Btrfs: add a new "type" field into the block reservation structure

Sometimes we need choose the method of the reservation according to the type
of the block reservation, such as the reservation for the delayed inode update.
Now we identify the type just by comparing the address of the reservation
variants, it is very ugly if it is a temporary one because we need compare it
with all the common reservation variants. So we add a new "type" field to keep
the type the reservation variants.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 07d5eeb..eb768c4 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -650,7 +650,7 @@
 	 * we're accounted for.
 	 */
 	if (!src_rsv || (!trans->bytes_reserved &&
-	    src_rsv != &root->fs_info->delalloc_block_rsv)) {
+			 src_rsv->type != BTRFS_BLOCK_RSV_DELALLOC)) {
 		ret = btrfs_block_rsv_add_noflush(root, dst_rsv, num_bytes);
 		/*
 		 * Since we're under a transaction reserve_metadata_bytes could
@@ -668,7 +668,7 @@
 						      num_bytes, 1);
 		}
 		return ret;
-	} else if (src_rsv == &root->fs_info->delalloc_block_rsv) {
+	} else if (src_rsv->type == BTRFS_BLOCK_RSV_DELALLOC) {
 		spin_lock(&BTRFS_I(inode)->lock);
 		if (test_and_clear_bit(BTRFS_INODE_DELALLOC_META_RESERVED,
 				       &BTRFS_I(inode)->runtime_flags)) {