btrfs: add define for oldest generation

Some functions can filter metadata by the generation. Add a define that
will annotate such arguments.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -66,6 +66,8 @@ struct btrfs_ordered_sum;
 
 #define BTRFS_MAX_LEVEL 8
 
+#define BTRFS_OLDEST_GENERATION	0ULL
+
 #define BTRFS_COMPAT_EXTENT_TREE_V0
 
 /*

fs/btrfs/ioctl.c

@@ -2600,7 +2600,7 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp)
 			range->len = (u64)-1;
 		}
 		ret = btrfs_defrag_file(file_inode(file), file,
-					range, 0, 0);
+					range, BTRFS_OLDEST_GENERATION, 0);
 		if (ret > 0)
 			ret = 0;
 		kfree(range);

fs/btrfs/tree-defrag.c

@@ -39,7 +39,6 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
 	int level;
 	int next_key_ret = 0;
 	u64 last_ret = 0;
-	u64 min_trans = 0;
 
 	if (root->fs_info->extent_root == root) {
 		/*
@@ -81,7 +80,7 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
 
 	path->keep_locks = 1;
 
-	ret = btrfs_search_forward(root, &key, path, min_trans);
+	ret = btrfs_search_forward(root, &key, path, BTRFS_OLDEST_GENERATION);
 	if (ret < 0)
 		goto out;
 	if (ret > 0) {
@@ -130,7 +129,7 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
 	 */
 	path->slots[1] = btrfs_header_nritems(path->nodes[1]);
 	next_key_ret = btrfs_find_next_key(root, path, &key, 1,
-					   min_trans);
+					   BTRFS_OLDEST_GENERATION);
 	if (next_key_ret == 0) {
 		memcpy(&root->defrag_progress, &key, sizeof(key));
 		ret = -EAGAIN;

fs/btrfs/uuid-tree.c

@@ -282,7 +282,7 @@ int btrfs_uuid_tree_iterate(struct btrfs_fs_info *fs_info,
 	key.offset = 0;
 
 again_search_slot:
-	ret = btrfs_search_forward(root, &key, path, 0);
+	ret = btrfs_search_forward(root, &key, path, BTRFS_OLDEST_GENERATION);
 	if (ret) {
 		if (ret > 0)
 			ret = 0;

fs/btrfs/volumes.c

@@ -4208,7 +4208,8 @@ static int btrfs_uuid_scan_kthread(void *data)
 	key.offset = 0;
 
 	while (1) {
-		ret = btrfs_search_forward(root, &key, path, 0);
+		ret = btrfs_search_forward(root, &key, path,
+				BTRFS_OLDEST_GENERATION);
 		if (ret) {
 			if (ret > 0)
 				ret = 0;