block: Catch possible entries missing from hctx_flag_name[]

Refresh values in BLK_MQ_F_x enum, and then re-arrange members in
hctx_flag_name[] to match that enum. Renumber
BLK_MQ_F_ALLOC_POLICY_START_BIT to match the value refresh.

Add a BUILD_BUG_ON() call to ensure that we are not missing entries in
hctx_flag_name[].

Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20240719112912.3830443-11-john.g.garry@oracle.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq-debugfs.c

@@ -196,6 +196,9 @@ static int hctx_flags_show(void *data, struct seq_file *m)
 	struct blk_mq_hw_ctx *hctx = data;
 	const int alloc_policy = BLK_MQ_FLAG_TO_ALLOC_POLICY(hctx->flags);
 
+	BUILD_BUG_ON(ARRAY_SIZE(hctx_flag_name) !=
+			BLK_MQ_F_ALLOC_POLICY_START_BIT);
+
 	seq_puts(m, "alloc_policy=");
 	if (alloc_policy < ARRAY_SIZE(alloc_policy_name) &&
 	    alloc_policy_name[alloc_policy])

include/linux/blk-mq.h

@@ -644,6 +644,7 @@ struct blk_mq_ops {
 #endif
 };
 
+/* Keep hctx_flag_name[] in sync with the definitions below */
 enum {
 	BLK_MQ_F_SHOULD_MERGE	= 1 << 0,
 	BLK_MQ_F_TAG_QUEUE_SHARED = 1 << 1,
@@ -653,15 +654,16 @@ enum {
 	 */
 	BLK_MQ_F_STACKING	= 1 << 2,
 	BLK_MQ_F_TAG_HCTX_SHARED = 1 << 3,
-	BLK_MQ_F_BLOCKING	= 1 << 5,
+	BLK_MQ_F_BLOCKING	= 1 << 4,
 	/* Do not allow an I/O scheduler to be configured. */
-	BLK_MQ_F_NO_SCHED	= 1 << 6,
+	BLK_MQ_F_NO_SCHED	= 1 << 5,
+
 	/*
 	 * Select 'none' during queue registration in case of a single hwq
 	 * or shared hwqs instead of 'mq-deadline'.
 	 */
-	BLK_MQ_F_NO_SCHED_BY_DEFAULT	= 1 << 7,
-	BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
+	BLK_MQ_F_NO_SCHED_BY_DEFAULT	= 1 << 6,
+	BLK_MQ_F_ALLOC_POLICY_START_BIT = 7,
 	BLK_MQ_F_ALLOC_POLICY_BITS = 1,
 };
 #define BLK_MQ_FLAG_TO_ALLOC_POLICY(flags) \