1/* SPDX-License-Identifier: GPL-2.0-or-later */
  2/*
  3 * Copyright (c) 2021-2024 Oracle.  All Rights Reserved.
  4 * Author: Darrick J. Wong <djwong@kernel.org>
  5 */
  6#ifndef __XFS_SCRUB_NLINKS_H__
  7#define __XFS_SCRUB_NLINKS_H__
  8
  9/* Live link count control structure. */
 10struct xchk_nlink_ctrs {
 11	struct xfs_scrub	*sc;
 12
 13	/* Shadow link count data and its mutex. */
 14	struct xfarray		*nlinks;
 15	struct mutex		lock;
 16
 17	/*
 18	 * The collection step uses a separate iscan context from the compare
 19	 * step because the collection iscan coordinates live updates to the
 20	 * observation data while this scanner is running.  The compare iscan
 21	 * is secondary and can be reinitialized as needed.
 22	 */
 23	struct xchk_iscan	collect_iscan;
 24	struct xchk_iscan	compare_iscan;
 25
 26	/*
 27	 * Hook into directory updates so that we can receive live updates
 28	 * from other writer threads.
 29	 */
 30	struct xfs_dir_hook	dhook;
 31};
 32
 33/*
 34 * In-core link counts for a given inode in the filesystem.
 35 *
 36 * For an empty rootdir, the directory entries and the field to which they are
 37 * accounted are as follows:
 38 *
 39 * Root directory:
 40 *
 41 * . points to self		(root.child)
 42 * .. points to self		(root.parent)
 43 * f1 points to a child file	(f1.parent)
 44 * d1 points to a child dir	(d1.parent, root.child)
 45 *
 46 * Subdirectory d1:
 47 *
 48 * . points to self		(d1.child)
 49 * .. points to root dir	(root.backref)
 50 * f2 points to child file	(f2.parent)
 51 * f3 points to root.f1		(f1.parent)
 52 *
 53 * root.nlink == 3 (root.dot, root.dotdot, root.d1)
 54 * d1.nlink == 2 (root.d1, d1.dot)
 55 * f1.nlink == 2 (root.f1, d1.f3)
 56 * f2.nlink == 1 (d1.f2)
 57 */
 58struct xchk_nlink {
 59	/* Count of forward links from parent directories to this file. */
 60	xfs_nlink_t		parents;
 61
 62	/*
 63	 * Count of back links to this parent directory from child
 64	 * subdirectories.
 65	 */
 66	xfs_nlink_t		backrefs;
 67
 68	/*
 69	 * Count of forward links from this directory to all child files and
 70	 * the number of dot entries.  Should be zero for non-directories.
 71	 */
 72	xfs_nlink_t		children;
 73
 74	/* Record state flags */
 75	unsigned int		flags;
 76};
 77
 78/*
 79 * This incore link count has been written at least once.  We never want to
 80 * store an xchk_nlink that looks uninitialized.
 81 */
 82#define XCHK_NLINK_WRITTEN		(1U << 0)
 83
 84/* Already checked this link count record. */
 85#define XCHK_NLINK_COMPARE_SCANNED	(1U << 1)
 86
 87/* Already made a repair with this link count record. */
 88#define XREP_NLINK_DIRTY		(1U << 2)
 89
 90/* Compute total link count, using large enough variables to detect overflow. */
 91static inline uint64_t
 92xchk_nlink_total(struct xfs_inode *ip, const struct xchk_nlink *live)
 93{
 94	uint64_t	ret = live->parents;
 95
 96	/* Add one link count for the dot entry of any linked directory. */
 97	if (ip && S_ISDIR(VFS_I(ip)->i_mode) && VFS_I(ip)->i_nlink)
 98		ret++;
 99	return ret + live->children;
100}
101
102#endif /* __XFS_SCRUB_NLINKS_H__ */