bcachefs: bcachefs_metadata_version_disk_accounting_v3

bcachefs_metadata_version_disk_accounting_v2 erroneously had padding
bytes in disk_accounting_key, which is a problem because we have to
guarantee that all unused bytes in disk_accounting_key are zeroed.

Fortunately 6.11 isn't out yet, so it's cheap to fix this by spinning a
new version.
Reported-by: Gabriel de Perthuis <g2p.code@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs_format.h

@@ -675,7 +675,8 @@ struct bch_sb_field_ext {
 	x(btree_subvolume_children,	BCH_VERSION(1,  6))		\
 	x(mi_btree_bitmap,		BCH_VERSION(1,  7))		\
 	x(bucket_stripe_sectors,	BCH_VERSION(1,  8))		\
-	x(disk_accounting_v2,		BCH_VERSION(1,  9))
+	x(disk_accounting_v2,		BCH_VERSION(1,  9))		\
+	x(disk_accounting_v3,		BCH_VERSION(1, 10))
 
 enum bcachefs_metadata_version {
 	bcachefs_metadata_version_min = 9,

fs/bcachefs/disk_accounting_format.h

@@ -130,11 +130,11 @@ struct bch_acct_compression {
 
 struct bch_acct_snapshot {
 	__u32			id;
-};
+} __packed;
 
 struct bch_acct_btree {
 	__u32			id;
-};
+} __packed;
 
 struct bch_acct_rebalance_work {
 };
@@ -152,8 +152,8 @@ struct disk_accounting_pos {
 		struct bch_acct_snapshot	snapshot;
 		struct bch_acct_btree		btree;
 		struct bch_acct_rebalance_work	rebalance_work;
-		};
-	};
+		} __packed;
+	} __packed;
 		struct bpos			_pad;
 	};
 };

fs/bcachefs/sb-downgrade.c

@@ -61,12 +61,37 @@
 	  BCH_FSCK_ERR_dev_usage_buckets_wrong,			\
 	  BCH_FSCK_ERR_dev_usage_sectors_wrong,			\
 	  BCH_FSCK_ERR_dev_usage_fragmented_wrong,		\
-	  BCH_FSCK_ERR_accounting_mismatch)
+	  BCH_FSCK_ERR_accounting_mismatch)			\
+	x(disk_accounting_v3,					\
+	  BIT_ULL(BCH_RECOVERY_PASS_check_allocations),		\
+	  BCH_FSCK_ERR_bkey_version_in_future,			\
+	  BCH_FSCK_ERR_dev_usage_buckets_wrong,			\
+	  BCH_FSCK_ERR_dev_usage_sectors_wrong,			\
+	  BCH_FSCK_ERR_dev_usage_fragmented_wrong,		\
+	  BCH_FSCK_ERR_accounting_mismatch,			\
+	  BCH_FSCK_ERR_accounting_key_replicas_nr_devs_0,	\
+	  BCH_FSCK_ERR_accounting_key_replicas_nr_required_bad,	\
+	  BCH_FSCK_ERR_accounting_key_replicas_devs_unsorted,	\
+	  BCH_FSCK_ERR_accounting_key_junk_at_end)
 
 #define DOWNGRADE_TABLE()					\
 	x(bucket_stripe_sectors,				\
 	  0)							\
 	x(disk_accounting_v2,					\
+	  BIT_ULL(BCH_RECOVERY_PASS_check_allocations),		\
+	  BCH_FSCK_ERR_dev_usage_buckets_wrong,			\
+	  BCH_FSCK_ERR_dev_usage_sectors_wrong,			\
+	  BCH_FSCK_ERR_dev_usage_fragmented_wrong,		\
+	  BCH_FSCK_ERR_fs_usage_hidden_wrong,			\
+	  BCH_FSCK_ERR_fs_usage_btree_wrong,			\
+	  BCH_FSCK_ERR_fs_usage_data_wrong,			\
+	  BCH_FSCK_ERR_fs_usage_cached_wrong,			\
+	  BCH_FSCK_ERR_fs_usage_reserved_wrong,			\
+	  BCH_FSCK_ERR_fs_usage_nr_inodes_wrong,		\
+	  BCH_FSCK_ERR_fs_usage_persistent_reserved_wrong,	\
+	  BCH_FSCK_ERR_fs_usage_replicas_wrong,			\
+	  BCH_FSCK_ERR_bkey_version_in_future)			\
+	x(disk_accounting_v3,					\
 	  BIT_ULL(BCH_RECOVERY_PASS_check_allocations),		\
 	  BCH_FSCK_ERR_dev_usage_buckets_wrong,			\
 	  BCH_FSCK_ERR_dev_usage_sectors_wrong,			\