block: expose QUEUE_FLAG_DAX in sysfs

Provides the ability to identify DAX enabled devices in userspace.

Signed-off-by: Yigal Korman <yigal@plexistor.com>
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-sysfs.c

@@ -379,6 +379,11 @@ static ssize_t queue_wc_store(struct request_queue *q, const char *page,
 	return count;
 }
 
+static ssize_t queue_dax_show(struct request_queue *q, char *page)
+{
+	return queue_var_show(blk_queue_dax(q), page);
+}
+
 static struct queue_sysfs_entry queue_requests_entry = {
 	.attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
 	.show = queue_requests_show,
@@ -516,6 +521,11 @@ static struct queue_sysfs_entry queue_wc_entry = {
 	.store = queue_wc_store,
 };
 
+static struct queue_sysfs_entry queue_dax_entry = {
+	.attr = {.name = "dax", .mode = S_IRUGO },
+	.show = queue_dax_show,
+};
+
 static struct attribute *default_attrs[] = {
 	&queue_requests_entry.attr,
 	&queue_ra_entry.attr,
@@ -542,6 +552,7 @@ static struct attribute *default_attrs[] = {
 	&queue_random_entry.attr,
 	&queue_poll_entry.attr,
 	&queue_wc_entry.attr,
+	&queue_dax_entry.attr,
 	NULL,
 };