btrfs: qgroup: check generation when recording simple quota delta

Simple quotas count extents only from the moment the feature is enabled.
Therefore, if we do something like:

1. create subvol S
2. write F in S
3. enable quotas
4. remove F
5. write G in S

then after 3. and 4. we would expect the simple quota usage of S to be 0
(putting aside some metadata extents that might be written) and after
5., it should be the size of G plus metadata. Therefore, we need to be
able to determine whether a particular quota delta we are processing
predates simple quota enablement.

To do this, store the transaction id when quotas were enabled. In
fs_info for immediate use and in the quota status item to make it
recoverable on mount. When we see a delta, check if the generation of
the extent item is less than that of quota enablement. If so, we should
ignore the delta from this extent.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/btrfs/qgroup.h b/fs/btrfs/qgroup.h
index 9858244eef20..855a4f978761 100644
--- a/fs/btrfs/qgroup.h
+++ b/fs/btrfs/qgroup.h
@@ -276,6 +276,8 @@ struct btrfs_squota_delta {
 	u64 num_bytes;
 	/* The number of bytes reserved for this extent. */
 	u64 rsv_bytes;
+	/* The generation the extent was created in. */
+	u64 generation;
 	/* Whether we are using or freeing the extent. */
 	bool is_inc;
 	/* Whether the extent is data or metadata. */