >> message when we try to commit qcow2 delta to raw image. Looking at the
> >>code, we
> >> realized that that patch you discussed above did not make it 1.6.90
> >>branch we
> >> are using. Am I missing something.
> >
> >I am not sure which error message you mean, but the patch that you
> >mentioned has been in qemu since version 0.14.0. You won't see it in the
> >current code any more because of later changes that switched to using
> >bdrv_reopen() instead.
> >
> >For me, committing to a raw image works fine with current git master:
> >
> >$ qemu-img create -f raw /tmp/backing.raw 4G
> >Formatting '/tmp/backing.raw', fmt=raw size=4294967296
> >$ qemu-img create -f qcow2 -b /tmp/backing.raw /tmp/overlay.qcow2
> >Formatting '/tmp/overlay.qcow2', fmt=qcow2 size=4294967296
> >backing_file='/tmp/backing.raw' encryption=off cluster_size=65536
> >lazy_refcounts=off
> >$ qemu-io -c 'write 0 4k' /tmp/overlay.qcow2
> >wrote 4096/4096 bytes at offset 0
> >4 KiB, 1 ops; 0.0009 sec (4.090 MiB/sec and 1047.1204 ops/sec)
> >$ qemu-img commit /tmp/overlay.qcow2
> >Image committed.
> >
> >Kevin
>