xref: /linux/fs/xfs/scrub/parent.c (revision d3426a6ed9d8398bfee2a1c5cd0ae50f2f4494a8)

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2017-2023 Oracle.  All Rights Reserved.
 * Author: Darrick J. Wong <djwong@kernel.org>
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_log_format.h"
#include "xfs_trans.h"
#include "xfs_inode.h"
#include "xfs_icache.h"
#include "xfs_dir2.h"
#include "xfs_dir2_priv.h"
#include "xfs_attr.h"
#include "xfs_parent.h"
#include "scrub/scrub.h"
#include "scrub/common.h"
#include "scrub/readdir.h"
#include "scrub/tempfile.h"
#include "scrub/repair.h"
#include "scrub/listxattr.h"
#include "scrub/xfile.h"
#include "scrub/xfarray.h"
#include "scrub/xfblob.h"
#include "scrub/trace.h"

/* Set us up to scrub parents. */
int
xchk_setup_parent(
	struct xfs_scrub	*sc)
{
	int			error;

	if (xchk_could_repair(sc)) {
		error = xrep_setup_parent(sc);
		if (error)
			return error;
	}

	return xchk_setup_inode_contents(sc, 0);
}

/* Parent pointers */

/* Look for an entry in a parent pointing to this inode. */

struct xchk_parent_ctx {
	struct xfs_scrub	*sc;
	xfs_nlink_t		nlink;
};

/* Look for a single entry in a directory pointing to an inode. */
STATIC int
xchk_parent_actor(
	struct xfs_scrub	*sc,
	struct xfs_inode	*dp,
	xfs_dir2_dataptr_t	dapos,
	const struct xfs_name	*name,
	xfs_ino_t		ino,
	void			*priv)
{
	struct xchk_parent_ctx	*spc = priv;
	int			error = 0;

	/* Does this name make sense? */
	if (!xfs_dir2_namecheck(name->name, name->len))
		error = -EFSCORRUPTED;
	if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0, &error))
		return error;

	if (sc->ip->i_ino == ino)
		spc->nlink++;

	if (xchk_should_terminate(spc->sc, &error))
		return error;

	return 0;
}

/*
 * Try to lock a parent directory for checking dirents.  Returns the inode
 * flags for the locks we now hold, or zero if we failed.
 */
STATIC unsigned int
xchk_parent_ilock_dir(
	struct xfs_inode	*dp)
{
	if (!xfs_ilock_nowait(dp, XFS_ILOCK_SHARED))
		return 0;

	if (!xfs_need_iread_extents(&dp->i_df))
		return XFS_ILOCK_SHARED;

	xfs_iunlock(dp, XFS_ILOCK_SHARED);

	if (!xfs_ilock_nowait(dp, XFS_ILOCK_EXCL))
		return 0;

	return XFS_ILOCK_EXCL;
}

/*
 * Given the inode number of the alleged parent of the inode being scrubbed,
 * try to validate that the parent has exactly one directory entry pointing
 * back to the inode being scrubbed.  Returns -EAGAIN if we need to revalidate
 * the dotdot entry.
 */
STATIC int
xchk_parent_validate(
	struct xfs_scrub	*sc,
	xfs_ino_t		parent_ino)
{
	struct xchk_parent_ctx	spc = {
		.sc		= sc,
		.nlink		= 0,
	};
	struct xfs_mount	*mp = sc->mp;
	struct xfs_inode	*dp = NULL;
	xfs_nlink_t		expected_nlink;
	unsigned int		lock_mode;
	int			error = 0;

	/* Is this the root dir?  Then '..' must point to itself. */
	if (sc->ip == mp->m_rootip) {
		if (sc->ip->i_ino != mp->m_sb.sb_rootino ||
		    sc->ip->i_ino != parent_ino)
			xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
		return 0;
	}

	/* '..' must not point to ourselves. */
	if (sc->ip->i_ino == parent_ino) {
		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
		return 0;
	}

	/*
	 * If we're an unlinked directory, the parent /won't/ have a link
	 * to us.  Otherwise, it should have one link.
	 */
	expected_nlink = VFS_I(sc->ip)->i_nlink == 0 ? 0 : 1;

	/*
	 * Grab the parent directory inode.  This must be released before we
	 * cancel the scrub transaction.
	 *
	 * If _iget returns -EINVAL or -ENOENT then the parent inode number is
	 * garbage and the directory is corrupt.  If the _iget returns
	 * -EFSCORRUPTED or -EFSBADCRC then the parent is corrupt which is a
	 *  cross referencing error.  Any other error is an operational error.
	 */
	error = xchk_iget(sc, parent_ino, &dp);
	if (error == -EINVAL || error == -ENOENT) {
		error = -EFSCORRUPTED;
		xchk_fblock_process_error(sc, XFS_DATA_FORK, 0, &error);
		return error;
	}
	if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0, &error))
		return error;
	if (dp == sc->ip || xrep_is_tempfile(dp) ||
	    !S_ISDIR(VFS_I(dp)->i_mode)) {
		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
		goto out_rele;
	}

	lock_mode = xchk_parent_ilock_dir(dp);
	if (!lock_mode) {
		xchk_iunlock(sc, XFS_ILOCK_EXCL);
		xchk_ilock(sc, XFS_ILOCK_EXCL);
		error = -EAGAIN;
		goto out_rele;
	}

	/*
	 * We cannot yet validate this parent pointer if the directory looks as
	 * though it has been zapped by the inode record repair code.
	 */
	if (xchk_dir_looks_zapped(dp)) {
		error = -EBUSY;
		xchk_set_incomplete(sc);
		goto out_unlock;
	}

	/* Look for a directory entry in the parent pointing to the child. */
	error = xchk_dir_walk(sc, dp, xchk_parent_actor, &spc);
	if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0, &error))
		goto out_unlock;

	/*
	 * Ensure that the parent has as many links to the child as the child
	 * thinks it has to the parent.
	 */
	if (spc.nlink != expected_nlink)
		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);

out_unlock:
	xfs_iunlock(dp, lock_mode);
out_rele:
	xchk_irele(sc, dp);
	return error;
}

/*
 * Checking of Parent Pointers
 * ===========================
 *
 * On filesystems with directory parent pointers, we check the referential
 * integrity by visiting each parent pointer of a child file and checking that
 * the directory referenced by the pointer actually has a dirent pointing
 * forward to the child file.
 */

/* Deferred parent pointer entry that we saved for later. */
struct xchk_pptr {
	/* Cookie for retrieval of the pptr name. */
	xfblob_cookie		name_cookie;

	/* Parent pointer record. */
	struct xfs_parent_rec	pptr_rec;

	/* Length of the pptr name. */
	uint8_t			namelen;
};

struct xchk_pptrs {
	struct xfs_scrub	*sc;

	/* How many parent pointers did we find at the end? */
	unsigned long long	pptrs_found;

	/* Parent of this directory. */
	xfs_ino_t		parent_ino;

	/* Fixed-size array of xchk_pptr structures. */
	struct xfarray		*pptr_entries;

	/* Blobs containing parent pointer names. */
	struct xfblob		*pptr_names;

	/* Scratch buffer for scanning pptr xattrs */
	struct xfs_da_args	pptr_args;

	/* If we've cycled the ILOCK, we must revalidate all deferred pptrs. */
	bool			need_revalidate;

	/* Name buffer */
	struct xfs_name		xname;
	char			namebuf[MAXNAMELEN];
};

/* Does this parent pointer match the dotdot entry? */
STATIC int
xchk_parent_scan_dotdot(
	struct xfs_scrub		*sc,
	struct xfs_inode		*ip,
	unsigned int			attr_flags,
	const unsigned char		*name,
	unsigned int			namelen,
	const void			*value,
	unsigned int			valuelen,
	void				*priv)
{
	struct xchk_pptrs		*pp = priv;
	xfs_ino_t			parent_ino;
	int				error;

	if (!(attr_flags & XFS_ATTR_PARENT))
		return 0;

	error = xfs_parent_from_attr(sc->mp, attr_flags, name, namelen, value,
			valuelen, &parent_ino, NULL);
	if (error)
		return error;

	if (pp->parent_ino == parent_ino)
		return -ECANCELED;

	return 0;
}

/* Look up the dotdot entry so that we can check it as we walk the pptrs. */
STATIC int
xchk_parent_pptr_and_dotdot(
	struct xchk_pptrs	*pp)
{
	struct xfs_scrub	*sc = pp->sc;
	int			error;

	/* Look up '..' */
	error = xchk_dir_lookup(sc, sc->ip, &xfs_name_dotdot, &pp->parent_ino);
	if (!xchk_fblock_process_error(sc, XFS_DATA_FORK, 0, &error))
		return error;
	if (!xfs_verify_dir_ino(sc->mp, pp->parent_ino)) {
		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
		return 0;
	}

	/* Is this the root dir?  Then '..' must point to itself. */
	if (sc->ip == sc->mp->m_rootip) {
		if (sc->ip->i_ino != pp->parent_ino)
			xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
		return 0;
	}

	/*
	 * If this is now an unlinked directory, the dotdot value is
	 * meaningless as long as it points to a valid inode.
	 */
	if (VFS_I(sc->ip)->i_nlink == 0)
		return 0;

	if (pp->sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
		return 0;

	/* Otherwise, walk the pptrs again, and check. */
	error = xchk_xattr_walk(sc, sc->ip, xchk_parent_scan_dotdot, NULL, pp);
	if (error == -ECANCELED) {
		/* Found a parent pointer that matches dotdot. */
		return 0;
	}
	if (!error || error == -EFSCORRUPTED) {
		/* Found a broken parent pointer or no match. */
		xchk_fblock_set_corrupt(sc, XFS_ATTR_FORK, 0);
		return 0;
	}
	return error;
}

/*
 * Try to lock a parent directory for checking dirents.  Returns the inode
 * flags for the locks we now hold, or zero if we failed.
 */
STATIC unsigned int
xchk_parent_lock_dir(
	struct xfs_scrub	*sc,
	struct xfs_inode	*dp)
{
	if (!xfs_ilock_nowait(dp, XFS_IOLOCK_SHARED))
		return 0;

	if (!xfs_ilock_nowait(dp, XFS_ILOCK_SHARED)) {
		xfs_iunlock(dp, XFS_IOLOCK_SHARED);
		return 0;
	}

	if (!xfs_need_iread_extents(&dp->i_df))
		return XFS_IOLOCK_SHARED | XFS_ILOCK_SHARED;

	xfs_iunlock(dp, XFS_ILOCK_SHARED);

	if (!xfs_ilock_nowait(dp, XFS_ILOCK_EXCL)) {
		xfs_iunlock(dp, XFS_IOLOCK_SHARED);
		return 0;
	}

	return XFS_IOLOCK_SHARED | XFS_ILOCK_EXCL;
}

/* Check the forward link (dirent) associated with this parent pointer. */
STATIC int
xchk_parent_dirent(
	struct xchk_pptrs	*pp,
	const struct xfs_name	*xname,
	struct xfs_inode	*dp)
{
	struct xfs_scrub	*sc = pp->sc;
	xfs_ino_t		child_ino;
	int			error;

	/*
	 * Use the name attached to this parent pointer to look up the
	 * directory entry in the alleged parent.
	 */
	error = xchk_dir_lookup(sc, dp, xname, &child_ino);
	if (error == -ENOENT) {
		xchk_fblock_xref_set_corrupt(sc, XFS_ATTR_FORK, 0);
		return 0;
	}
	if (!xchk_fblock_xref_process_error(sc, XFS_ATTR_FORK, 0, &error))
		return error;

	/* Does the inode number match? */
	if (child_ino != sc->ip->i_ino) {
		xchk_fblock_xref_set_corrupt(sc, XFS_ATTR_FORK, 0);
		return 0;
	}

	return 0;
}

/* Try to grab a parent directory. */
STATIC int
xchk_parent_iget(
	struct xchk_pptrs	*pp,
	const struct xfs_parent_rec	*pptr,
	struct xfs_inode	**dpp)
{
	struct xfs_scrub	*sc = pp->sc;
	struct xfs_inode	*ip;
	xfs_ino_t		parent_ino = be64_to_cpu(pptr->p_ino);
	int			error;

	/* Validate inode number. */
	error = xfs_dir_ino_validate(sc->mp, parent_ino);
	if (error) {
		xchk_fblock_set_corrupt(sc, XFS_ATTR_FORK, 0);
		return -ECANCELED;
	}

	error = xchk_iget(sc, parent_ino, &ip);
	if (error == -EINVAL || error == -ENOENT) {
		xchk_fblock_set_corrupt(sc, XFS_ATTR_FORK, 0);
		return -ECANCELED;
	}
	if (!xchk_fblock_xref_process_error(sc, XFS_ATTR_FORK, 0, &error))
		return error;

	/* The parent must be a directory. */
	if (!S_ISDIR(VFS_I(ip)->i_mode)) {
		xchk_fblock_xref_set_corrupt(sc, XFS_ATTR_FORK, 0);
		goto out_rele;
	}

	/* Validate generation number. */
	if (VFS_I(ip)->i_generation != be32_to_cpu(pptr->p_gen)) {
		xchk_fblock_xref_set_corrupt(sc, XFS_ATTR_FORK, 0);
		goto out_rele;
	}

	*dpp = ip;
	return 0;
out_rele:
	xchk_irele(sc, ip);
	return 0;
}

/*
 * Walk an xattr of a file.  If this xattr is a parent pointer, follow it up
 * to a parent directory and check that the parent has a dirent pointing back
 * to us.
 */
STATIC int
xchk_parent_scan_attr(
	struct xfs_scrub	*sc,
	struct xfs_inode	*ip,
	unsigned int		attr_flags,
	const unsigned char	*name,
	unsigned int		namelen,
	const void		*value,
	unsigned int		valuelen,
	void			*priv)
{
	struct xfs_name		xname = {
		.name		= name,
		.len		= namelen,
	};
	struct xchk_pptrs	*pp = priv;
	struct xfs_inode	*dp = NULL;
	const struct xfs_parent_rec *pptr_rec = value;
	xfs_ino_t		parent_ino;
	unsigned int		lockmode;
	int			error;

	if (!(attr_flags & XFS_ATTR_PARENT))
		return 0;

	error = xfs_parent_from_attr(sc->mp, attr_flags, name, namelen, value,
			valuelen, &parent_ino, NULL);
	if (error) {
		xchk_fblock_set_corrupt(sc, XFS_ATTR_FORK, 0);
		return error;
	}

	/* No self-referential parent pointers. */
	if (parent_ino == sc->ip->i_ino) {
		xchk_fblock_set_corrupt(sc, XFS_ATTR_FORK, 0);
		return -ECANCELED;
	}

	pp->pptrs_found++;

	error = xchk_parent_iget(pp, pptr_rec, &dp);
	if (error)
		return error;
	if (!dp)
		return 0;

	/* Try to lock the inode. */
	lockmode = xchk_parent_lock_dir(sc, dp);
	if (!lockmode) {
		struct xchk_pptr	save_pp = {
			.pptr_rec	= *pptr_rec, /* struct copy */
			.namelen	= namelen,
		};

		/* Couldn't lock the inode, so save the pptr for later. */
		trace_xchk_parent_defer(sc->ip, &xname, dp->i_ino);

		error = xfblob_storename(pp->pptr_names, &save_pp.name_cookie,
				&xname);
		if (!xchk_fblock_xref_process_error(sc, XFS_ATTR_FORK, 0,
					&error))
			goto out_rele;

		error = xfarray_append(pp->pptr_entries, &save_pp);
		if (!xchk_fblock_xref_process_error(sc, XFS_ATTR_FORK, 0,
					&error))
			goto out_rele;

		goto out_rele;
	}

	error = xchk_parent_dirent(pp, &xname, dp);
	if (error)
		goto out_unlock;

out_unlock:
	xfs_iunlock(dp, lockmode);
out_rele:
	xchk_irele(sc, dp);
	return error;
}

/*
 * Revalidate a parent pointer that we collected in the past but couldn't check
 * because of lock contention.  Returns 0 if the parent pointer is still valid,
 * -ENOENT if it has gone away on us, or a negative errno.
 */
STATIC int
xchk_parent_revalidate_pptr(
	struct xchk_pptrs		*pp,
	const struct xfs_name		*xname,
	struct xfs_parent_rec		*pptr)
{
	struct xfs_scrub		*sc = pp->sc;
	int				error;

	error = xfs_parent_lookup(sc->tp, sc->ip, xname, pptr, &pp->pptr_args);
	if (error == -ENOATTR) {
		/* Parent pointer went away, nothing to revalidate. */
		return -ENOENT;
	}

	return error;
}

/*
 * Check a parent pointer the slow way, which means we cycle locks a bunch
 * and put up with revalidation until we get it done.
 */
STATIC int
xchk_parent_slow_pptr(
	struct xchk_pptrs	*pp,
	const struct xfs_name	*xname,
	struct xfs_parent_rec	*pptr)
{
	struct xfs_scrub	*sc = pp->sc;
	struct xfs_inode	*dp = NULL;
	unsigned int		lockmode;
	int			error;

	/* Check that the deferred parent pointer still exists. */
	if (pp->need_revalidate) {
		error = xchk_parent_revalidate_pptr(pp, xname, pptr);
		if (error == -ENOENT)
			return 0;
		if (!xchk_fblock_xref_process_error(sc, XFS_ATTR_FORK, 0,
					&error))
			return error;
	}

	error = xchk_parent_iget(pp, pptr, &dp);
	if (error)
		return error;
	if (!dp)
		return 0;

	/*
	 * If we can grab both IOLOCK and ILOCK of the alleged parent, we
	 * can proceed with the validation.
	 */
	lockmode = xchk_parent_lock_dir(sc, dp);
	if (lockmode) {
		trace_xchk_parent_slowpath(sc->ip, xname, dp->i_ino);
		goto check_dirent;
	}

	/*
	 * We couldn't lock the parent dir.  Drop all the locks and try to
	 * get them again, one at a time.
	 */
	xchk_iunlock(sc, sc->ilock_flags);
	pp->need_revalidate = true;

	trace_xchk_parent_ultraslowpath(sc->ip, xname, dp->i_ino);

	error = xchk_dir_trylock_for_pptrs(sc, dp, &lockmode);
	if (error)
		goto out_rele;

	/* Revalidate the parent pointer now that we cycled locks. */
	error = xchk_parent_revalidate_pptr(pp, xname, pptr);
	if (error == -ENOENT) {
		error = 0;
		goto out_unlock;
	}
	if (!xchk_fblock_xref_process_error(sc, XFS_ATTR_FORK, 0, &error))
		goto out_unlock;

check_dirent:
	error = xchk_parent_dirent(pp, xname, dp);
out_unlock:
	xfs_iunlock(dp, lockmode);
out_rele:
	xchk_irele(sc, dp);
	return error;
}

/* Check all the parent pointers that we deferred the first time around. */
STATIC int
xchk_parent_finish_slow_pptrs(
	struct xchk_pptrs	*pp)
{
	xfarray_idx_t		array_cur;
	int			error;

	foreach_xfarray_idx(pp->pptr_entries, array_cur) {
		struct xchk_pptr	pptr;

		if (pp->sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
			return 0;

		error = xfarray_load(pp->pptr_entries, array_cur, &pptr);
		if (error)
			return error;

		error = xfblob_loadname(pp->pptr_names, pptr.name_cookie,
				&pp->xname, pptr.namelen);
		if (error)
			return error;

		error = xchk_parent_slow_pptr(pp, &pp->xname, &pptr.pptr_rec);
		if (error)
			return error;
	}

	/* Empty out both xfiles now that we've checked everything. */
	xfarray_truncate(pp->pptr_entries);
	xfblob_truncate(pp->pptr_names);
	return 0;
}

/* Count the number of parent pointers. */
STATIC int
xchk_parent_count_pptr(
	struct xfs_scrub		*sc,
	struct xfs_inode		*ip,
	unsigned int			attr_flags,
	const unsigned char		*name,
	unsigned int			namelen,
	const void			*value,
	unsigned int			valuelen,
	void				*priv)
{
	struct xchk_pptrs		*pp = priv;
	int				error;

	if (!(attr_flags & XFS_ATTR_PARENT))
		return 0;

	error = xfs_parent_from_attr(sc->mp, attr_flags, name, namelen, value,
			valuelen, NULL, NULL);
	if (error)
		return error;

	pp->pptrs_found++;
	return 0;
}

/*
 * Compare the number of parent pointers to the link count.  For
 * non-directories these should be the same.  For unlinked directories the
 * count should be zero; for linked directories, it should be nonzero.
 */
STATIC int
xchk_parent_count_pptrs(
	struct xchk_pptrs	*pp)
{
	struct xfs_scrub	*sc = pp->sc;
	int			error;

	/*
	 * If we cycled the ILOCK while cross-checking parent pointers with
	 * dirents, then we need to recalculate the number of parent pointers.
	 */
	if (pp->need_revalidate) {
		pp->pptrs_found = 0;
		error = xchk_xattr_walk(sc, sc->ip, xchk_parent_count_pptr,
				NULL, pp);
		if (error == -EFSCORRUPTED) {
			/* Found a bad parent pointer */
			xchk_fblock_set_corrupt(sc, XFS_ATTR_FORK, 0);
			return 0;
		}
		if (error)
			return error;
	}

	if (S_ISDIR(VFS_I(sc->ip)->i_mode)) {
		if (sc->ip == sc->mp->m_rootip)
			pp->pptrs_found++;

		if (VFS_I(sc->ip)->i_nlink == 0 && pp->pptrs_found > 0)
			xchk_ino_set_corrupt(sc, sc->ip->i_ino);
		else if (VFS_I(sc->ip)->i_nlink > 0 &&
			 pp->pptrs_found == 0)
			xchk_ino_set_corrupt(sc, sc->ip->i_ino);
	} else {
		if (VFS_I(sc->ip)->i_nlink != pp->pptrs_found)
			xchk_ino_set_corrupt(sc, sc->ip->i_ino);
	}

	return 0;
}

/* Check parent pointers of a file. */
STATIC int
xchk_parent_pptr(
	struct xfs_scrub	*sc)
{
	struct xchk_pptrs	*pp;
	char			*descr;
	int			error;

	pp = kvzalloc(sizeof(struct xchk_pptrs), XCHK_GFP_FLAGS);
	if (!pp)
		return -ENOMEM;
	pp->sc = sc;
	pp->xname.name = pp->namebuf;

	/*
	 * Set up some staging memory for parent pointers that we can't check
	 * due to locking contention.
	 */
	descr = xchk_xfile_ino_descr(sc, "slow parent pointer entries");
	error = xfarray_create(descr, 0, sizeof(struct xchk_pptr),
			&pp->pptr_entries);
	kfree(descr);
	if (error)
		goto out_pp;

	descr = xchk_xfile_ino_descr(sc, "slow parent pointer names");
	error = xfblob_create(descr, &pp->pptr_names);
	kfree(descr);
	if (error)
		goto out_entries;

	error = xchk_xattr_walk(sc, sc->ip, xchk_parent_scan_attr, NULL, pp);
	if (error == -ECANCELED) {
		error = 0;
		goto out_names;
	}
	if (error)
		goto out_names;

	error = xchk_parent_finish_slow_pptrs(pp);
	if (error == -ETIMEDOUT) {
		/* Couldn't grab a lock, scrub was marked incomplete */
		error = 0;
		goto out_names;
	}
	if (error)
		goto out_names;

	if (pp->sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
		goto out_names;

	/*
	 * For subdirectories, make sure the dotdot entry references the same
	 * inode as the parent pointers.
	 *
	 * If we're scanning a /consistent/ directory, there should only be
	 * one parent pointer, and it should point to the same directory as
	 * the dotdot entry.
	 *
	 * However, a corrupt directory tree might feature a subdirectory with
	 * multiple parents.  The directory loop scanner is responsible for
	 * correcting that kind of problem, so for now we only validate that
	 * the dotdot entry matches /one/ of the parents.
	 */
	if (S_ISDIR(VFS_I(sc->ip)->i_mode)) {
		error = xchk_parent_pptr_and_dotdot(pp);
		if (error)
			goto out_names;
	}

	if (pp->sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
		goto out_names;

	/*
	 * Complain if the number of parent pointers doesn't match the link
	 * count.  This could be a sign of missing parent pointers (or an
	 * incorrect link count).
	 */
	error = xchk_parent_count_pptrs(pp);
	if (error)
		goto out_names;

out_names:
	xfblob_destroy(pp->pptr_names);
out_entries:
	xfarray_destroy(pp->pptr_entries);
out_pp:
	kvfree(pp);
	return error;
}

/* Scrub a parent pointer. */
int
xchk_parent(
	struct xfs_scrub	*sc)
{
	struct xfs_mount	*mp = sc->mp;
	xfs_ino_t		parent_ino;
	int			error = 0;

	if (xfs_has_parent(mp))
		return xchk_parent_pptr(sc);

	/*
	 * If we're a directory, check that the '..' link points up to
	 * a directory that has one entry pointing to us.
	 */
	if (!S_ISDIR(VFS_I(sc->ip)->i_mode))
		return -ENOENT;

	/* We're not a special inode, are we? */
	if (!xfs_verify_dir_ino(mp, sc->ip->i_ino)) {
		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
		return 0;
	}

	do {
		if (xchk_should_terminate(sc, &error))
			break;

		/* Look up '..' */
		error = xchk_dir_lookup(sc, sc->ip, &xfs_name_dotdot,
				&parent_ino);
		if (!xchk_fblock_process_error(sc, XFS_DATA_FORK, 0, &error))
			return error;
		if (!xfs_verify_dir_ino(mp, parent_ino)) {
			xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
			return 0;
		}

		/*
		 * Check that the dotdot entry points to a parent directory
		 * containing a dirent pointing to this subdirectory.
		 */
		error = xchk_parent_validate(sc, parent_ino);
	} while (error == -EAGAIN);
	if (error == -EBUSY) {
		/*
		 * We could not scan a directory, so we marked the check
		 * incomplete.  No further error return is necessary.
		 */
		return 0;
	}

	return error;
}

/*
 * Decide if this file's extended attributes (and therefore its parent
 * pointers) have been zapped to satisfy the inode and ifork verifiers.
 * Checking and repairing should be postponed until the extended attribute
 * structure is fixed.
 */
bool
xchk_pptr_looks_zapped(
	struct xfs_inode	*ip)
{
	struct xfs_mount	*mp = ip->i_mount;
	struct inode		*inode = VFS_I(ip);

	ASSERT(xfs_has_parent(mp));

	/*
	 * Temporary files that cannot be linked into the directory tree do not
	 * have attr forks because they cannot ever have parents.
	 */
	if (inode->i_nlink == 0 && !(inode->i_state & I_LINKABLE))
		return false;

	/*
	 * Directory tree roots do not have parents, so the expected outcome
	 * of a parent pointer scan is always the empty set.  It's safe to scan
	 * them even if the attr fork was zapped.
	 */
	if (ip == mp->m_rootip)
		return false;

	/*
	 * Metadata inodes are all rooted in the superblock and do not have
	 * any parents.  Hence the attr fork will not be initialized, but
	 * there are no parent pointers that might have been zapped.
	 */
	if (xfs_is_metadata_inode(ip))
		return false;

	/*
	 * Linked and linkable non-rootdir files should always have an
	 * attribute fork because that is where parent pointers are
	 * stored.  If the fork is absent, something is amiss.
	 */
	if (!xfs_inode_has_attr_fork(ip))
		return true;

	/* Repair zapped this file's attr fork a short time ago */
	if (xfs_ifork_zapped(ip, XFS_ATTR_FORK))
		return true;

	/*
	 * If the dinode repair found a bad attr fork, it will reset the fork
	 * to extents format with zero records and wait for the bmapbta
	 * scrubber to reconstruct the block mappings.  The extended attribute
	 * structure always contain some content when parent pointers are
	 * enabled, so this is a clear sign of a zapped attr fork.
	 */
	return ip->i_af.if_format == XFS_DINODE_FMT_EXTENTS &&
	       ip->i_af.if_nextents == 0;
}