/*      $NetBSD: ufs_lookup.c,v 1.161 2026/01/22 03:24:19 riastradh Exp $       */

/*
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * 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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *      @(#)ufs_lookup.c        8.9 (Berkeley) 8/11/94
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: ufs_lookup.c,v 1.161 2026/01/22 03:24:19 riastradh Exp $");

#ifdef _KERNEL_OPT
#include "opt_ffs.h"
#endif

#include <sys/param.h>
#include <sys/types.h>

#include <sys/buf.h>
#include <sys/file.h>
#include <sys/kauth.h>
#include <sys/kernel.h>
#include <sys/kmem.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/proc.h>
#include <sys/sdt.h>
#include <sys/stat.h>
#include <sys/systm.h>
#include <sys/vnode.h>
#include <sys/wapbl.h>

#include <ufs/ufs/dir.h>
#ifdef UFS_DIRHASH
#include <ufs/ufs/dirhash.h>
#endif
#include <ufs/ufs/inode.h>
#include <ufs/ufs/ufs_bswap.h>
#include <ufs/ufs/ufs_extern.h>
#include <ufs/ufs/ufs_wapbl.h>
#include <ufs/ufs/ufsmount.h>

#include <miscfs/genfs/genfs.h>

#ifdef DIAGNOSTIC
int     dirchk = 1;
#else
int     dirchk = 0;
#endif

#if BYTE_ORDER == LITTLE_ENDIAN
# define ENDIANSWAP(needswap) ((needswap) == 0)
#else
# define ENDIANSWAP(needswap) ((needswap) != 0)
#endif

#define NAMLEN(fsfmt, needswap, dp) \
    ((fsfmt) && ENDIANSWAP(needswap) ? (dp)->d_type : (dp)->d_namlen)

static void
ufs_dirswap(struct direct *dirp)
{
        uint8_t tmp = dirp->d_namlen;
        dirp->d_namlen = dirp->d_type;
        dirp->d_type = tmp;
}

struct slotinfo {
        enum {
                NONE,           /* need to search a slot for our new entry */
                COMPACT,        /* a compaction can make a slot in the current
                                   DIRBLKSIZ block */
                FOUND,          /* found a slot (or no need to search) */
        } status;
        doff_t offset;          /* offset of area with free space.
                                   a special value -1 for invalid */
        int size;               /* size of area at slotoffset */
        int freespace;          /* accumulated amount of space free in
                                   the current DIRBLKSIZ block */
        int needed;             /* size of the entry we're seeking */
};

static void
calc_count(struct ufs_lookup_results *results, int dirblksiz, doff_t prevoff)
{
        if ((results->ulr_offset & (dirblksiz - 1)) == 0)
                results->ulr_count = 0;
        else
                results->ulr_count = results->ulr_offset - prevoff;
}

static void
slot_init(struct slotinfo *slot)
{
        slot->status = FOUND;
        slot->offset = -1;
        slot->freespace = slot->size = slot->needed = 0;
}

#ifdef UFS_DIRHASH
static doff_t
slot_findfree(struct slotinfo *slot, struct inode *dp)
{
        if (slot->status == FOUND)
                return dp->i_size;

        slot->offset = ufsdirhash_findfree(dp, slot->needed, &slot->size);
        if (slot->offset < 0)
                return dp->i_size;

        slot->status = COMPACT;
        doff_t enduseful = ufsdirhash_enduseful(dp);
        if (enduseful < 0)
                return dp->i_size;
        return enduseful;
}
#endif

static void
slot_white(struct slotinfo *slot, uint16_t reclen,
    struct ufs_lookup_results *results)
{
        slot->status = FOUND;
        slot->offset = results->ulr_offset;
        slot->size = reclen;
        results->ulr_reclen = slot->size;
}

static void
slot_update(struct slotinfo *slot, int size, uint16_t reclen, doff_t offset)
{
        if (size >= slot->needed) {
                slot->status = FOUND;
                slot->offset = offset;
                slot->size = reclen;
        } else if (slot->status == NONE) {
                slot->freespace += size;
                if (slot->offset == -1)
                        slot->offset = offset;
                if (slot->freespace >= slot->needed) {
                        slot->status = COMPACT;
                        slot->size = offset + reclen - slot->offset;
                }
        }
}

/*
 * Return an indication of where the new directory entry should be put.
 * If we didn't find a slot, then set results->ulr_count to 0 indicating
 * that the new slot belongs at the end of the directory. If we found a slot,
 * then the new entry can be put in the range from results->ulr_offset to
 * results->ulr_offset + results->ulr_count.
 */
static int
slot_estimate(const struct slotinfo *slot, int dirblksiz, int nameiop,
    doff_t prevoff, doff_t enduseful, const struct inode *ip,
    struct ufs_lookup_results *results)
{
        if (slot->status == NONE) {
                results->ulr_offset = roundup(ip->i_size, dirblksiz);
                results->ulr_count = 0;
                enduseful = results->ulr_offset;
        } else if (nameiop == DELETE) {
                results->ulr_offset = slot->offset;
                calc_count(results, dirblksiz, prevoff);
        } else {
                results->ulr_offset = slot->offset;
                results->ulr_count = slot->size;
                if (enduseful < slot->offset + slot->size)
                        enduseful = slot->offset + slot->size;
        }
        results->ulr_endoff = roundup(enduseful, dirblksiz);
#if 0 /* commented out by dbj. none of the on disk fields changed */
        ip->i_flag |= IN_CHANGE | IN_UPDATE;
#endif
        return SET_ERROR(EJUSTRETURN);
}

/*
 * Check if we can delete inode tdp in directory vdp with inode ip and creds.
 */
static int
ufs_can_delete(struct vnode *tdp, struct vnode *vdp, struct inode *ip,
    kauth_cred_t cred)
{
        int error;

#ifdef UFS_ACL
        /*
         * NFSv4 Minor Version 1, draft-ietf-nfsv4-minorversion1-03.txt
         *
         * 3.16.2.1. ACE4_DELETE vs. ACE4_DELETE_CHILD
         */

        /*
         * XXX: Is this check required?
         */
        error = VOP_ACCESS(vdp, VEXEC, cred);
        if (error)
                goto out;

#if 0
        /* Moved to ufs_remove, ufs_rmdir because they hold the lock */
        error = VOP_ACCESSX(tdp, VDELETE, cred);
        if (error == 0)
                return 0;
#endif

        error = VOP_ACCESSX(vdp, VDELETE_CHILD, cred);
        if (error == 0)
                return 0;

        error = VOP_ACCESSX(vdp, VEXPLICIT_DENY | VDELETE_CHILD, cred);
        if (error)
                goto out;

#endif /* !UFS_ACL */

        /*
         * Write access to directory required to delete files.
         */
        error = VOP_ACCESS(vdp, VWRITE, cred);
        if (error)
                goto out;

        if (!(ip->i_mode & ISVTX))
                return 0;

        /*
         * If directory is "sticky", then user must own
         * the directory, or the file in it, else she
         * may not delete it (unless she's root). This
         * implements append-only directories.
         */
        error = kauth_authorize_vnode(cred, KAUTH_VNODE_DELETE, tdp, vdp,
            genfs_can_sticky(vdp, cred, ip->i_uid, VTOI(tdp)->i_uid));
        if (error) {
                error = SET_ERROR(EPERM);       // Why override?
                goto out;
        }
        return 0;
out:
        vrele(tdp);
        return error;
}

static int
ufs_getino(struct vnode *vdp, struct inode *ip, ino_t foundino,
    struct vnode **tdp, bool same)
{
        if (ip->i_number == foundino) {
                if (same)
                        return SET_ERROR(EISDIR);
                vref(vdp);
                *tdp = vdp;
                return 0;
        }
        return vcache_get(vdp->v_mount, &foundino, sizeof(foundino), tdp);
}


/*
 * Convert a component of a pathname into a pointer to a locked inode.
 * This is a very central and rather complicated routine.
 * If the file system is not maintained in a strict tree hierarchy,
 * this can result in a deadlock situation (see comments in code below).
 *
 * The cnp->cn_nameiop argument is LOOKUP, CREATE, RENAME, or DELETE depending
 * on whether the name is to be looked up, created, renamed, or deleted.
 * When CREATE, RENAME, or DELETE is specified, information usable in
 * creating, renaming, or deleting a directory entry may be calculated.
 * If flag has LOCKPARENT or'ed into it and the target of the pathname
 * exists, lookup returns both the target and its parent directory locked.
 * When creating or renaming and LOCKPARENT is specified, the target may
 * not be ".".  When deleting and LOCKPARENT is specified, the target may
 * be ".", but the caller must check to ensure it does a vrele and vput
 * instead of two vputs.
 *
 * Overall outline of ufs_lookup:
 *
 *      check accessibility of directory
 *      look for name in cache, if found, then if at end of path
 *        and deleting or creating, drop it, else return name
 *      search for name in directory, to found or notfound
 * notfound:
 *      if creating, return locked directory, leaving info on available slots
 *      else return error
 * found:
 *      if at end of path and deleting, return information to allow delete
 *      if at end of path and rewriting (RENAME and LOCKPARENT), lock target
 *        inode and return info to allow rewrite
 *      if not at end, add name to cache; if at end and neither creating
 *        nor deleting, add name to cache
 */
int
ufs_lookup(void *v)
{
        struct vop_lookup_v2_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
        } */ *ap = v;
        struct vnode *vdp = ap->a_dvp;  /* vnode for directory being searched */
        struct inode *dp = VTOI(vdp);   /* inode for directory being searched */
        struct buf *bp;                 /* a buffer of directory entries */
        struct direct *ep;              /* the current directory entry */
        int entryoffsetinblock;         /* offset of ep in bp's buffer */
        struct slotinfo slot;
        int numdirpasses;               /* strategy for directory search */
        doff_t endsearch;               /* offset to end directory search */
        doff_t prevoff;                 /* previous value of ulr_offset */
        struct vnode *tdp;              /* returned by vcache_get */
        doff_t enduseful;               /* pointer past last used dir slot.
                                           used for directory truncation. */
        u_long bmask;                   /* block offset mask */
        int error;
        struct vnode **vpp = ap->a_vpp;
        struct componentname *cnp = ap->a_cnp;
        kauth_cred_t cred = cnp->cn_cred;
        int flags;
        int nameiop = cnp->cn_nameiop;
        struct ufsmount *ump = dp->i_ump;
        const int needswap = UFS_MPNEEDSWAP(ump);
        int dirblksiz = ump->um_dirblksiz;
        ino_t foundino;
        struct ufs_lookup_results *results;
        int iswhiteout;                 /* temp result from cache_lookup() */
        const int fsfmt = FSFMT(vdp);
        uint16_t reclen;

        flags = cnp->cn_flags;

        bp = NULL;
        *vpp = NULL;
        endsearch = 0; /* silence compiler warning */

        /*
         * Check accessibility of directory.
         */
        if ((error = VOP_ACCESS(vdp, VEXEC, cred)) != 0)
                return error;

        if ((flags & ISLASTCN) && (vdp->v_mount->mnt_flag & MNT_RDONLY) &&
            (nameiop == DELETE || nameiop == RENAME))
                return SET_ERROR(EROFS);

        /*
         * We now have a segment name to search for, and a directory to search.
         *
         * Before tediously performing a linear scan of the directory,
         * check the name cache to see if the directory/name pair
         * we are looking for is known already.
         */
        if (cache_lookup(vdp, cnp->cn_nameptr, cnp->cn_namelen,
            cnp->cn_nameiop, cnp->cn_flags, &iswhiteout, vpp)) {
                if (iswhiteout) {
                        cnp->cn_flags |= ISWHITEOUT;
                }
                return *vpp == NULLVP ? SET_ERROR(ENOENT) : 0;
        }

        /* May need to restart the lookup with an exclusive lock. */
        if (VOP_ISLOCKED(vdp) != LK_EXCLUSIVE) {
                return SET_ERROR(ENOLCK);
        }

        /*
         * Produce the auxiliary lookup results into i_crap. Increment
         * its serial number so elsewhere we can tell if we're using
         * stale results. This should not be done this way. XXX.
         */
        results = &dp->i_crap;
        dp->i_crapcounter++;

        if (iswhiteout) {
                /*
                 * The namecache set iswhiteout without finding a
                 * cache entry. As of this writing (20121014), this
                 * can happen if there was a whiteout entry that has
                 * been invalidated by the lookup. It is not clear if
                 * it is correct to set ISWHITEOUT in this case or
                 * not; however, doing so retains the prior behavior,
                 * so we'll go with that until some clearer answer
                 * appears. XXX
                 */
                cnp->cn_flags |= ISWHITEOUT;
        }

        /*
         * Suppress search for slots unless creating
         * file and at end of pathname, in which case
         * we watch for a place to put the new file in
         * case it doesn't already exist.
         */
        slot_init(&slot);

        if ((nameiop == CREATE || nameiop == RENAME) && (flags & ISLASTCN)) {
                slot.status = NONE;
                slot.needed = UFS_DIRECTSIZ(cnp->cn_namelen);
        }

        /*
         * If there is cached information on a previous search of
         * this directory, pick up where we last left off.
         * We cache only lookups as these are the most common
         * and have the greatest payoff. Caching CREATE has little
         * benefit as it usually must search the entire directory
         * to determine that the entry does not exist. Caching the
         * location of the last DELETE or RENAME has not reduced
         * profiling time and hence has been removed in the interest
         * of simplicity.
         */
        bmask = vdp->v_mount->mnt_stat.f_iosize - 1;

#ifdef UFS_DIRHASH
        /*
         * Use dirhash for fast operations on large directories. The logic
         * to determine whether to hash the directory is contained within
         * ufsdirhash_build(); a zero return means that it decided to hash
         * this directory and it successfully built up the hash table.
         */
        if (ufsdirhash_build(dp) == 0) {
                /* Look for a free slot if needed. */
                enduseful = slot_findfree(&slot, dp);
                /* Look up the component. */
                numdirpasses = 1;
                entryoffsetinblock = 0; /* silence compiler warning */
                switch (ufsdirhash_lookup(dp, cnp->cn_nameptr, cnp->cn_namelen,
                    &results->ulr_offset, &bp,
                    nameiop == DELETE ? &prevoff : NULL)) {
                case 0:
                        ep = (void *)((char *)bp->b_data +
                            (results->ulr_offset & bmask));
                        reclen = ufs_rw16(ep->d_reclen, needswap);
                        goto foundentry;
                case ENOENT:
                        results->ulr_offset = roundup(dp->i_size, dirblksiz);
                        goto notfound;
                default:
                        /* Something failed; just do a linear search. */
                        break;
                }
        }
#endif /* UFS_DIRHASH */

        if (nameiop != LOOKUP || results->ulr_diroff == 0 ||
            results->ulr_diroff >= dp->i_size) {
                entryoffsetinblock = 0;
                results->ulr_offset = 0;
                numdirpasses = 1;
        } else {
                results->ulr_offset = results->ulr_diroff;
                entryoffsetinblock = results->ulr_offset & bmask;
                if (entryoffsetinblock != 0 &&
                    (error = ufs_blkatoff(vdp, (off_t)results->ulr_offset,
                    NULL, &bp, false)))
                        goto out;
                numdirpasses = 2;
                namecache_count_2passes();
        }
        prevoff = results->ulr_offset;
        endsearch = roundup(dp->i_size, dirblksiz);
        enduseful = 0;

searchloop:
        while (results->ulr_offset < endsearch) {
                preempt_point();

                /*
                 * If necessary, get the next directory block.
                 */
                if ((results->ulr_offset & bmask) == 0) {
                        if (bp != NULL)
                                brelse(bp, 0);
                        error = ufs_blkatoff(vdp, (off_t)results->ulr_offset,
                            NULL, &bp, false);
                        if (error)
                                goto out;
                        entryoffsetinblock = 0;
                }
                /*
                 * If still looking for a slot, and at a DIRBLKSIZ
                 * boundary, have to start looking for free space again.
                 */
                if (slot.status == NONE &&
                    (entryoffsetinblock & (dirblksiz - 1)) == 0) {
                        slot.offset = -1;
                        slot.freespace = 0;
                }
                /*
                 * Get pointer to next entry.
                 * Full validation checks are slow, so we only check
                 * enough to insure forward progress through the
                 * directory. Complete checks can be run by patching
                 * "dirchk" to be true.
                 */
                KASSERT(bp != NULL);
                ep = (void *)((char *)bp->b_data + entryoffsetinblock);
                const char *msg;
                reclen = ufs_rw16(ep->d_reclen, needswap);
                if ((reclen == 0 && (msg = "null entry")) || (dirchk &&
                    (msg = ufs_dirbadentry(vdp, ep, entryoffsetinblock)))) {
                        ufs_dirbad(dp, results->ulr_offset, msg);
                        reclen = dirblksiz -
                            (entryoffsetinblock & (dirblksiz - 1));
                        goto next;
                }

                /*
                 * If an appropriate sized slot has not yet been found,
                 * check to see if one is available. Also accumulate space
                 * in the current block so that we can determine if
                 * compaction is viable.
                 */
                if (slot.status != FOUND) {
                        int size = reclen;
                        if (ep->d_ino != 0)
                                size -= UFS_DIRSIZ(fsfmt, ep, needswap);
                        if (size > 0)
                                slot_update(&slot, size, reclen,
                                    results->ulr_offset);
                }

                if (ep->d_ino == 0)
                        goto next;

                /*
                 * Check for a name match.
                 */
                const uint16_t namlen = NAMLEN(fsfmt, needswap, ep);
                if (namlen != cnp->cn_namelen ||
                    memcmp(cnp->cn_nameptr, ep->d_name, (size_t)namlen))
                        goto next;

#ifdef UFS_DIRHASH
foundentry:
#endif
                /*
                 * Save directory entry's inode number and
                 * reclen, and release directory buffer.
                 */
                if (!fsfmt && ep->d_type == DT_WHT) {
                        slot_white(&slot, reclen, results);
                        /*
                         * This is used to set results->ulr_endoff, which may
                         * be used by ufs_direnter() as a length to truncate
                         * the directory to. Therefore, it must point past the
                         * end of the last non-empty directory entry. We don't
                         * know where that is in this case, so we effectively
                         * disable shrinking by using the existing size of the
                         * directory.
                         *
                         * Note that we wouldn't expect to shrink the
                         * directory while rewriting an existing entry anyway.
                         */
                        enduseful = endsearch;
                        cnp->cn_flags |= ISWHITEOUT;
                        numdirpasses--;
                        goto notfound;
                }
                foundino = ufs_rw32(ep->d_ino, needswap);
                results->ulr_reclen = reclen;
                goto found;
next:
                prevoff = results->ulr_offset;
                results->ulr_offset += reclen;
                entryoffsetinblock += reclen;
                if (ep->d_ino)
                        enduseful = results->ulr_offset;
        }
notfound:
        /*
         * If we started in the middle of the directory and failed
         * to find our target, we must check the beginning as well.
         */
        if (numdirpasses == 2) {
                numdirpasses--;
                results->ulr_offset = 0;
                endsearch = results->ulr_diroff;
                goto searchloop;
        }
        if (bp != NULL)
                brelse(bp, 0);
        /*
         * If creating, and at end of pathname and current
         * directory has not been removed, then can consider
         * allowing file to be created.
         */
        if ((nameiop == CREATE || nameiop == RENAME ||
             (nameiop == DELETE &&
              (cnp->cn_flags & DOWHITEOUT) &&
              (cnp->cn_flags & ISWHITEOUT))) &&
            (flags & ISLASTCN) && dp->i_nlink != 0) {
                /*
                 * Access for write is interpreted as allowing
                 * creation of files in the directory.
                 */
                if (flags & WILLBEDIR)
                        error = VOP_ACCESSX(vdp, VWRITE | VAPPEND, cred);
                else
                        error = VOP_ACCESS(vdp, VWRITE, cred);
                if (error)
                        goto out;
                error = slot_estimate(&slot, dirblksiz, nameiop,
                    prevoff, enduseful, dp, results);
                /*
                 * We return with the directory locked, so that
                 * the parameters we set up above will still be
                 * valid if we actually decide to do a direnter().
                 * We return ni_vp == NULL to indicate that the entry
                 * does not currently exist; we leave a pointer to
                 * the (locked) directory inode in ndp->ni_dvp.
                 *
                 * NB - if the directory is unlocked, then this
                 * information cannot be used.
                 */
                goto out;
        }
        /*
         * Insert name into cache (as non-existent) if appropriate.
         */
        if (nameiop != CREATE) {
                cache_enter(vdp, *vpp, cnp->cn_nameptr, cnp->cn_namelen,
                            cnp->cn_flags);
        }
        error = SET_ERROR(ENOENT);
        goto out;

found:
        if (numdirpasses == 2)
                namecache_count_pass2();
        /*
         * Check that directory length properly reflects presence
         * of this entry.
         */
        const uint64_t newisize =
            results->ulr_offset + UFS_DIRSIZ(fsfmt, ep, needswap);
        if (newisize > dp->i_size) {
                ufs_dirbad(dp, results->ulr_offset, "i_size too small");
                dp->i_size = newisize;
                DIP_ASSIGN(dp, size, dp->i_size);
                dp->i_flag |= IN_CHANGE | IN_UPDATE;
                UFS_WAPBL_UPDATE(vdp, NULL, NULL, UPDATE_DIROP);
        }
        brelse(bp, 0);

        /*
         * Found component in pathname.
         * If the final component of path name, save information
         * in the cache as to where the entry was found.
         */
        if ((flags & ISLASTCN) && nameiop == LOOKUP)
                results->ulr_diroff = results->ulr_offset & ~(dirblksiz - 1);

        /*
         * If deleting, and at end of pathname, return
         * parameters which can be used to remove file.
         * Lock the inode, being careful with ".".
         */
        if (nameiop == DELETE && (flags & ISLASTCN)) {
                /*
                 * Return pointer to current entry in results->ulr_offset,
                 * and distance past previous entry (if there
                 * is a previous entry in this block) in results->ulr_count.
                 * Save directory inode pointer in ndp->ni_dvp for dirremove().
                 */
                calc_count(results, dirblksiz, prevoff);

                if ((error = ufs_getino(vdp, dp, foundino, &tdp, false)) != 0)
                        goto out;

                if ((error = ufs_can_delete(tdp, vdp, dp, cred)) != 0)
                        goto out;

                *vpp = tdp;
                goto out;
        }

        /*
         * If rewriting (RENAME), return the inode and the
         * information required to rewrite the present directory
         * Must get inode of directory entry to verify it's a
         * regular file, or empty directory.
         */
        if (nameiop == RENAME && (flags & ISLASTCN)) {
                if (flags & WILLBEDIR)
                        error = VOP_ACCESSX(vdp, VWRITE | VAPPEND, cred);
                else
                        error = VOP_ACCESS(vdp, VWRITE, cred);
                if (error)
                        goto out;
                /*
                 * Careful about locking second inode.
                 * This can only occur if the target is ".".
                 */
                if ((error = ufs_getino(vdp, dp, foundino, &tdp, true)) != 0)
                        goto out;
                *vpp = tdp;
                goto out;
        }

        if ((error = ufs_getino(vdp, dp, foundino, &tdp, false)) != 0)
                goto out;

        *vpp = tdp;
        /*
         * Insert name into cache if appropriate.
         */
        cache_enter(vdp, *vpp, cnp->cn_nameptr, cnp->cn_namelen, cnp->cn_flags);
        error = 0;

out:
        return error;
}

void
ufs_dirbad(struct inode *ip, doff_t offset, const char *how)
{
        struct mount *mp = ITOV(ip)->v_mount;
        void (*p)(const char  *, ...) __printflike(1, 2) =
            (mp->mnt_flag & MNT_RDONLY) == 0 ? panic : printf;

        (*p)("%s: bad dir ino %ju at offset %d: %s\n",
            mp->mnt_stat.f_mntonname, (uintmax_t)ip->i_number,
            offset, how);
}

/*
 * Do consistency checking on a directory entry:
 *      record length must be multiple of 4
 *      entry must fit in rest of its DIRBLKSIZ block
 *      record must be large enough to contain entry
 *      name is not longer than FFS_MAXNAMLEN
 *      name must be as long as advertised, and null terminated
 */
const char *
ufs_dirbadentry(const struct vnode *dp, const struct direct *ep,
    int entryoffsetinblock)
{
        const struct ufsmount *ump = VFSTOUFS(dp->v_mount);
        const int needswap = UFS_MPNEEDSWAP(ump);
        const int dirblksiz = ump->um_dirblksiz;
        const int maxsize = dirblksiz - (entryoffsetinblock & (dirblksiz - 1));
        const int fsfmt = FSFMT(dp);
        const uint8_t namlen = NAMLEN(fsfmt, needswap, ep);
        const uint16_t reclen = ufs_rw16(ep->d_reclen, needswap);
        const int dirsiz = (int)UFS_DIRSIZ(fsfmt, ep, needswap);
        const char *name = ep->d_name;
        const char *str;
#ifdef DIAGNOSTIC
        static char buf[512];
#endif

        if ((reclen & 0x3) != 0)
                str = "not rounded";
        else if (reclen > maxsize)
                str = "too big";
        else if (reclen < dirsiz)
                str = "too small";
#if FFS_MAXNAMLEN < 255
        else if (namlen > FFS_MAXNAMLEN)
                str = "long name";
#endif
        else
                str = NULL;

        if (str) {
#ifdef DIAGNOSTIC
                snprintf(buf, sizeof(buf), "Bad dir (%s), reclen=%#x, "
                    "namlen=%d, dirsiz=%d <= reclen=%d <= maxsize=%d, "
                    "flags=%#x, entryoffsetinblock=%d, dirblksiz=%d",
                    str, reclen, namlen, dirsiz, reclen, maxsize,
                    dp->v_mount->mnt_flag, entryoffsetinblock, dirblksiz);
                str = buf;
#endif
                return str;
        }

        if (ep->d_ino == 0)
                return NULL;

        for (uint8_t i = 0; i < namlen; i++)
                if (name[i] == '\0') {
                        str = "NUL in name";
#ifdef DIAGNOSTIC
                        snprintf(buf, sizeof(buf), "%s [%s] i=%d, namlen=%d",
                            str, name, i, namlen);
                        str = buf;
#endif
                        return str;
                }

        if (name[namlen]) {
                str = "missing NUL in name";
#ifdef DIAGNOSTIC
                snprintf(buf, sizeof(buf), "%s [%*.*s] namlen=%d", str,
                    namlen, namlen, name, namlen);
                str = buf;
#endif
                return str;
        }
        return NULL;
}

/*
 * Construct a new directory entry after a call to namei, using the
 * name in the componentname argument cnp. The argument ip is the
 * inode to which the new directory entry will refer.
 */
void
ufs_makedirentry(struct inode *ip, struct componentname *cnp,
    struct direct *newdirp)
{
        size_t namelen = cnp->cn_namelen;

        newdirp->d_ino = ip->i_number;
        newdirp->d_namlen = namelen;
        memcpy(newdirp->d_name, cnp->cn_nameptr, namelen);

        /* NUL terminate and zero out padding */
        memset(&newdirp->d_name[namelen], 0, UFS_NAMEPAD(namelen));

        if (FSFMT(ITOV(ip)))
                newdirp->d_type = 0;
        else
                newdirp->d_type = IFTODT(ip->i_mode);
}


static int
ufs_dirgrow(struct vnode *dvp, const struct ufs_lookup_results *ulr,
    struct vnode *tvp, struct direct *dirp,
    struct componentname *cnp, struct buf *newdirbp)
{
        const kauth_cred_t cr = cnp->cn_cred;
        const struct ufsmount *ump = VFSTOUFS(dvp->v_mount);
        const int needswap = UFS_MPNEEDSWAP(ump);
        const int dirblksiz = ump->um_dirblksiz;
        const int fsfmt = FSFMT(dvp);
        const u_int newentrysize = UFS_DIRSIZ(0, dirp, 0);
        struct inode *dp = VTOI(dvp);
        int error, ret, blkoff;
        struct timespec ts;
        struct buf *bp;

        /*
         * If ulr_count is 0, then namei could find no
         * space in the directory. Here, ulr_offset will
         * be on a directory block boundary and we will write the
         * new entry into a fresh block.
         */
        if (ulr->ulr_offset & (dirblksiz - 1))
                panic("%s: newblk", __func__);
        if ((error = UFS_BALLOC(dvp, (off_t)ulr->ulr_offset, dirblksiz,
            cr, B_CLRBUF | B_SYNC, &bp)) != 0) {
                return error;
        }

        dp->i_size = ulr->ulr_offset + dirblksiz;
        DIP_ASSIGN(dp, size, dp->i_size);
        dp->i_flag |= IN_CHANGE | IN_UPDATE;
        uvm_vnp_setsize(dvp, dp->i_size);
        dirp->d_reclen = ufs_rw16(dirblksiz, needswap);
        dirp->d_ino = ufs_rw32(dirp->d_ino, needswap);
        if (fsfmt && ENDIANSWAP(needswap))
                ufs_dirswap(dirp);
        blkoff = ulr->ulr_offset & (ump->um_mountp->mnt_stat.f_iosize - 1);
        memcpy((char *)bp->b_data + blkoff, dirp, newentrysize);
#ifdef UFS_DIRHASH
        if (dp->i_dirhash != NULL) {
                ufsdirhash_newblk(dp, ulr->ulr_offset);
                ufsdirhash_add(dp, dirp, ulr->ulr_offset);
                ufsdirhash_checkblock(dp, (char *)bp->b_data + blkoff,
                    ulr->ulr_offset);
        }
#endif
        error = VOP_BWRITE(bp->b_vp, bp);
        vfs_timestamp(&ts);
        ret = UFS_UPDATE(dvp, &ts, &ts, UPDATE_DIROP);
        if (error == 0)
                return ret;
        return error;
}

static int
#if __GNUC_PREREQ__(5, 3)
/* This gets miscompiled by gcc 5.3 PR/51094 */
__attribute__((__optimize__("no-tree-vrp")))
#endif
ufs_dircompact(struct vnode *dvp, const struct ufs_lookup_results *ulr,
    struct vnode *tvp, struct direct *dirp,
    struct componentname *cnp, struct buf *newdirbp)
{
        const struct ufsmount *ump = VFSTOUFS(dvp->v_mount);
        const int needswap = UFS_MPNEEDSWAP(ump);
        const int fsfmt = FSFMT(dvp);
        const u_int newentrysize = UFS_DIRSIZ(0, dirp, 0);
        struct inode *dp = VTOI(dvp);
        struct buf *bp;
        u_int dsize;
        struct direct *ep, *nep;
        int error, loc, spacefree;
        char *dirbuf;
        uint16_t reclen;

        UFS_WAPBL_JLOCK_ASSERT(dvp->v_mount);

        /*
         * If ulr_count is non-zero, then namei found space for the new
         * entry in the range ulr_offset to ulr_offset + ulr_count
         * in the directory. To use this space, we may have to compact
         * the entries located there, by copying them together towards the
         * beginning of the block, leaving the free space in one usable
         * chunk at the end.
         */

        /*
         * Increase size of directory if entry eats into new space.
         * This should never push the size past a new multiple of
         * DIRBLKSIZ.
         *
         * N.B. - THIS IS AN ARTIFACT OF 4.2 AND SHOULD NEVER HAPPEN.
         */
        if (ulr->ulr_offset + ulr->ulr_count > dp->i_size) {
#ifdef DIAGNOSTIC
                printf("%s: reached 4.2-only block, not supposed to happen\n",
                    __func__);
#endif
                dp->i_size = ulr->ulr_offset + ulr->ulr_count;
                DIP_ASSIGN(dp, size, dp->i_size);
                dp->i_flag |= IN_CHANGE | IN_UPDATE;
                UFS_WAPBL_UPDATE(dvp, NULL, NULL, UPDATE_DIROP);
        }
        /*
         * Get the block containing the space for the new directory entry.
         */
        error = ufs_blkatoff(dvp, (off_t)ulr->ulr_offset, &dirbuf, &bp, true);
        if (error)
                return error;

        /*
         * Find space for the new entry. In the simple case, the entry at
         * offset base will have the space. If it does not, then namei
         * arranged that compacting the region ulr_offset to
         * ulr_offset + ulr_count would yield the space.
         */
        ep = (void *)dirbuf;
        dsize = (ep->d_ino != 0) ? UFS_DIRSIZ(fsfmt, ep, needswap) : 0;
        reclen = ufs_rw16(ep->d_reclen, needswap);
        spacefree = reclen - dsize;
        for (loc = reclen; loc < ulr->ulr_count; ) {
                nep = (void *)(dirbuf + loc);

                /* Trim the existing slot (NB: dsize may be zero). */
                ep->d_reclen = ufs_rw16(dsize, needswap);
                ep = (void *)((char *)ep + dsize);

                reclen = ufs_rw16(nep->d_reclen, needswap);
                loc += reclen;
                if (nep->d_ino == 0) {
                        /*
                         * A mid-block unused entry. Such entries are
                         * never created by the kernel, but fsck_ffs
                         * can create them (and it doesn't fix them).
                         *
                         * Add up the free space, and initialise the
                         * relocated entry since we don't memcpy it.
                         */
                        spacefree += reclen;
                        ep->d_ino = 0;
                        dsize = 0;
                        continue;
                }
                dsize = UFS_DIRSIZ(fsfmt, nep, needswap);
                spacefree += reclen - dsize;
#ifdef UFS_DIRHASH
                if (dp->i_dirhash != NULL)
                        ufsdirhash_move(dp, nep,
                            ulr->ulr_offset + ((char *)nep - dirbuf),
                            ulr->ulr_offset + ((char *)ep - dirbuf));
#endif
                memcpy(ep, nep, dsize);
        }
        /*
         * Here, `ep' points to a directory entry containing `dsize' in-use
         * bytes followed by `spacefree' unused bytes. If ep->d_ino == 0,
         * then the entry is completely unused (dsize == 0). The value
         * of ep->d_reclen is always indeterminate.
         *
         * Update the pointer fields in the previous entry (if any),
         * copy in the new entry, and write out the block.
         */
        if (ep->d_ino == 0 ||
            (ufs_rw32(ep->d_ino, needswap) == UFS_WINO &&
             memcmp(ep->d_name, dirp->d_name, dirp->d_namlen) == 0)) {
                if (spacefree + dsize < newentrysize)
                        panic("%s: too big", __func__);
                dirp->d_reclen = spacefree + dsize;
        } else {
                if (spacefree < newentrysize)
                        panic("%s: nospace", __func__);
                dirp->d_reclen = spacefree;
                ep->d_reclen = ufs_rw16(dsize, needswap);
                ep = (void *)((char *)ep + dsize);
        }

        dirp->d_reclen = ufs_rw16(dirp->d_reclen, needswap);
        dirp->d_ino = ufs_rw32(dirp->d_ino, needswap);
        if (fsfmt && ENDIANSWAP(needswap))
                ufs_dirswap(dirp);
#ifdef UFS_DIRHASH
        if (dp->i_dirhash != NULL && (ep->d_ino == 0 ||
            dirp->d_reclen == spacefree))
                ufsdirhash_add(dp, dirp, ulr->ulr_offset + ((char *)ep - dirbuf));
#endif
        memcpy(ep, dirp, newentrysize);
#ifdef UFS_DIRHASH
        if (dp->i_dirhash != NULL) {
                const int dirblkmsk = ump->um_dirblksiz - 1;
                ufsdirhash_checkblock(dp, dirbuf -
                    (ulr->ulr_offset & dirblkmsk),
                    ulr->ulr_offset & ~dirblkmsk);
        }
#endif
        error = VOP_BWRITE(bp->b_vp, bp);
        dp->i_flag |= IN_CHANGE | IN_UPDATE;
        /*
         * If all went well, and the directory can be shortened, proceed
         * with the truncation. Note that we have to unlock the inode for
         * the entry that we just entered, as the truncation may need to
         * lock other inodes which can lead to deadlock if we also hold a
         * lock on the newly entered node.
         */
        if (error == 0 && ulr->ulr_endoff && ulr->ulr_endoff < dp->i_size) {
                const kauth_cred_t cr = cnp->cn_cred;
#ifdef UFS_DIRHASH
                if (dp->i_dirhash != NULL)
                        ufsdirhash_dirtrunc(dp, ulr->ulr_endoff);
#endif
                (void) UFS_TRUNCATE(dvp, (off_t)ulr->ulr_endoff, IO_SYNC, cr);
        }
        UFS_WAPBL_UPDATE(dvp, NULL, NULL, UPDATE_DIROP);
        return error;
}

/*
 * Write a directory entry after a call to namei, using the parameters
 * that ufs_lookup left in nameidata and in the ufs_lookup_results.
 *
 * DVP is the directory to be updated. It must be locked.
 * ULR is the ufs_lookup_results structure from the final lookup step.
 * TVP is not used. (XXX: why is it here? remove it)
 * DIRP is the new directory entry contents.
 * CNP is the componentname from the final lookup step.
 * NEWDIRBP is not used and (XXX) should be removed. The previous
 * comment here said it was used by the now-removed softupdates code.
 *
 * The link count of the target inode is *not* incremented; the
 * caller does that.
 *
 * If ulr->ulr_count is 0, ufs_lookup did not find space to insert the
 * directory entry. ulr_offset, which is the place to put the entry,
 * should be on a block boundary (and should be at the end of the
 * directory AFAIK) and a fresh block is allocated to put the new
 * directory entry in.
 *
 * If ulr->ulr_count is not zero, ufs_lookup found a slot to insert
 * the entry into. This slot ranges from ulr_offset to ulr_offset +
 * ulr_count. However, this slot may already be partially populated
 * requiring compaction. See notes below.
 *
 * Furthermore, if ulr_count is not zero and ulr_endoff is not the
 * same as i_size, the directory is truncated to size ulr_endoff.
 */
int
ufs_direnter(struct vnode *dvp, const struct ufs_lookup_results *ulr,
    struct vnode *tvp, struct direct *dirp,
    struct componentname *cnp, struct buf *newdirbp)
{
        if (ulr->ulr_count == 0)
                return ufs_dirgrow(dvp, ulr, tvp, dirp, cnp, newdirbp);
        else
                return ufs_dircompact(dvp, ulr, tvp, dirp, cnp, newdirbp);
}

/*
 * Remove a directory entry after a call to namei, using the
 * parameters that ufs_lookup left in nameidata and in the
 * ufs_lookup_results.
 *
 * DVP is the directory to be updated. It must be locked.
 * ULR is the ufs_lookup_results structure from the final lookup step.
 * IP, if not null, is the inode being unlinked.
 * FLAGS may contain DOWHITEOUT.
 * ISRMDIR is not used and (XXX) should be removed.
 *
 * If FLAGS contains DOWHITEOUT the entry is replaced with a whiteout
 * instead of being cleared.
 *
 * ulr->ulr_offset contains the position of the directory entry
 * to be removed.
 *
 * ulr->ulr_reclen contains the size of the directory entry to be
 * removed.
 *
 * ulr->ulr_count contains the size of the *previous* directory
 * entry. This allows finding it, for free space management. If
 * ulr_count is 0, the target entry is at the beginning of the
 * directory. (Does this ever happen? The first entry should be ".",
 * which should only be removed at rmdir time. Does rmdir come here
 * to clear out the "." and ".." entries? Perhaps, but I doubt it.)
 *
 * The space is marked free by adding it to the record length (not
 * name length) of the preceding entry. If the first entry becomes
 * free, it is marked free by setting the inode number to 0.
 *
 * The link count of IP is decremented. Note that this is not the
 * inverse behavior of ufs_direnter, which does not adjust link
 * counts. Sigh.
 */
int
ufs_dirremove(struct vnode *dvp, const struct ufs_lookup_results *ulr,
    struct inode *ip, int flags, int isrmdir)
{
        struct inode *dp = VTOI(dvp);
        struct direct *ep;
        struct buf *bp;
        int error;
        const int needswap = UFS_MPNEEDSWAP(dp->i_ump);
        uint16_t reclen;

        UFS_WAPBL_JLOCK_ASSERT(dvp->v_mount);

        if (flags & DOWHITEOUT) {
                /*
                 * Whiteout entry: set d_ino to UFS_WINO.
                 */
                error = ufs_blkatoff(dvp, (off_t)ulr->ulr_offset, &ep,
                                     &bp, true);
                if (error)
                        return error;
                ep->d_ino = ufs_rw32(UFS_WINO, needswap);
                ep->d_type = DT_WHT;
                goto out;
        }

        if ((error = ufs_blkatoff(dvp,
            (off_t)(ulr->ulr_offset - ulr->ulr_count), &ep, &bp, true)) != 0)
                return error;

        reclen = ufs_rw16(ep->d_reclen, needswap);
#ifdef UFS_DIRHASH
        /*
         * Remove the dirhash entry. This is complicated by the fact
         * that `ep' is the previous entry when ulr_count != 0.
         */
        if (dp->i_dirhash != NULL)
                ufsdirhash_remove(dp, (ulr->ulr_count == 0) ? ep :
                   (void *)((char *)ep + reclen), ulr->ulr_offset);
#endif

        if (ulr->ulr_count == 0) {
                /*
                 * First entry in block: set d_ino to zero.
                 */
                ep->d_ino = 0;
        } else {
                /*
                 * Collapse new free space into previous entry.
                 */
                ep->d_reclen = ufs_rw16(reclen + ulr->ulr_reclen, needswap);
        }

#ifdef UFS_DIRHASH
        if (dp->i_dirhash != NULL) {
                int dirblksiz = ip->i_ump->um_dirblksiz;
                ufsdirhash_checkblock(dp, (char *)ep -
                    ((ulr->ulr_offset - ulr->ulr_count) & (dirblksiz - 1)),
                    ulr->ulr_offset & ~(dirblksiz - 1));
        }
#endif

out:
        if (ip) {
                ip->i_nlink--;
                DIP_ASSIGN(ip, nlink, ip->i_nlink);
                ip->i_flag |= IN_CHANGE;
                UFS_WAPBL_UPDATE(ITOV(ip), NULL, NULL, 0);
        }
        /*
         * XXX did it ever occur to anyone that it might be a good
         * idea to restore ip->i_nlink if this fails? Or something?
         * Currently on error return from this function the state of
         * ip->i_nlink depends on what happened, and callers
         * definitely do not take this into account.
         */
        error = VOP_BWRITE(bp->b_vp, bp);
        dp->i_flag |= IN_CHANGE | IN_UPDATE;
        /*
         * If the last named reference to a snapshot goes away,
         * drop its snapshot reference so that it will be reclaimed
         * when last open reference goes away.
         */
        if (ip != 0 && (ip->i_flags & SF_SNAPSHOT) != 0 &&
            ip->i_nlink == 0)
                UFS_SNAPGONE(ITOV(ip));
        UFS_WAPBL_UPDATE(dvp, NULL, NULL, 0);
        return error;
}

/*
 * Rewrite an existing directory entry to point at the inode supplied.
 *
 * DP is the directory to update.
 * OFFSET is the position of the entry in question. It may come
 * from ulr_offset of a ufs_lookup_results.
 * OIP is the old inode the directory previously pointed to.
 * NEWINUM is the number of the new inode.
 * NEWTYPE is the new value for the type field of the directory entry.
 * (This is ignored if the fs doesn't support that.)
 * ISRMDIR is not used and (XXX) should be removed.
 * IFLAGS are added to DP's inode flags.
 *
 * The link count of OIP is decremented. Note that the link count of
 * the new inode is *not* incremented. Yay for symmetry.
 */
int
ufs_dirrewrite(struct inode *dp, off_t offset,
    struct inode *oip, ino_t newinum, int newtype,
    int isrmdir, int iflags)
{
        struct buf *bp;
        struct direct *ep;
        struct vnode *vdp = ITOV(dp);
        int error;

        error = ufs_blkatoff(vdp, offset, &ep, &bp, true);
        if (error)
                return error;
        ep->d_ino = ufs_rw32(newinum, UFS_MPNEEDSWAP(dp->i_ump));
        if (!FSFMT(vdp))
                ep->d_type = newtype;
        oip->i_nlink--;
        DIP_ASSIGN(oip, nlink, oip->i_nlink);
        oip->i_flag |= IN_CHANGE;
        UFS_WAPBL_UPDATE(ITOV(oip), NULL, NULL, UPDATE_DIROP);
        error = VOP_BWRITE(bp->b_vp, bp);
        dp->i_flag |= iflags;
        /*
         * If the last named reference to a snapshot goes away,
         * drop its snapshot reference so that it will be reclaimed
         * when last open reference goes away.
         */
        if ((oip->i_flags & SF_SNAPSHOT) != 0 && oip->i_nlink == 0)
                UFS_SNAPGONE(ITOV(oip));
        UFS_WAPBL_UPDATE(vdp, NULL, NULL, UPDATE_DIROP);
        return error;
}

/*
 * Check if a directory is empty or not.
 * Inode supplied must be locked.
 *
 * Using a struct dirtemplate here is not precisely
 * what we want, but better than using a struct direct.
 *
 * NB: does not handle corrupted directories.
 */
int
ufs_dirempty(struct inode *ip, ino_t parentino, kauth_cred_t cred)
{
        doff_t off;
        struct direct dbuf;
        struct direct *dp = &dbuf;
        int error;
        size_t count;
        const int needswap = UFS_IPNEEDSWAP(ip);
        const int fsfmt = FSFMT(ITOV(ip));
#define MINDIRSIZ (sizeof (struct dirtemplate) / 2)

        for (off = 0; off < ip->i_size;
            off += ufs_rw16(dp->d_reclen, needswap)) {
                error = ufs_bufio(UIO_READ, ITOV(ip), dp, MINDIRSIZ,
                    off, IO_NODELOCKED, cred, &count, NULL);
                /*
                 * Since we read MINDIRSIZ, residual must
                 * be 0 unless we're at end of file.
                 */
                if (error || count != 0)
                        return 0;
                /* avoid infinite loops */
                if (dp->d_reclen == 0)
                        return 0;
                /* skip empty entries */
                ino_t ino = ufs_rw32(dp->d_ino, needswap);
                if (ino == 0 || ino == UFS_WINO)
                        continue;
                /* accept only "." and ".." */
                const uint8_t namlen = NAMLEN(fsfmt, needswap, dp);
                if (namlen > 2)
                        return 0;
                if (dp->d_name[0] != '.')
                        return 0;
                /*
                 * At this point namlen must be 1 or 2.
                 * 1 implies ".", 2 implies ".." if second
                 * char is also "."
                 */
                if (namlen == 1 && ino == ip->i_number)
                        continue;
                if (dp->d_name[1] == '.' && ino == parentino)
                        continue;
                return 0;
        }
        return 1;
}

#define UFS_DIRRABLKS 0
int ufs_dirrablks = UFS_DIRRABLKS;

/*
 * ufs_blkatoff: Return buffer with the contents of block "offset" from
 * the beginning of directory "vp".  If "res" is non-NULL, fill it in with
 * a pointer to the remaining space in the directory.  If the caller intends
 * to modify the buffer returned, "modify" must be true.
 */

int
ufs_blkatoff(struct vnode *vp, off_t offset, void *v, struct buf **bpp,
    bool modify)
{
        char **res = v;
        struct inode *ip __diagused;
        struct buf *bp;
        daddr_t lbn;
        const int dirrablks = ufs_dirrablks;
        daddr_t *blks;
        int *blksizes;
        int run, error;
        struct mount *mp = vp->v_mount;
        const int bshift = mp->mnt_fs_bshift;
        const int bsize = 1 << bshift;
        off_t eof;

        blks = kmem_alloc((1 + dirrablks) * sizeof(daddr_t), KM_SLEEP);
        blksizes = kmem_alloc((1 + dirrablks) * sizeof(int), KM_SLEEP);
        ip = VTOI(vp);
        KASSERT(vp->v_size == ip->i_size);
        GOP_SIZE(vp, vp->v_size, &eof, 0);
        lbn = offset >> bshift;

        for (run = 0; run <= dirrablks;) {
                const off_t curoff = lbn << bshift;
                const int size = MIN(eof - curoff, bsize);

                if (size == 0) {
                        break;
                }
                KASSERT(curoff < eof);
                blks[run] = lbn;
                blksizes[run] = size;
                lbn++;
                run++;
                if (size != bsize) {
                        break;
                }
        }
        KASSERT(run >= 1);
        error = breadn(vp, blks[0], blksizes[0], &blks[1], &blksizes[1],
            run - 1, (modify ? B_MODIFY : 0), &bp);
        if (error != 0) {
                *bpp = NULL;
                goto out;
        }
        if (res) {
                *res = (char *)bp->b_data + (offset & (bsize - 1));
        }
        *bpp = bp;

 out:
        kmem_free(blks, (1 + dirrablks) * sizeof(daddr_t));
        kmem_free(blksizes, (1 + dirrablks) * sizeof(int));
        return error;
}