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

[Eric Blake]

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.

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.

> +++ 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.

> +#
>  # 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

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