bcache: return a pointer to the on-disk sb from read_super

Returning the properly typed actual data structure insteaf of the
containing struct page will save the callers some work going
forward.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/super.c

@@ -60,7 +60,7 @@ struct workqueue_struct *bch_journal_wq;
 /* Superblock */
 
 static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
-			      struct page **res)
+			      struct cache_sb_disk **res)
 {
 	const char *err;
 	struct cache_sb_disk *s;
@@ -191,7 +191,7 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
 	err = NULL;
 
 	get_page(bh->b_page);
-	*res = bh->b_page;
+	*res = s;
 err:
 	put_bh(bh);
 	return err;
@@ -1353,7 +1353,7 @@ static int cached_dev_init(struct cached_dev *dc, unsigned int block_size)
 
 /* Cached device - bcache superblock */
 
-static int register_bdev(struct cache_sb *sb, struct page *sb_page,
+static int register_bdev(struct cache_sb *sb, struct cache_sb_disk *sb_disk,
 				 struct block_device *bdev,
 				 struct cached_dev *dc)
 {
@@ -1367,7 +1367,7 @@ static int register_bdev(struct cache_sb *sb, struct page *sb_page,
 	dc->bdev->bd_holder = dc;
 
 	bio_init(&dc->sb_bio, dc->sb_bio.bi_inline_vecs, 1);
-	bio_first_bvec_all(&dc->sb_bio)->bv_page = sb_page;
+	bio_first_bvec_all(&dc->sb_bio)->bv_page = virt_to_page(sb_disk);
 
 	if (cached_dev_init(dc, sb->block_size << 9))
 		goto err;
@@ -2260,7 +2260,7 @@ static int cache_alloc(struct cache *ca)
 	return ret;
 }
 
-static int register_cache(struct cache_sb *sb, struct page *sb_page,
+static int register_cache(struct cache_sb *sb, struct cache_sb_disk *sb_disk,
 				struct block_device *bdev, struct cache *ca)
 {
 	const char *err = NULL; /* must be set for any error case */
@@ -2272,7 +2272,7 @@ static int register_cache(struct cache_sb *sb, struct page *sb_page,
 	ca->bdev->bd_holder = ca;
 
 	bio_init(&ca->sb_bio, ca->sb_bio.bi_inline_vecs, 1);
-	bio_first_bvec_all(&ca->sb_bio)->bv_page = sb_page;
+	bio_first_bvec_all(&ca->sb_bio)->bv_page = virt_to_page(sb_disk);
 
 	if (blk_queue_discard(bdev_get_queue(bdev)))
 		ca->discard = CACHE_DISCARD(&ca->sb);
@@ -2375,8 +2375,8 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 	const char *err;
 	char *path = NULL;
 	struct cache_sb *sb;
+	struct cache_sb_disk *sb_disk;
 	struct block_device *bdev;
-	struct page *sb_page;
 	ssize_t ret;
 
 	ret = -EBUSY;
@@ -2426,7 +2426,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 	if (set_blocksize(bdev, 4096))
 		goto out_blkdev_put;
 
-	err = read_super(sb, bdev, &sb_page);
+	err = read_super(sb, bdev, &sb_disk);
 	if (err)
 		goto out_blkdev_put;
 
@@ -2438,7 +2438,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 			goto out_put_sb_page;
 
 		mutex_lock(&bch_register_lock);
-		ret = register_bdev(sb, sb_page, bdev, dc);
+		ret = register_bdev(sb, sb_disk, bdev, dc);
 		mutex_unlock(&bch_register_lock);
 		/* blkdev_put() will be called in cached_dev_free() */
 		if (ret < 0)
@@ -2450,7 +2450,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 			goto out_put_sb_page;
 
 		/* blkdev_put() will be called in bch_cache_release() */
-		if (register_cache(sb, sb_page, bdev, ca) != 0)
+		if (register_cache(sb, sb_disk, bdev, ca) != 0)
 			goto out_free_sb;
 	}
 
@@ -2461,7 +2461,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 	return size;
 
 out_put_sb_page:
-	put_page(sb_page);
+	put_page(virt_to_page(sb_disk));
 out_blkdev_put:
 	blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
 out_free_sb: