blk-sysfs: add io queue depth show

index 27aceab..66cba2b 100644
@@ -256,6 +256,11 @@ static ssize_t queue_max_hw_sectors_show(struct request_queue *q, char *page)
 	return queue_var_show(max_hw_sectors_kb, (page));
 }
 
+static ssize_t queue_io_queue_depth_show(struct request_queue *q, char *page)
+{
+	return queue_var_show(queue_io_queue_depth(q), (page));
+}
+
 #define QUEUE_SYSFS_BIT_FNS(name, flag, neg)				\
 static ssize_t								\
 queue_show_##name(struct request_queue *q, char *page)			\

@@ -678,6 +683,11 @@ static struct queue_sysfs_entry queue_wb_lat_entry = {
 	.store = queue_wb_lat_store,
 };
 
+static struct queue_sysfs_entry queue_io_queue_depth_entry = {
+	.attr = {.name = "io_queue_depth", .mode = S_IRUGO },
+	.show = queue_io_queue_depth_show,
+};
+
 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
 static struct queue_sysfs_entry throtl_sample_time_entry = {
 	.attr = {.name = "throttle_sample_time", .mode = S_IRUGO | S_IWUSR },

@@ -719,6 +729,7 @@ static struct attribute *default_attrs[] = {
 	&queue_dax_entry.attr,
 	&queue_wb_lat_entry.attr,
 	&queue_poll_delay_entry.attr,
+	&queue_io_queue_depth_entry.attr,
 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
 	&throtl_sample_time_entry.attr,
 #endif

index 25f6a0c..bcd0af4 100644
@@ -1405,6 +1405,11 @@ static inline unsigned int queue_max_hw_sectors(struct request_queue *q)
 	return q->limits.max_hw_sectors;
 }
 
+static inline unsigned int queue_io_queue_depth(struct request_queue *q)
+{
+	return q->queue_depth;
+}
+
 static inline unsigned short queue_max_segments(struct request_queue *q)
 {
 	return q->limits.max_segments;