On 06/19/2016 06:10 AM, Paolo Bonzini wrote:

On 13/06/2016 11:58, Bob Liu wrote:

quoted

A guest might be migrated to other hosts with different num_queues, the
blk-core should aware of that else the reference of &vblk->vqs[qid] may be wrong.

Signed-off-by: Bob Liu <redacted>
---
 drivers/block/virtio_blk.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 42758b5..c169238 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c

@@ -819,6 +819,9 @@ static int virtblk_restore(struct virtio_device *vdev)
 	if (ret)
 		return ret;
 
+	if (vblk->num_vqs != vblk->tag_set.nr_hw_queues)
+		blk_mq_update_nr_hw_queues(&vblk->tag_set, vblk->num_vqs);
+
 	virtio_device_ready(vdev);
 
 	blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);

This should never happen; it'd be a configuration problem.

Do you mean all hosts have to be configured with the same number of ->num_vqs?
What about cases like migrating a guest from HostA to HostB while HostB is much more powerful
and would like to run more hardware queues to get better performance.

Thanks,
Bob Liu