btrfs: use the super_block as holder when mounting file systems

The file system type is not a very useful holder as it doesn't allow us
to go back to the actual file system instance.  Pass the super_block
instead which is useful when passed back to the file system driver.

This matches what is done for all other block device based file systems,
and allows us to remove btrfs_fs_info::bdev_holder completely.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: Christoph Hellwig

fs/btrfs/dev-replace.c

@@ -250,7 +250,7 @@ static int btrfs_init_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
 	}
 
 	bdev_file = bdev_file_open_by_path(device_path, BLK_OPEN_WRITE,
-					fs_info->bdev_holder, NULL);
+					   fs_info->sb, NULL);
 	if (IS_ERR(bdev_file)) {
 		btrfs_err(fs_info, "target device %s is invalid!", device_path);
 		return PTR_ERR(bdev_file);

fs/btrfs/fs.h

@@ -715,8 +715,6 @@ struct btrfs_fs_info {
 	u32 data_chunk_allocations;
 	u32 metadata_ratio;
 
-	void *bdev_holder;
-
 	/* Private scrub information */
 	struct mutex scrub_lock;
 	atomic_t scrubs_running;

fs/btrfs/super.c

@@ -1927,7 +1927,7 @@ static int btrfs_get_tree_super(struct fs_context *fc)
 
 		mutex_lock(&uuid_mutex);
 		btrfs_fs_devices_dec_holding(fs_devices);
-		ret = btrfs_open_devices(fs_devices, mode, &btrfs_fs_type);
+		ret = btrfs_open_devices(fs_devices, mode, sb);
 		if (ret < 0)
 			fs_info->fs_devices = NULL;
 		mutex_unlock(&uuid_mutex);
@@ -1942,7 +1942,6 @@ static int btrfs_get_tree_super(struct fs_context *fc)
 		bdev = fs_devices->latest_dev->bdev;
 		snprintf(sb->s_id, sizeof(sb->s_id), "%pg", bdev);
 		shrinker_debugfs_rename(sb->s_shrink, "sb-btrfs:%s", sb->s_id);
-		btrfs_sb(sb)->bdev_holder = &btrfs_fs_type;
 		ret = btrfs_fill_super(sb, fs_devices);
 		if (ret) {
 			deactivate_locked_super(sb);

fs/btrfs/volumes.c

@@ -2705,7 +2705,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 		return -EROFS;
 
 	bdev_file = bdev_file_open_by_path(device_path, BLK_OPEN_WRITE,
-					fs_info->bdev_holder, NULL);
+					   fs_info->sb, NULL);
 	if (IS_ERR(bdev_file))
 		return PTR_ERR(bdev_file);
 
@@ -7174,7 +7174,7 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info,
 	if (IS_ERR(fs_devices))
 		return fs_devices;
 
-	ret = open_fs_devices(fs_devices, BLK_OPEN_READ, fs_info->bdev_holder);
+	ret = open_fs_devices(fs_devices, BLK_OPEN_READ, fs_info->sb);
 	if (ret) {
 		free_fs_devices(fs_devices);
 		return ERR_PTR(ret);