Re: [PATCH v4 3/6] migration/block-dirty-bitmap: fix bitmaps pre-blockdev migration during mirror job

[Eric Blake <eblake@redhat.com>]

On 5/21/20 5:06 PM, Vladimir Sementsov-Ogievskiy wrote:
> Important thing for bitmap migration is to select destination block
> node to obtain the migrated bitmap.
> 
> Prepatch, on source we use bdrv_get_device_or_node_name() to identify
> the node, and on target we do bdrv_lookup_bs.
> bdrv_get_device_or_node_name() returns blk name only for direct
> children of blk. So, bitmaps of direct children of blks are migrated by
> blk name and others - by node name.
> 
> Old libvirt is unprepared to bitmap migration by node-name,
> node-names are mostly auto-generated. So actually only migration by blk
> name works for it.
> 
> Newer libvirt will use new interface (which will be added soon) to
> specify node-mapping for bitmaps migration explicitly. Still, let's
> improve the current behavior a bit.
> 
> Now, consider classic libvirt migrations assisted by mirror block job:
> mirror block job inserts filter, so our source is not a direct child of
> blk, and bitmaps are migrated by node-names. And this just doesn't work
> with auto-generated node names.
> 
> Let's fix it by using blk-name even if some implicit filters are
> inserted.
> 
> Note2: we, of course, can't skip filters and use blk name to migrate
> bitmaps in filtered node by blk name for this blk if these filters have
> named bitmaps which should be migrated.
> 
> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1652424
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   migration/block-dirty-bitmap.c | 45 +++++++++++++++++++++++++++++++++-
>   1 file changed, 44 insertions(+), 1 deletion(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

Thanks; I'm queuing this series through my bitmaps tree, and will send a 
pull request probably on Monday.


> +
> +        /* Skip filters without bitmaos */

bitmaps - I'm touching that up

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org