On Mon, May 25, 2020 at 12:00:10AM -0400, Raphael Norwitz wrote:
> I'm mostly happy with this. A couple comments.
>
> On Wed, May 20, 2020 at 11:54 AM Dima Stepanov <dimas...@yandex-team.ru>
> wrote:
> >
> > A socket write during vhost-user communication may trigger a disconnect
> > event, calling vhost_user_blk_disconnect() and clearing all the
> > vhost_dev structures holding data that vhost-user functions expect to
> > remain valid to roll back initialization correctly. Delay the cleanup to
> > keep vhost_dev structure valid.
> > There are two possible states to handle:
> > 1. RUN_STATE_PRELAUNCH: skip bh oneshot call and perform disconnect in
> > the caller routine.
> > 2. RUN_STATE_RUNNING: delay by using bh
> >
> > BH changes are based on the similar changes for the vhost-user-net
> > device:
> > commit e7c83a885f865128ae3cf1946f8cb538b63cbfba
> > "vhost-user: delay vhost_user_stop"
> >
> I'd also give credit to Li Feng here - he sent a similar patch:
>
> https://lists.gnu.org/archive/html/qemu-devel/2020-04/msg02255.html
Yes, thanks for pointing me to it.
>
> > Signed-off-by: Dima Stepanov <dimas...@yandex-team.ru>
> > ---
> > hw/block/vhost-user-blk.c | 49
> > +++++++++++++++++++++++++++++++++++++++++------
> > 1 file changed, 43 insertions(+), 6 deletions(-)
> >
> > diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> > index 9d8c0b3..447fc9c 100644
> > --- a/hw/block/vhost-user-blk.c
> > +++ b/hw/block/vhost-user-blk.c
> > @@ -337,11 +337,6 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
> > VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> > VHostUserBlk *s = VHOST_USER_BLK(vdev);
> >
> > - if (!s->connected) {
> > - return;
> > - }
> > - s->connected = false;
> > -
> > if (s->dev.started) {
> > vhost_user_blk_stop(vdev);
> > }
> > @@ -349,6 +344,19 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
> > vhost_dev_cleanup(&s->dev);
> > }
> >
> > +static void vhost_user_blk_event(void *opaque, QEMUChrEvent event);
> > +
> > +static void vhost_user_blk_chr_closed_bh(void *opaque)
> > +{
> > + DeviceState *dev = opaque;
> > + VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> > + VHostUserBlk *s = VHOST_USER_BLK(vdev);
> > +
> > + vhost_user_blk_disconnect(dev);
> > + qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, vhost_user_blk_event,
> > + NULL, opaque, NULL, true);
> > +}
> > +
> > static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
> > {
> > DeviceState *dev = opaque;
> > @@ -363,7 +371,28 @@ static void vhost_user_blk_event(void *opaque,
> > QEMUChrEvent event)
> > }
> > break;
> > case CHR_EVENT_CLOSED:
> > - vhost_user_blk_disconnect(dev);
> > + /*
> > + * A close event may happen during a read/write, but vhost
> > + * code assumes the vhost_dev remains setup, so delay the
> > + * stop & clear. There are two possible paths to hit this
> > + * disconnect event:
> > + * 1. When VM is in the RUN_STATE_PRELAUNCH state. The
> > + * vhost_user_blk_device_realize() is a caller.
> > + * 2. In tha main loop phase after VM start.
> > + *
> > + * For p2 the disconnect event will be delayed. We can't
> > + * do the same for p1, because we are not running the loop
> > + * at this moment. So just skip this step and perform
> > + * disconnect in the caller function.
> > + */
> > + if (s->connected && runstate_is_running()) {
> > + AioContext *ctx = qemu_get_current_aio_context();
> > +
> > + qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, NULL, NULL,
> > + NULL, NULL, false);
> > + aio_bh_schedule_oneshot(ctx, vhost_user_blk_chr_closed_bh,
> > opaque);
> > + }
> > + s->connected = false;
> > break;
> > case CHR_EVENT_BREAK:
> > case CHR_EVENT_MUX_IN:
> > @@ -428,6 +457,14 @@ reconnect:
> >
> > ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
> > sizeof(struct virtio_blk_config));
>
> I find checking s->connected before ret a little confusing. I think we
> should also enforce a reconnect if s->connected is false. AFIK if
> s->connected is false, ret must also be less than 0, but to be safe
> I’d prefer something like:
>
> if (ret < 0 || !s->connected) {
> if (!s->connected) {
> /*
> * Perform disconnect before making reconnect. More detailed
> * comment why it was delayed is in the vhost_user_blk_event()
> * routine.
> */
> vhost_user_blk_disconnect(dev);
> }
> if (ret < 0) {
> error_report(“vhost-user-blk: get block config failed”);
> }
> goto reconnect;
> }
>
True. Thanks to Li Feng's patch i understood that i've overcomplicated the
logic. We don't need this disconnect call here at all.
I'll send a smaller reworked patch in this e-mail thread, just to
continue review and discussion.
> > + if (!s->connected) {
> > + /*
> > + * Perform disconnect before making reconnect. More detailed
> > + * comment why it was delayed is in the vhost_user_blk_event()
> > + * routine.
> > + */
> > + vhost_user_blk_disconnect(dev);
> > + }
> > if (ret < 0) {
> > error_report("vhost-user-blk: get block config failed");
> > goto reconnect;
> > --
> > 2.7.4
> >
> >
