[libvirt] [PATCH 2/2] qemu: Clear source path of removable block if it is ejected.

[Daniel P. Berrange]

On Fri, Aug 12, 2011 at 09:14:09PM +0800, Osier Yang wrote:
> 于 2011年08月12日 21:04, Daniel P. Berrange 写道:

> >>   The changes affect the running domain config, (e.g. for a running
> >>domain, "virsh dumpxml" won't display the source path of the media
> >>anymore once it's ejected inside guest. But think it's reasonable
> >>to do like so.
> >No, IMHO, we really do not want to be going to the QEMU monitor every
> >time we dump XML. We want the dump XML operation to be fast&  reliable
> >even in the face of a stuck/deadlocked QEMU [1].
> >
> >If we want Dump XML to always show the corect state, then we need
> >QEMU to be giving us an event notification.
> >
> >
> >Daniel
> >
> >[1] Yes we have a problem with the balloon query update in this respect
> >     too, but we need to fix that, not make the problem worse.
> 
> Agree, but there is no better idea in my mind to solve the migration
> problem with
> "info block" but no qemu event.
> 
> Both the public migration APIs and the internal qemu migration APIs
> need to get
> the domain XML before doing preparation on dest host, all of them
> need a way to
> let the dest known if the disk is ejected. That's why I choosed to change
> "qemuDomainFormatXML".

I see the problem is that with the v2 migration protocol, we simply
call into the normal  virDomainGetXMLDesc API call. This was fixed
in v3 migration to use the virDomainMigrateBegin call to get the
XML.

> Or do you have any good idea? Thanks

I really think we should invest our time in getting QEMU to provide us
with event notifications, rather than trying to hack around it by using
info block. It really shouldn't be this hard to get an event from QEMU
when they already have the data we need.

Daniel
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