From 9dd6cc92a736a7943dd29776b6eb1938c7f9b94c Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <djwong@kernel.org>
Date: Wed, 26 Aug 2026 22:32:12 -0700
Subject: [PATCH] xfs: handle reconnecting metadir subdirectories

A longstanding weakness of the metapath repair code is that it can only
reattach non-directories to the metadata directory tree.  Let's fix
that by allowing reconnection of subdirectories.

Note that with the initial users of metadir (rtgroups and quota),
there's no way to mount a filesystem with broken /rtgroups or /quota
subdirectories, so this code won't be all that useful until something
adds deeper directory trees.  But we shouldn't leave a logic bomb for
those futures users wherein we get the link count wrong for a subdir.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
---
 fs/xfs/scrub/metapath.c | 83 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 82 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/scrub/metapath.c b/fs/xfs/scrub/metapath.c
index 9f44c82910ea..a760523f40e6 100644
--- a/fs/xfs/scrub/metapath.c
+++ b/fs/xfs/scrub/metapath.c
@@ -23,6 +23,7 @@
 #include "xfs_rtgroup.h"
 #include "xfs_rtrmap_btree.h"
 #include "xfs_rtrefcount_btree.h"
+#include "xfs_ag.h"
 #include "scrub/scrub.h"
 #include "scrub/common.h"
 #include "scrub/trace.h"
@@ -348,12 +349,78 @@ xchk_metapath(
 }
 
 #ifdef CONFIG_XFS_ONLINE_REPAIR
+/*
+ * Given a directory @dp, an existing inode @ip, and a @name, link @ip into @dp
+ * under the given @name.
+ */
+static int
+xrep_metadir_add_child(
+	struct xchk_metapath	*mpath,
+	xfs_ino_t		old_dotdot)
+{
+	struct xfs_trans	*tp = mpath->sc->tp;
+	struct xfs_dir_update	*du = &mpath->du;
+	struct xfs_inode	*dp = du->dp;
+	const struct xfs_name	*name = du->name;
+	struct xfs_inode	*ip = du->ip;
+	struct xfs_mount	*mp = tp->t_mountp;
+	const unsigned int	resblks = mpath->link_resblks;
+	int			error;
+
+	/*
+	 * The metadata file shouldn't be on the unlinked list, but we'll fix
+	 * it if that is the case.
+	 */
+	if (VFS_I(ip)->i_nlink == 0) {
+		struct xfs_perag	*pag;
+
+		pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, I_INO(ip)));
+		error = xfs_iunlink_remove(tp, pag, ip);
+		xfs_perag_put(pag);
+		if (error)
+			return error;
+	}
+
+	error = xfs_dir_createname(tp, dp, name, I_INO(ip), resblks);
+	if (error)
+		return error;
+
+	xfs_trans_log_inode(tp, dp, XFS_ILOG_CORE);
+
+	xfs_bumplink(tp, ip);
+
+	/* update dotdot entry in child */
+	if (S_ISDIR(VFS_I(ip)->i_mode)) {
+		xfs_bumplink(tp, dp);
+
+		/* Replace the dotdot entry in the child */
+		if (old_dotdot != I_INO(dp)) {
+			error = xfs_dir_replace(tp, ip, &xfs_name_dotdot,
+					I_INO(dp), resblks);
+			if (error)
+				return error;
+		}
+	}
+
+	/* Update the child's parent pointer */
+	if (du->ppargs) {
+		error = xfs_parent_addname(tp, du->ppargs, dp, name, ip);
+		if (error)
+			return error;
+	}
+
+	xfs_dir_update_hook(dp, ip, 1, name);
+	return 0;
+}
+
 /* Create the dirent represented by the final component of the path. */
 STATIC int
 xrep_metapath_link(
 	struct xchk_metapath	*mpath)
 {
 	struct xfs_scrub	*sc = mpath->sc;
+	xfs_ino_t		old_dotdot = NULLFSINO;
+	int			error;
 
 	mpath->du.dp = mpath->dp;
 	mpath->du.name = &mpath->xname;
@@ -366,7 +433,21 @@ xrep_metapath_link(
 
 	trace_xrep_metapath_link(sc, mpath->path, mpath->dp, I_INO(sc->ip));
 
-	return xfs_dir_add_child(sc->tp, mpath->link_resblks, &mpath->du);
+	if (S_ISDIR(VFS_I(sc->ip)->i_mode)) {
+		error = xchk_dir_lookup(sc, sc->ip, &xfs_name_dotdot,
+				&old_dotdot);
+		if (error && error != -ENOENT)
+			return error;
+
+		/*
+		 * subdir didn't give us a dotdot entry, so we just give up
+		 * and let the repair get marked as failed.
+		 */
+		if (old_dotdot == NULLFSINO)
+			return 0;
+	}
+
+	return xrep_metadir_add_child(mpath, old_dotdot);
 }
 
 /* Remove the dirent at the final component of the path. */