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

[Yury Kotov]

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.

Regards,
Yury