btrfs: use enum for btrfs_block_rsv::type

The number of block group reserve types BTRFS_BLOCK_RSV_* is small and
fits to u8 and there's enough left in case we want to add more.
For type safety use the enum but make it 8 bits in the structure to save
space.

The structure size is now 48 on release build, making a slight
improvement in structures where it's embedded, like btrfs_fs_info or
btrfs_inode.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-rsv.c

@@ -171,7 +171,7 @@ int btrfs_block_rsv_migrate(struct btrfs_block_rsv *src,
 	return 0;
 }
 
-void btrfs_init_block_rsv(struct btrfs_block_rsv *rsv, unsigned short type)
+void btrfs_init_block_rsv(struct btrfs_block_rsv *rsv, enum btrfs_rsv_type type)
 {
 	memset(rsv, 0, sizeof(*rsv));
 	spin_lock_init(&rsv->lock);
@@ -180,7 +180,7 @@ void btrfs_init_block_rsv(struct btrfs_block_rsv *rsv, unsigned short type)
 
 void btrfs_init_metadata_block_rsv(struct btrfs_fs_info *fs_info,
 				   struct btrfs_block_rsv *rsv,
-				   unsigned short type)
+				   enum btrfs_rsv_type type)
 {
 	btrfs_init_block_rsv(rsv, type);
 	rsv->space_info = btrfs_find_space_info(fs_info,
@@ -188,7 +188,7 @@ void btrfs_init_metadata_block_rsv(struct btrfs_fs_info *fs_info,
 }
 
 struct btrfs_block_rsv *btrfs_alloc_block_rsv(struct btrfs_fs_info *fs_info,
-					      unsigned short type)
+					      enum btrfs_rsv_type type)
 {
 	struct btrfs_block_rsv *block_rsv;
 

fs/btrfs/block-rsv.h

@@ -9,7 +9,7 @@ enum btrfs_reserve_flush_enum;
 /*
  * Types of block reserves
  */
-enum {
+enum btrfs_rsv_type {
 	BTRFS_BLOCK_RSV_GLOBAL,
 	BTRFS_BLOCK_RSV_DELALLOC,
 	BTRFS_BLOCK_RSV_TRANS,
@@ -27,7 +27,8 @@ struct btrfs_block_rsv {
 	spinlock_t lock;
 	bool full;
 	bool failfast;
-	unsigned short type;
+	/* Block reserve type, one of BTRFS_BLOCK_RSV_* */
+	enum btrfs_rsv_type type:8;
 
 	/*
 	 * Qgroup equivalent for @size @reserved
@@ -49,13 +50,13 @@ struct btrfs_block_rsv {
 	u64 qgroup_rsv_reserved;
 };
 
-void btrfs_init_block_rsv(struct btrfs_block_rsv *rsv, unsigned short type);
+void btrfs_init_block_rsv(struct btrfs_block_rsv *rsv, enum btrfs_rsv_type type);
 void btrfs_init_root_block_rsv(struct btrfs_root *root);
 struct btrfs_block_rsv *btrfs_alloc_block_rsv(struct btrfs_fs_info *fs_info,
-					      unsigned short type);
+					      enum btrfs_rsv_type type);
 void btrfs_init_metadata_block_rsv(struct btrfs_fs_info *fs_info,
 				   struct btrfs_block_rsv *rsv,
-				   unsigned short type);
+				   enum btrfs_rsv_type type);
 void btrfs_free_block_rsv(struct btrfs_fs_info *fs_info,
 			  struct btrfs_block_rsv *rsv);
 int btrfs_block_rsv_add(struct btrfs_fs_info *fs_info,