[PATCH v2 3/7] btrfs-progs: Enable read-write ability for 'bg_tree' feature

[Qu Wenruo <wqu@suse.com>]

Allow btrfs-progs to open, read and write 'bg_tree' enabled fs.

The modification itself is not large, as block groups items are only
used at 4 timing:
1) open_ctree()
   We only need to populate fs_info->bg_root and read block group items
   from fs_info->bg_root.
   The obvious change is, we don't need to do btrfs_search_slot() for
   each block group item, but btrfs_next_item() is enough.

   This should hugely reduce open_ctree() execution duration.

2) btrfs_commit_transaction()
   We need to write back dirty block group items back to bg_root.

   The modification here is to insert new block group item if we can't
   find one existing in bg_root, and delete the old one in extent tree
   if we're converting to bg_tree feature.

3) btrfs_make_block_group()
   Just change @root for btrfs_insert_item() from @extent_root to
   @bg_root for fs with that feature.

   This modification needs extra handling for converting case, where
   block group items can be either in extent tree or bg tree.

4) free_block_group_item()
   Just delete the block group item in extent tree.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 ctree.h       |  11 +++-
 disk-io.c     |  20 +++++++
 extent-tree.c | 152 +++++++++++++++++++++++++++++++++++++++++++++-----
 3 files changed, 168 insertions(+), 15 deletions(-)

diff --git a/ctree.h b/ctree.h
index 2899de358613..c2a18c8ab72f 100644
--- a/ctree.h
+++ b/ctree.h
@@ -89,6 +89,9 @@ struct btrfs_free_space_ctl;
 /* tracks free space in block groups. */
 #define BTRFS_FREE_SPACE_TREE_OBJECTID 10ULL
 
+/* store BLOCK_GROUP_ITEMS in a seperate tree */
+#define BTRFS_BLOCK_GROUP_TREE_OBJECTID 11ULL
+
 /* device stats in the device tree */
 #define BTRFS_DEV_STATS_OBJECTID 0ULL
 
@@ -490,6 +493,7 @@ struct btrfs_super_block {
 #define BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA	(1ULL << 8)
 #define BTRFS_FEATURE_INCOMPAT_NO_HOLES		(1ULL << 9)
 #define BTRFS_FEATURE_INCOMPAT_METADATA_UUID    (1ULL << 10)
+#define BTRFS_FEATURE_INCOMPAT_BG_TREE		(1ULL << 11)
 
 #define BTRFS_FEATURE_COMPAT_SUPP		0ULL
 
@@ -513,7 +517,8 @@ struct btrfs_super_block {
 	 BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS |		\
 	 BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA |	\
 	 BTRFS_FEATURE_INCOMPAT_NO_HOLES |		\
-	 BTRFS_FEATURE_INCOMPAT_METADATA_UUID)
+	 BTRFS_FEATURE_INCOMPAT_METADATA_UUID |		\
+	 BTRFS_FEATURE_INCOMPAT_BG_TREE)
 
 /*
  * A leaf is full of items. offset and size tell us where to find
@@ -1123,6 +1128,7 @@ struct btrfs_fs_info {
 	struct btrfs_root *quota_root;
 	struct btrfs_root *free_space_root;
 	struct btrfs_root *uuid_root;
+	struct btrfs_root *bg_root;
 
 	struct rb_root fs_root_tree;
 
@@ -1175,6 +1181,9 @@ struct btrfs_fs_info {
 	unsigned int avoid_sys_chunk_alloc:1;
 	unsigned int finalize_on_close:1;
 
+	/* Converting from bg in extent tree to bg tree */
+	unsigned int convert_to_bg_tree:1;
+
 	int transaction_aborted;
 
 	int (*free_extent_hook)(struct btrfs_fs_info *fs_info,
diff --git a/disk-io.c b/disk-io.c
index 8978f0cb60c7..38248aa895b8 100644
--- a/disk-io.c
+++ b/disk-io.c
@@ -716,6 +716,8 @@ struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info,
 	if (location->objectid == BTRFS_FREE_SPACE_TREE_OBJECTID)
 		return fs_info->free_space_root ? fs_info->free_space_root :
 						ERR_PTR(-ENOENT);
+	if (location->objectid == BTRFS_BLOCK_GROUP_TREE_OBJECTID)
+		return fs_info->bg_root ? fs_info->bg_root : ERR_PTR(-ENOENT);
 
 	BUG_ON(location->objectid == BTRFS_TREE_RELOC_OBJECTID ||
 	       location->offset != (u64)-1);
@@ -768,6 +770,7 @@ struct btrfs_fs_info *btrfs_new_fs_info(int writable, u64 sb_bytenr)
 	fs_info->quota_root = calloc(1, sizeof(struct btrfs_root));
 	fs_info->free_space_root = calloc(1, sizeof(struct btrfs_root));
 	fs_info->uuid_root = calloc(1, sizeof(struct btrfs_root));
+	fs_info->bg_root = calloc(1, sizeof(struct btrfs_root));
 	fs_info->super_copy = calloc(1, BTRFS_SUPER_INFO_SIZE);
 
 	if (!fs_info->tree_root || !fs_info->extent_root ||
@@ -930,6 +933,21 @@ int btrfs_setup_all_roots(struct btrfs_fs_info *fs_info, u64 root_tree_bytenr,
 		return ret;
 	fs_info->extent_root->track_dirty = 1;
 
+	if (btrfs_fs_incompat(fs_info, BG_TREE)) {
+		ret = setup_root_or_create_block(fs_info, flags,
+					fs_info->bg_root,
+					BTRFS_BLOCK_GROUP_TREE_OBJECTID, "bg");
+		if (ret < 0) {
+			error("Couldn't setup bg tree");
+			return ret;
+		}
+		fs_info->bg_root->track_dirty = 1;
+		fs_info->bg_root->ref_cows = 0;
+	} else {
+		free(fs_info->bg_root);
+		fs_info->bg_root = NULL;
+	}
+
 	ret = find_and_setup_root(root, fs_info, BTRFS_DEV_TREE_OBJECTID,
 				  fs_info->dev_root);
 	if (ret) {
@@ -1012,6 +1030,8 @@ void btrfs_release_all_roots(struct btrfs_fs_info *fs_info)
 		free_extent_buffer(fs_info->free_space_root->node);
 	if (fs_info->quota_root)
 		free_extent_buffer(fs_info->quota_root->node);
+	if (fs_info->bg_root)
+		free_extent_buffer(fs_info->bg_root->node);
 	if (fs_info->csum_root)
 		free_extent_buffer(fs_info->csum_root->node);
 	if (fs_info->dev_root)
diff --git a/extent-tree.c b/extent-tree.c
index 9713d627764c..cb3d7a1add0f 100644
--- a/extent-tree.c
+++ b/extent-tree.c
@@ -1528,22 +1528,68 @@ static int write_one_cache_group(struct btrfs_trans_handle *trans,
 				 struct btrfs_path *path,
 				 struct btrfs_block_group_cache *cache)
 {
+	bool is_bg_tree = btrfs_fs_incompat(trans->fs_info, BG_TREE);
 	int ret;
-	struct btrfs_root *extent_root = trans->fs_info->extent_root;
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_root *root;
 	unsigned long bi;
 	struct extent_buffer *leaf;
 
-	ret = btrfs_search_slot(trans, extent_root, &cache->key, path, 0, 1);
+	if (is_bg_tree)
+		root = fs_info->bg_root;
+	else
+		root = fs_info->extent_root;
+
+	ret = btrfs_search_slot(trans, root, &cache->key, path, 0, 1);
 	if (ret < 0)
-		goto fail;
-	BUG_ON(ret);
+		goto out;
 
-	leaf = path->nodes[0];
-	bi = btrfs_item_ptr_offset(leaf, path->slots[0]);
-	write_extent_buffer(leaf, &cache->item, bi, sizeof(cache->item));
-	btrfs_mark_buffer_dirty(leaf);
-	btrfs_release_path(path);
-fail:
+	if (ret == 0) {
+		/* Update existing bg */
+		leaf = path->nodes[0];
+		bi = btrfs_item_ptr_offset(leaf, path->slots[0]);
+		write_extent_buffer(leaf, &cache->item, bi, sizeof(cache->item));
+		btrfs_mark_buffer_dirty(leaf);
+		btrfs_release_path(path);
+	} else {
+		btrfs_release_path(path);
+
+		/*
+		 * Insert new bg item
+		 *
+		 * This only happens for bg_tree feature
+		 */
+		if (!is_bg_tree) {
+			error("can't find block group item for bytenr %llu",
+			      cache->key.objectid);
+			ret = -ENOENT;
+			goto out;
+		}
+		ret = btrfs_insert_item(trans, root, &cache->key, &cache->item,
+					sizeof(cache->item));
+		if (ret < 0)
+			goto out;
+
+		/* Also delete the existing one in next tree if needed */
+		if (fs_info->convert_to_bg_tree) {
+			ret = btrfs_search_slot(trans, fs_info->extent_root,
+						&cache->key, path, -1, 1);
+			if (ret < 0) {
+				btrfs_release_path(path);
+				goto out;
+			}
+			/* Good, already converted */
+			if (ret > 0) {
+				ret = 0;
+				btrfs_release_path(path);
+				goto out;
+			}
+			/* Delete old block group item in extent tree */
+			ret = btrfs_del_item(trans, fs_info->extent_root, path);
+			btrfs_release_path(path);
+		}
+	}
+out:
 	if (ret)
 		return ret;
 	return 0;
@@ -2717,14 +2763,66 @@ static int read_one_block_group(struct btrfs_fs_info *fs_info,
 	return 0;
 }
 
+static int read_block_group_tree(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_root *root = fs_info->bg_root;
+	struct btrfs_key key = { 0 };
+	struct btrfs_path path;
+	int ret;
+
+	btrfs_init_path(&path);
+	ret = btrfs_search_slot(NULL, root, &key, &path, 0, 0);
+	if (ret < 0) {
+		errno = -ret;
+		error("failed to search block group tree: %m");
+		return ret;
+	}
+	if (ret == 0)
+		goto invalid_key;
+
+	while (1) {
+		btrfs_item_key_to_cpu(path.nodes[0], &key, path.slots[0]);
+		if (key.type != BTRFS_BLOCK_GROUP_ITEM_KEY)
+			goto invalid_key;
+
+		ret = read_one_block_group(fs_info, &path);
+		if (ret < 0) {
+			errno = -ret;
+			error("failed to read one block group: %m");
+			goto out;
+		}
+		ret = btrfs_next_item(root, &path);
+		if (ret < 0) {
+			errno = -ret;
+			error("failed to search block group tree: %m");
+			goto out;
+		}
+		if (ret > 0) {
+			ret = 0;
+			break;
+		}
+	}
+out:
+	btrfs_release_path(&path);
+	return ret;
+
+invalid_key:
+	error("invalid key (%llu, %u, %llu) found in block group tree",
+	      key.objectid, key.type, key.offset);
+	btrfs_release_path(&path);
+	return -EUCLEAN;
+}
+
 int btrfs_read_block_groups(struct btrfs_fs_info *fs_info)
 {
 	struct btrfs_path path;
-	struct btrfs_root *root;
+	struct btrfs_root *root = fs_info->extent_root;
 	int ret;
 	struct btrfs_key key;
 
-	root = fs_info->extent_root;
+	if (btrfs_fs_incompat(fs_info, BG_TREE))
+		return read_block_group_tree(fs_info);
+
 	key.objectid = 0;
 	key.offset = 0;
 	key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
@@ -2804,12 +2902,17 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans,
 			   u64 type, u64 chunk_offset, u64 size)
 {
 	int ret;
-	struct btrfs_root *extent_root = fs_info->extent_root;
+	struct btrfs_root *root;
 	struct btrfs_block_group_cache *cache;
 
+	if (btrfs_fs_incompat(fs_info, BG_TREE))
+		root = fs_info->bg_root;
+	else
+		root = fs_info->extent_root;
+
 	cache = btrfs_add_block_group(fs_info, bytes_used, type, chunk_offset,
 				      size);
-	ret = btrfs_insert_item(trans, extent_root, &cache->key, &cache->item,
+	ret = btrfs_insert_item(trans, root, &cache->key, &cache->item,
 				sizeof(cache->item));
 	BUG_ON(ret);
 
@@ -2943,8 +3046,16 @@ static int free_block_group_item(struct btrfs_trans_handle *trans,
 	if (!path)
 		return -ENOMEM;
 
+	/* Using bg tree only */
+	if (btrfs_fs_incompat(fs_info, BG_TREE) && !fs_info->convert_to_bg_tree)
+		goto bg_tree;
+
 	ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
 	if (ret > 0) {
+		if (btrfs_fs_incompat(fs_info, BG_TREE)) {
+			btrfs_release_path(path);
+			goto bg_tree;
+		}
 		ret = -ENOENT;
 		goto out;
 	}
@@ -2952,6 +3063,19 @@ static int free_block_group_item(struct btrfs_trans_handle *trans,
 		goto out;
 
 	ret = btrfs_del_item(trans, root, path);
+	goto out;
+
+bg_tree:
+	root = fs_info->bg_root;
+	ret = btrfs_search_slot(trans, fs_info->bg_root, &key, path, -1, 1);
+	if (ret < 0)
+		goto out;
+	if (ret > 0) {
+		ret = -ENOENT;
+		goto out;
+	}
+	ret = btrfs_del_item(trans, root, path);
+
 out:
 	btrfs_free_path(path);
 	return ret;
-- 
2.23.0