xfs: teach scrub to check file nlinks

Copy-pasta the online quotacheck code to check inode link counts too.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/fs/xfs/scrub/nlinks.h b/fs/xfs/scrub/nlinks.h
new file mode 100644
index 000000000000..0ece2ab5dd38
--- /dev/null
+++ b/fs/xfs/scrub/nlinks.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2021 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 bumplink/droplink so that we can receive live updates
+	 * from other writer threads.
+	 */
+	struct notifier_block	nlink_delta_hook;
+};
+
+struct xchk_nlink {
+	/* Links from a parent directory to this inode. */
+	xfs_nlink_t		parent;
+
+	/* Links from children of this inode (e.g. dot and dotdot). */
+	xfs_nlink_t		child;
+
+	/* Record state flags */
+	unsigned int		flags;
+};
+
+/* This data item was seen by the check-time compare function. */
+#define XCHK_NLINK_COMPARE_SCANNED	(1U << 0)
+
+/* Compute total link count, using large enough variables to detect overflow. */
+static inline uint64_t
+xchk_nlink_total(const struct xchk_nlink *live)
+{
+	uint64_t	ret = live->parent;
+
+	return ret + live->child;
+}
+
+#endif /* __XFS_SCRUB_NLINKS_H__ */