FreeBSD/Linux Kernel Cross Reference
sys/ufs/ufs/ufs_lookup.c

     /*      $NetBSD: ufs_lookup.c,v 1.156 2022/08/06 18:26:42 andvar 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 1.156 2022/08/06 18:26:42 andvar Exp $");
    
    #ifdef _KERNEL_OPT
    #include "opt_ffs.h"
    #endif
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/namei.h>
    #include <sys/buf.h>
    #include <sys/file.h>
    #include <sys/stat.h>
    #include <sys/mount.h>
    #include <sys/vnode.h>
    #include <sys/kernel.h>
    #include <sys/kauth.h>
    #include <sys/wapbl.h>
    #include <sys/proc.h>
    #include <sys/kmem.h>
    
    #include <ufs/ufs/inode.h>
    #include <ufs/ufs/dir.h>
    #ifdef UFS_DIRHASH
    #include <ufs/ufs/dirhash.h>
    #endif
    #include <ufs/ufs/ufsmount.h>
    #include <ufs/ufs/ufs_extern.h>
    #include <ufs/ufs/ufs_bswap.h>
    #include <ufs/ufs/ufs_wapbl.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 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 = 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 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 an 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 (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 ? ENOENT : 0;
           }
   
           /* May need to restart the lookup with an exclusive lock. */
           if (VOP_ISLOCKED(vdp) != LK_EXCLUSIVE) {
                   return 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 = 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 dirtemplate dbuf;
          struct direct *dp = (void *)&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;
  }

Cache object: d07256c31d95d0c97b68643c98a16473