Re: [Qemu-devel] [PATCH v2 for-4.0 6/7] vhost-user-blk: Add support to reconnect backend

[Yongji Xie]

On Tue, 18 Dec 2018 at 23:33, Yury Kotov <address@hidden> wrote:
>
>
>
> 18.12.2018, 17:59, "Yongji Xie" <address@hidden>:
> > On Tue, 18 Dec 2018 at 22:35, Yury Kotov <address@hidden> wrote:
> >>  18.12.2018, 17:16, "Yongji Xie" <address@hidden>:
> >>  > On Tue, 18 Dec 2018 at 20:30, Yury Kotov <address@hidden> wrote:
> >>  >> + wrfsh@
> >>  >>
> >>  >> Hi,
> >>  >>
> >>  >> 18.12.2018, 13:01, "address@hidden" <address@hidden>:
> >>  >> > From: Xie Yongji <address@hidden>
> >>  >> >
> >>  >> > Since we now support the message VHOST_USER_GET_SHM_SIZE
> >>  >> > and VHOST_USER_SET_SHM_FD. The backend is able to restart
> >>  >> > safely because it can record inflight I/O in shared memory.
> >>  >> > This patch allows qemu to reconnect the backend after
> >>  >> > connection closed.
> >>  >> >
> >>  >> > Signed-off-by: Xie Yongji <address@hidden>
> >>  >> > Signed-off-by: Ni Xun <address@hidden>
> >>  >> > Signed-off-by: Zhang Yu <address@hidden>
> >>  >> > ---
> >>  >> > hw/block/vhost-user-blk.c | 183 ++++++++++++++++++++++++-----
> >>  >> > include/hw/virtio/vhost-user-blk.h | 4 +
> >>  >> > 2 files changed, 160 insertions(+), 27 deletions(-)
> >>  >> >
> >>  >> > diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> >>  >> > index 27028cf996..80f2e2d765 100644
> >>  >> > --- a/hw/block/vhost-user-blk.c
> >>  >> > +++ b/hw/block/vhost-user-blk.c
> >>  >> > @@ -101,7 +101,7 @@ const VhostDevConfigOps blk_ops = {
> >>  >> > .vhost_dev_config_notifier = vhost_user_blk_handle_config_change,
> >>  >> > };
> >>  >> >
> >>  >> > -static void vhost_user_blk_start(VirtIODevice *vdev)
> >>  >> > +static int vhost_user_blk_start(VirtIODevice *vdev)
> >>  >> > {
> >>  >> > VHostUserBlk *s = VHOST_USER_BLK(vdev);
> >>  >> > BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
> >>  >> > @@ -110,13 +110,13 @@ static void vhost_user_blk_start(VirtIODevice 
> >> *vdev)
> >>  >> >
> >>  >> > if (!k->set_guest_notifiers) {
> >>  >> > error_report("binding does not support guest notifiers");
> >>  >> > - return;
> >>  >> > + return -ENOSYS;
> >>  >> > }
> >>  >> >
> >>  >> > ret = vhost_dev_enable_notifiers(&s->dev, vdev);
> >>  >> > if (ret < 0) {
> >>  >> > error_report("Error enabling host notifiers: %d", -ret);
> >>  >> > - return;
> >>  >> > + return ret;
> >>  >> > }
> >>  >> >
> >>  >> > ret = k->set_guest_notifiers(qbus->parent, s->dev.nvqs, true);
> >>  >> > @@ -147,12 +147,13 @@ static void vhost_user_blk_start(VirtIODevice 
> >> *vdev)
> >>  >> > vhost_virtqueue_mask(&s->dev, vdev, i, false);
> >>  >> > }
> >>  >> >
> >>  >> > - return;
> >>  >> > + return ret;
> >>  >> >
> >>  >> > err_guest_notifiers:
> >>  >> > k->set_guest_notifiers(qbus->parent, s->dev.nvqs, false);
> >>  >> > err_host_notifiers:
> >>  >> > vhost_dev_disable_notifiers(&s->dev, vdev);
> >>  >> > + return ret;
> >>  >> > }
> >>  >> >
> >>  >> > static void vhost_user_blk_stop(VirtIODevice *vdev)
> >>  >> > @@ -171,7 +172,6 @@ static void vhost_user_blk_stop(VirtIODevice 
> >> *vdev)
> >>  >> > ret = k->set_guest_notifiers(qbus->parent, s->dev.nvqs, false);
> >>  >> > if (ret < 0) {
> >>  >> > error_report("vhost guest notifier cleanup failed: %d", ret);
> >>  >> > - return;
> >>  >> > }
> >>  >> >
> >>  >> > vhost_dev_disable_notifiers(&s->dev, vdev);
> >>  >> > @@ -181,21 +181,43 @@ static void 
> >> vhost_user_blk_set_status(VirtIODevice *vdev, uint8_t status)
> >>  >> > {
> >>  >> > VHostUserBlk *s = VHOST_USER_BLK(vdev);
> >>  >> > bool should_start = status & VIRTIO_CONFIG_S_DRIVER_OK;
> >>  >> > + int ret;
> >>  >> >
> >>  >> > if (!vdev->vm_running) {
> >>  >> > should_start = false;
> >>  >> > }
> >>  >> >
> >>  >> > - if (s->dev.started == should_start) {
> >>  >> > + if (s->should_start == should_start) {
> >>  >> > + return;
> >>  >> > + }
> >>  >> > +
> >>  >> > + if (!s->connected || s->dev.started == should_start) {
> >>  >> > + s->should_start = should_start;
> >>  >> > return;
> >>  >> > }
> >>  >> >
> >>  >> > if (should_start) {
> >>  >> > - vhost_user_blk_start(vdev);
> >>  >> > + s->should_start = true;
> >>  >> > + /*
> >>  >> > + * make sure vhost_user_blk_handle_output() ignores fake
> >>  >> > + * guest kick by vhost_dev_enable_notifiers()
> >>  >> > + */
> >>  >> > + barrier();
> >>  >> > + ret = vhost_user_blk_start(vdev);
> >>  >> > + if (ret < 0) {
> >>  >> > + error_report("vhost-user-blk: vhost start failed: %s",
> >>  >> > + strerror(-ret));
> >>  >> > + qemu_chr_fe_disconnect(&s->chardev);
> >>  >> > + }
> >>  >> > } else {
> >>  >> > vhost_user_blk_stop(vdev);
> >>  >> > + /*
> >>  >> > + * make sure vhost_user_blk_handle_output() ignore fake
> >>  >> > + * guest kick by vhost_dev_disable_notifiers()
> >>  >> > + */
> >>  >> > + barrier();
> >>  >> > + s->should_start = false;
> >>  >> > }
> >>  >> > -
> >>  >> > }
> >>  >> >
> >>  >> > static uint64_t vhost_user_blk_get_features(VirtIODevice *vdev,
> >>  >> > @@ -225,13 +247,22 @@ static uint64_t 
> >> vhost_user_blk_get_features(VirtIODevice *vdev,
> >>  >> > static void vhost_user_blk_handle_output(VirtIODevice *vdev, 
> >> VirtQueue *vq)
> >>  >> > {
> >>  >> > VHostUserBlk *s = VHOST_USER_BLK(vdev);
> >>  >> > - int i;
> >>  >> > + int i, ret;
> >>  >> >
> >>  >> > if (!(virtio_host_has_feature(vdev, VIRTIO_F_VERSION_1) &&
> >>  >> > !virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1))) {
> >>  >> > return;
> >>  >> > }
> >>  >> >
> >>  >> > + if (s->should_start) {
> >>  >> > + return;
> >>  >> > + }
> >>  >> > + s->should_start = true;
> >>  >> > +
> >>  >> > + if (!s->connected) {
> >>  >> > + return;
> >>  >> > + }
> >>  >> > +
> >>  >> > if (s->dev.started) {
> >>  >> > return;
> >>  >> > }
> >>  >> > @@ -239,7 +270,13 @@ static void 
> >> vhost_user_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
> >>  >> > /* Some guests kick before setting VIRTIO_CONFIG_S_DRIVER_OK so start
> >>  >> > * vhost here instead of waiting for .set_status().
> >>  >> > */
> >>  >> > - vhost_user_blk_start(vdev);
> >>  >> > + ret = vhost_user_blk_start(vdev);
> >>  >> > + if (ret < 0) {
> >>  >> > + error_report("vhost-user-blk: vhost start failed: %s",
> >>  >> > + strerror(-ret));
> >>  >> > + qemu_chr_fe_disconnect(&s->chardev);
> >>  >> > + return;
> >>  >> > + }
> >>  >> >
> >>  >> > /* Kick right away to begin processing requests already in vring */
> >>  >> > for (i = 0; i < s->dev.nvqs; i++) {
> >>  >> > @@ -259,12 +296,105 @@ static void vhost_user_blk_reset(VirtIODevice 
> >> *vdev)
> >>  >> > vhost_dev_reset_shm(s->shm);
> >>  >> > }
> >>  >> >
> >>  >> > +static int vhost_user_blk_connect(DeviceState *dev)
> >>  >> > +{
> >>  >> > + VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> >>  >> > + VHostUserBlk *s = VHOST_USER_BLK(vdev);
> >>  >> > + int ret = 0;
> >>  >> > +
> >>  >> > + if (s->connected) {
> >>  >> > + return 0;
> >>  >> > + }
> >>  >> > + s->connected = true;
> >>  >> > +
> >>  >> > + s->dev.nvqs = s->num_queues;
> >>  >> > + s->dev.vqs = s->vqs;
> >>  >> > + s->dev.vq_index = 0;
> >>  >> > + s->dev.backend_features = 0;
> >>  >> > +
> >>  >> > + vhost_dev_set_config_notifier(&s->dev, &blk_ops);
> >>  >> > +
> >>  >> > + ret = vhost_dev_init(&s->dev, s->vhost_user, 
> >> VHOST_BACKEND_TYPE_USER, 0);
> >>  >> > + if (ret < 0) {
> >>  >> > + error_report("vhost-user-blk: vhost initialization failed: %s",
> >>  >> > + strerror(-ret));
> >>  >> > + return ret;
> >>  >> > + }
> >>  >> > +
> >>  >> > + /* restore vhost state */
> >>  >> > + if (s->should_start) {
> >>  >> > + ret = vhost_user_blk_start(vdev);
> >>  >> > + if (ret < 0) {
> >>  >> > + error_report("vhost-user-blk: vhost start failed: %s",
> >>  >> > + strerror(-ret));
> >>  >> > + return ret;
> >>  >> > + }
> >>  >> > + }
> >>  >> > +
> >>  >> > + return 0;
> >>  >> > +}
> >>  >> > +
> >>  >> > +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);
> >>  >> > + }
> >>  >> > +
> >>  >> > + vhost_dev_cleanup(&s->dev);
> >>  >> > +}
> >>  >> > +
> >>  >> > +static gboolean vhost_user_blk_watch(GIOChannel *chan, GIOCondition 
> >> cond,
> >>  >> > + void *opaque)
> >>  >> > +{
> >>  >> > + DeviceState *dev = opaque;
> >>  >> > + VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> >>  >> > + VHostUserBlk *s = VHOST_USER_BLK(vdev);
> >>  >> > +
> >>  >> > + qemu_chr_fe_disconnect(&s->chardev);
> >>  >> > +
> >>  >> > + return true;
> >>  >> > +}
> >>  >> > +
> >>  >> > +static void vhost_user_blk_event(void *opaque, int event)
> >>  >> > +{
> >>  >> > + DeviceState *dev = opaque;
> >>  >> > + VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> >>  >> > + VHostUserBlk *s = VHOST_USER_BLK(vdev);
> >>  >> > +
> >>  >> > + switch (event) {
> >>  >> > + case CHR_EVENT_OPENED:
> >>  >> > + if (vhost_user_blk_connect(dev) < 0) {
> >>  >> > + qemu_chr_fe_disconnect(&s->chardev);
> >>  >> > + return;
> >>  >> > + }
> >>  >> > + s->watch = qemu_chr_fe_add_watch(&s->chardev, G_IO_HUP,
> >>  >> > + vhost_user_blk_watch, dev);
> >>  >> > + break;
> >>  >> > + case CHR_EVENT_CLOSED:
> >>  >> > + vhost_user_blk_disconnect(dev);
> >>  >> > + if (s->watch) {
> >>  >> > + g_source_remove(s->watch);
> >>  >> > + s->watch = 0;
> >>  >> > + }
> >>  >> > + break;
> >>  >> > + }
> >>  >> > +}
> >>  >> > +
> >>  >> > static void vhost_user_blk_device_realize(DeviceState *dev, Error 
> >> **errp)
> >>  >> > {
> >>  >> > VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> >>  >> > VHostUserBlk *s = VHOST_USER_BLK(vdev);
> >>  >> > VhostUserState *user;
> >>  >> > int i, ret;
> >>  >> > + Error *err = NULL;
> >>  >> >
> >>  >> > if (!s->chardev.chr) {
> >>  >> > error_setg(errp, "vhost-user-blk: chardev is mandatory");
> >>  >> > @@ -299,23 +429,21 @@ static void 
> >> vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
> >>  >> > }
> >>  >> >
> >>  >> > s->shm = g_new0(struct vhost_shm, 1);
> >>  >> > -
> >>  >> > - s->dev.nvqs = s->num_queues;
> >>  >> > - s->dev.vqs = g_new(struct vhost_virtqueue, s->dev.nvqs);
> >>  >> > - s->dev.vq_index = 0;
> >>  >> > - s->dev.backend_features = 0;
> >>  >> > -
> >>  >> > - vhost_dev_set_config_notifier(&s->dev, &blk_ops);
> >>  >> > -
> >>  >> > - ret = vhost_dev_init(&s->dev, s->vhost_user, 
> >> VHOST_BACKEND_TYPE_USER, 0);
> >>  >> > - if (ret < 0) {
> >>  >> > - error_setg(errp, "vhost-user-blk: vhost initialization failed: %s",
> >>  >> > - strerror(-ret));
> >>  >> > - goto virtio_err;
> >>  >> > + s->vqs = g_new(struct vhost_virtqueue, s->num_queues);
> >>  >> > + s->watch = 0;
> >>  >> > + s->should_start = false;
> >>  >> > + s->connected = false;
> >>  >> > +
> >>  >> > + while (qemu_chr_fe_wait_connected(&s->chardev, &err) < 0) {
> >>  >> > + error_report_err(err);
> >>  >> > + err = NULL;
> >>  >> > + sleep(1);
> >>  >> > }
> >>  >>
> >>  >> After the reconnect loop we have some function calls to vhost backend:
> >>  >> * qemu_chr_fe_set_handlers implicit calls vhost_dev_init
> >>  >> * vhost_dev_get_config
> >>  >> * vhost_dev_init_shm
> >>  >>
> >>  >> If vhost backend will restart during their execution the initialzation 
> >> will be
> >>  >> failed. What do you think? May be we can call these functions inside of
> >>  >> the reconnect loop to fix it?
> >>  >
> >>  > qemu_chr_fe_wait_connected() should be called only when we are in
> >>  > disconnected state. Otherwise, it will be conflicted with reconnect
> >>  > thread.
> >>  >
> >>
> >>  Reconnect thread is started by reconnet timer callback from the main loop 
> >> but
> >>  vhost_user_blk_device_realize is also runs in the main loop, so we don't 
> >> a race
> >>  in this case I think.
> >
> > The reconnet timer callback have an assert: assert(s->connected == 0).
> > And it's odd to call qemu_chr_fe_wait_connected() when reconnect
> > thread is running.
> >
>
> Reconnect timer callback is a function socket_reconnect_timeout. This function
> doesn't have any asserts. Do you mean qemu_chr_socket_restart_timer? It has an
> assert, yes. But it is called from tcp_chr_disconnect in the same thread.
>
> E.g. vhost_user_get_config ->
>      vhost_user_read ->
>      qemu_chr_fe_read_all ->
>      tcp_chr_sync_read ->
>      tcp_chr_disconnect ->
>      qemu_chr_socket_restart_timer
>
> May be I misunderstand something, but don't see any problems here...
>
> I see that reconnect timer callback is postponed until main loop run and we 
> may
> safely call qemu_chr_fe_wait_connected.
>

Oh, yes, you are right! I made a mistake here. The reconnect thread
would not run in this case.

Thanks,
Yongji