[PATCH v2 4/5] vhost: add statistics for guest notifications

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

This patch adds a new virtqueue statistic for guest
notifications. It is useful to deduce from hypervisor side
whether the corresponding guest Virtio device is using
Kernel Virtio-net driver or DPDK Virtio PMD.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 lib/vhost/vhost.c | 1 +
 lib/vhost/vhost.h | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
index 80ed024019..58b58fc40e 100644
--- a/lib/vhost/vhost.c
+++ b/lib/vhost/vhost.c
@@ -42,6 +42,7 @@ static const struct vhost_vq_stats_name_off vhost_vq_stat_strings[] = {
 	{"size_512_1023_packets",  offsetof(struct vhost_virtqueue, stats.size_bins[5])},
 	{"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)},
 };
 
 #define VHOST_NB_VQ_STATS RTE_DIM(vhost_vq_stat_strings)
diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
index 01b97011aa..13c5c2266d 100644
--- a/lib/vhost/vhost.h
+++ b/lib/vhost/vhost.h
@@ -133,6 +133,7 @@ struct virtqueue_stats {
 	uint64_t broadcast;
 	/* Size bins in array as RFC 2819, undersized [0], 64 [1], etc */
 	uint64_t size_bins[8];
+	uint64_t guest_notifications;
 };
 
 /**
@@ -871,6 +872,8 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
 					(vq->callfd >= 0)) ||
 				unlikely(!signalled_used_valid)) {
 			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);
 		}
@@ -879,6 +882,8 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
 		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);
 		}
-- 
2.35.1