9:43 a.m.
Hi,
Attempting to migration from session to system qemu fails because of the
following checks in qemuMigrationCookieXMLParse():
if (STREQ(mig->remoteHostname, mig->localHostname)) {
virReportError(VIR_ERR_INTERNAL_ERROR,
_("Attempt to migrate guest to the same host %s"),
mig->remoteHostname);
goto error;
}
....
if (memcmp(mig->remoteHostuuid, mig->localHostuuid, VIR_UUID_BUFLEN) ==
0) {
virReportError(VIR_ERR_INTERNAL_ERROR,
_("Attempt to migrate guest to the same host %s"),
tmp);
goto error;
Is there a technical limitation for this error? If not, could it be
overriden with an additional flag?
cheers
--
Marc-André Lureau
9:49 a.m.
On 11/04/2014 10:43 AM, Marc-André Lureau wrote:
Hi,
Attempting to migration from session to system qemu fails because of the
following checks in qemuMigrationCookieXMLParse():
if (STREQ(mig->remoteHostname, mig->localHostname)) {
virReportError(VIR_ERR_INTERNAL_ERROR,
_("Attempt to migrate guest to the same host %s"),
mig->remoteHostname);
goto error;
}
....
if (memcmp(mig->remoteHostuuid, mig->localHostuuid, VIR_UUID_BUFLEN) == 0) {
virReportError(VIR_ERR_INTERNAL_ERROR,
_("Attempt to migrate guest to the same host %s"),
tmp);
goto error;
Is there a technical limitation for this error? If not, could it be overriden
with an additional flag?
Trying to prevent migrating to the same libvirtd instance which would
historically deadlock in libvirt's qemu driver. But migrating session ->
system shouldn't suffer from that problem, so maybe it should be smarter.
Maybe with the more fine grained locking these days we can actually make
localhost migration work? Would be useful for testing
- Cole
2:10 a.m.
On Tue, Nov 04, 2014 at 10:49:44AM -0500, Cole Robinson wrote:
On 11/04/2014 10:43 AM, Marc-André Lureau wrote:
>Hi,
>
>Attempting to migration from session to system qemu fails because of the
>following checks in qemuMigrationCookieXMLParse():
>
> if (STREQ(mig->remoteHostname, mig->localHostname)) {
> virReportError(VIR_ERR_INTERNAL_ERROR,
> _("Attempt to migrate guest to the same host %s"),
> mig->remoteHostname);
> goto error;
> }
>....
> if (memcmp(mig->remoteHostuuid, mig->localHostuuid, VIR_UUID_BUFLEN) == 0)
{
> virReportError(VIR_ERR_INTERNAL_ERROR,
> _("Attempt to migrate guest to the same host %s"),
> tmp);
> goto error;
>
>Is there a technical limitation for this error? If not, could it be overriden
>with an additional flag?
Trying to prevent migrating to the same libvirtd instance which would
historically deadlock in libvirt's qemu driver. But migrating session ->
system shouldn't suffer from that problem, so maybe it should be smarter.
Maybe with the more fine grained locking these days we can actually make
localhost migration work? Would be useful for testing
Nope, there's stuff that's on the filesystem that is tied to the QEMU
process and that would clash when migrating as you have two copies of
the same VM running at the sme time.
Regards,
Daniel
--
|: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org -o- http://virt-manager.org :|
|: http://autobuild.org -o- http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
6:16 a.m.
Hi
On Wed, Nov 5, 2014 at 9:10 AM, Daniel P. Berrange <berrange(a)redhat.com>
wrote:
Nope, there's stuff that's on the filesystem that is tied to
the QEMU
process and that would clash when migrating as you have two copies of
the same VM running at the sme time.
Ok, there is no guarantee that the VMs won't write concurrently to the disk
during migration?
Also, there are cases where VM disks/images are readonly, or image-less VMs.
Except the obvious testing case, there are other use cases that could be
interesting: moving a running VM from system to session libvirt, or the
other way around, or to a different user.
--
Marc-André Lureau
6:28 a.m.
On Wed, Nov 05, 2014 at 01:16:08PM +0100, Marc-André Lureau wrote:
Hi
On Wed, Nov 5, 2014 at 9:10 AM, Daniel P. Berrange <berrange(a)redhat.com>
wrote:
> Nope, there's stuff that's on the filesystem that is tied to the QEMU
> process and that would clash when migrating as you have two copies of
> the same VM running at the sme time.
>
Ok, there is no guarantee that the VMs won't write concurrently to the disk
during migration?
Also, there are cases where VM disks/images are readonly, or image-less VMs.
No, it isn't about the disk images. The actual guest CPUs are only executing
in one QEMU at a time, so there's not a problem wrt disk image usage. The
issue is with various other files we use. For example the QEMU monitor is a
UNIX domain socket at a specific path - you can't have both QEMUs have the
same UNIX domain socket. That's not under user control so we could change
the monitor socket path, but the problem extends to stuff that is directly
from the guest XML. ie VNC can be told to listen on a UNIX domain socket
path. virtio-serial devices are typically bound to UNIX domain sockets.
Serial ports, parallel ports, certain network device backends, and so on.
Migration fundamentally requires that the two QEMU processes involved have
completely separate filesystem namespaces, which effectively means separate
hosts (or at least separate containers which is effectively the same thing)
Except the obvious testing case, there are other use cases that could
be
interesting: moving a running VM from system to session libvirt, or the
other way around, or to a different user.
Migrating from session to system libvirt or vica-verca isn't something
that is reasonable to support either because of the different privilege
levels. The session QEMU will require the disk images to be owned by
one user account, the system QEMU will require them to be owned by a
different user account. We can't chown the images to satisfy both the
system and session QEMU at the same time.
Regards,
Daniel
--
|: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org -o- http://virt-manager.org :|
|: http://autobuild.org -o- http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
7:54 a.m.
On 11/05/2014 01:28 PM, Daniel P. Berrange wrote:
On Wed, Nov 05, 2014 at 01:16:08PM +0100, Marc-André Lureau wrote:
> Hi
>
> On Wed, Nov 5, 2014 at 9:10 AM, Daniel P. Berrange <berrange(a)redhat.com>
> wrote:
>
>> Nope, there's stuff that's on the filesystem that is tied to the QEMU
>> process and that would clash when migrating as you have two copies of
>> the same VM running at the sme time.
>>
>
> Ok, there is no guarantee that the VMs won't write concurrently to the disk
> during migration?
>
> Also, there are cases where VM disks/images are readonly, or image-less VMs.
No, it isn't about the disk images. The actual guest CPUs are only executing
in one QEMU at a time, so there's not a problem wrt disk image usage. The
issue is with various other files we use. For example the QEMU monitor is a
UNIX domain socket at a specific path - you can't have both QEMUs have the
same UNIX domain socket. That's not under user control so we could change
the monitor socket path, but the problem extends to stuff that is directly
from the guest XML. ie VNC can be told to listen on a UNIX domain socket
path. virtio-serial devices are typically bound to UNIX domain sockets.
Serial ports, parallel ports, certain network device backends, and so on.
The monitor socket location is different for qemu:///system than for
qemu:///session (or when going between two different users'
qemu:///session). But things like the VNC port do start to be an issue.
Migration fundamentally requires that the two QEMU processes involved have
completely separate filesystem namespaces, which effectively means separate
hosts (or at least separate containers which is effectively the same thing)
> Except the obvious testing case, there are other use cases that could be
> interesting: moving a running VM from system to session libvirt, or the
> other way around, or to a different user.
Migrating from session to system libvirt or vica-verca isn't something
that is reasonable to support either because of the different privilege
levels. The session QEMU will require the disk images to be owned by
one user account, the system QEMU will require them to be owned by a
different user account. We can't chown the images to satisfy both the
system and session QEMU at the same time.
This, coupled with the fact that we don't allow connection to a remote
qemu:///session instance (right now, the RPC code assumes that it will
only connect to qemu:///system), means that it is not possible to do
live migration in or out of a session instance, regardless of whether it
is on the same machine, and regardless of whether it is between the
session libvirtd of two different users.
It might be possible to migrate to file (such as virsh save), then
update permissions on the save file and other resources, then reload
from that file; but it is not a live migration.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
8:28 a.m.
On Wed, Nov 5, 2014 at 2:54 PM, Eric Blake <eblake(a)redhat.com> wrote:
The monitor socket location is different for qemu:///system than for
qemu:///session (or when going between two different users'
qemu:///session). But things like the VNC port do start to be an issue.
Not if the port is allocated, or the unix path is namespaced. But I
understand better where the problems may come from. Still, I would imagine
that libvirt would simply fail to migrate and no bad things would happen in
those cases.
> Migration fundamentally requires that the two QEMU processes involved
have
> completely separate filesystem namespaces, which effectively means
separate
> hosts (or at least separate containers which is effectively the same
thing)
>
>> Except the obvious testing case, there are other use cases that could be
>> interesting: moving a running VM from system to session libvirt, or the
>> other way around, or to a different user.
>
> Migrating from session to system libvirt or vica-verca isn't something
> that is reasonable to support either because of the different privilege
> levels. The session QEMU will require the disk images to be owned by
> one user account, the system QEMU will require them to be owned by a
> different user account. We can't chown the images to satisfy both the
> system and session QEMU at the same time.
This, coupled with the fact that we don't allow connection to a remote
qemu:///session instance (right now, the RPC code assumes that it will
only connect to qemu:///system), means that it is not possible to do
live migration in or out of a session instance, regardless of whether it
is on the same machine, and regardless of whether it is between the
session libvirtd of two different users.
Well, I managed to migrate from system to session with a disk less VM, it
was useful for testing.
All you have to do is to provide the unix socket path, ex:
qemu+unix:///session?socket=/run/user/1000/libvirt/libvirt-sock
Although it would be nice to make this easier to lookup eventually
It might be possible to migrate to file (such as virsh save), then
update permissions on the save file and other resources, then reload
from that file; but it is not a live migration.
Yes, that's what Boxes is doing afaik. I should have stated clearly I was
talking about live migration
cheers
--
Marc-André Lureau
3706
days inactive
3707
days old
6 comments
4 participants
participants (4)
-
Cole Robinson -
Daniel P. Berrange -
Eric Blake -
Marc-André Lureau