Re: [Qemu-devel] [PATCH for-4.0 5/6] vhost-user-blk: Add support for reconnecting backend

[Yury Kotov]

06.12.2018, 09:38, "address@hidden" <address@hidden>:
> From: Xie Yongji <address@hidden>
>
> Since the new message VHOST_USER_SET_VRING_INFLIGHT,
> the backend is able to restart safely. This patch
> allow 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 | 169 +++++++++++++++++++++++++++--
>  include/hw/virtio/vhost-user-blk.h | 4 +
>  2 files changed, 161 insertions(+), 12 deletions(-)
>
> diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> index 1451940845..663e91bcf6 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);
> @@ -140,12 +140,13 @@ 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)
> @@ -164,7 +165,6 @@ 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);
> @@ -174,21 +174,39 @@ 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 we ignore 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 we ignore fake guest kick by
> + * vhost_dev_disable_notifiers() */
> + barrier();
> + s->should_start = false;
>      }
> -
>  }
>
>  static uint64_t vhost_user_blk_get_features(VirtIODevice *vdev,
> @@ -218,13 +236,22 @@ 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))) {

This condition looks complicated. Is it correct? I'm not sure but may be
the second '!' is odd. Sorry, I know that it isn't part of this patch, but it
looks like this cond was added in one of your old patches.

>          return;
>      }
>
> + if (s->should_start) {
> + return;
> + }
> + s->should_start = true;
> +
> + if (!s->connected) {
> + return;
> + }
> +
>      if (s->dev.started) {
>          return;
>      }
> @@ -232,7 +259,13 @@ 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++) {
> @@ -245,6 +278,106 @@ static void vhost_user_blk_handle_output(VirtIODevice 
> *vdev, VirtQueue *vq)
>      }
>  }
>
> +static void vhost_user_blk_reset(VirtIODevice *vdev)
> +{
> + VHostUserBlk *s = VHOST_USER_BLK(vdev);
> +
> + if (s->vhost_user) {
> + vhost_user_inflight_reset(s->vhost_user);
> + }
> +}
> +
> +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;
> + }
> +
> + if (s->should_start && !s->dev.started) {

It seems that `!s->dev.started` is always true here because
vhost_dev_init sets dev.started = 0 on success.

> + 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);
> @@ -284,8 +417,13 @@ static void vhost_user_blk_device_realize(DeviceState 
> *dev, Error **errp)
>                           vhost_user_blk_handle_output);
>      }
>
> + s->vqs = g_new(struct vhost_virtqueue, s->num_queues);
> + s->watch = 0;
> + s->should_start = false;
> + s->connected = true;
> +
>      s->dev.nvqs = s->num_queues;
> - s->dev.vqs = g_new(struct vhost_virtqueue, s->dev.nvqs);
> + s->dev.vqs = s->vqs;
>      s->dev.vq_index = 0;
>      s->dev.backend_features = 0;
>
> @@ -309,6 +447,9 @@ static void vhost_user_blk_device_realize(DeviceState 
> *dev, Error **errp)
>          s->blkcfg.num_queues = s->num_queues;
>      }
>
> + qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, vhost_user_blk_event,
> + NULL, (void *)dev, NULL, true);
> +
>      return;
>
>  vhost_err:
> @@ -328,8 +469,11 @@ static void vhost_user_blk_device_unrealize(DeviceState 
> *dev, Error **errp)
>      VHostUserBlk *s = VHOST_USER_BLK(dev);
>
>      vhost_user_blk_set_status(vdev, 0);
> + qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, NULL,
> + NULL, NULL, NULL, false);
>      vhost_dev_cleanup(&s->dev);
> - g_free(s->dev.vqs);
> +
> + g_free(s->vqs);
>      virtio_cleanup(vdev);
>
>      if (s->vhost_user) {
> @@ -379,6 +523,7 @@ static void vhost_user_blk_class_init(ObjectClass *klass, 
> void *data)
>      vdc->set_config = vhost_user_blk_set_config;
>      vdc->get_features = vhost_user_blk_get_features;
>      vdc->set_status = vhost_user_blk_set_status;
> + vdc->reset = vhost_user_blk_reset;
>  }
>
>  static const TypeInfo vhost_user_blk_info = {
> diff --git a/include/hw/virtio/vhost-user-blk.h 
> b/include/hw/virtio/vhost-user-blk.h
> index d52944aeeb..560bb21459 100644
> --- a/include/hw/virtio/vhost-user-blk.h
> +++ b/include/hw/virtio/vhost-user-blk.h
> @@ -37,6 +37,10 @@ typedef struct VHostUserBlk {
>      uint32_t config_wce;
>      struct vhost_dev dev;
>      VhostUserState *vhost_user;
> + struct vhost_virtqueue *vqs;
> + guint watch;
> + bool should_start;
> + bool connected;
>  } VHostUserBlk;
>
>  #endif
> --
> 2.17.1

Regards,
Yury