bcachefs: Repair code for directory i_size

We had a bug due due to an incomplete revert of the patch implementing
directory i_size (summing up the size of the dirents), leading to
completely screwy i_size values that underflow.

Most userspace programs don't seem to care (e.g. du ignores it), but it
turns out this broke sshfs, so needs to be repaired.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Author: Kent Overstreet

fs/bcachefs/fsck.c

@@ -1167,6 +1167,14 @@ static int check_inode(struct btree_trans *trans,
 		ret = 0;
 	}
 
+	if (fsck_err_on(S_ISDIR(u.bi_mode) && u.bi_size,
+			trans, inode_dir_has_nonzero_i_size,
+			"directory %llu:%u with nonzero i_size %lli",
+			u.bi_inum, u.bi_snapshot, u.bi_size)) {
+		u.bi_size = 0;
+		do_update = true;
+	}
+
 	ret = bch2_inode_has_child_snapshots(trans, k.k->p);
 	if (ret < 0)
 		goto err;

fs/bcachefs/sb-errors_format.h

@@ -232,6 +232,7 @@ enum bch_fsck_flags {
 	x(inode_dir_multiple_links,				206,	FSCK_AUTOFIX)	\
 	x(inode_dir_missing_backpointer,			284,	FSCK_AUTOFIX)	\
 	x(inode_dir_unlinked_but_not_empty,			286,	FSCK_AUTOFIX)	\
+	x(inode_dir_has_nonzero_i_size,				319,	FSCK_AUTOFIX)	\
 	x(inode_multiple_links_but_nlink_0,			207,	FSCK_AUTOFIX)	\
 	x(inode_wrong_backpointer,				208,	FSCK_AUTOFIX)	\
 	x(inode_wrong_nlink,					209,	FSCK_AUTOFIX)	\
@@ -328,7 +329,7 @@ enum bch_fsck_flags {
 	x(dirent_stray_data_after_cf_name,			305,	0)		\
 	x(rebalance_work_incorrectly_set,			309,	FSCK_AUTOFIX)	\
 	x(rebalance_work_incorrectly_unset,			310,	FSCK_AUTOFIX)	\
-	x(MAX,							319,	0)
+	x(MAX,							320,	0)
 
 enum bch_sb_error_id {
 #define x(t, n, ...) BCH_FSCK_ERR_##t = n,