vdpa: add new attribute VDPA_ATTR_DEV_MIN_VQ_SIZE

This attribute advertises the min value of virtqueue size. The value is
1 by default.

Signed-off-by: Wu Zongyong <wuzongyong@linux.alibaba.com>
Link: https://lore.kernel.org/r/2bbc417355c4d22298050b1ba887cecfbde3e85d.1635493219.git.wuzongyong@linux.alibaba.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vdpa/vdpa.c

@@ -500,6 +500,7 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
 	      int flags, struct netlink_ext_ack *extack)
 {
 	u16 max_vq_size;
+	u16 min_vq_size = 1;
 	u32 device_id;
 	u32 vendor_id;
 	void *hdr;
@@ -516,6 +517,8 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
 	device_id = vdev->config->get_device_id(vdev);
 	vendor_id = vdev->config->get_vendor_id(vdev);
 	max_vq_size = vdev->config->get_vq_num_max(vdev);
+	if (vdev->config->get_vq_num_min)
+		min_vq_size = vdev->config->get_vq_num_min(vdev);
 
 	err = -EMSGSIZE;
 	if (nla_put_string(msg, VDPA_ATTR_DEV_NAME, dev_name(&vdev->dev)))
@@ -528,6 +531,8 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
 		goto msg_err;
 	if (nla_put_u16(msg, VDPA_ATTR_DEV_MAX_VQ_SIZE, max_vq_size))
 		goto msg_err;
+	if (nla_put_u16(msg, VDPA_ATTR_DEV_MIN_VQ_SIZE, min_vq_size))
+		goto msg_err;
 
 	genlmsg_end(msg, hdr);
 	return 0;

include/uapi/linux/vdpa.h

@@ -32,6 +32,7 @@ enum vdpa_attr {
 	VDPA_ATTR_DEV_VENDOR_ID,		/* u32 */
 	VDPA_ATTR_DEV_MAX_VQS,			/* u32 */
 	VDPA_ATTR_DEV_MAX_VQ_SIZE,		/* u16 */
+	VDPA_ATTR_DEV_MIN_VQ_SIZE,		/* u16 */
 
 	/* new attributes must be added above here */
 	VDPA_ATTR_MAX,