/* 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;

        /* Orphanage reparenting request. */
        struct xrep_adoption    adoption;

        /* Directory entry name, plus the trailing null. */
        struct xfs_name         xname;
        char                    namebuf[MAXNAMELEN];
};

/*
 * 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__ */