libvirt users - Sep 2013 - Is virsh blockcommit supported? Thanks a lot

I had test the command virsh blockcommit, but it failed, with the libvirt
version 1.1.0, and qemu version 1.6.0.
Is this feature being developing? Thanks

root at cvk-31:/vms/images# virsh -v
1.1.0
root at cvk-31:/vms/images# qemu-img -V
qemu-img version 1.6.0, Copyright (c) 2004-2008 Fabrice Bellard
usage: qemu-img command [command options]


root at cvk-31:/vms/images# virsh blockcommit Vmtest /vms/images/Vmtest1 --base
/vms/image
s/Vmtest1_base --top /vms/images/Vmtest1_base_1 --wait --verbose ;echo $?
error: invalid argument: top '/vms/images/Vmtest1_base_1' in chain for
'/vms/images/Vmtest1' has no backing file

1
root at cvk-31:/vms/images# qemu-img info /vms/images/Vmtest1_base_1
image: /vms/images/Vmtest1_base_1
file format: qcow2
virtual size: 9.8G (10485760000 bytes)
disk size: 6.0M
cluster_size: 2097152
backing file: /vms/images/Vmtest1_base

root at cvk-31:/vms/images# qemu-img info --backing-chain /vms/images/Vmtest1
image: /vms/images/Vmtest1
file format: qcow2
virtual size: 9.8G (10485760000 bytes)
disk size: 140M
cluster_size: 2097152
backing file: /vms/images/Vmtest1_base_1

image: /vms/images/Vmtest1_base_1
file format: qcow2
virtual size: 9.8G (10485760000 bytes)
disk size: 6.0M
cluster_size: 2097152
backing file: /vms/images/Vmtest1_base

image: /vms/images/Vmtest1_base
file format: qcow2
virtual size: 9.8G (10485760000 bytes)
disk size: 3.4G
cluster_size: 2097152


root at cvk-31:/vms/images# virsh blockcommit Vmtest /vms/images/Vmtest1 --base
/vms/image
s/Vmtest1_base --wait --verbose ;echo $?
error: invalid argument: could not find base '/vms/images/Vmtest1_base'
below '/vms/images/Vmtest1' in chain for '/vms/images/Vmtest1'

1
root at cvk-31:/vms/images# ls -al /vms/images/Vmtest1_base
-rw------- 1 root root 3705667584 Aug 23 10:19 /vms/images/Vmtest1_base
root at cvk-31:/vms/images# qemu-img info /vms/images/Vmtest1_base
image: /vms/images/Vmtest1_base
file format: qcow2
virtual size: 9.8G (10485760000 bytes)
disk size: 3.4G
cluster_size: 2097152


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[dropping libvir-list - this is a usage question, not a development
question]

On 09/02/2013 11:29 PM, Guozhonghua wrote:
> I had test the command virsh blockcommit, but it failed, with the libvirt
version 1.1.0, and qemu version 1.6.0.
> Is this feature being developing? Thanks
The feature is supported, but you have to use it correctly.  In
particular, your backing chain MUST label the backing format of all
backing files in the image metadata, or you must set
'allow_disk_format_probing' to 1 in /etc/libvirt/qemu.conf (be aware
that doing so is a security risk if you use any raw images and have
untrustworthy guests).
> root@cvk-31:/vms/images# virsh blockcommit Vmtest /vms/images/Vmtest1
--base /vms/image
> s/Vmtest1_base --top /vms/images/Vmtest1_base_1 --wait --verbose ;echo $?
> error: invalid argument: top '/vms/images/Vmtest1_base_1' in chain
for '/vms/images/Vmtest1' has no backing file
Your command line looks correct, so I suspect that what happened is that
you failed to mark the format of Vmtest1_base_1 in Vmtest1, which means
that libvirt is treating it as raw rather than qcow2; and raw files do
not have backing images.

I _really_ need to add a command to virsh that will show the entire
backing chain, according to libvirt, as it would immensely help in
debugging such issues.
> root@cvk-31:/vms/images# qemu-img info --backing-chain /vms/images/Vmtest1
> image: /vms/images/Vmtest1
> file format: qcow2
> virtual size: 9.8G (10485760000 bytes)
> disk size: 140M
> cluster_size: 2097152
> backing file: /vms/images/Vmtest1_base_1
Yep, my suspicion is confirmed - libvirt is treating Vmtest1_base_1 as
raw instead of qcow2, because Vmtest1 has missing metadata.  When done
PROPERLY, this block would ALSO have the following line:

backing file format: qcow2

How are you creating your backing chain?  By hand with 'qemu-img
create'?  If so, be sure you pass the '-o backing_fmt=qcow2' option
for
any file that wraps another qcow2 file.
> This e-mail and its attachments contain confidential information from H3C,
which is
This list is publicly archived, rendering such a disclaimer
unenforceable.  It is considered poor netiquette to send from an
employer's account if they tack on such legalese, and you may want to
consider using a personal account instead.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Thanks a lot. :)


I will check it and have a test on it.

Guozhonghua


-----邮件原件-----
发件人: Eric Blake [mailto:eblake@redhat.com]
发送时间: 2013年9月3日 23:47
收件人: guozhonghua 02084
抄送: libvirt-users@redhat.com
主题: Re: [libvirt-users] Is virsh blockcommit supported? Thanks a lot

[dropping libvir-list - this is a usage question, not a development question]

On 09/02/2013 11:29 PM, Guozhonghua wrote:
> I had test the command virsh blockcommit, but it failed, with the libvirt
version 1.1.0, and qemu version 1.6.0.
> Is this feature being developing? Thanks
The feature is supported, but you have to use it correctly.  In particular, your
backing chain MUST label the backing format of all backing files in the image
metadata, or you must set 'allow_disk_format_probing' to 1 in
/etc/libvirt/qemu.conf (be aware that doing so is a security risk if you use any
raw images and have untrustworthy guests).
> root@cvk-31:/vms/images# virsh blockcommit Vmtest /vms/images/Vmtest1
> --base /vms/image s/Vmtest1_base --top /vms/images/Vmtest1_base_1 --wait
--verbose ;echo $?
> error: invalid argument: top '/vms/images/Vmtest1_base_1' in chain
for
> '/vms/images/Vmtest1' has no backing file
Your command line looks correct, so I suspect that what happened is that you
failed to mark the format of Vmtest1_base_1 in Vmtest1, which means that libvirt
is treating it as raw rather than qcow2; and raw files do not have backing
images.

I _really_ need to add a command to virsh that will show the entire backing
chain, according to libvirt, as it would immensely help in debugging such
issues.
> root@cvk-31:/vms/images# qemu-img info --backing-chain
> /vms/images/Vmtest1
> image: /vms/images/Vmtest1
> file format: qcow2
> virtual size: 9.8G (10485760000 bytes) disk size: 140M
> cluster_size: 2097152
> backing file: /vms/images/Vmtest1_base_1
Yep, my suspicion is confirmed - libvirt is treating Vmtest1_base_1 as raw
instead of qcow2, because Vmtest1 has missing metadata.  When done PROPERLY,
this block would ALSO have the following line:

backing file format: qcow2

How are you creating your backing chain?  By hand with 'qemu-img
create'?  If so, be sure you pass the '-o backing_fmt=qcow2' option
for any file that wraps another qcow2 file.
> This e-mail and its attachments contain confidential information from
> H3C, which is
This list is publicly archived, rendering such a disclaimer unenforceable.  It
is considered poor netiquette to send from an employer's account if they
tack on such legalese, and you may want to consider using a personal account
instead.

--
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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Hi,

I have another question, when I do the blockcommit command and get the result
" Top image as the active layer is currently unsupported ", is it
being developed?
root@cvk-31:/vms/images# virsh blockcommit Vmtest /vms/images/Vmtest1;echo $?
error: internal error unable to execute QEMU command 'block-commit': Top
image as the active layer is currently unsupported

1

But as I specified the commit file which is not the current image file, it will
be work, such as below:
root@cvk-31:/vms/images# qemu-img info --backing-chain /vms/images/Vmtest1
image: /vms/images/Vmtest1
file format: qcow2
virtual size: 9.8G (10485760000 bytes)
disk size: 18M
cluster_size: 65536
backing file: /vms/images/Vmtest1_base_1
backing file format: qcow2

image: /vms/images/Vmtest1_base_1
file format: qcow2
virtual size: 9.8G (10485760000 bytes)
disk size: 196K
cluster_size: 65536
backing file: /vms/images/Vmtest1_base
backing file format: qcow2

image: /vms/images/Vmtest1_base
file format: qcow2
virtual size: 9.8G (10485760000 bytes)
disk size: 3.4G
cluster_size: 2097152
root@cvk-31:/vms/images# virsh blockcommit Vmtest /vms/images/Vmtest1 --base
/vms/images/Vmtest1_base --top /vms/images/Vmtest1_base_1 --wait --verbose;echo
$?
Block Commit: [100 %]
Commit complete
0

-------------------------------------------------------------------------------------------------------------------------------------
本邮件及其附件含有杭州华三通信技术有限公司的保密信息，仅限于发送给上面地址中列出
的个人或群组。禁止任何其他人以任何形式使用（包括但不限于全部或部分地泄露、复制、
或散发）本邮件中的信息。如果您错收了本邮件，请您立即电话或邮件通知发件人并删除本
邮件！
This e-mail and its attachments contain confidential information from H3C, which
is
intended only for the person or entity whose address is listed above. Any use of
the
information contained herein in any way (including, but not limited to, total or
partial
disclosure, reproduction, or dissemination) by persons other than the intended
recipient(s) is prohibited. If you receive this e-mail in error, please notify
the sender
by phone or email immediately and delete it!