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

[Yury Kotov]

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.

Regards,
Yury