vDPA: report virtio-block max segments in a request to user space

This commit allows vDPA reporting the maximum number of
segments in a request of virtio-block devices to
user space.
Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Message-Id: <20240218185606.13509-5-lingshan.zhu@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vdpa/vdpa.c

@@ -985,6 +985,20 @@ vdpa_dev_blk_block_size_config_fill(struct sk_buff *msg, u64 features,
 	return nla_put_u32(msg, VDPA_ATTR_DEV_BLK_CFG_BLK_SIZE, val_u32);
 }
 
+static int
+vdpa_dev_blk_seg_max_config_fill(struct sk_buff *msg, u64 features,
+				 const struct virtio_blk_config *config)
+{
+	u32 val_u32;
+
+	if ((features & BIT_ULL(VIRTIO_BLK_F_SEG_MAX)) == 0)
+		return 0;
+
+	val_u32 = __virtio32_to_cpu(true, config->seg_max);
+
+	return nla_put_u32(msg, VDPA_ATTR_DEV_BLK_CFG_SEG_MAX, val_u32);
+}
+
 static int vdpa_dev_blk_config_fill(struct vdpa_device *vdev,
 				    struct sk_buff *msg)
 {
@@ -1008,6 +1022,9 @@ static int vdpa_dev_blk_config_fill(struct vdpa_device *vdev,
 	if (vdpa_dev_blk_block_size_config_fill(msg, features_device, &config))
 		return -EMSGSIZE;
 
+	if (vdpa_dev_blk_seg_max_config_fill(msg, features_device, &config))
+		return -EMSGSIZE;
+
 	return 0;
 }
 

include/uapi/linux/vdpa.h

@@ -59,6 +59,7 @@ enum vdpa_attr {
 	VDPA_ATTR_DEV_BLK_CFG_CAPACITY,		/* u64 */
 	VDPA_ATTR_DEV_BLK_CFG_SEG_SIZE,		/* u32 */
 	VDPA_ATTR_DEV_BLK_CFG_BLK_SIZE,		/* u32 */
+	VDPA_ATTR_DEV_BLK_CFG_SEG_MAX,		/* u32 */
 
 	/* new attributes must be added above here */
 	VDPA_ATTR_MAX,