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Re: [libvirt] [PATCH] qemu: Fix migration with dname

On 10/05/2011 02:29 AM, Jiri Denemark wrote:
Quick questions (from a latecomer to the thread): what happens if I use
both the @dname and @dxml arguments?  Are we properly requiring that the
new name in both arguments match, and rejecting the migration as
impossible otherwise (since you can't request two different names), or
are we having one of the two names take priority over the other?

These are actually very good questions :-) If dname is provided, it overrides
the name from XML (no matter if that's from GetXMLDesc or dxml).

Sounds like that is worth documenting.

Also, if @dname is NULL but @dxml is provided, I think that we currently
refuse migration to a server that only understands v2 migration (since
only v3 can take @dxml).  Can @dxml in isolation be used to change the
name, without the use of @dname?

However, if dname is not provided by dxml is and it contains domain name which
is different, the destination libvirtd will have the name from dxml while
source libvirtd will use the original name and migration will not work if
those names do not match. But we don't currently have an explicit check for
dxml name. I'm thinking about requiring the name to match either original name
or dname (if set).

Yeah, after more thought, I think the following semantics are worth enforcing:

no dname or dxml - remote name is unchanged
dname but no dxml - remote name becomes dname
dname present, dxml with no name change - valid, remote uses dname
dname present, dxml with name change - dxml MUST match dname
dxml with no name change, no dname - remote name is unchanged
dxml with name change, no dname - remote name changes to dxml (*)

(*) if we can't easily change destination name using just dxml, then we could change this case to instead be an error, on the grounds that only dname can change the remote name (but once dname is present to change the name, then dxml can match either source or dname)

Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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