[PATCH v2 2/7] btrfs-progs: Refactor btrfs_read_block_groups()

Qu Wenruo
2019-10-08T04:49:50Z

This patch does the following refactor:
- Refactor parameter from @root to @fs_info

- Refactor the large loop body into another function
Now we have a helper function, read_one_block_group(), to handle
block group cache and space info related routine.

- Refactor the return value
Even we have the code handling ret > 0 from find_first_block_group(),
it never works, as when there is no more block group,
find_first_block_group() just return -ENOENT other than 1.

This is super confusing, it's almost a mircle it even works.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
ctree.h | 2 +-
disk-io.c | 9 ++-
extent-tree.c | 160 ++++++++++++++++++++++++++++----------------------
3 files changed, 97 insertions(+), 74 deletions(-)

diff --git a/ctree.h b/ctree.h
index 8c7b3cb40151..2899de358613 100644
--- a/ctree.h
+++ b/ctree.h
@@ -2550,7 +2550,7 @@ int update_space_info(struct btrfs_fs_info *info, u64 flags,
u64 total_bytes, u64 bytes_used,
struct btrfs_space_info **space_info);
int btrfs_free_block_groups(struct btrfs_fs_info *info);
-int btrfs_read_block_groups(struct btrfs_root *root);
+int btrfs_read_block_groups(struct btrfs_fs_info *info);
struct btrfs_block_group_cache *
btrfs_add_block_group(struct btrfs_fs_info *fs_info, u64 bytes_used, u64 type,
u64 chunk_offset, u64 size);
diff --git a/disk-io.c b/disk-io.c
index be44eead5cef..8978f0cb60c7 100644
--- a/disk-io.c
+++ b/disk-io.c
@@ -983,14 +983,17 @@ int btrfs_setup_all_roots(struct btrfs_fs_info *fs_info, u64 root_tree_bytenr,
fs_info->last_trans_committed = generation;
if (extent_buffer_uptodate(fs_info->extent_root->node) &&
!(flags & OPEN_CTREE_NO_BLOCK_GROUPS)) {
- ret = btrfs_read_block_groups(fs_info->tree_root);
+ ret = btrfs_read_block_groups(fs_info);
/*
* If we don't find any blockgroups (ENOENT) we're either
* restoring or creating the filesystem, where it's expected,
* anything else is error
*/
- if (ret != -ENOENT)
- return -EIO;
+ if (ret < 0 && ret != -ENOENT) {
+ errno = -ret;
+ error("failed to read block groups: %m");
+ return ret;
+ }
}

key.objectid = BTRFS_FS_TREE_OBJECTID;
diff --git a/extent-tree.c b/extent-tree.c
index 19d1ea0df570..9713d627764c 100644
--- a/extent-tree.c
+++ b/extent-tree.c
@@ -2607,6 +2607,13 @@ int btrfs_free_block_groups(struct btrfs_fs_info *info)
return 0;
}

+/*
+ * Find a block group which starts >= @key->objectid in extent tree.
+ *
+ * Return 0 for found
+ * Retrun >0 for not found
+ * Return <0 for error
+ */
static int find_first_block_group(struct btrfs_root *root,
struct btrfs_path *path, struct btrfs_key *key)
{
@@ -2636,36 +2643,95 @@ static int find_first_block_group(struct btrfs_root *root,
return 0;
path->slots[0]++;
}
- ret = -ENOENT;
+ ret = 1;
error:
return ret;
}

-int btrfs_read_block_groups(struct btrfs_root *root)
+/*
+ * Helper function to read out one BLOCK_GROUP_ITEM and insert it into
+ * block group cache.
+ *
+ * Return 0 if nothing wrong (either insert the bg cache or skip 0 sized bg)
+ * Return <0 for error.
+ */
+static int read_one_block_group(struct btrfs_fs_info *fs_info,
+ struct btrfs_path *path)
{
- struct btrfs_path *path;
- int ret;
- int bit;
- struct btrfs_block_group_cache *cache;
- struct btrfs_fs_info *info = root->fs_info;
+ struct extent_io_tree *block_group_cache = &fs_info->block_group_cache;
+ struct extent_buffer *leaf = path->nodes[0];
struct btrfs_space_info *space_info;
- struct extent_io_tree *block_group_cache;
+ struct btrfs_block_group_cache *cache;
struct btrfs_key key;
- struct btrfs_key found_key;
- struct extent_buffer *leaf;
+ int slot = path->slots[0];
+ int bit = 0;
+ int ret;

- block_group_cache = &info->block_group_cache;
+ btrfs_item_key_to_cpu(leaf, &key, slot);
+ ASSERT(key.type == BTRFS_BLOCK_GROUP_ITEM_KEY);
+
+ /*
+ * Skip 0 sized block group, don't insert them into block
+ * group cache tree, as its length is 0, it won't get
+ * freed at close_ctree() time.
+ */
+ if (key.offset == 0)
+ return 0;
+
+ cache = kzalloc(sizeof(*cache), GFP_NOFS);
+ if (!cache)
+ return -ENOMEM;
+ read_extent_buffer(leaf, &cache->item,
+ btrfs_item_ptr_offset(leaf, slot),
+ sizeof(cache->item));
+ memcpy(&cache->key, &key, sizeof(key));
+ cache->cached = 0;
+ cache->pinned = 0;
+ cache->flags = btrfs_block_group_flags(&cache->item);
+ if (cache->flags & BTRFS_BLOCK_GROUP_DATA) {
+ bit = BLOCK_GROUP_DATA;
+ } else if (cache->flags & BTRFS_BLOCK_GROUP_SYSTEM) {
+ bit = BLOCK_GROUP_SYSTEM;
+ } else if (cache->flags & BTRFS_BLOCK_GROUP_METADATA) {
+ bit = BLOCK_GROUP_METADATA;
+ }
+ set_avail_alloc_bits(fs_info, cache->flags);
+ if (btrfs_chunk_readonly(fs_info, cache->key.objectid))
+ cache->ro = 1;
+ exclude_super_stripes(fs_info, cache);
+
+ ret = update_space_info(fs_info, cache->flags, cache->key.offset,
+ btrfs_block_group_used(&cache->item),
+ &space_info);
+ if (ret < 0) {
+ free(cache);
+ return ret;
+ }
+ cache->space_info = space_info;
+
+ set_extent_bits(block_group_cache, cache->key.objectid,
+ cache->key.objectid + cache->key.offset - 1,
+ bit | EXTENT_LOCKED);
+ set_state_private(block_group_cache, cache->key.objectid,
+ (unsigned long)cache);
+ return 0;
+}

- root = info->extent_root;
+int btrfs_read_block_groups(struct btrfs_fs_info *fs_info)
+{
+ struct btrfs_path path;
+ struct btrfs_root *root;
+ int ret;
+ struct btrfs_key key;
+
+ root = fs_info->extent_root;
key.objectid = 0;
key.offset = 0;
key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
- path = btrfs_alloc_path();
- if (!path)
- return -ENOMEM;
+ btrfs_init_path(&path);

while(1) {
- ret = find_first_block_group(root, path, &key);
+ ret = find_first_block_group(root, &path, &key);
if (ret > 0) {
ret = 0;
goto error;
@@ -2673,67 +2739,21 @@ int btrfs_read_block_groups(struct btrfs_root *root)
if (ret != 0) {
goto error;
}
- leaf = path->nodes[0];
- btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
+ btrfs_item_key_to_cpu(path.nodes[0], &key, path.slots[0]);

- cache = kzalloc(sizeof(*cache), GFP_NOFS);
- if (!cache) {
- ret = -ENOMEM;
+ ret = read_one_block_group(fs_info, &path);
+ if (ret < 0)
goto error;
- }

- read_extent_buffer(leaf, &cache->item,
- btrfs_item_ptr_offset(leaf, path->slots[0]),
- sizeof(cache->item));
- memcpy(&cache->key, &found_key, sizeof(found_key));
- cache->cached = 0;
- cache->pinned = 0;
- key.objectid = found_key.objectid + found_key.offset;
- if (found_key.offset == 0)
+ if (key.offset == 0)
key.objectid++;
- btrfs_release_path(path);
-
- /*
- * Skip 0 sized block group, don't insert them into block
- * group cache tree, as its length is 0, it won't get
- * freed at close_ctree() time.
- */
- if (found_key.offset == 0) {
- free(cache);
- continue;
- }
-
- cache->flags = btrfs_block_group_flags(&cache->item);
- bit = 0;
- if (cache->flags & BTRFS_BLOCK_GROUP_DATA) {
- bit = BLOCK_GROUP_DATA;
- } else if (cache->flags & BTRFS_BLOCK_GROUP_SYSTEM) {
- bit = BLOCK_GROUP_SYSTEM;
- } else if (cache->flags & BTRFS_BLOCK_GROUP_METADATA) {
- bit = BLOCK_GROUP_METADATA;
- }
- set_avail_alloc_bits(info, cache->flags);
- if (btrfs_chunk_readonly(info, cache->key.objectid))
- cache->ro = 1;
-
- exclude_super_stripes(info, cache);
-
- ret = update_space_info(info, cache->flags, found_key.offset,
- btrfs_block_group_used(&cache->item),
- &space_info);
- BUG_ON(ret);
- cache->space_info = space_info;
-
- /* use EXTENT_LOCKED to prevent merging */
- set_extent_bits(block_group_cache, found_key.objectid,
- found_key.objectid + found_key.offset - 1,
- bit | EXTENT_LOCKED);
- set_state_private(block_group_cache, found_key.objectid,
- (unsigned long)cache);
+ else
+ key.objectid = key.objectid + key.offset;
+ btrfs_release_path(&path);
}
ret = 0;
error:
- btrfs_free_path(path);
+ btrfs_release_path(&path);
return ret;
}

--
2.23.0