virtio: Add get_vq_count() callback

Modern virtio requires devices to report how many queues they support. Add
an operation to query all devices about their capacities.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

include/kvm/virtio.h

@@ -184,6 +184,7 @@ struct virtio_ops {
 	u8 *(*get_config)(struct kvm *kvm, void *dev);
 	u32 (*get_host_features)(struct kvm *kvm, void *dev);
 	void (*set_guest_features)(struct kvm *kvm, void *dev, u32 features);
+	int (*get_vq_count)(struct kvm *kvm, void *dev);
 	int (*init_vq)(struct kvm *kvm, void *dev, u32 vq, u32 page_size,
 		       u32 align, u32 pfn);
 	int (*notify_vq)(struct kvm *kvm, void *dev, u32 vq);

virtio/9p.c

@@ -1440,6 +1440,11 @@ static int set_size_vq(struct kvm *kvm, void *dev, u32 vq, int size)
 	return size;
 }
 
+static int get_vq_count(struct kvm *kvm, void *dev)
+{
+	return NUM_VIRT_QUEUES;
+}
+
 struct virtio_ops p9_dev_virtio_ops = {
 	.get_config		= get_config,
 	.get_host_features	= get_host_features,
@@ -1450,6 +1455,7 @@ struct virtio_ops p9_dev_virtio_ops = {
 	.get_pfn_vq		= get_pfn_vq,
 	.get_size_vq		= get_size_vq,
 	.set_size_vq		= set_size_vq,
+	.get_vq_count		= get_vq_count,
 };
 
 int virtio_9p_rootdir_parser(const struct option *opt, const char *arg, int unset)

virtio/balloon.c

@@ -243,6 +243,11 @@ static int set_size_vq(struct kvm *kvm, void *dev, u32 vq, int size)
 	return size;
 }
 
+static int get_vq_count(struct kvm *kvm, void *dev)
+{
+	return NUM_VIRT_QUEUES;
+}
+
 struct virtio_ops bln_dev_virtio_ops = {
 	.get_config		= get_config,
 	.get_host_features	= get_host_features,
@@ -253,6 +258,7 @@ struct virtio_ops bln_dev_virtio_ops = {
 	.get_pfn_vq		= get_pfn_vq,
 	.get_size_vq		= get_size_vq,
 	.set_size_vq            = set_size_vq,
+	.get_vq_count		= get_vq_count,
 };
 
 int virtio_bln__init(struct kvm *kvm)

virtio/blk.c

@@ -248,10 +248,16 @@ static int set_size_vq(struct kvm *kvm, void *dev, u32 vq, int size)
 	return size;
 }
 
+static int get_vq_count(struct kvm *kvm, void *dev)
+{
+	return NUM_VIRT_QUEUES;
+}
+
 static struct virtio_ops blk_dev_virtio_ops = {
 	.get_config		= get_config,
 	.get_host_features	= get_host_features,
 	.set_guest_features	= set_guest_features,
+	.get_vq_count		= get_vq_count,
 	.init_vq		= init_vq,
 	.notify_status		= notify_status,
 	.notify_vq		= notify_vq,

virtio/console.c

@@ -202,10 +202,16 @@ static int set_size_vq(struct kvm *kvm, void *dev, u32 vq, int size)
 	return size;
 }
 
+static int get_vq_count(struct kvm *kvm, void *dev)
+{
+	return VIRTIO_CONSOLE_NUM_QUEUES;
+}
+
 static struct virtio_ops con_dev_virtio_ops = {
 	.get_config		= get_config,
 	.get_host_features	= get_host_features,
 	.set_guest_features	= set_guest_features,
+	.get_vq_count		= get_vq_count,
 	.init_vq		= init_vq,
 	.notify_status		= notify_status,
 	.notify_vq		= notify_vq,

virtio/net.c

@@ -681,10 +681,18 @@ static int set_size_vq(struct kvm *kvm, void *dev, u32 vq, int size)
 	return size;
 }
 
+static int get_vq_count(struct kvm *kvm, void *dev)
+{
+	struct net_dev *ndev = dev;
+
+	return ndev->queue_pairs * 2 + 1;
+}
+
 static struct virtio_ops net_dev_virtio_ops = {
 	.get_config		= get_config,
 	.get_host_features	= get_host_features,
 	.set_guest_features	= set_guest_features,
+	.get_vq_count		= get_vq_count,
 	.init_vq		= init_vq,
 	.get_pfn_vq		= get_pfn_vq,
 	.get_size_vq		= get_size_vq,

virtio/rng.c

@@ -141,6 +141,11 @@ static int set_size_vq(struct kvm *kvm, void *dev, u32 vq, int size)
 	return size;
 }
 
+static int get_vq_count(struct kvm *kvm, void *dev)
+{
+	return NUM_VIRT_QUEUES;
+}
+
 static struct virtio_ops rng_dev_virtio_ops = {
 	.get_config		= get_config,
 	.get_host_features	= get_host_features,
@@ -150,6 +155,7 @@ static struct virtio_ops rng_dev_virtio_ops = {
 	.get_pfn_vq		= get_pfn_vq,
 	.get_size_vq		= get_size_vq,
 	.set_size_vq		= set_size_vq,
+	.get_vq_count		= get_vq_count,
 };
 
 int virtio_rng__init(struct kvm *kvm)

virtio/scsi.c

@@ -167,6 +167,11 @@ static int set_size_vq(struct kvm *kvm, void *dev, u32 vq, int size)
 	return size;
 }
 
+static int get_vq_count(struct kvm *kvm, void *dev)
+{
+	return NUM_VIRT_QUEUES;
+}
+
 static struct virtio_ops scsi_dev_virtio_ops = {
 	.get_config		= get_config,
 	.get_host_features	= get_host_features,
@@ -179,6 +184,7 @@ static struct virtio_ops scsi_dev_virtio_ops = {
 	.notify_vq		= notify_vq,
 	.notify_vq_gsi		= notify_vq_gsi,
 	.notify_vq_eventfd	= notify_vq_eventfd,
+	.get_vq_count		= get_vq_count,
 };
 
 static void virtio_scsi_vhost_init(struct kvm *kvm, struct scsi_dev *sdev)