btrfs: new inline ref storing owning subvol of data extents

In order to implement simple quota groups, we need to be able to
associate a data extent with the subvolume that created it. Once you
account for reflink, this information cannot be recovered without
explicitly storing it. Options for storing it are:

- a new key/item
- a new extent inline ref item

The former is backwards compatible, but wastes space, the latter is
incompat, but is efficient in space and reuses the existing inline ref
machinery, while only abusing it a tiny amount -- specifically, the new
item is not a ref, per-se.

Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
index a1d5347f6adb..8b4def6aee52 100644
--- a/include/uapi/linux/btrfs_tree.h
+++ b/include/uapi/linux/btrfs_tree.h
@@ -234,6 +234,14 @@
 #define BTRFS_SHARED_DATA_REF_KEY	184
 
 /*
+ * Special inline ref key which stores the id of the subvolume which originally
+ * created the extent. This subvolume owns the extent permanently from the
+ * perspective of simple quotas. Needed to know which subvolume to free quota
+ * usage from when the extent is deleted.
+ */
+#define BTRFS_EXTENT_OWNER_REF_KEY	188
+
+/*
  * block groups give us hints into the extent allocation trees.  Which
  * blocks are free etc etc
  */
@@ -816,6 +824,10 @@ struct btrfs_shared_data_ref {
 	__le32 count;
 } __attribute__ ((__packed__));
 
+struct btrfs_extent_owner_ref {
+	__le64 root_id;
+} __attribute__ ((__packed__));
+
 struct btrfs_extent_inline_ref {
 	__u8 type;
 	__le64 offset;