[libvirt] [PATCH v13] support offline migration

[li guang]

在 2012-11-08四的 20:28 -0700，Eric Blake写道：
> On 11/08/2012 07:57 PM, li guang wrote:
> >> What if you want to offline migrate a domain that is currently running?
> >> I think it's better to first move qemuDomainCheckEjectableMedia down to
> >> qemuMigrationBegin in a separate patch and then just use the code from
> >> v12 (without using the offline label).
> > 
> > sorry, I don't like to do offline migrate for a domain that's running.
> 
> Why not, when we've already argued it can be useful?  You don't have to
> support it in the same patch, but you should at least take the advice on
> how to refactor things so that someone else that does like the idea can
> extend things to provide it.  There's nothing wrong with having
> persistent definitions of the same domain on more than one machine, as
> long as only one machine at a time is running it; and after all, with
> live migration, if you _don't_ pass the --undefinesource flag, you will
> be left in the same situation where a persistent domain on the source is
> left behind even when the running domain has migrated.

I mean we should do this explicitly, e.g. an flag to notify us we are 
doing job for active domain by walking through offline path.
I said this before, at comment on virsh change.

> 
> >>
> >> Oh, I'm sorry for not noticing this earlier, but why exactly do we need
> >> this <offline/> element in migration cookie? It doesn't look like we need to
> >> store some additional data required for offline migration. I think just
> >> passing the VIR_MIGRATE_OFFLINE flag will be better. Not to mention that if an older
> >> libvirt gets a cookie with <offline/> element, it will just ignore it
> >> while passing a flag (which the code should already been doing anyway) should
> >> make it fail for unsupported flag.
> > 
> > without this how do you know you a offline migration at target side?
> 
> By the presence or absence of the flag.  If the flag is present, you are

seem flags was forgotten at qemuDomainMigratePrepare3, so any
preparation for offline migration will be impossible, isn't it?
do you mean I should change MigratePrepare functions to add
flags as a parameter?

> doing an offline migration.  I agree that we don't need to add anything
> to the cookie, since the only way to get offline migration is via the
> new flag, and both source and destination will see the same set of flags.
> 

-- 
li guang  lig.fnst at cn.fujitsu.com
linux kernel team at FNST, china