btrfs: block-group: refactor how we read one block group item

Structure btrfs_block_group has the following members which are
currently read from on-disk block group item and key:

- length - from item key
- used
- flags - from block group item

However for incoming skinny block group tree, we are going to read those
members from different sources.

This patch will refactor such read by:

- Don't initialize btrfs_block_group::length at allocation
  Caller should initialize them manually.
  Also to avoid possible (well, only two callers) missing
  initialization, add extra ASSERT() in btrfs_add_block_group_cache().

- Refactor length/used/flags initialization into one function
  The new function, fill_one_block_group() will handle the
  initialization of such members.

- Use btrfs_block_group::length to replace key::offset
  Since skinny block group item would have a different meaning for its
  key offset.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 1137597..e9232ba 100644 (file)
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -161,6 +161,8 @@ static int btrfs_add_block_group_cache(struct btrfs_fs_info *info,
        struct rb_node *parent = NULL;
        struct btrfs_block_group *cache;
 
+       ASSERT(block_group->length != 0);
+
        spin_lock(&info->block_group_cache_lock);
        p = &info->block_group_cache_tree.rb_node;
 
@@ -1771,7 +1773,7 @@ static void link_block_group(struct btrfs_block_group *cache)
 }
 
 static struct btrfs_block_group *btrfs_create_block_group_cache(
-               struct btrfs_fs_info *fs_info, u64 start, u64 size)
+               struct btrfs_fs_info *fs_info, u64 start)
 {
        struct btrfs_block_group *cache;
 
@@ -1787,7 +1789,6 @@ static struct btrfs_block_group *btrfs_create_block_group_cache(
        }
 
        cache->start = start;
-       cache->length = size;
 
        cache->fs_info = fs_info;
        cache->full_stripe_len = btrfs_full_stripe_len(fs_info, start);
@@ -1867,25 +1868,44 @@ static int check_chunk_block_group_mappings(struct btrfs_fs_info *fs_info)
        return ret;
 }
 
+static int read_block_group_item(struct btrfs_block_group *cache,
+                                struct btrfs_path *path,
+                                const struct btrfs_key *key)
+{
+       struct extent_buffer *leaf = path->nodes[0];
+       struct btrfs_block_group_item bgi;
+       int slot = path->slots[0];
+
+       cache->length = key->offset;
+
+       read_extent_buffer(leaf, &bgi, btrfs_item_ptr_offset(leaf, slot),
+                          sizeof(bgi));
+       cache->used = btrfs_stack_block_group_used(&bgi);
+       cache->flags = btrfs_stack_block_group_flags(&bgi);
+
+       return 0;
+}
+
 static int read_one_block_group(struct btrfs_fs_info *info,
                                struct btrfs_path *path,
                                const struct btrfs_key *key,
                                int need_clear)
 {
-       struct extent_buffer *leaf = path->nodes[0];
        struct btrfs_block_group *cache;
        struct btrfs_space_info *space_info;
-       struct btrfs_block_group_item bgi;
        const bool mixed = btrfs_fs_incompat(info, MIXED_GROUPS);
-       int slot = path->slots[0];
        int ret;
 
        ASSERT(key->type == BTRFS_BLOCK_GROUP_ITEM_KEY);
 
-       cache = btrfs_create_block_group_cache(info, key->objectid, key->offset);
+       cache = btrfs_create_block_group_cache(info, key->objectid);
        if (!cache)
                return -ENOMEM;
 
+       ret = read_block_group_item(cache, path, key);
+       if (ret < 0)
+               goto error;
+
        if (need_clear) {
                /*
                 * When we mount with old space cache, we need to
@@ -1900,10 +1920,6 @@ static int read_one_block_group(struct btrfs_fs_info *info,
                if (btrfs_test_opt(info, SPACE_CACHE))
                        cache->disk_cache_state = BTRFS_DC_CLEAR;
        }
-       read_extent_buffer(leaf, &bgi, btrfs_item_ptr_offset(leaf, slot),
-                          sizeof(bgi));
-       cache->used = btrfs_stack_block_group_used(&bgi);
-       cache->flags = btrfs_stack_block_group_flags(&bgi);
        if (!mixed && ((cache->flags & BTRFS_BLOCK_GROUP_METADATA) &&
            (cache->flags & BTRFS_BLOCK_GROUP_DATA))) {
                        btrfs_err(info,
@@ -1931,15 +1947,15 @@ static int read_one_block_group(struct btrfs_fs_info *info,
         * are empty, and we can just add all the space in and be done with it.
         * This saves us _a_lot_ of time, particularly in the full case.
         */
-       if (key->offset == cache->used) {
+       if (cache->length == cache->used) {
                cache->last_byte_to_unpin = (u64)-1;
                cache->cached = BTRFS_CACHE_FINISHED;
                btrfs_free_excluded_extents(cache);
        } else if (cache->used == 0) {
                cache->last_byte_to_unpin = (u64)-1;
                cache->cached = BTRFS_CACHE_FINISHED;
-               add_new_free_space(cache, key->objectid,
-                                  key->objectid + key->offset);
+               add_new_free_space(cache, cache->start,
+                                  cache->start + cache->length);
                btrfs_free_excluded_extents(cache);
        }
 
@@ -1949,7 +1965,7 @@ static int read_one_block_group(struct btrfs_fs_info *info,
                goto error;
        }
        trace_btrfs_add_block_group(info, cache, 0);
-       btrfs_update_space_info(info, cache->flags, key->offset,
+       btrfs_update_space_info(info, cache->flags, cache->length,
                                cache->used, cache->bytes_super, &space_info);
 
        cache->space_info = space_info;
@@ -2096,10 +2112,11 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans, u64 bytes_used,
 
        btrfs_set_log_full_commit(trans);
 
-       cache = btrfs_create_block_group_cache(fs_info, chunk_offset, size);
+       cache = btrfs_create_block_group_cache(fs_info, chunk_offset);
        if (!cache)
                return -ENOMEM;
 
+       cache->length = size;
        cache->used = bytes_used;
        cache->flags = type;
        cache->last_byte_to_unpin = (u64)-1;