bcache: move bucket related code into read_super_common()

Setting sb->first_bucket and checking sb->keys indeed are only for cache
device, it does not make sense to do them in read_super() for backing
device too.

This patch moves the related code piece into read_super_common()
explicitly for cache device and avoid the confusion.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/md/bcache/super.c

@@ -66,12 +66,17 @@ static const char *read_super_common(struct cache_sb *sb,  struct block_device *
 	const char *err;
 	unsigned int i;
 
+	sb->first_bucket= le16_to_cpu(s->first_bucket);
 	sb->nbuckets	= le64_to_cpu(s->nbuckets);
 	sb->bucket_size	= le16_to_cpu(s->bucket_size);
 
 	sb->nr_in_set	= le16_to_cpu(s->nr_in_set);
 	sb->nr_this_dev	= le16_to_cpu(s->nr_this_dev);
 
+	err = "Too many journal buckets";
+	if (sb->keys > SB_JOURNAL_BUCKETS)
+		goto err;
+
 	err = "Too many buckets";
 	if (sb->nbuckets > LONG_MAX)
 		goto err;
@@ -155,7 +160,6 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
 	sb->flags		= le64_to_cpu(s->flags);
 	sb->seq			= le64_to_cpu(s->seq);
 	sb->last_mount		= le32_to_cpu(s->last_mount);
-	sb->first_bucket	= le16_to_cpu(s->first_bucket);
 	sb->keys		= le16_to_cpu(s->keys);
 
 	for (i = 0; i < SB_JOURNAL_BUCKETS; i++)
@@ -172,10 +176,6 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
 	if (memcmp(sb->magic, bcache_magic, 16))
 		goto err;
 
-	err = "Too many journal buckets";
-	if (sb->keys > SB_JOURNAL_BUCKETS)
-		goto err;
-
 	err = "Bad checksum";
 	if (s->csum != csum_set(s))
 		goto err;