#x27;s a timing race. Whatever your system has that reads block devices
(udev?) may or may not have completed by the time you disconnect
/dev/nbd0. If it wins the race and your disconnect is slow enough,
you get no messages.
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Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
eded to drive the kernel module?
Can you add a --trace parameter to qemu-nbd to cause it to log more
details about what is going on?
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Eric Blake, Principal Software Engineer
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Virtualization: qemu.org | libvirt.org
lf to give you a sample command
line.
> >>
> >> access to the E: drive is extremely slow and the system events report
> >> many storahci (129: reinit \device\RaidPort0 sent) and disk (153: I/O
> >> @0x3f on disk 1 \device\0001f replayed) warnings.
> >>
> >> regards.
> >>
> >
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Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
ugin to use python instead of perl, which
means it is that much easier for a future RHEL to pull it in. We still
ought to consider having a tar filter, either in place of or in addition
to, the tar plugin (similar to how we recently converted nbdkit's ext4
support from a plugin to a filter) - hav
ould be able to do all this on your behalf - except that
getting libvirt to use blockdev-add has been a multi-year project, and
Peter Krempa is still producing patches that will hopefully land in
libvirt 5.1 along those lines. But again, libvirt questions may be
better asked on the libvirt list.
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Eric Blake, Principal Software Engineer
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Virtualization: qemu.org | libvirt.org
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ion bugs or lack of
> some nice functionality that we are talking here?
Lack of functionality. In particular, the 4.0 commands
block-dirty-bitmap-{enable,merge,disable} (or their 3.1 counterparts
x-block-dirty-bitmap-*) are essential to the workflow of differential
backups (without being able to
irtied,
and pull those portions of the disk over NBD rather than qemu pushing
them); I even have a working demo of preliminary libvirt code driving
that which I presented at last year's KVM Forum.
> Workaround: Couldnot achieve this. So if an incremental fails after block
> jobs succee
to the kernel folks; nothing
qemu can do about it (a userspace socket serving NBD data should not be
able to cause the kernel NBD client to result in a subsequent kernel
crash, regardless of how bad data loss is when the socket disappears out
from under the kernel).
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Eric Blake, Principal Software Engineer
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Virtualization: qemu.org | libvirt.org
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isible data from the image, we don't really care whether the
guest-visible data is consistent. BDRV_O_NO_IO is our promise that we
are reading only metadata, not guest-visible data. So that change makes
sense.
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Eric Blake, Principal Software Engineer
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Virtualization: qemu.org | libvirt.org
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mage, IS currently documented and supported (so we DO have a
safe fallback, regardless of when 'qemu-img create -u ... size' actually
lands).
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Virtualization: qemu.org | libvirt.org
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nt, because it makes more sense to implement the
working feature than to document the workaround to a missing feature.
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Eric Blake, Principal Software Engineer
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Virtualization: qemu.org | libvirt.org
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then providing the size alone will no longer be sufficient to
prevent the probe - you'd have to use -u to prevent the probe, or change
your workflow to create the image without a backing file then add in the
backing information via 'qemu-img rebase -u'.
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Eric Blake, Principal Software Engineer
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Virtualization: qemu.org | libvirt.org
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On 06/28/2017 08:07 AM, Eric Blake wrote:
> On 06/27/2017 04:04 AM, Han Han wrote:
>> Hi all, I get an error when block-commit to nbd backend:
>> First, prepare a back file for nbd storage:
>> # qemu-img create -f qcow2 -b 'json:{"file.driver":"nbd&q
you get (especially via libvirt) is
expected. Live commit to a backing file is only possible where it is
easy to convert the backing file to writable, which is not easy with NBD.
>
> qemu command:
> {"execute":"block-commit","arguments":{"device":"drive-virtio-disk0","top":"/tmp/n2.s1","base":"nbd://xx.xx.xx.xx:10803/nbd_raw"},"id":"libvirt-22"}
>
> So is it a expected result? Does it support to block-commit to nbd?
> Thanks
>
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Eric Blake, Principal Software Engineer
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Virtualization: qemu.org | libvirt.org
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support both ways. Maybe:
qemu-img query-max-size -O qcow2 --size 20G
qemu-img query-max-size -O qcow2 -f raw input.raw
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Eric Blake eblake redhat com+1-919-301-3266
Libvirt virtualization library http://libvirt.org
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on
> qemu-i386 version 2.4.90, Copyright (c) 2003-2008 Fabrice Bellard
>
> with the referenced commit reverted apt-get and maple work fine.
I don't see how that commit would expose any core dumps - it was just
deleting unused code. Showing more details about the crash would help
di
.18 where older
libvirt got thrown off by newer qemu returning a status with 0 progress
but equal to the block job size, and libvirt interpreting it as job
complete with a result of failing the command; splitting the job into
distinct parts was indeed the right workaround as it prevented hitting
the window. See libvirt commit eae5924
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things down to the point that
it cannot reply; instead, to learn if the command was successful, you
must listen to the ordinary QMP monitor for an event notification
corresponding to the change in guest state.
Libvirt already handles this interaction correctly.
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Eric Blake eblake redha
s raw,
>> rather than qcow2. My platform is libvirt+qemu. the image type of this vm
>> is indeed qcow2. I do not know how to let nbd know this image format.
>
> Hmm, I wonder if `virsh --migrate` should have a --format (or -F) option
> that one can specify the format. Let'
what the NBD is serving - the NBD connection MUST be raw, unless you
have a funky situation with a qcow2 file whose contents are also a
nested qcow2 encoding of data.
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Eric Blake eblake redhat com+1-919-301-3266
Libvirt virtualization library http://libvirt.org
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act, modern
libvirt/qemu does this for you by setting up an NBD server on the
destination, doing a data mirror from the source into the destination
(so that you DO have shared storage, at least for the duration of the
migration), then doing the live migration, then tearing down the NBD
mirroring link.
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Eric Blake eblake redhat com+1-919-301-3266
Libvirt virtualization library http://libvirt.org
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hot with shared storage destination
base <- mid <- active(frozen) <- shared
copy base, mid, and active to the destination
live migrate using shared storage instead of doing storage migration
block-commit shared back into active
base <- mid <- active
where the shared storage only needs to
rameter, hw_qemu_guest_agent=yes for
> the guest image.
> And then installing qemu-guest-agent inside the guest.
>
> What steps do i have to follow for windows ?
The same steps - qemu-guest-agent is available for both Linux and
Windows guests.
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Eric Blake eblake redhat com+1-91
tall qemu-kvm-rhev
with yum. All features will be available. It would be simpler to have
a CentOS SIG build this, but it hasn't happened yet.
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Eric Blake eblake redhat com+1-919-301-3266
Libvirt virtualization library http://libvirt.org
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t. Since
you are using CentOS, I'd look into finding the qemu-kvm-rhev package
(the default qemu-kvm package is intentionally shipped with fewer
supported features, and you have run into one of those features).
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Eric Blake eblake redhat com+1-919-301-3266
Libvirt virtualization libr
try to build qga
yourself, instead of relying on someone else to provide a pre-built binary.
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Eric Blake eblake redhat com+1-919-301-3266
Libvirt virtualization library http://libvirt.org
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>
> [root@sdsr720-14 ~]# virsh qemu-agent-command vm_win_06 '{ "execute":
> "guest_ping"}'
and compare it to here. There is no guest_ping command, only
guest-ping. It's a bug in libvirt that guest-agent-command doesn't
output a useful error
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