btrfs: rename BTRFS_ROOT_REF_COWS to BTRFS_ROOT_SHAREABLE
The name BTRFS_ROOT_REF_COWS is not very clear about the meaning.
In fact, that bit can only be set to those trees:
- Subvolume roots
- Data reloc root
- Reloc roots for above roots
All other trees won't get this bit set. So just by the result, it is
obvious that, roots with this bit set can have tree blocks shared with
other trees. Either shared by snapshots, or by reloc roots (an special
snapshot created by relocation).
This patch will rename BTRFS_ROOT_REF_COWS to BTRFS_ROOT_SHAREABLE to
make it easier to understand, and update all comment mentioning
"reference counted" to follow the rename.
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/ctree.h b/fs/btrfs/ctree.h
index 0a1fa15..bf46093b 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -969,7 +969,28 @@ enum {
* is used to tell us when more checks are required
*/
BTRFS_ROOT_IN_TRANS_SETUP,
- BTRFS_ROOT_REF_COWS,
+
+ /*
+ * Set if tree blocks of this root can be shared by other roots.
+ * Only subvolume trees and their reloc trees have this bit set.
+ * Conflicts with TRACK_DIRTY bit.
+ *
+ * This affects two things:
+ *
+ * - How balance works
+ * For shareable roots, we need to use reloc tree and do path
+ * replacement for balance, and need various pre/post hooks for
+ * snapshot creation to handle them.
+ *
+ * While for non-shareable trees, we just simply do a tree search
+ * with COW.
+ *
+ * - How dirty roots are tracked
+ * For shareable roots, btrfs_record_root_in_trans() is needed to
+ * track them, while non-subvolume roots have TRACK_DIRTY bit, they
+ * don't need to set this manually.
+ */
+ BTRFS_ROOT_SHAREABLE,
BTRFS_ROOT_TRACK_DIRTY,
BTRFS_ROOT_IN_RADIX,
BTRFS_ROOT_ORPHAN_ITEM_INSERTED,
@@ -1055,7 +1076,7 @@ struct btrfs_root {
struct btrfs_key defrag_progress;
struct btrfs_key defrag_max;
- /* the dirty list is only used by non-reference counted roots */
+ /* The dirty list is only used by non-shareable roots */
struct list_head dirty_list;
struct list_head root_list;