On Fri, Jun 25, 2021 at 11:52:10AM +0300, Denis Plotnikov wrote:
> On vhost-user-blk migration, qemu normally sends a number of commands
> to enable logging if VHOST_USER_PROTOCOL_F_LOG_SHMFD is negotiated.
> Qemu sends VHOST_USER_SET_FEATURES to enable buffers logging and
> VHOST_USER_SET_FEATURES per each started ring to enable "used ring"
> data logging.
> The issue is that qemu doesn't wait for reply from the vhost daemon
> for these commands which may result in races between qemu expectation
> of logging starting and actual login starting in vhost daemon.
Could you be more explicit please? What kind of race have you
observed? Getting a reply slows down the setup considerably and
should not be done lightly.
Thanks!
> To resolve this issue, this patch makes qemu wait for the commands result
> explicilty if VHOST_USER_PROTOCOL_F_REPLY_ACK is negotiated.
> Also, this patch adds the reply waiting for VHOST_USER_SET_PROTOCOL_FEATURES
> command to make the features setting functions work similary.
>
> Signed-off-by: Denis Plotnikov <den-plotni...@yandex-team.ru>
> ---
> hw/virtio/vhost-user.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index ee57abe04526..e47b82adab00 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -1105,10 +1105,20 @@ static int vhost_user_set_vring_addr(struct vhost_dev
> *dev,
> .hdr.size = sizeof(msg.payload.addr),
> };
>
> + bool reply_supported = virtio_has_feature(dev->protocol_features,
> +
> VHOST_USER_PROTOCOL_F_REPLY_ACK);
> + if (reply_supported) {
> + msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
> + }
> +
> if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> return -1;
> }
>
> + if (reply_supported) {
> + return process_message_reply(dev, &msg);
> + }
> +
> return 0;
> }
>
> @@ -1297,10 +1307,20 @@ static int vhost_user_set_u64(struct vhost_dev *dev,
> int request, uint64_t u64)
> .hdr.size = sizeof(msg.payload.u64),
> };
>
> + bool reply_supported = virtio_has_feature(dev->protocol_features,
> +
> VHOST_USER_PROTOCOL_F_REPLY_ACK);
> + if (reply_supported) {
> + msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
> + }
> +
> if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> return -1;
> }
>
> + if (reply_supported) {
> + return process_message_reply(dev, &msg);
> + }
> +
> return 0;
> }
>
> --
> 2.25.1
