btrfs: add comments for btrfs_reserve_flush_enum

int btrfs_extent_readonly(struct btrfs_fs_info *fs_info, u64 bytenr);

void btrfs_clear_space_info_full(struct btrfs_fs_info *info);

/*

 * Different levels for to flush space when doing space reservations.

 *

 * The higher the level, the more methods we try to reclaim space.

 */

enum btrfs_reserve_flush_enum {

	/* If we are in the transaction, we can't flush anything.*/

	BTRFS_RESERVE_NO_FLUSH,

	/*

	 * Flushing delalloc may cause deadlock somewhere, in this

	 * case, use FLUSH LIMIT

	 * Flush space by:

	 * - Running delayed inode items

	 * - Allocating a new chunk

	 */

	BTRFS_RESERVE_FLUSH_LIMIT,

	/*

	 * Flush space by:

	 * - Running delayed inode items

	 * - Running delayed refs

	 * - Running delalloc and waiting for ordered extents

	 * - Allocating a new chunk

	 */

	BTRFS_RESERVE_FLUSH_EVICT,

	/*

	 * Flush space by above mentioned methods and by:

	 * - Running delayed iputs

	 * - Commiting transaction

	 *

	 * Can be interruped by fatal signal.

	 */

	BTRFS_RESERVE_FLUSH_ALL,

	/*

	 * Pretty much the same as FLUSH_ALL, but can also steal space from

	 * global rsv.

	 *

	 * Can be interruped by fatal signal.

	 */

	BTRFS_RESERVE_FLUSH_ALL_STEAL,

};