Re: [PATCH] tcm_vhost: Add hotplug/hotunplug support

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Mar 05, 2013 at 05:17:07PM +0800, Asias He wrote:
> In commit 365a7150094 ([SCSI] virtio-scsi: hotplug support for
> virtio-scsi), hotplug support is added to virtio-scsi.
> 
> This patch adds hotplug and hotunplug support to tcm_vhost.
> 
> You can create or delate a LUN in targetcli to hotplug or hotplug a LUN
> in guest.
> 
> Signed-off-by: Asias He <asias@redhat.com>
> ---
>  drivers/vhost/tcm_vhost.c | 171 ++++++++++++++++++++++++++++++++++++++++++++--
>  drivers/vhost/tcm_vhost.h |   9 +++
>  2 files changed, 175 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> index 9951297..6693695 100644
> --- a/drivers/vhost/tcm_vhost.c
> +++ b/drivers/vhost/tcm_vhost.c
> @@ -63,6 +63,8 @@ enum {
>  #define VHOST_SCSI_MAX_TARGET	256
>  #define VHOST_SCSI_MAX_VQ	128
>  
> +#define VHOST_SCSI_FEATURES (VHOST_FEATURES | (1ULL << VIRTIO_SCSI_F_HOTPLUG))
> +
>  struct vhost_scsi {
>  	/* Protected by vhost_scsi->dev.mutex */
>  	struct tcm_vhost_tpg *vs_tpg[VHOST_SCSI_MAX_TARGET];
> @@ -74,6 +76,11 @@ struct vhost_scsi {
>  
>  	struct vhost_work vs_completion_work; /* cmd completion work item */
>  	struct llist_head vs_completion_list; /* cmd completion queue */
> +
> +	struct vhost_work vs_event_work; /* evt injection work item */
> +	struct llist_head vs_event_list; /* evt injection queue */
> +
> +	bool vs_events_dropped;

Documentation pls.
Also - how is this handled during migration?
Don't we need a way for userspace to retrieve this bit?

>  };
>  
>  /* Local pointer to allocated TCM configfs fabric module */
> @@ -341,6 +348,23 @@ static int tcm_vhost_queue_tm_rsp(struct se_cmd *se_cmd)
>  	return 0;
>  }
>  
> +static void tcm_vhost_free_evt(struct tcm_vhost_evt *evt)
> +{
> +	kfree(evt);
> +}
> +
> +static struct tcm_vhost_evt *tcm_vhost_allocate_evt(u32 event, u32 reason)
> +{
> +	struct tcm_vhost_evt *evt;
> +
> +	evt = kzalloc(sizeof(*evt), GFP_KERNEL);

And if this fails?

> +
> +	evt->event.event = event;
> +	evt->event.reason = reason;
> +
> +	return evt;
> +}
> +
>  static void vhost_scsi_free_cmd(struct tcm_vhost_cmd *tv_cmd)
>  {
>  	struct se_cmd *se_cmd = &tv_cmd->tvc_se_cmd;
> @@ -359,6 +383,71 @@ static void vhost_scsi_free_cmd(struct tcm_vhost_cmd *tv_cmd)
>  	kfree(tv_cmd);
>  }
>  
> +static void tcm_vhost_do_evt_work(struct vhost_scsi *vs,
> +		struct virtio_scsi_event *event)
> +{
> +	struct vhost_virtqueue *vq = &vs->vqs[VHOST_SCSI_VQ_EVT];
> +	struct virtio_scsi_event __user *eventp;
> +	unsigned out, in;
> +	int head, ret;
> +
> +	if (!vs || !vs->vs_endpoint)
> +		return;
> +
> +	mutex_lock(&vq->mutex);
> +again:
> +	vhost_disable_notify(&vs->dev, vq);
> +	head = vhost_get_vq_desc(&vs->dev, vq, vq->iov,
> +			ARRAY_SIZE(vq->iov), &out, &in,
> +			NULL, NULL);
> +	if (head < 0) {
> +		vs->vs_events_dropped = true;
> +		goto out;
> +	}
> +	if (head == vq->num) {
> +		if (vhost_enable_notify(&vs->dev, vq))
> +			goto again;

Could you code this up using loop, without goto please?

> +		vs->vs_events_dropped = true;
> +		goto out;
> +	}
> +
> +	if ((vq->iov[out].iov_len != sizeof(struct virtio_scsi_event))) {

We should avoid making layout assumptions. Please don't.

> +		vq_err(vq, "Expecting virtio_scsi_event, got %zu bytes\n",
> +				vq->iov[out].iov_len);
> +		goto out;
> +	}
> +
> +	if (vs->vs_events_dropped) {
> +		event->event |= VIRTIO_SCSI_T_EVENTS_MISSED;
> +		vs->vs_events_dropped = false;
> +	}
> +
> +	eventp = vq->iov[out].iov_base;
> +	ret = __copy_to_user(eventp, event, sizeof(*event));
> +	if (!ret)
> +		vhost_add_used_and_signal(&vs->dev, vq, head, 0);
> +	else
> +		pr_err("Faulted on tcm_vhost_send_event\n");

vq_err please, this is guest triggerable.

> +out:
> +	mutex_unlock(&vq->mutex);
> +}
> +
> +static void tcm_vhost_evt_work(struct vhost_work *work)
> +{
> +	struct vhost_scsi *vs = container_of(work, struct vhost_scsi,
> +					vs_event_work);
> +	struct tcm_vhost_evt *evt;
> +	struct llist_node *llnode;
> +
> +	llnode = llist_del_all(&vs->vs_event_list);
> +	while (llnode) {
> +		evt = llist_entry(llnode, struct tcm_vhost_evt, list);
> +		llnode = llist_next(llnode);
> +		tcm_vhost_do_evt_work(vs, &evt->event);
> +		tcm_vhost_free_evt(evt);
> +	}
> +}
> +
>  /* Fill in status and signal that we are done processing this command
>   *
>   * This is scheduled in the vhost work queue so we are called with the owner
> @@ -757,9 +846,41 @@ static void vhost_scsi_ctl_handle_kick(struct vhost_work *work)
>  	pr_debug("%s: The handling func for control queue.\n", __func__);
>  }
>  
> +static int tcm_vhost_send_evt(struct vhost_scsi *vs, struct tcm_vhost_tpg *tpg,
> +		struct se_lun *lun, u32 event, u32 reason)

Align ) on ( please.

> +{
> +	struct tcm_vhost_evt *evt;
> +
> +	if (!vs->vs_endpoint)
> +		return -EOPNOTSUPP;
> +

Pls add a comment explaining the abive.
Is this dereference safe without any locking?

> +	evt = tcm_vhost_allocate_evt(event, reason);
> +	if (!evt)
> +		return -ENOMEM;

And what happens then? How about we set event missed flag too?

> +
> +	if (tpg && lun) {
> +		evt->event.lun[0] = 0x01;
> +		evt->event.lun[1] = tpg->tport_tpgt & 0xFF;
> +		if (lun->unpacked_lun >= 256)
> +			evt->event.lun[2] = lun->unpacked_lun >> 8 | 0x40 ;
> +		evt->event.lun[3] = lun->unpacked_lun & 0xFF;

I know it's not your fault but we really should share this code with
virtio scsi. Pls add TODO now.

> +	}
> +
> +	llist_add(&evt->list, &vs->vs_event_list);

This can queue up quite a bit of memory if the handler thread
is delayed, no? Can we limit the # of outstanding events?
Will guest recover from a missed event?

> +	vhost_work_queue(&vs->dev, &vs->vs_event_work);
> +
> +	return 0;
> +}
> +
>  static void vhost_scsi_evt_handle_kick(struct vhost_work *work)
>  {
> -	pr_debug("%s: The handling func for event queue.\n", __func__);
> +	struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
> +						poll.work);
> +	struct vhost_scsi *vs = container_of(vq->dev, struct vhost_scsi, dev);
> +
> +	if (vs->vs_events_dropped)
> +		tcm_vhost_send_evt(vs, NULL, NULL, VIRTIO_SCSI_T_NO_EVENT, 0);
> +
>  }
>  
>  static void vhost_scsi_handle_kick(struct vhost_work *work)
> @@ -815,6 +936,7 @@ static int vhost_scsi_set_endpoint(
>  				return -EEXIST;
>  			}
>  			tv_tpg->tv_tpg_vhost_count++;
> +			tv_tpg->vhost_scsi = vs;
>  			vs->vs_tpg[tv_tpg->tport_tpgt] = tv_tpg;
>  			smp_mb__after_atomic_inc();
>  			match = true;
> @@ -875,6 +997,7 @@ static int vhost_scsi_clear_endpoint(
>  			goto err;
>  		}
>  		tv_tpg->tv_tpg_vhost_count--;
> +		tv_tpg->vhost_scsi = NULL;
>  		vs->vs_tpg[target] = NULL;
>  		vs->vs_endpoint = false;
>  	}
> @@ -896,6 +1019,7 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
>  		return -ENOMEM;
>  
>  	vhost_work_init(&s->vs_completion_work, vhost_scsi_complete_cmd_work);
> +	vhost_work_init(&s->vs_event_work, tcm_vhost_evt_work);
>  
>  	s->vqs[VHOST_SCSI_VQ_CTL].handle_kick = vhost_scsi_ctl_handle_kick;
>  	s->vqs[VHOST_SCSI_VQ_EVT].handle_kick = vhost_scsi_evt_handle_kick;
> @@ -941,7 +1065,7 @@ static void vhost_scsi_flush(struct vhost_scsi *vs)
>  
>  static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
>  {
> -	if (features & ~VHOST_FEATURES)
> +	if (features & ~VHOST_SCSI_FEATURES)
>  		return -EOPNOTSUPP;
>  
>  	mutex_lock(&vs->dev.mutex);
> @@ -987,7 +1111,7 @@ static long vhost_scsi_ioctl(struct file *f, unsigned int ioctl,
>  			return -EFAULT;
>  		return 0;
>  	case VHOST_GET_FEATURES:
> -		features = VHOST_FEATURES;
> +		features = VHOST_SCSI_FEATURES;
>  		if (copy_to_user(featurep, &features, sizeof features))
>  			return -EFAULT;
>  		return 0;
> @@ -1057,6 +1181,40 @@ static char *tcm_vhost_dump_proto_id(struct tcm_vhost_tport *tport)
>  	return "Unknown";
>  }
>  
> +static int tcm_vhost_hotplug(struct tcm_vhost_tpg *tpg, struct se_lun *lun)
> +{
> +	struct vhost_scsi *vs = tpg->vhost_scsi;
> +	u64 features;
> +
> +	if (!vs)
> +		return -EOPNOTSUPP;
> +
> +	features = vs->dev.acked_features;
> +	if (!(features & 1ULL << VIRTIO_SCSI_F_HOTPLUG))
> +		return -EOPNOTSUPP;
> +
> +	return tcm_vhost_send_evt(vs, tpg, lun,
> +			VIRTIO_SCSI_T_TRANSPORT_RESET,
> +			VIRTIO_SCSI_EVT_RESET_RESCAN);
> +}
> +
> +static int tcm_vhost_hotunplug(struct tcm_vhost_tpg *tpg, struct se_lun *lun)
> +{
> +	struct vhost_scsi *vs = tpg->vhost_scsi;
> +	u64 features;
> +
> +	if (!vs)
> +		return -EOPNOTSUPP;
> +

What are we checking for here, and why is it safe to do
outside any lock?

> +	features = vs->dev.acked_features;
> +	if (!(features & 1ULL << VIRTIO_SCSI_F_HOTPLUG))
> +		return -EOPNOTSUPP;
> +
> +	return tcm_vhost_send_evt(vs, tpg, lun,
> +			VIRTIO_SCSI_T_TRANSPORT_RESET,
> +			VIRTIO_SCSI_EVT_RESET_REMOVED);
> +}
> +
>  static int tcm_vhost_port_link(struct se_portal_group *se_tpg,
>  	struct se_lun *lun)
>  {
> @@ -1067,18 +1225,21 @@ static int tcm_vhost_port_link(struct se_portal_group *se_tpg,
>  	tv_tpg->tv_tpg_port_count++;
>  	mutex_unlock(&tv_tpg->tv_tpg_mutex);
>  
> +	tcm_vhost_hotplug(tv_tpg, lun);
> +
>  	return 0;
>  }
>  
>  static void tcm_vhost_port_unlink(struct se_portal_group *se_tpg,
> -	struct se_lun *se_lun)
> +	struct se_lun *lun)
>  {
>  	struct tcm_vhost_tpg *tv_tpg = container_of(se_tpg,
>  				struct tcm_vhost_tpg, se_tpg);
> -
>  	mutex_lock(&tv_tpg->tv_tpg_mutex);
>  	tv_tpg->tv_tpg_port_count--;
>  	mutex_unlock(&tv_tpg->tv_tpg_mutex);
> +
> +	tcm_vhost_hotunplug(tv_tpg, lun);
>  }
>  
>  static struct se_node_acl *tcm_vhost_make_nodeacl(
> diff --git a/drivers/vhost/tcm_vhost.h b/drivers/vhost/tcm_vhost.h
> index 1d2ae7a..191a945 100644
> --- a/drivers/vhost/tcm_vhost.h
> +++ b/drivers/vhost/tcm_vhost.h
> @@ -70,6 +70,8 @@ struct tcm_vhost_tpg {
>  	struct tcm_vhost_tport *tport;
>  	/* Returned by tcm_vhost_make_tpg() */
>  	struct se_portal_group se_tpg;
> +	/* Pointer back to struct vhost_scsi*/
> +	void *vhost_scsi;

Does it have to be void? Any why?
What lock protects this field? Please add a comment.

>  };
>  
>  struct tcm_vhost_tport {
> @@ -83,6 +85,13 @@ struct tcm_vhost_tport {
>  	struct se_wwn tport_wwn;
>  };
>  
> +struct tcm_vhost_evt {
> +	/* virtio_scsi event */
> +	struct virtio_scsi_event event;
> +	/* virtio_scsi event list, serviced from vhost worker thread */
> +	struct llist_node list;
> +};
> +
>  /*
>   * As per request from MST, keep TCM_VHOST related ioctl defines out of
>   * linux/vhost.h (user-space) for now..
> -- 
> 1.8.1.4