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Re: [Qemu-devel] [PATCH v2] migration: Convert 'status' of MigrationInfo

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v2] migration: Convert 'status' of MigrationInfo to use an enum type
Date: Mon, 02 Mar 2015 08:57:09 -0700
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On 02/27/2015 08:09 PM, zhanghailiang wrote:
> On 2015/2/28 1:42, Eric Blake wrote:
>> On 02/27/2015 10:07 AM, Dr. David Alan Gilbert wrote:
>>>> Rather than pollute the user-exposed enum with a state that we will
>>>> never report, can we come up with some internal-only method for
>>>> tracking
>>>> cancelling separate from the enum?
>>> Well I guess we could just report it; but would that break any
>>> external tools?
>> It might - I seem to recall in the past that when we added a new state
>> string, that at least libvirt choked when encountering the unknown
>> string (but I don't recall if it was migration or something else).

> Er, i have tested with returning 'cancelling' to users, and
> only when we try to cancel a migration, libvirt sometimes will report :
> Migration: [ 69 %]^Cerror: internal error: unexpected migration status
> in cancelling.
> But the cancelling process is still completed.
> And, yes, it is very rare, depend on the time window. (In my test, i add
> a sleep of 5s
> to extend the time between cancelling and cancelled.)
>> or if it would still end up resolving nicely (after all, cancelling only
>> occurs for a short window before the migration aborts anyway, so it
>> might just sort itself out when it finally gets to cancelled).
>> On the other hand, we can argue that clients that are unprepared to
>> handle new enum states gracefully are broken, and we also have the
>> argument that it is okay for a new qemu to require a new libvirt release
>> (the other direction is not okay - a new libvirt must not require
> Agreed, upgrade libvirt is reasonable.
> So, should i send v3 with exposing 'cancelling'to user, and CC libvirt ?

Yes, that sounds reasonable to me

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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