Re: [Qemu-devel] [PATCH 1/3] migration: Add x-validate-uuid capability

[Yury Kotov]

27.08.2019, 17:02, "Eric Blake" <address@hidden>:
> On 8/27/19 7:02 AM, Yury Kotov wrote:
>>  This capability realizes simple source validation by UUID.
>>  It's useful for live migration between hosts.
>>
>>  Signed-off-by: Yury Kotov <address@hidden>
>>  ---
>>   migration/migration.c | 9 +++++++++
>>   migration/migration.h | 1 +
>>   migration/savevm.c | 45 +++++++++++++++++++++++++++++++++++++++++++
>>   qapi/migration.json | 5 ++++-
>>   4 files changed, 59 insertions(+), 1 deletion(-)
>
> Any reason why this is marked experimental? It seems useful enough that
> we could probably just add it as a fully-supported feature (dropping the
> x- prefix) - but I'll leave that up to the migration maintainers.
>

I thought that all new capabilities have x- prefix... May be it's really
unnecessary here, I'm not sure.

> In fact, do we even need this to be a tunable feature? Why not just
> always enable it? As long as the UUID is sent in a way that new->old
> doesn't break the old qemu from receiving the migration stream, and that
> old->new copes with UUID being absent, then new->new will always benefit
> from the additional safety check.
>

In such case we couldn't migrate from e.g. 4.2 to 3.1
If it's not a problem then we can always use it.

>>  +++ b/qapi/migration.json
>>  @@ -415,6 +415,9 @@
>>   #
>>   # @x-ignore-shared: If enabled, QEMU will not migrate shared memory (since 
>> 4.0)
>>   #
>>  +# @x-validate-uuid: Check whether the UUID is the same on both sides or 
>> not.
>>  +# (since 4.2)
>
> Maybe:
>
> @x-validate-uuid: Send the UUID of the source to allow the destination
> to ensure it is the same.
>
> if we even need a tunable capability.
>

Yes, it sounds better. Thanks!

>>  +#
>>   # Since: 1.2
>>   ##
>>   { 'enum': 'MigrationCapability',
>>  @@ -422,7 +425,7 @@
>>              'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram',
>>              'block', 'return-path', 'pause-before-switchover', 'multifd',
>>              'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
>>  - 'x-ignore-shared' ] }
>>  + 'x-ignore-shared', 'x-validate-uuid' ] }
>>
>>   ##
>>   # @MigrationCapabilityStatus:
>
> --
> Eric Blake, Principal Software Engineer
> Red Hat, Inc. +1-919-301-3226
> Virtualization: qemu.org | libvirt.org

Regards,
Yury