/*      $NetBSD: ext2fs_rename.c,v 1.13 2023/08/26 05:22:50 riastradh Exp $     */

/*-
 * Copyright (c) 2012 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Taylor R Campbell.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Ext2fs Rename
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: ext2fs_rename.c,v 1.13 2023/08/26 05:22:50 riastradh Exp $");

#include <sys/param.h>
#include <sys/buf.h>
#include <sys/errno.h>
#include <sys/kauth.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/vnode.h>
#include <sys/vnode_if.h>
#include <sys/dirent.h>

#include <miscfs/genfs/genfs.h>

#include <ufs/ext2fs/ext2fs.h>
#include <ufs/ext2fs/ext2fs_dir.h>
#include <ufs/ext2fs/ext2fs_extern.h>
#include <ufs/ufs/inode.h>
#include <ufs/ufs/ufs_extern.h>
#include <ufs/ufs/ufsmount.h>

/*
 * Forward declarations
 */
static int ext2fs_sane_rename(struct vnode *, struct componentname *,
    struct vnode *, struct componentname *,
    kauth_cred_t, bool);
static bool ext2fs_rename_ulr_overlap_p(const struct ufs_lookup_results *,
    const struct ufs_lookup_results *);
static int ext2fs_rename_recalculate_fulr(struct vnode *,
    struct ufs_lookup_results *, const struct ufs_lookup_results *,
    const struct componentname *);
static bool ext2fs_rmdired_p(struct vnode *);
static int ext2fs_read_dotdot(struct vnode *, kauth_cred_t, ino_t *);
static int ext2fs_rename_replace_dotdot(struct vnode *,
    struct vnode *, struct vnode *, kauth_cred_t);
static int ext2fs_gro_lock_directory(struct mount *, struct vnode *);

static const struct genfs_rename_ops ext2fs_genfs_rename_ops;

/*
 * ext2fs_sane_rename: The hairiest vop, with the saner API.
 *
 * Arguments:
 *
 * . fdvp (from directory vnode),
 * . fcnp (from component name),
 * . tdvp (to directory vnode),
 * . tcnp (to component name),
 * . cred (credentials structure), and
 * . posixly_correct (flag for behaviour if target & source link same file).
 *
 * fdvp and tdvp may be the same, and must be referenced and unlocked.
 */
static int
ext2fs_sane_rename(
    struct vnode *fdvp, struct componentname *fcnp,
    struct vnode *tdvp, struct componentname *tcnp,
    kauth_cred_t cred, bool posixly_correct)
{
        struct ufs_lookup_results fulr, tulr;

        return genfs_sane_rename(&ext2fs_genfs_rename_ops,
            fdvp, fcnp, &fulr, tdvp, tcnp, &tulr,
            cred, posixly_correct);
}

/*
 * ext2fs_rename: The hairiest vop, with the insanest API.  Defer to
 * genfs_insane_rename immediately.
 */
int
ext2fs_rename(void *v)
{

        return genfs_insane_rename(v, &ext2fs_sane_rename);
}

/*
 * ext2fs_gro_directory_empty_p: Return true if the directory vp is
 * empty.  dvp is its parent.
 *
 * vp and dvp must be locked and referenced.
 */
static bool
ext2fs_gro_directory_empty_p(struct mount *mp, kauth_cred_t cred,
    struct vnode *vp, struct vnode *dvp)
{

        (void)mp;
        KASSERT(mp != NULL);
        KASSERT(vp != NULL);
        KASSERT(dvp != NULL);
        KASSERT(vp != dvp);
        KASSERT(vp->v_mount == mp);
        KASSERT(dvp->v_mount == mp);
        KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE);
        KASSERT(VOP_ISLOCKED(dvp) == LK_EXCLUSIVE);

        return ext2fs_dirempty(VTOI(vp), VTOI(dvp)->i_number, cred);
}

/*
 * ext2fs_gro_rename_check_possible: Check whether a rename is possible
 * independent of credentials.
 */
static int
ext2fs_gro_rename_check_possible(struct mount *mp,
    struct vnode *fdvp, struct vnode *fvp,
    struct vnode *tdvp, struct vnode *tvp)
{

        (void)mp;
        KASSERT(mp != NULL);
        KASSERT(fdvp != NULL);
        KASSERT(fvp != NULL);
        KASSERT(tdvp != NULL);
        KASSERT(fdvp != fvp);
        KASSERT(fdvp != tvp);
        KASSERT(tdvp != fvp);
        KASSERT(tdvp != tvp);
        KASSERT(fvp != tvp);
        KASSERT(fdvp->v_type == VDIR);
        KASSERT(tdvp->v_type == VDIR);
        KASSERT(fdvp->v_mount == mp);
        KASSERT(fvp->v_mount == mp);
        KASSERT(tdvp->v_mount == mp);
        KASSERT((tvp == NULL) || (tvp->v_mount == mp));
        KASSERT(VOP_ISLOCKED(fdvp) == LK_EXCLUSIVE);
        KASSERT(VOP_ISLOCKED(fvp) == LK_EXCLUSIVE);
        KASSERT(VOP_ISLOCKED(tdvp) == LK_EXCLUSIVE);
        KASSERT((tvp == NULL) || (VOP_ISLOCKED(tvp) == LK_EXCLUSIVE));

        return genfs_ufslike_rename_check_possible(
            VTOI(fdvp)->i_e2fs_flags, VTOI(fvp)->i_e2fs_flags,
            VTOI(tdvp)->i_e2fs_flags, (tvp? VTOI(tvp)->i_e2fs_flags : 0),
            (tvp != NULL),
            EXT2_IMMUTABLE, EXT2_APPEND);
}

/*
 * ext2fs_gro_rename_check_permitted: Check whether a rename is
 * permitted given our credentials.
 */
static int
ext2fs_gro_rename_check_permitted(struct mount *mp, kauth_cred_t cred,
    struct vnode *fdvp, struct vnode *fvp,
    struct vnode *tdvp, struct vnode *tvp)
{

        (void)mp;
        KASSERT(mp != NULL);
        KASSERT(fdvp != NULL);
        KASSERT(fvp != NULL);
        KASSERT(tdvp != NULL);
        KASSERT(fdvp != fvp);
        KASSERT(fdvp != tvp);
        KASSERT(tdvp != fvp);
        KASSERT(tdvp != tvp);
        KASSERT(fvp != tvp);
        KASSERT(fdvp->v_type == VDIR);
        KASSERT(tdvp->v_type == VDIR);
        KASSERT(fdvp->v_mount == mp);
        KASSERT(fvp->v_mount == mp);
        KASSERT(tdvp->v_mount == mp);
        KASSERT((tvp == NULL) || (tvp->v_mount == mp));
        KASSERT(VOP_ISLOCKED(fdvp) == LK_EXCLUSIVE);
        KASSERT(VOP_ISLOCKED(fvp) == LK_EXCLUSIVE);
        KASSERT(VOP_ISLOCKED(tdvp) == LK_EXCLUSIVE);
        KASSERT((tvp == NULL) || (VOP_ISLOCKED(tvp) == LK_EXCLUSIVE));

        return genfs_ufslike_rename_check_permitted(cred,
            fdvp, VTOI(fdvp)->i_e2fs_mode, VTOI(fdvp)->i_uid,
            fvp, VTOI(fvp)->i_uid,
            tdvp, VTOI(tdvp)->i_e2fs_mode, VTOI(tdvp)->i_uid,
            tvp, (tvp? VTOI(tvp)->i_uid : 0));
}

/*
 * ext2fs_gro_remove_check_possible: Check whether a remove is possible
 * independent of credentials.
 */
static int
ext2fs_gro_remove_check_possible(struct mount *mp,
    struct vnode *dvp, struct vnode *vp)
{

        (void)mp;
        KASSERT(mp != NULL);
        KASSERT(dvp != NULL);
        KASSERT(vp != NULL);
        KASSERT(dvp != vp);
        KASSERT(dvp->v_type == VDIR);
        KASSERT(vp->v_type != VDIR);
        KASSERT(dvp->v_mount == mp);
        KASSERT(vp->v_mount == mp);
        KASSERT(VOP_ISLOCKED(dvp) == LK_EXCLUSIVE);
        KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE);

        return genfs_ufslike_remove_check_possible(
            VTOI(dvp)->i_e2fs_flags, VTOI(vp)->i_e2fs_flags,
            EXT2_IMMUTABLE, EXT2_APPEND);
}

/*
 * ext2fs_gro_remove_check_permitted: Check whether a remove is
 * permitted given our credentials.
 */
static int
ext2fs_gro_remove_check_permitted(struct mount *mp, kauth_cred_t cred,
    struct vnode *dvp, struct vnode *vp)
{

        (void)mp;
        KASSERT(mp != NULL);
        KASSERT(dvp != NULL);
        KASSERT(vp != NULL);
        KASSERT(dvp != vp);
        KASSERT(dvp->v_type == VDIR);
        KASSERT(vp->v_type != VDIR);
        KASSERT(dvp->v_mount == mp);
        KASSERT(vp->v_mount == mp);
        KASSERT(VOP_ISLOCKED(dvp) == LK_EXCLUSIVE);
        KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE);

        return genfs_ufslike_remove_check_permitted(cred,
            dvp, VTOI(dvp)->i_e2fs_mode, VTOI(dvp)->i_uid,
            vp, VTOI(vp)->i_uid);
}

/*
 * ext2fs_gro_rename: Actually perform the rename operation.
 */
static int
ext2fs_gro_rename(struct mount *mp, kauth_cred_t cred,
    struct vnode *fdvp, struct componentname *fcnp,
    void *fde, struct vnode *fvp,
    struct vnode *tdvp, struct componentname *tcnp,
    void *tde, struct vnode *tvp, nlink_t *tvp_nlinkp)
{
        struct ufs_lookup_results *fulr = fde;
        struct ufs_lookup_results *tulr = tde;
        bool directory_p, reparent_p;
        int error;

        (void)mp;
        KASSERT(mp != NULL);
        KASSERT(fdvp != NULL);
        KASSERT(fcnp != NULL);
        KASSERT(fulr != NULL);
        KASSERT(fvp != NULL);
        KASSERT(tdvp != NULL);
        KASSERT(tcnp != NULL);
        KASSERT(tulr != NULL);
        KASSERT(fulr != tulr);
        KASSERT(fdvp != fvp);
        KASSERT(fdvp != tvp);
        KASSERT(tdvp != fvp);
        KASSERT(tdvp != tvp);
        KASSERT(fvp != tvp);
        KASSERT(fdvp->v_mount == mp);
        KASSERT(fvp->v_mount == mp);
        KASSERT(tdvp->v_mount == mp);
        KASSERT((tvp == NULL) || (tvp->v_mount == mp));
        KASSERT(VOP_ISLOCKED(fdvp) == LK_EXCLUSIVE);
        KASSERT(VOP_ISLOCKED(fvp) == LK_EXCLUSIVE);
        KASSERT(VOP_ISLOCKED(tdvp) == LK_EXCLUSIVE);
        KASSERT((tvp == NULL) || (VOP_ISLOCKED(tvp) == LK_EXCLUSIVE));

        /*
         * We shall need to temporarily bump the link count, so make
         * sure there is room to do so.
         */
        if ((nlink_t)VTOI(fvp)->i_e2fs_nlink >= EXT2FS_LINK_MAX)
                return EMLINK;

        directory_p = (fvp->v_type == VDIR);
        KASSERT(directory_p == ((VTOI(fvp)->i_e2fs_mode & IFMT) == IFDIR));
        KASSERT((tvp == NULL) || (directory_p == (tvp->v_type == VDIR)));
        KASSERT((tvp == NULL) || (directory_p ==
                ((VTOI(tvp)->i_e2fs_mode & IFMT) == IFDIR)));

        reparent_p = (fdvp != tdvp);
        KASSERT(reparent_p == (VTOI(fdvp)->i_number != VTOI(tdvp)->i_number));

        /*
         * Commence hacking of the data on disk.
         */

        /*
         * 1) Bump link count while we're moving stuff
         *    around.  If we crash somewhere before
         *    completing our work, the link count
         *    may be wrong, but correctable.
         */

        KASSERT((nlink_t)VTOI(fvp)->i_e2fs_nlink < EXT2FS_LINK_MAX);
        VTOI(fvp)->i_e2fs_nlink++;
        VTOI(fvp)->i_flag |= IN_CHANGE;
        error = ext2fs_update(fvp, NULL, NULL, UPDATE_WAIT);
        if (error)
                goto whymustithurtsomuch;

        /*
         * 2) If target doesn't exist, link the target
         *    to the source and unlink the source.
         *    Otherwise, rewrite the target directory
         *    entry to reference the source inode and
         *    expunge the original entry's existence.
         */

        if (tvp == NULL) {
                /*
                 * Account for ".." in new directory.
                 * When source and destination have the same
                 * parent we don't fool with the link count.
                 */
                if (directory_p && reparent_p) {
                        if ((nlink_t)VTOI(tdvp)->i_e2fs_nlink >= EXT2FS_LINK_MAX) {
                                error = EMLINK;
                                goto whymustithurtsomuch;
                        }
                        KASSERT((nlink_t)VTOI(tdvp)->i_e2fs_nlink < EXT2FS_LINK_MAX);
                        VTOI(tdvp)->i_e2fs_nlink++;
                        VTOI(tdvp)->i_flag |= IN_CHANGE;
                        error = ext2fs_update(tdvp, NULL, NULL, UPDATE_WAIT);
                        if (error) {
                                /*
                                 * Link count update didn't take --
                                 * back out the in-memory link count.
                                 */
                                KASSERT(0 < VTOI(tdvp)->i_e2fs_nlink);
                                VTOI(tdvp)->i_e2fs_nlink--;
                                VTOI(tdvp)->i_flag |= IN_CHANGE;
                                goto whymustithurtsomuch;
                        }
                }

                error = ext2fs_direnter(VTOI(fvp), tdvp, tulr, tcnp);
                if (error) {
                        if (directory_p && reparent_p) {
                                /*
                                 * Directory update didn't take, but
                                 * the link count update did -- back
                                 * out the in-memory link count and the
                                 * on-disk link count.
                                 */
                                KASSERT(0 < VTOI(tdvp)->i_e2fs_nlink);
                                VTOI(tdvp)->i_e2fs_nlink--;
                                VTOI(tdvp)->i_flag |= IN_CHANGE;
                                (void)ext2fs_update(tdvp, NULL, NULL,
                                    UPDATE_WAIT);
                        }
                        goto whymustithurtsomuch;
                }
        } else {
                if (directory_p)
                        /* XXX WTF?  Why purge here?  Why not purge others?  */
                        cache_purge(tdvp);

                /*
                 * Make the target directory's entry for tcnp point at
                 * the source node.
                 */
                error = ext2fs_dirrewrite(VTOI(tdvp), tulr, VTOI(fvp), tcnp);
                if (error)
                        goto whymustithurtsomuch;

                /*
                 * If the source and target are directories, and the
                 * target is in the same directory as the source,
                 * decrement the link count of the common parent
                 * directory, since we are removing the target from
                 * that directory.
                 */
                if (directory_p && !reparent_p) {
                        KASSERT(fdvp == tdvp);
                        /* XXX check, don't kassert */
                        KASSERT(0 < VTOI(tdvp)->i_e2fs_nlink);
                        VTOI(tdvp)->i_e2fs_nlink--;
                        VTOI(tdvp)->i_flag |= IN_CHANGE;
                }

                /*
                 * Adjust the link count of the target to
                 * reflect the dirrewrite above.  If this is
                 * a directory it is empty and there are
                 * no links to it, so we can squash the inode and
                 * any space associated with it.  We disallowed
                 * renaming over top of a directory with links to
                 * it above, as the remaining link would point to
                 * a directory without "." or ".." entries.
                 */
                /* XXX check, don't kassert */
                KASSERT(0 < VTOI(tvp)->i_e2fs_nlink);
                VTOI(tvp)->i_e2fs_nlink--;
                if (directory_p) {
                        /*
                         * XXX The ext2fs_dirempty call earlier does
                         * not guarantee anything about nlink.
                         */
                        if (VTOI(tvp)->i_e2fs_nlink != 1)
                                ufs_dirbad(VTOI(tvp), (doff_t)0,
                                    "hard-linked directory");
                        VTOI(tvp)->i_e2fs_nlink = 0;
                        error = ext2fs_truncate(tvp, (off_t)0, IO_SYNC, cred);
#if 0                   /* XXX This branch was not in ext2fs_rename!  */
                        if (error)
                                goto whymustithurtsomuch;
#endif
                }
                *tvp_nlinkp = VTOI(tvp)->i_e2fs_nlink;
                /*
                 * XXX Why is this here, and not above the preceding
                 * conditional?
                 */
                VTOI(tvp)->i_flag |= IN_CHANGE;
        }

        /*
         * If the source is a directory with a new parent, the link
         * count of the old parent directory must be decremented and
         * ".." set to point to the new parent.
         */
        if (directory_p && reparent_p) {
                error = ext2fs_rename_replace_dotdot(fvp, fdvp, tdvp, cred);
                if (error)
                        goto whymustithurtsomuch;

                /* XXX WTF?  Why purge here?  Why not purge others?  */
                cache_purge(fdvp);
        }

        /*
         * 3) Unlink the source.
         */

        /*
         * ext2fs_direnter may compact the directory in the process of
         * inserting a new entry.  That may invalidate fulr, which we
         * need in order to remove the old entry.  In that case, we
         * need to recalculate what fulr should be.
         */
        if (!reparent_p && (tvp == NULL) &&
            ext2fs_rename_ulr_overlap_p(fulr, tulr)) {
                error = ext2fs_rename_recalculate_fulr(fdvp, fulr, tulr, fcnp);
#if 0                           /* XXX */
                if (error)      /* XXX Try to back out changes?  */
                        goto whymustithurtsomuch;
#endif
        }

        error = ext2fs_dirremove(fdvp, fulr, fcnp);
        if (error)
                goto whymustithurtsomuch;

#if 0                           /* XXX */
        genfs_rename_cache_purge(fdvp, fvp, tdvp, tvp);
#endif

whymustithurtsomuch:
        KASSERT(0 < VTOI(fvp)->i_e2fs_nlink);
        VTOI(fvp)->i_e2fs_nlink--;
        VTOI(fvp)->i_flag |= IN_CHANGE;
        return error;
}

/*
 * ext2fs_rename_ulr_overlap_p: True iff tulr overlaps with fulr so
 * that entering a directory entry at tulr may move fulr.
 */
static bool
ext2fs_rename_ulr_overlap_p(const struct ufs_lookup_results *fulr,
    const struct ufs_lookup_results *tulr)
{
        doff_t from_prev_start, from_prev_end, to_start, to_end;

        KASSERT(fulr != NULL);
        KASSERT(tulr != NULL);
        KASSERT(fulr != tulr);

        /*
         * fulr is from a DELETE lookup, so fulr->ulr_count is the size
         * of the preceding entry (d_reclen).
         */
        from_prev_end = fulr->ulr_offset;
        KASSERT(fulr->ulr_count <= from_prev_end);
        from_prev_start = (from_prev_end - fulr->ulr_count);

        /*
         * tulr is from a RENAME lookup, so tulr->ulr_count is the size
         * of the free space for an entry that we are about to fill.
         */
        to_start = tulr->ulr_offset;
        KASSERT(tulr->ulr_count < (EXT2FS_MAXDIRSIZE - to_start));
        to_end = (to_start + tulr->ulr_count);

        return
            (((to_start <= from_prev_start) && (from_prev_start < to_end)) ||
                ((to_start <= from_prev_end) && (from_prev_end < to_end)));
}

/*
 * ext2fs_rename_recalculate_fulr: If we have just entered a directory
 * into dvp at tulr, and we were about to remove one at fulr for an
 * entry named fcnp, fulr may be invalid.  So, if necessary,
 * recalculate it.
 */
static int
ext2fs_rename_recalculate_fulr(struct vnode *dvp,
    struct ufs_lookup_results *fulr, const struct ufs_lookup_results *tulr,
    const struct componentname *fcnp)
{
        struct mount *mp;
        struct ufsmount *ump;
        /* XXX int is a silly type for this; blame ufsmount::um_dirblksiz.  */
        int dirblksiz;
        doff_t search_start, search_end;
        doff_t offset;          /* Offset of entry we're examining.  */
        struct buf *bp;         /* I/O block we're examining.  */
        char *dirbuf;           /* Pointer into directory at search_start.  */
        struct ext2fs_direct *ep; /* Pointer to the entry we're examining.  */
        /* XXX direct::d_reclen is 16-bit;
         * ufs_lookup_results::ulr_reclen is 32-bit.  Blah.  */
        uint32_t reclen;        /* Length of the entry we're examining.  */
        uint32_t prev_reclen;   /* Length of the preceding entry.  */
        int error;

        KASSERT(dvp != NULL);
        KASSERT(dvp->v_mount != NULL);
        KASSERT(VTOI(dvp) != NULL);
        KASSERT(fulr != NULL);
        KASSERT(tulr != NULL);
        KASSERT(fulr != tulr);
        KASSERT(ext2fs_rename_ulr_overlap_p(fulr, tulr));

        mp = dvp->v_mount;
        ump = VFSTOUFS(mp);
        KASSERT(ump != NULL);
        KASSERT(ump == VTOI(dvp)->i_ump);

        dirblksiz = ump->um_dirblksiz;
        KASSERT(0 < dirblksiz);
        KASSERT((dirblksiz & (dirblksiz - 1)) == 0);

        /* A directory block may not span across multiple I/O blocks.  */
        KASSERT(dirblksiz <= mp->mnt_stat.f_iosize);

        /* Find the bounds of the search.  */
        search_start = tulr->ulr_offset;
        KASSERT(fulr->ulr_reclen < (EXT2FS_MAXDIRSIZE - fulr->ulr_offset));
        search_end = (fulr->ulr_offset + fulr->ulr_reclen);

        /* Compaction must happen only within a directory block. (*)  */
        KASSERT(search_start <= search_end);
        KASSERT((search_end - (search_start &~ (dirblksiz - 1))) <= dirblksiz);

        dirbuf = NULL;
        bp = NULL;
        error = ext2fs_blkatoff(dvp, (off_t)search_start, &dirbuf, &bp);
        if (error)
                return error;
        KASSERT(dirbuf != NULL);
        KASSERT(bp != NULL);

        /*
         * Guarantee we sha'n't go past the end of the buffer we got.
         * dirbuf is bp->b_data + (search_start & (iosize - 1)), and
         * the valid range is [bp->b_data, bp->b_data + bp->b_bcount).
         */
        KASSERT((search_end - search_start) <=
            (bp->b_bcount - (search_start & (mp->mnt_stat.f_iosize - 1))));

        prev_reclen = fulr->ulr_count;
        offset = search_start;

        /*
         * Search from search_start to search_end for the entry matching
         * fcnp, which must be there because we found it before and it
         * should only at most have moved earlier.
         */
        for (;;) {
                KASSERT(search_start <= offset);
                KASSERT(offset < search_end);

                /*
                 * Examine the directory entry at offset.
                 */
                ep = (struct ext2fs_direct *)
                    (dirbuf + (offset - search_start));
                reclen = fs2h16(ep->e2d_reclen);

                if (ep->e2d_ino == 0)
                        goto next;      /* Entry is unused.  */

                if (fs2h32(ep->e2d_ino) == UFS_WINO)
                        goto next;      /* Entry is whiteout.  */

                if (fcnp->cn_namelen != ep->e2d_namlen)
                        goto next;      /* Wrong name length.  */

                if (memcmp(ep->e2d_name, fcnp->cn_nameptr, fcnp->cn_namelen))
                        goto next;      /* Wrong name.  */

                /* Got it!  */
                break;

next:
                if (! ((reclen < search_end) &&
                        (offset < (search_end - reclen)))) {
                        brelse(bp, 0);
                        return EIO;     /* XXX Panic?  What?  */
                }

                /* We may not move past the search end.  */
                KASSERT(reclen < search_end);
                KASSERT(offset < (search_end - reclen));

                /*
                 * We may not move across a directory block boundary;
                 * see (*) above.
                 */
                KASSERT((offset &~ (dirblksiz - 1)) ==
                    ((offset + reclen) &~ (dirblksiz - 1)));

                prev_reclen = reclen;
                offset += reclen;
        }

        /*
         * Found the entry.  Record where.
         */
        fulr->ulr_offset = offset;
        fulr->ulr_reclen = reclen;

        /*
         * Record the preceding record length, but not if we're at the
         * start of a directory block.
         */
        fulr->ulr_count = ((offset & (dirblksiz - 1))? prev_reclen : 0);

        brelse(bp, 0);
        return 0;
}

/*
 * ext2fs_gro_remove: Rename an object over another link to itself,
 * effectively removing just the original link.
 */
static int
ext2fs_gro_remove(struct mount *mp, kauth_cred_t cred,
    struct vnode *dvp, struct componentname *cnp, void *de, struct vnode *vp,
    nlink_t *tvp_nlinkp)
{
        struct ufs_lookup_results *ulr = de;
        int error;

        (void)mp;
        KASSERT(mp != NULL);
        KASSERT(dvp != NULL);
        KASSERT(cnp != NULL);
        KASSERT(ulr != NULL);
        KASSERT(vp != NULL);
        KASSERT(dvp != vp);
        KASSERT(dvp->v_mount == mp);
        KASSERT(vp->v_mount == mp);
        KASSERT(dvp->v_type == VDIR);
        KASSERT(vp->v_type != VDIR);
        KASSERT(VOP_ISLOCKED(dvp) == LK_EXCLUSIVE);
        KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE);

        error = ext2fs_dirremove(dvp, ulr, cnp);
        if (error)
                return error;

        KASSERT(0 < VTOI(vp)->i_e2fs_nlink);
        VTOI(vp)->i_e2fs_nlink--;
        VTOI(vp)->i_flag |= IN_CHANGE;

        *tvp_nlinkp = VTOI(vp)->i_e2fs_nlink;

        return 0;
}

/*
 * ext2fs_gro_lookup: Look up and save the lookup results.
 */
static int
ext2fs_gro_lookup(struct mount *mp, struct vnode *dvp,
    struct componentname *cnp, void *de_ret, struct vnode **vp_ret)
{
        struct ufs_lookup_results *ulr_ret = de_ret;
        struct vnode *vp;
        int error;

        (void)mp;
        KASSERT(mp != NULL);
        KASSERT(dvp != NULL);
        KASSERT(cnp != NULL);
        KASSERT(ulr_ret != NULL);
        KASSERT(vp_ret != NULL);
        KASSERT(VOP_ISLOCKED(dvp) == LK_EXCLUSIVE);

        /* Kludge cargo-culted from dholland's ufs_rename.  */
        cnp->cn_flags &=~ MODMASK;
        cnp->cn_flags |= (LOCKPARENT | LOCKLEAF);

        error = relookup(dvp, &vp, cnp, 0 /* dummy */);
        if ((error == 0) && (vp == NULL)) {
                error = ENOENT;
                goto out;
        } else if (error) {
                return error;
        }

        /*
         * Thanks to VFS insanity, relookup locks vp, which screws us
         * in various ways.
         */
        KASSERT(vp != NULL);
        VOP_UNLOCK(vp);

out:    *ulr_ret = VTOI(dvp)->i_crap;
        *vp_ret = vp;
        return error;
}

/*
 * ext2fs_rmdired_p: Check whether the directory vp has been rmdired.
 *
 * vp must be locked and referenced.
 */
static bool
ext2fs_rmdired_p(struct vnode *vp)
{

        KASSERT(vp != NULL);
        KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE);
        KASSERT(vp->v_type == VDIR);

        /* XXX Is this correct?  */
        return ext2fs_size(VTOI(vp)) == 0;
}

/*
 * ext2fs_gro_genealogy: Analyze the genealogy of the source and target
 * directories.
 */
static int
ext2fs_gro_genealogy(struct mount *mp, kauth_cred_t cred,
    struct vnode *fdvp, struct vnode *tdvp,
    struct vnode **intermediate_node_ret)
{
        struct vnode *vp, *dvp;
        ino_t dotdot_ino = -1;  /* XXX gcc 4.8.3: maybe-uninitialized */
        int error;

        KASSERT(mp != NULL);
        KASSERT(fdvp != NULL);
        KASSERT(tdvp != NULL);
        KASSERT(fdvp != tdvp);
        KASSERT(intermediate_node_ret != NULL);
        KASSERT(fdvp->v_mount == mp);
        KASSERT(tdvp->v_mount == mp);
        KASSERT(fdvp->v_type == VDIR);
        KASSERT(tdvp->v_type == VDIR);

        /*
         * We need to provisionally lock tdvp to keep rmdir from
         * deleting it -- or any ancestor -- at an inopportune moment.
         */
        error = ext2fs_gro_lock_directory(mp, tdvp);
        if (error)
                return error;

        vp = tdvp;
        vref(vp);

        for (;;) {
                KASSERT(vp != NULL);
                KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE);
                KASSERT(vp->v_mount == mp);
                KASSERT(vp->v_type == VDIR);
                KASSERT(!ext2fs_rmdired_p(vp));

                /* Did we hit the root without finding fdvp?  */
                if (VTOI(vp)->i_number == UFS_ROOTINO) {
                        vput(vp);
                        *intermediate_node_ret = NULL;
                        return 0;
                }

                error = ext2fs_read_dotdot(vp, cred, &dotdot_ino);
                if (error) {
                        vput(vp);
                        return error;
                }

                /* Did we find that fdvp is an ancestor of tdvp?  */
                if (VTOI(fdvp)->i_number == dotdot_ino) {
                        /* Unlock vp, but keep it referenced.  */
                        VOP_UNLOCK(vp);
                        *intermediate_node_ret = vp;
                        return 0;
                }

                /* Neither -- keep ascending the family tree.  */
                error = vcache_get(mp, &dotdot_ino, sizeof(dotdot_ino), &dvp);
                vput(vp);
                if (error)
                        return error;
                error = vn_lock(dvp, LK_EXCLUSIVE);
                if (error) {
                        vrele(dvp);
                        return error;
                }

                KASSERT(dvp != NULL);
                KASSERT(VOP_ISLOCKED(dvp) == LK_EXCLUSIVE);
                vp = dvp;

                if (vp->v_type != VDIR) {
                        /*
                         * XXX Panic?  Print a warning?  Can this
                         * happen if we lose the race I suspect to
                         * exist above, and the `..' inode number has
                         * been recycled?
                         */
                        vput(vp);
                        return ENOTDIR;
                }

                if (ext2fs_rmdired_p(vp)) {
                        vput(vp);
                        return ENOENT;
                }
        }
}

/*
 * ext2fs_read_dotdot: Store in *ino_ret the inode number of the parent
 * of the directory vp.
 */
static int
ext2fs_read_dotdot(struct vnode *vp, kauth_cred_t cred, ino_t *ino_ret)
{
        struct ext2fs_dirtemplate dirbuf;
        int error;

        KASSERT(vp != NULL);
        KASSERT(ino_ret != NULL);
        KASSERT(vp->v_type == VDIR);

        error = ufs_bufio(UIO_READ, vp, &dirbuf, sizeof dirbuf, (off_t)0,
            IO_NODELOCKED, cred, NULL, NULL);
        if (error)
                return error;

        if (dirbuf.dotdot_namlen != 2 ||
            dirbuf.dotdot_name[0] != '.' ||
            dirbuf.dotdot_name[1] != '.')
                /* XXX Panic?  Print warning?  */
                return ENOTDIR;

        *ino_ret = fs2h32(dirbuf.dotdot_ino);
        return 0;
}

/*
 * ext2fs_rename_replace_dotdot: Change the target of the `..' entry of
 * the directory vp from fdvp to tdvp.
 */
static int
ext2fs_rename_replace_dotdot(struct vnode *vp,
    struct vnode *fdvp, struct vnode *tdvp,
    kauth_cred_t cred)
{
        struct ext2fs_dirtemplate dirbuf;
        int error;

        /* XXX Does it make sense to do this before the sanity checks below?  */
        KASSERT(0 < VTOI(fdvp)->i_e2fs_nlink);
        VTOI(fdvp)->i_e2fs_nlink--;
        VTOI(fdvp)->i_flag |= IN_CHANGE;

        error = ufs_bufio(UIO_READ, vp, &dirbuf, sizeof dirbuf, (off_t)0,
            IO_NODELOCKED, cred, NULL, NULL);
        if (error)
                return error;

        if (dirbuf.dotdot_namlen != 2 ||
            dirbuf.dotdot_name[0] != '.' ||
            dirbuf.dotdot_name[1] != '.') {
                ufs_dirbad(VTOI(vp), (doff_t)12, "bad `..' entry");
                return 0;
        }

        if (fs2h32(dirbuf.dotdot_ino) != VTOI(fdvp)->i_number) {
                ufs_dirbad(VTOI(vp), (doff_t)12,
                    "`..' does not point at parent");
                return 0;
        }

        dirbuf.dotdot_ino = h2fs32(VTOI(tdvp)->i_number);
        /* XXX WTF?  Why not check error?  */
        (void)ufs_bufio(UIO_WRITE, vp, &dirbuf, sizeof dirbuf, (off_t)0,
            (IO_NODELOCKED | IO_SYNC), cred, NULL, NULL);

        return 0;
}

/*
 * ext2fs_gro_lock_directory: Lock the directory vp, but fail if it has
 * been rmdir'd.
 */
static int
ext2fs_gro_lock_directory(struct mount *mp, struct vnode *vp)
{

        (void)mp;
        KASSERT(mp != NULL);
        KASSERT(vp != NULL);
        KASSERT(vp->v_mount == mp);

        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);

        if (ext2fs_rmdired_p(vp)) {
                VOP_UNLOCK(vp);
                return ENOENT;
        }

        return 0;
}

static const struct genfs_rename_ops ext2fs_genfs_rename_ops = {
        .gro_directory_empty_p          = ext2fs_gro_directory_empty_p,
        .gro_rename_check_possible      = ext2fs_gro_rename_check_possible,
        .gro_rename_check_permitted     = ext2fs_gro_rename_check_permitted,
        .gro_remove_check_possible      = ext2fs_gro_remove_check_possible,
        .gro_remove_check_permitted     = ext2fs_gro_remove_check_permitted,
        .gro_rename                     = ext2fs_gro_rename,
        .gro_remove                     = ext2fs_gro_remove,
        .gro_lookup                     = ext2fs_gro_lookup,
        .gro_genealogy                  = ext2fs_gro_genealogy,
        .gro_lock_directory             = ext2fs_gro_lock_directory,
};