1 files changed, 102 insertions, 0 deletions
diff --git a/fs/xfs/scrub/nlinks.h b/fs/xfs/scrub/nlinks.h
new file mode 100644
index 000000000000..a950f3daf204
--- /dev/null
+++ b/fs/xfs/scrub/nlinks.h
@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (c) 2021-2024 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#ifndef __XFS_SCRUB_NLINKS_H__
+#define __XFS_SCRUB_NLINKS_H__
+
+/* Live link count control structure. */
+struct xchk_nlink_ctrs {
+	struct xfs_scrub	*sc;
+
+	/* Shadow link count data and its mutex. */
+	struct xfarray		*nlinks;
+	struct mutex		lock;
+
+	/*
+	 * The collection step uses a separate iscan context from the compare
+	 * step because the collection iscan coordinates live updates to the
+	 * observation data while this scanner is running.  The compare iscan
+	 * is secondary and can be reinitialized as needed.
+	 */
+	struct xchk_iscan	collect_iscan;
+	struct xchk_iscan	compare_iscan;
+
+	/*
+	 * Hook into directory updates so that we can receive live updates
+	 * from other writer threads.
+	 */
+	struct xfs_dir_hook	dhook;
+};
+
+/*
+ * In-core link counts for a given inode in the filesystem.
+ *
+ * For an empty rootdir, the directory entries and the field to which they are
+ * accounted are as follows:
+ *
+ * Root directory:
+ *
+ * . points to self		(root.child)
+ * .. points to self		(root.parent)
+ * f1 points to a child file	(f1.parent)
+ * d1 points to a child dir	(d1.parent, root.child)
+ *
+ * Subdirectory d1:
+ *
+ * . points to self		(d1.child)
+ * .. points to root dir	(root.backref)
+ * f2 points to child file	(f2.parent)
+ * f3 points to root.f1		(f1.parent)
+ *
+ * root.nlink == 3 (root.dot, root.dotdot, root.d1)
+ * d1.nlink == 2 (root.d1, d1.dot)
+ * f1.nlink == 2 (root.f1, d1.f3)
+ * f2.nlink == 1 (d1.f2)
+ */
+struct xchk_nlink {
+	/* Count of forward links from parent directories to this file. */
+	xfs_nlink_t		parents;
+
+	/*
+	 * Count of back links to this parent directory from child
+	 * subdirectories.
+	 */
+	xfs_nlink_t		backrefs;
+
+	/*
+	 * Count of forward links from this directory to all child files and
+	 * the number of dot entries.  Should be zero for non-directories.
+	 */
+	xfs_nlink_t		children;
+
+	/* Record state flags */
+	unsigned int		flags;
+};
+
+/*
+ * This incore link count has been written at least once.  We never want to
+ * store an xchk_nlink that looks uninitialized.
+ */
+#define XCHK_NLINK_WRITTEN		(1U << 0)
+
+/* Already checked this link count record. */
+#define XCHK_NLINK_COMPARE_SCANNED	(1U << 1)
+
+/* Already made a repair with this link count record. */
+#define XREP_NLINK_DIRTY		(1U << 2)
+
+/* Compute total link count, using large enough variables to detect overflow. */
+static inline uint64_t
+xchk_nlink_total(struct xfs_inode *ip, const struct xchk_nlink *live)
+{
+	uint64_t	ret = live->parents;
+
+	/* Add one link count for the dot entry of any linked directory. */
+	if (ip && S_ISDIR(VFS_I(ip)->i_mode) && VFS_I(ip)->i_nlink)
+		ret++;
+	return ret + live->children;
+}
+
+#endif /* __XFS_SCRUB_NLINKS_H__ */