block: Catch possible entries missing from hctx_state_name[]

Add a build-time assert that we are not missing entries from
hctx_state_name[]. For this, create a separate enum for state flags and add
a "max" entry for BLK_MQ_S_x flags.

The numbering for those enum values is as default, so don't explicitly
number.
Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20240719112912.3830443-10-john.g.garry@oracle.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq-debugfs.c

@@ -165,6 +165,7 @@ static int hctx_state_show(void *data, struct seq_file *m)
 {
 	struct blk_mq_hw_ctx *hctx = data;
 
+	BUILD_BUG_ON(ARRAY_SIZE(hctx_state_name) != BLK_MQ_S_MAX);
 	blk_flags_show(m, hctx->state, hctx_state_name,
 		       ARRAY_SIZE(hctx_state_name));
 	seq_puts(m, "\n");

include/linux/blk-mq.h

@@ -663,13 +663,6 @@ enum {
 	BLK_MQ_F_NO_SCHED_BY_DEFAULT	= 1 << 7,
 	BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
 	BLK_MQ_F_ALLOC_POLICY_BITS = 1,
-
-	BLK_MQ_S_STOPPED	= 0,
-	BLK_MQ_S_TAG_ACTIVE	= 1,
-	BLK_MQ_S_SCHED_RESTART	= 2,
-
-	/* hw queue is inactive after all its CPUs become offline */
-	BLK_MQ_S_INACTIVE	= 3,
 };
 #define BLK_MQ_FLAG_TO_ALLOC_POLICY(flags) \
 	((flags >> BLK_MQ_F_ALLOC_POLICY_START_BIT) & \
@@ -681,6 +674,16 @@ enum {
 #define BLK_MQ_MAX_DEPTH	(10240)
 #define BLK_MQ_NO_HCTX_IDX	(-1U)
 
+enum {
+	/* Keep hctx_state_name[] in sync with the definitions below */
+	BLK_MQ_S_STOPPED,
+	BLK_MQ_S_TAG_ACTIVE,
+	BLK_MQ_S_SCHED_RESTART,
+	/* hw queue is inactive after all its CPUs become offline */
+	BLK_MQ_S_INACTIVE,
+	BLK_MQ_S_MAX
+};
+
 struct gendisk *__blk_mq_alloc_disk(struct blk_mq_tag_set *set,
 		struct queue_limits *lim, void *queuedata,
 		struct lock_class_key *lkclass);