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


From: Murali Balcha
Subject: Re: [Qemu-devel] committing qcow2 to raw backing file
Date: Wed, 29 Jan 2014 13:50:04 +0000

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.

Regards,
Murali Balcah

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
>> donĀ¹t 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




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