On Thu, 14 Mar 2019 at 19:18, Michael S. Tsirkin <m...@redhat.com> wrote:
>
> On Wed, Mar 13, 2019 at 10:47:08AM +0800, Yongji Xie wrote:
> > On Wed, 13 Mar 2019 at 09:16, Michael S. Tsirkin <m...@redhat.com> wrote:
> > >
> > > On Thu, Feb 28, 2019 at 04:53:54PM +0800, elohi...@gmail.com wrote:
> > > > From: Xie Yongji <xieyon...@baidu.com>
> > > >
> > > > Since we now support the message VHOST_USER_GET_INFLIGHT_FD
> > > > and VHOST_USER_SET_INFLIGHT_FD. The backend is able to restart
> > > > safely because it can track inflight I/O in shared memory.
> > > > This patch allows qemu to reconnect the backend after
> > > > connection closed.
> > > >
> > > > Signed-off-by: Xie Yongji <xieyon...@baidu.com>
> > > > Signed-off-by: Ni Xun <ni...@baidu.com>
> > > > Signed-off-by: Zhang Yu <zhangy...@baidu.com>
> > > > ---
> > > > hw/block/vhost-user-blk.c | 205 +++++++++++++++++++++++------
> > > > include/hw/virtio/vhost-user-blk.h | 4 +
> > > > 2 files changed, 167 insertions(+), 42 deletions(-)
> > > >
> > > > diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> > > > index 9682df1a7b..539ea2e571 100644
> > > > --- a/hw/block/vhost-user-blk.c
> > > > +++ b/hw/block/vhost-user-blk.c
> > > > @@ -103,7 +103,7 @@ 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)));
> > > > @@ -112,13 +112,13 @@ 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);
> > > > @@ -157,12 +157,13 @@ 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)
> > > > @@ -181,7 +182,6 @@ 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);
> > > > @@ -191,21 +191,43 @@ 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;
> > > > }
> > >
> > > I don't understand the comment about ignoring fake guest kicks.
> > > Please add an explanation about what does barrier do here.
> >
> > We may get stack like this:
> >
> > vhost_user_blk_stop()
> > vhost_dev_disable_notifiers()
> > virtio_bus_cleanup_host_notifier()
> > virtio_queue_host_notifier_read()
> > virtio_queue_notify_vq() /* fake guest kick */
> > vhost_user_blk_handle_output()
> >
> > vhost_user_blk_handle_output() will re-start vhost-user if
> > should_start is false. This is not what we expect. The same to
> > vhost_dev_enable_notifiers().
>
> Well what does a compiler barrier have to do with it?
>
> Anyway, it's there to avoid losing kicks e.g. across migration. If you
> have something else that prevents losing kicks (e.g. migrate a "started"
> flag) then add code to skip the notify - don't work around it.
>
OK, I see. Thanks.
IIUC, vhost-user-blk device actually does not need this kind of kick
because dataplane is not in qemu side, right?
>
> > > And maybe a detailed explanation about what "fake kick"
> > > is in the commit log.
> > >
> >
> > Sure.
> > >
> > > > -
> > > > }
> > > >
> > > > static uint64_t vhost_user_blk_get_features(VirtIODevice *vdev,
> > > > @@ -237,13 +259,22 @@ 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;
> > > > }
> > > > @@ -251,7 +282,13 @@ 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++) {
> > > > @@ -271,13 +308,106 @@ static void vhost_user_blk_reset(VirtIODevice
> > > > *vdev)
> > > > vhost_dev_free_inflight(s->inflight);
> > > > }
> > > >
> > > > +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;
> > > > - struct vhost_virtqueue *vqs = NULL;
> > > > int i, ret;
> > > > + Error *err = NULL;
> > > >
> > > > if (!s->chardev.chr) {
> > > > error_setg(errp, "vhost-user-blk: chardev is mandatory");
> > > > @@ -312,27 +442,28 @@ static void
> > > > vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
> > > > }
> > > >
> > > > s->inflight = g_new0(struct vhost_inflight, 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;
> > > > - vqs = s->dev.vqs;
> > > > -
> > > > - 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;
> > > > +
> > > > + qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL,
> > > > vhost_user_blk_event,
> > > > + NULL, (void *)dev, NULL, true);
> > > > +
> > > > +reconnect:
> > > > + do {
> > > > + if (qemu_chr_fe_wait_connected(&s->chardev, &err) < 0) {
> > > > + error_report_err(err);
> > > > + err = NULL;
> > > > + sleep(1);
> > > > + }
> > > > + } while (!s->connected);
> > > >
> > > > ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
> > > > - sizeof(struct virtio_blk_config));
> > > > + sizeof(struct virtio_blk_config));
> > > > if (ret < 0) {
> > > > - error_setg(errp, "vhost-user-blk: get block config failed");
> > > > - goto vhost_err;
> > > > + error_report("vhost-user-blk: get block config failed");
> > > > + goto reconnect;
> > > > }
> > > >
> > > > if (s->blkcfg.num_queues != s->num_queues) {
> > > > @@ -340,29 +471,19 @@ static void
> > > > vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
> > > > }
> > > >
> > > > return;
> > >
> > > With this we end up with return at end of function
> > > which makes no sense.
> > >
> >
> > Oh, yes. I will remove it.
> >
> > > > -
> > > > -vhost_err:
> > > > - vhost_dev_cleanup(&s->dev);
> > > > -virtio_err:
> > > > - g_free(vqs);
> > > > - g_free(s->inflight);
> > > > - virtio_cleanup(vdev);
> > > > -
> > > > - vhost_user_cleanup(user);
> > > > - g_free(user);
> > > > - s->vhost_user = NULL;
> > > > }
> > > >
> > > > static void vhost_user_blk_device_unrealize(DeviceState *dev, Error
> > > > **errp)
> > > > {
> > > > VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> > > > VHostUserBlk *s = VHOST_USER_BLK(dev);
> > > > - struct vhost_virtqueue *vqs = s->dev.vqs;
> > > >
> > > > 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);
> > > > vhost_dev_free_inflight(s->inflight);
> > > > - g_free(vqs);
> > > > + g_free(s->vqs);
> > > > g_free(s->inflight);
> > > > virtio_cleanup(vdev);
> > > >
> > > > diff --git a/include/hw/virtio/vhost-user-blk.h
> > > > b/include/hw/virtio/vhost-user-blk.h
> > > > index 445516604a..4849aa5eb5 100644
> > > > --- a/include/hw/virtio/vhost-user-blk.h
> > > > +++ b/include/hw/virtio/vhost-user-blk.h
> > > > @@ -38,6 +38,10 @@ typedef struct VHostUserBlk {
> > > > struct vhost_dev dev;
> > > > struct vhost_inflight *inflight;
> > > > VhostUserState *vhost_user;
> > > > + struct vhost_virtqueue *vqs;
> > > > + guint watch;
> > > > + bool should_start;
> > >
> > > Please add comments about fields.
> > > Also should_start seems to be set on guest activity.
> > > Does it need to be migrated?
> > > It would be better not to track guest state like this.
> > > Why do we need it?
> > > Pls add comments with an explanation.
> > >
> >
> > We can't relay on vhost_dev.started to track guest's state in
> > vhost_user_blk_set_status() when we enable reconnecting. For example,
> > qemu will lose guest's state if guest stop device during backend is
> > disconnected. So vhost_dev.started is used to track backend's state
> > and should_start is used to track guest's state in this patch. And
> > this variable is based on VirtIODevice.status, so I think it is not
> > necessary to migrate it. What do you think about it?
>
> If it's based on VirtIODevice.status then how about not keeping
> it around at all and just calculating from VirtIODevice.status
> when necessary?
>
Sorry, I made a mistake before. Normally, should_start is based on
VirtIODevice.status. But it's not the case for virtio 1.0 transitional
devices. Then I realize there may be a bug. If migration completes
between kicking virtqueue and setting VIRTIO_CONFIG_S_DRIVER_OK, guest
may be hung. So I think should_start should be migrated in this case.
Thanks,
Yongji
