[RFC 14/27] vhost: add helper for interrupt injection

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Vhost-user uses eventfd to inject IRQs, but VDUSE uses
an ioctl.

This patch prepares vhost_vring_call_split() and
vhost_vring_call_packed() to support VDUSE by introducing
a new helper.

It also adds a new counter to for guest notification
failures, which could happen in case of uninitialized call
file descriptor for example.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 lib/vhost/vhost.c      |  6 +++++
 lib/vhost/vhost.h      | 54 +++++++++++++++++++++++-------------------
 lib/vhost/vhost_user.c | 10 ++++++++
 3 files changed, 46 insertions(+), 24 deletions(-)

diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
index 790eb06b28..c07028f2b3 100644
--- a/lib/vhost/vhost.c
+++ b/lib/vhost/vhost.c
@@ -44,6 +44,7 @@ static const struct vhost_vq_stats_name_off vhost_vq_stat_strings[] = {
 	{"size_1024_1518_packets", offsetof(struct vhost_virtqueue, stats.size_bins[6])},
 	{"size_1519_max_packets",  offsetof(struct vhost_virtqueue, stats.size_bins[7])},
 	{"guest_notifications",    offsetof(struct vhost_virtqueue, stats.guest_notifications)},
+	{"guest_notifications_error",    offsetof(struct vhost_virtqueue, stats.guest_notifications_error)},
 	{"iotlb_hits",             offsetof(struct vhost_virtqueue, stats.iotlb_hits)},
 	{"iotlb_misses",           offsetof(struct vhost_virtqueue, stats.iotlb_misses)},
 	{"inflight_submitted",     offsetof(struct vhost_virtqueue, stats.inflight_submitted)},
@@ -697,6 +698,11 @@ vhost_new_device(struct vhost_backend_ops *ops)
 		return -1;
 	}
 
+	if (ops->inject_irq == NULL) {
+		VHOST_LOG_CONFIG("device", ERR, "missing IRQ injection backend op.\n");
+		return -1;
+	}
+
 	pthread_mutex_lock(&vhost_dev_lock);
 	for (i = 0; i < RTE_MAX_VHOST_DEVICE; i++) {
 		if (vhost_devices[i] == NULL)
diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
index ee7640e901..8f0875b4e2 100644
--- a/lib/vhost/vhost.h
+++ b/lib/vhost/vhost.h
@@ -90,16 +90,20 @@
 #endif
 
 struct virtio_net;
+struct vhost_virtqueue;
+
 typedef void (*vhost_iotlb_remove_notify)(uint64_t addr, uint64_t off, uint64_t size);
 
 typedef int (*vhost_iotlb_miss_cb)(struct virtio_net *dev, uint64_t iova, uint8_t perm);
 
+typedef int (*vhost_vring_inject_irq_cb)(struct virtio_net *dev, struct vhost_virtqueue *vq);
 /**
  * Structure that contains backend-specific ops.
  */
 struct vhost_backend_ops {
 	vhost_iotlb_remove_notify iotlb_remove_notify;
 	vhost_iotlb_miss_cb iotlb_miss;
+	vhost_vring_inject_irq_cb inject_irq;
 };
 
 /**
@@ -149,6 +153,7 @@ struct virtqueue_stats {
 	/* Size bins in array as RFC 2819, undersized [0], 64 [1], etc */
 	uint64_t size_bins[8];
 	uint64_t guest_notifications;
+	uint64_t guest_notifications_error;
 	uint64_t iotlb_hits;
 	uint64_t iotlb_misses;
 	uint64_t inflight_submitted;
@@ -900,6 +905,24 @@ vhost_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
 	return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
 }
 
+static __rte_always_inline void
+vhost_vring_inject_irq(struct virtio_net *dev, struct vhost_virtqueue *vq)
+{
+	int ret;
+
+	ret = dev->backend_ops->inject_irq(dev, vq);
+	if (ret) {
+		if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
+			vq->stats.guest_notifications_error++;
+		return;
+	}
+
+	if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
+		vq->stats.guest_notifications++;
+	if (dev->notify_ops->guest_notified)
+		dev->notify_ops->guest_notified(dev->vid);
+}
+
 static __rte_always_inline void
 vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
 {
@@ -919,25 +942,13 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
 			"%s: used_event_idx=%d, old=%d, new=%d\n",
 			__func__, vhost_used_event(vq), old, new);
 
-		if ((vhost_need_event(vhost_used_event(vq), new, old) ||
-					unlikely(!signalled_used_valid)) &&
-				vq->callfd >= 0) {
-			eventfd_write(vq->callfd, (eventfd_t) 1);
-			if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
-				vq->stats.guest_notifications++;
-			if (dev->notify_ops->guest_notified)
-				dev->notify_ops->guest_notified(dev->vid);
-		}
+		if (vhost_need_event(vhost_used_event(vq), new, old) ||
+					unlikely(!signalled_used_valid))
+			vhost_vring_inject_irq(dev, vq);
 	} else {
 		/* Kick the guest if necessary. */
-		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
-				&& (vq->callfd >= 0)) {
-			eventfd_write(vq->callfd, (eventfd_t)1);
-			if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
-				vq->stats.guest_notifications++;
-			if (dev->notify_ops->guest_notified)
-				dev->notify_ops->guest_notified(dev->vid);
-		}
+		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT))
+			vhost_vring_inject_irq(dev, vq);
 	}
 }
 
@@ -988,13 +999,8 @@ vhost_vring_call_packed(struct virtio_net *dev, struct vhost_virtqueue *vq)
 	if (vhost_need_event(off, new, old))
 		kick = true;
 kick:
-	if (kick && vq->callfd >= 0) {
-		eventfd_write(vq->callfd, (eventfd_t)1);
-		if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
-			vq->stats.guest_notifications++;
-		if (dev->notify_ops->guest_notified)
-			dev->notify_ops->guest_notified(dev->vid);
-	}
+	if (kick)
+		vhost_vring_inject_irq(dev, vq);
 }
 
 static __rte_always_inline void
diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
index 6a9f32972a..2e4a9fdea4 100644
--- a/lib/vhost/vhost_user.c
+++ b/lib/vhost/vhost_user.c
@@ -3465,8 +3465,18 @@ int rte_vhost_host_notifier_ctrl(int vid, uint16_t qid, bool enable)
 	return ret;
 }
 
+static int
+vhost_user_inject_irq(struct virtio_net *dev __rte_unused, struct vhost_virtqueue *vq)
+{
+	if (vq->callfd < 0)
+		return -1;
+
+	return eventfd_write(vq->callfd, (eventfd_t)1);
+}
+
 static struct vhost_backend_ops vhost_user_backend_ops = {
 	.iotlb_miss = vhost_user_iotlb_miss,
+	.inject_irq = vhost_user_inject_irq,
 };
 
 int
-- 
2.39.2