block: Expose stacked device queues in sysfs

Currently stacking devices do not have a queue directory in sysfs.
However, many of the I/O characteristics like sector size, maximum
request size, etc. are queue properties.

This patch enables the queue directory for MD/DM devices.  The elevator
code has been modified to deal with queues that do not have an I/O
scheduler.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/block/elevator.c b/block/elevator.c
index ebee948293eb..bd78f693fcf2 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -575,6 +575,9 @@ void elv_drain_elevator(struct request_queue *q)
  */
 void elv_quiesce_start(struct request_queue *q)
 {
+        if (!q->elevator)
+                return;
+
         queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
 
         /*
@@ -1050,6 +1053,9 @@ ssize_t elv_iosched_store(struct request_queue *q, const char *name,
         char elevator_name[ELV_NAME_MAX];
         struct elevator_type *e;
 
+        if (!q->elevator)
+                return count;
+
         strlcpy(elevator_name, name, sizeof(elevator_name));
         strstrip(elevator_name);
 
@@ -1073,10 +1079,15 @@ ssize_t elv_iosched_store(struct request_queue *q, const char *name,
 ssize_t elv_iosched_show(struct request_queue *q, char *name)
 {
         struct elevator_queue *e = q->elevator;
-        struct elevator_type *elv = e->elevator_type;
+        struct elevator_type *elv;
         struct elevator_type *__e;
         int len = 0;
 
+        if (!q->elevator)
+                return sprintf(name, "none\n");
+
+        elv = e->elevator_type;
+
         spin_lock(&elv_list_lock);
         list_for_each_entry(__e, &elv_list, list) {
                 if (!strcmp(elv->elevator_name, __e->elevator_name))