Re: [Qemu-devel] [PULL 05/21] migration: Introduce ignore-shared capability

[Markus Armbruster]

"Dr. David Alan Gilbert (git)" <address@hidden> writes:

> From: Yury Kotov <address@hidden>
>
> We want to use local migration to update QEMU for running guests.
> In this case we don't need to migrate shared (file backed) RAM.
> So, add a capability to ignore such blocks during live migration.
>
> Signed-off-by: Yury Kotov <address@hidden>
> Message-Id: <address@hidden>
> Reviewed-by: Dr. David Alan Gilbert <address@hidden>
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> ---
[...]
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 1fd7bbea9b..eab87340b2 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -409,13 +409,16 @@
>  #           devices (and thus take locks) immediately at the end of 
> migration.
>  #           (since 3.0)
>  #
> +# @x-ignore-shared: If enabled, QEMU will not migrate shared memory (since 
> 4.0)

What exactly is considered "shared memory"?

Specifically: say you have an ivshmem-plain device.  Is its shared
memory migrated?

No objection to the pull request; if documentation improvements are
necessary, we can do them in a follow-up patch.

> +#
>  # Since: 1.2
>  ##
>  { 'enum': 'MigrationCapability',
>    'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
>             'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram',
>             'block', 'return-path', 'pause-before-switchover', 'x-multifd',
> -           'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate' ] }
> +           'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
> +           'x-ignore-shared' ] }
>  
>  ##
>  # @MigrationCapabilityStatus: