Re: [PATCH 09/16] vhost-user: enable/disable a single vring

[Jason Wang <jasowang@redhat.com>]

On Tue, Jul 26, 2022 at 1:27 PM Kangjie Xu <kangjie.xu@linux.alibaba.com> wrote:
>
>
> 在 2022/7/26 12:07, Jason Wang 写道:
> >
> > 在 2022/7/18 19:17, Kangjie Xu 写道:
> >> Implement the vhost_set_single_vring_enable, which is to enable or
> >> disable a single vring.
> >>
> >> The parameter wait_for_reply is added to help for some cases such as
> >> vq reset.
> >>
> >> Meanwhile, vhost_user_set_vring_enable() is refactored.
> >>
> >> Signed-off-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
> >> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> >> ---
> >>   hw/virtio/vhost-user.c | 55 ++++++++++++++++++++++++++++++++++++------
> >>   1 file changed, 48 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> >> index 75b8df21a4..5a80a415f0 100644
> >> --- a/hw/virtio/vhost-user.c
> >> +++ b/hw/virtio/vhost-user.c
> >> @@ -267,6 +267,8 @@ struct scrub_regions {
> >>       int fd_idx;
> >>   };
> >>   +static int enforce_reply(struct vhost_dev *dev, const VhostUserMsg
> >> *msg);
> >> +
> >>   static bool ioeventfd_enabled(void)
> >>   {
> >>       return !kvm_enabled() || kvm_eventfds_enabled();
> >> @@ -1198,6 +1200,49 @@ static int vhost_user_set_vring_base(struct
> >> vhost_dev *dev,
> >>       return vhost_set_vring(dev, VHOST_USER_SET_VRING_BASE, ring);
> >>   }
> >>   +
> >> +static int vhost_user_set_single_vring_enable(struct vhost_dev *dev,
> >> +                                              int index,
> >> +                                              int enable,
> >> +                                              bool wait_for_reply)
> >> +{
> >> +    int ret;
> >> +
> >> +    if (index < dev->vq_index || index >= dev->vq_index + dev->nvqs) {
> >> +        return -EINVAL;
> >> +    }
> >> +
> >> +    struct vhost_vring_state state = {
> >> +        .index = index,
> >> +        .num   = enable,
> >> +    };
> >> +
> >> +    VhostUserMsg msg = {
> >> +        .hdr.request = VHOST_USER_SET_VRING_ENABLE,
> >> +        .hdr.flags = VHOST_USER_VERSION,
> >> +        .payload.state = state,
> >> +        .hdr.size = sizeof(msg.payload.state),
> >> +    };
> >> +
> >> +    bool reply_supported = virtio_has_feature(dev->protocol_features,
> >> + VHOST_USER_PROTOCOL_F_REPLY_ACK);
> >> +
> >> +    if (reply_supported && wait_for_reply) {
> >> +        msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
> >> +    }
> >
> >
> > Do we need to fail if !realy_supported && wait_for_reply?
> >
> > Thanks
> >
> >
> I guess you mean "should we fail if VHOST_USER_PROTOCOL_F_REPLY_ACK
> feature is not supported?".
>
> The implementation here is similar to that in vhost_user_set_vring_addr().
>
> If this feature is not supported, it will call enforce_reply(), then
> call vhost_user_get_features() to get a reply.

Ok, so you meant we can then fallback to VHOST_USER_GET_FEATURES? I
wonder how robust is this, e.g is the bakcend required to process
vhost-user request in order?

Thanks

>
> Since the messages will be processed sequentailly in DPDK, success of
> enforce_reply() means the previous message VHOST_USER_SET_VRING_ENABLE
> has been processed.
>
> Thanks
>
> >
> >> +
> >> +    ret = vhost_user_write(dev, &msg, NULL, 0);
> >> +    if (ret < 0) {
> >> +        return ret;
> >> +    }
> >> +
> >> +    if (wait_for_reply) {
> >> +        return enforce_reply(dev, &msg);
> >> +    }
> >> +
> >> +    return ret;
> >> +}
> >> +
> >>   static int vhost_user_set_vring_enable(struct vhost_dev *dev, int
> >> enable)
> >>   {
> >>       int i;
> >> @@ -1207,13 +1252,8 @@ static int vhost_user_set_vring_enable(struct
> >> vhost_dev *dev, int enable)
> >>       }
> >>         for (i = 0; i < dev->nvqs; ++i) {
> >> -        int ret;
> >> -        struct vhost_vring_state state = {
> >> -            .index = dev->vq_index + i,
> >> -            .num   = enable,
> >> -        };
> >> -
> >> -        ret = vhost_set_vring(dev, VHOST_USER_SET_VRING_ENABLE,
> >> &state);
> >> +        int ret = vhost_user_set_single_vring_enable(dev,
> >> dev->vq_index + i,
> >> +                                                     enable, false);
> >>           if (ret < 0) {
> >>               /*
> >>                * Restoring the previous state is likely infeasible,
> >> as well as
> >> @@ -2627,6 +2667,7 @@ const VhostOps user_ops = {
> >>           .vhost_set_owner = vhost_user_set_owner,
> >>           .vhost_reset_device = vhost_user_reset_device,
> >>           .vhost_get_vq_index = vhost_user_get_vq_index,
> >> +        .vhost_set_single_vring_enable =
> >> vhost_user_set_single_vring_enable,
> >>           .vhost_set_vring_enable = vhost_user_set_vring_enable,
> >>           .vhost_requires_shm_log = vhost_user_requires_shm_log,
> >>           .vhost_migration_done = vhost_user_migration_done,
>