xnu-344.12.2.tar.gz

[apple/xnu.git] / bsd / vfs / vfs_lookup.c

/*
 * Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * Copyright (c) 1982, 1986, 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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.
 *
 *      @(#)vfs_lookup.c        8.10 (Berkeley) 5/27/95
 */

#include <sys/param.h>
#include <sys/syslimits.h>
#include <sys/time.h>
#include <sys/namei.h>
#include <sys/vm.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/errno.h>
#include <sys/malloc.h>
#include <sys/filedesc.h>
#include <sys/proc.h>
#include <sys/kdebug.h>
#include <sys/unistd.h>         /* For _PC_NAME_MAX */

#if KTRACE
#include <sys/ktrace.h>
#endif

/*
 * Convert a pathname into a pointer to a locked inode.
 *
 * The FOLLOW flag is set when symbolic links are to be followed
 * when they occur at the end of the name translation process.
 * Symbolic links are always followed for all other pathname
 * components other than the last.
 *
 * The segflg defines whether the name is to be copied from user
 * space or kernel space.
 *
 * Overall outline of namei:
 *
 *      copy in name
 *      get starting directory
 *      while (!done && !error) {
 *              call lookup to search path.
 *              if symbolic link, massage name in buffer and continue
 *      }
 */
int
namei(ndp)
        register struct nameidata *ndp;
{
        register struct filedesc *fdp;  /* pointer to file descriptor state */
        register char *cp;              /* pointer into pathname argument */
        register struct vnode *dp;      /* the directory we are searching */
        struct iovec aiov;              /* uio for reading symbolic links */
        struct uio auio;
        int error, linklen;
        struct componentname *cnp = &ndp->ni_cnd;
        struct proc *p = cnp->cn_proc;

        ndp->ni_cnd.cn_cred = ndp->ni_cnd.cn_proc->p_ucred;
#if DIAGNOSTIC
        if (!cnp->cn_cred || !cnp->cn_proc)
                panic ("namei: bad cred/proc");
        if (cnp->cn_nameiop & (~OPMASK))
                panic ("namei: nameiop contaminated with flags");
        if (cnp->cn_flags & OPMASK)
                panic ("namei: flags contaminated with nameiops");
#endif
        fdp = cnp->cn_proc->p_fd;

        /*
         * Get a buffer for the name to be translated, and copy the
         * name into the buffer.
         */
        if ((cnp->cn_flags & HASBUF) == 0) {
                MALLOC_ZONE(cnp->cn_pnbuf, caddr_t,
                                MAXPATHLEN, M_NAMEI, M_WAITOK);
                cnp->cn_pnlen = MAXPATHLEN;
        }
        if (ndp->ni_segflg == UIO_SYSSPACE)
                error = copystr(ndp->ni_dirp, cnp->cn_pnbuf,
                            MAXPATHLEN, &ndp->ni_pathlen);
        else
                error = copyinstr(ndp->ni_dirp, cnp->cn_pnbuf,
                            MAXPATHLEN, &ndp->ni_pathlen);
        /*
         * Do not allow empty pathnames
         */
        if (!error && *cnp->cn_pnbuf == '\0')
                error = ENOENT;

        if (error) {
                _FREE_ZONE(cnp->cn_pnbuf, cnp->cn_pnlen, M_NAMEI);
                ndp->ni_vp = NULL;
                return (error);
        }
        ndp->ni_loopcnt = 0;
#if KTRACE
        if (KTRPOINT(cnp->cn_proc, KTR_NAMEI))
                ktrnamei(cnp->cn_proc->p_tracep, cnp->cn_pnbuf);
#endif

        /*
         * Get starting point for the translation.
         */
        if ((ndp->ni_rootdir = fdp->fd_rdir) == NULL)
                ndp->ni_rootdir = rootvnode;
        dp = fdp->fd_cdir;
        VREF(dp);
        for (;;) {
                /*
                 * Check if root directory should replace current directory.
                 * Done at start of translation and after symbolic link.
                 */
                cnp->cn_nameptr = cnp->cn_pnbuf;
                if (*(cnp->cn_nameptr) == '/') {
                        vrele(dp);
                        while (*(cnp->cn_nameptr) == '/') {
                                cnp->cn_nameptr++;
                                ndp->ni_pathlen--;
                        }
                        dp = ndp->ni_rootdir;
                        VREF(dp);
                }
                ndp->ni_startdir = dp;
                if (error = lookup(ndp)) {
                        FREE_ZONE(cnp->cn_pnbuf, cnp->cn_pnlen, M_NAMEI);
                        return (error);
                }
                /*
                 * Check for symbolic link
                 */
                if ((cnp->cn_flags & ISSYMLINK) == 0) {
                        if ((cnp->cn_flags & (SAVENAME | SAVESTART)) == 0) {
                                FREE_ZONE(cnp->cn_pnbuf,
                                                cnp->cn_pnlen, M_NAMEI);
                        } else {
                                cnp->cn_flags |= HASBUF;
                        }
                        return (0);
                }
                if ((cnp->cn_flags & LOCKPARENT) && ndp->ni_pathlen == 1)
                        VOP_UNLOCK(ndp->ni_dvp, 0, p);
                if (ndp->ni_loopcnt++ >= MAXSYMLINKS) {
                        error = ELOOP;
                        break;
                }
                if (ndp->ni_pathlen > 1) {
                        MALLOC_ZONE(cp, char *, MAXPATHLEN, M_NAMEI, M_WAITOK);
                } else {
                        cp = cnp->cn_pnbuf;
                }
                aiov.iov_base = cp;
                aiov.iov_len = MAXPATHLEN;
                auio.uio_iov = &aiov;
                auio.uio_iovcnt = 1;
                auio.uio_offset = 0;
                auio.uio_rw = UIO_READ;
                auio.uio_segflg = UIO_SYSSPACE;
                auio.uio_procp = (struct proc *)0;
                auio.uio_resid = MAXPATHLEN;
                if (error = VOP_READLINK(ndp->ni_vp, &auio, cnp->cn_cred)) {
                        if (ndp->ni_pathlen > 1)
                                _FREE_ZONE(cp, MAXPATHLEN, M_NAMEI);
                        break;
                }
                linklen = MAXPATHLEN - auio.uio_resid;
                if (linklen + ndp->ni_pathlen >= MAXPATHLEN) {
                        if (ndp->ni_pathlen > 1)
                                _FREE_ZONE(cp, MAXPATHLEN, M_NAMEI);
                        error = ENAMETOOLONG;
                        break;
                }
                if (ndp->ni_pathlen > 1) {
                        bcopy(ndp->ni_next, cp + linklen, ndp->ni_pathlen);
                        FREE_ZONE(cnp->cn_pnbuf, cnp->cn_pnlen, M_NAMEI);
                        cnp->cn_pnbuf = cp;
                        cnp->cn_pnlen = MAXPATHLEN;
                } else
                        cnp->cn_pnbuf[linklen] = '\0';
                ndp->ni_pathlen += linklen;
                vput(ndp->ni_vp);
                dp = ndp->ni_dvp;
        }
        FREE_ZONE(cnp->cn_pnbuf, cnp->cn_pnlen, M_NAMEI);
        vrele(ndp->ni_dvp);
        vput(ndp->ni_vp);
        ndp->ni_vp = NULL;
        return (error);
}

/*
 * Search a pathname.
 * This is a very central and rather complicated routine.
 *
 * The pathname is pointed to by ni_ptr and is of length ni_pathlen.
 * The starting directory is taken from ni_startdir. The pathname is
 * descended until done, or a symbolic link is encountered. The variable
 * ni_more is clear if the path is completed; it is set to one if a
 * symbolic link needing interpretation is encountered.
 *
 * The flag 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, the parent directory is returned
 * locked. If flag has WANTPARENT or'ed into it, the parent directory is
 * returned unlocked. Otherwise the parent directory is not returned. If
 * the target of the pathname exists and LOCKLEAF is or'ed into the flag
 * the target is returned locked, otherwise it is returned unlocked.
 * When creating or renaming and LOCKPARENT is specified, the target may not
 * be ".".  When deleting and LOCKPARENT is specified, the target may be ".".
 * 
 * Overall outline of lookup:
 *
 * dirloop:
 *      identify next component of name at ndp->ni_ptr
 *      handle degenerate case where name is null string
 *      if .. and crossing mount points and on mounted filesys, find parent
 *      call VOP_LOOKUP routine for next component name
 *          directory vnode returned in ni_dvp, unlocked unless LOCKPARENT set
 *          component vnode returned in ni_vp (if it exists), locked.
 *      if result vnode is mounted on and crossing mount points,
 *          find mounted on vnode
 *      if more components of name, do next level at dirloop
 *      return the answer in ni_vp, locked if LOCKLEAF set
 *          if LOCKPARENT set, return locked parent in ni_dvp
 *          if WANTPARENT set, return unlocked parent in ni_dvp
 */
int
lookup(ndp)
        register struct nameidata *ndp;
{
        register char *cp;              /* pointer into pathname argument */
        register struct vnode *dp = 0;  /* the directory we are searching */
        struct vnode *tdp;              /* saved dp */
        struct mount *mp;               /* mount table entry */
        int namemax = 0;                        /* maximun number of bytes for filename returned by pathconf() */
        int docache;                    /* == 0 do not cache last component */
        int wantparent;                 /* 1 => wantparent or lockparent flag */
        int dp_unlocked = 0;    /* 1 => dp already VOP_UNLOCK()-ed */
        int rdonly;                     /* lookup read-only flag bit */
        int trailing_slash;
        int error = 0;
        struct componentname *cnp = &ndp->ni_cnd;
        struct proc *p = cnp->cn_proc;
        int i;

        /*
         * Setup: break out flag bits into variables.
         */
        wantparent = cnp->cn_flags & (LOCKPARENT | WANTPARENT);
        docache = (cnp->cn_flags & NOCACHE) ^ NOCACHE;
        if (cnp->cn_nameiop == DELETE ||
            (wantparent && cnp->cn_nameiop != CREATE &&
             cnp->cn_nameiop != LOOKUP))
                docache = 0;
        rdonly = cnp->cn_flags & RDONLY;
        ndp->ni_dvp = NULL;
        cnp->cn_flags &= ~ISSYMLINK;
        dp = ndp->ni_startdir;
        ndp->ni_startdir = NULLVP;
        vn_lock(dp, LK_EXCLUSIVE | LK_RETRY, p);

dirloop:
        /*
         * Search a new directory.
         *
         * The cn_hash value is for use by vfs_cache.
         * Check pathconf for maximun length of name
         * The last component of the filename is left accessible via
         * cnp->cn_nameptr for callers that need the name. Callers needing
         * the name set the SAVENAME flag. When done, they assume
         * responsibility for freeing the pathname buffer.
         */
        cnp->cn_consume = 0;
        cnp->cn_hash = 0;
        for (cp = cnp->cn_nameptr, i=1; *cp != 0 && *cp != '/'; i++, cp++)
                cnp->cn_hash += (unsigned char)*cp * i;
        cnp->cn_namelen = cp - cnp->cn_nameptr;
    if (VOP_PATHCONF(dp, _PC_NAME_MAX, &namemax))
                namemax = NAME_MAX;
    if (cnp->cn_namelen > namemax) {
                error = ENAMETOOLONG;
                goto bad;
        }
#ifdef NAMEI_DIAGNOSTIC
        { char c = *cp;
        *cp = '\0';
        printf("{%s}: ", cnp->cn_nameptr);
        *cp = c; }
#endif
        ndp->ni_pathlen -= cnp->cn_namelen;
        ndp->ni_next = cp;

        /*
         * Replace multiple slashes by a single slash and trailing slashes
         * by a null.  This must be done before VOP_LOOKUP() because some
         * fs's don't know about trailing slashes.  Remember if there were
         * trailing slashes to handle symlinks, existing non-directories
         * and non-existing files that won't be directories specially later.
         */
        trailing_slash = 0;
        while (*cp == '/' && (cp[1] == '/' || cp[1] == '\0')) {
                cp++;
                ndp->ni_pathlen--;
                if (*cp == '\0') {
                        trailing_slash = 1;
                        *ndp->ni_next = '\0';
                }
        }
        ndp->ni_next = cp;

        cnp->cn_flags |= MAKEENTRY;
        if (*cp == '\0' && docache == 0)
                cnp->cn_flags &= ~MAKEENTRY;
        if (cnp->cn_namelen == 2 &&
            cnp->cn_nameptr[1] == '.' && cnp->cn_nameptr[0] == '.')
                cnp->cn_flags |= ISDOTDOT;
        else
                cnp->cn_flags &= ~ISDOTDOT;
        if (*ndp->ni_next == 0)
                cnp->cn_flags |= ISLASTCN;
        else
                cnp->cn_flags &= ~ISLASTCN;


        /*
         * Check for degenerate name (e.g. / or "")
         * which is a way of talking about a directory,
         * e.g. like "/." or ".".
         */
        if (cnp->cn_nameptr[0] == '\0') {
                if (dp->v_type != VDIR) {
                        error = ENOTDIR;
                        goto bad;
                }
                if (cnp->cn_nameiop != LOOKUP) {
                        error = EISDIR;
                        goto bad;
                }
                if (wantparent) {
                        ndp->ni_dvp = dp;
                        VREF(dp);
                }
                ndp->ni_vp = dp;
                if (!(cnp->cn_flags & (LOCKPARENT | LOCKLEAF)))
                        VOP_UNLOCK(dp, 0, p);
                if (cnp->cn_flags & SAVESTART)
                        panic("lookup: SAVESTART");
                return (0);
        }

        /*
         * Handle "..": two special cases.
         * 1. If at root directory (e.g. after chroot)
         *    or at absolute root directory
         *    then ignore it so can't get out.
         * 2. If this vnode is the root of a mounted
         *    filesystem, then replace it with the
         *    vnode which was mounted on so we take the
         *    .. in the other file system.
         */
        if (cnp->cn_flags & ISDOTDOT) {
                for (;;) {
                        if (dp == ndp->ni_rootdir || dp == rootvnode) {
                                ndp->ni_dvp = dp;
                                ndp->ni_vp = dp;
                                VREF(dp);
                                goto nextname;
                        }
                        if ((dp->v_flag & VROOT) == 0 ||
                            (cnp->cn_flags & NOCROSSMOUNT))
                                break;
                        if (dp->v_mount == NULL) {      /* forced umount */
                                error = EBADF;
                                goto bad;
                        }

                        tdp = dp;
                        dp = dp->v_mount->mnt_vnodecovered;
                        vput(tdp);
                        VREF(dp);
                        vn_lock(dp, LK_EXCLUSIVE | LK_RETRY, p);
                }
        }

        /*
         * We now have a segment name to search for, and a directory to search.
         */
unionlookup:
        ndp->ni_dvp = dp;
        ndp->ni_vp = NULL;
        if (error = VOP_LOOKUP(dp, &ndp->ni_vp, cnp)) {
#if DIAGNOSTIC
                if (ndp->ni_vp != NULL)
                        panic("leaf should be empty");
#endif
#ifdef NAMEI_DIAGNOSTIC
                printf("not found\n");
#endif
                if ((error == ENOENT) &&
                    (dp->v_flag & VROOT) && (dp->v_mount != NULL) &&
                    (dp->v_mount->mnt_flag & MNT_UNION)) {
                        tdp = dp;
                        dp = dp->v_mount->mnt_vnodecovered;
                        vput(tdp);
                        VREF(dp);
                        vn_lock(dp, LK_EXCLUSIVE | LK_RETRY, p);
                        goto unionlookup;
                }

                if (error != EJUSTRETURN)
                        goto bad;
                /*
                 * If creating and at end of pathname, then can consider
                 * allowing file to be created.
                 */
                if (rdonly) {
                        error = EROFS;
                        goto bad;
                }
                if (*cp == '\0' && trailing_slash &&
                        !(cnp->cn_flags & WILLBEDIR)) {
                        error = ENOENT;
                        goto bad;
                }
                /*
                 * We return with ni_vp NULL to indicate that the entry
                 * doesn't currently exist, leaving a pointer to the
                 * (possibly locked) directory inode in ndp->ni_dvp.
                 */
                if (cnp->cn_flags & SAVESTART) {
                        ndp->ni_startdir = ndp->ni_dvp;
                        VREF(ndp->ni_startdir);
                }
                if (kdebug_enable)
                        kdebug_lookup(ndp->ni_dvp, cnp);
                return (0);
        }
#ifdef NAMEI_DIAGNOSTIC
        printf("found\n");
#endif

        /*
         * Take into account any additional components consumed by
         * the underlying filesystem.
         */
        if (cnp->cn_consume > 0) {
                cnp->cn_nameptr += cnp->cn_consume;
                ndp->ni_next += cnp->cn_consume;
                ndp->ni_pathlen -= cnp->cn_consume;
                cnp->cn_consume = 0;
        }

        dp = ndp->ni_vp;
        /*
         * Check to see if the vnode has been mounted on;
         * if so find the root of the mounted file system.
         */
        while (dp->v_type == VDIR && (mp = dp->v_mountedhere) &&
               (cnp->cn_flags & NOCROSSMOUNT) == 0) {
                if (vfs_busy(mp, 0, 0, p))
                        continue;
                VOP_UNLOCK(dp, 0, p);
                error = VFS_ROOT(mp, &tdp);
                vfs_unbusy(mp, p);
                if (error) {
                        dp_unlocked = 1;                /* Signal error path 'dp' has already been unlocked */
                        goto bad2;
                };
                vrele(dp);
                ndp->ni_vp = dp = tdp;
        }

        /*
         * Check for symbolic link
         */
        if ((dp->v_type == VLNK) &&
            ((cnp->cn_flags & FOLLOW) || trailing_slash ||
                *ndp->ni_next == '/')) {
                cnp->cn_flags |= ISSYMLINK;
                return (0);
        }

        /*
         * Check for bogus trailing slashes.
         */
         if (trailing_slash && dp->v_type != VDIR) {
                error = ENOTDIR;
                goto bad2;
         }

nextname:
        /*
         * Not a symbolic link.  If more pathname,
         * continue at next component, else return.
         */
        if (*ndp->ni_next == '/') {
                cnp->cn_nameptr = ndp->ni_next;
                while (*cnp->cn_nameptr == '/') {
                        cnp->cn_nameptr++;
                        ndp->ni_pathlen--;
                }
                vrele(ndp->ni_dvp);
                goto dirloop;
        }
                                  
        /*
         * Disallow directory write attempts on read-only file systems.
         */
        if (rdonly &&
            (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
                error = EROFS;
                goto bad2;
        }
        if (cnp->cn_flags & SAVESTART) {
                ndp->ni_startdir = ndp->ni_dvp;
                VREF(ndp->ni_startdir);
        }
        if (!wantparent)
                vrele(ndp->ni_dvp);
        if ((cnp->cn_flags & LOCKLEAF) == 0)
                VOP_UNLOCK(dp, 0, p);
        if (kdebug_enable)
                kdebug_lookup(dp, cnp);
        return (0);

bad2:
        if ((cnp->cn_flags & LOCKPARENT) && *ndp->ni_next == '\0')
                VOP_UNLOCK(ndp->ni_dvp, 0, p);
        vrele(ndp->ni_dvp);
bad:
        if (dp_unlocked) {
                vrele(dp);
        } else {
                vput(dp);
        };
        ndp->ni_vp = NULL;
        if (kdebug_enable)
                kdebug_lookup(dp, cnp);
        return (error);
}

/*
 * relookup - lookup a path name component
 *    Used by lookup to re-aquire things.
 */
int
relookup(dvp, vpp, cnp)
        struct vnode *dvp, **vpp;
        struct componentname *cnp;
{
        struct proc *p = cnp->cn_proc;
        struct vnode *dp = 0;           /* the directory we are searching */
        int docache;                    /* == 0 do not cache last component */
        int wantparent;                 /* 1 => wantparent or lockparent flag */
        int rdonly;                     /* lookup read-only flag bit */
        int error = 0;
#ifdef NAMEI_DIAGNOSTIC
        int newhash;                    /* DEBUG: check name hash */
        char *cp;                       /* DEBUG: check name ptr/len */
#endif

        /*
         * Setup: break out flag bits into variables.
         */
        wantparent = cnp->cn_flags & (LOCKPARENT|WANTPARENT);
        docache = (cnp->cn_flags & NOCACHE) ^ NOCACHE;
        if (cnp->cn_nameiop == DELETE ||
            (wantparent && cnp->cn_nameiop != CREATE))
                docache = 0;
        rdonly = cnp->cn_flags & RDONLY;
        cnp->cn_flags &= ~ISSYMLINK;
        dp = dvp;
        vn_lock(dp, LK_EXCLUSIVE | LK_RETRY, p);

/* dirloop: */
        /*
         * Search a new directory.
         *
         * The cn_hash value is for use by vfs_cache.
         * The last component of the filename is left accessible via
         * cnp->cn_nameptr for callers that need the name. Callers needing
         * the name set the SAVENAME flag. When done, they assume
         * responsibility for freeing the pathname buffer.
         */
#ifdef NAMEI_DIAGNOSTIC
        for (newhash = 0, cp = cnp->cn_nameptr; *cp != 0 && *cp != '/'; cp++)
                newhash += (unsigned char)*cp;
        if (newhash != cnp->cn_hash)
                panic("relookup: bad hash");
        if (cnp->cn_namelen != cp - cnp->cn_nameptr)
                panic ("relookup: bad len");
        if (*cp != 0)
                panic("relookup: not last component");
        printf("{%s}: ", cnp->cn_nameptr);
#endif

        /*
         * Check for degenerate name (e.g. / or "")
         * which is a way of talking about a directory,
         * e.g. like "/." or ".".
         */
        if (cnp->cn_nameptr[0] == '\0') {
                if (cnp->cn_nameiop != LOOKUP || wantparent) {
                        error = EISDIR;
                        goto bad;
                }
                if (dp->v_type != VDIR) {
                        error = ENOTDIR;
                        goto bad;
                }
                if (!(cnp->cn_flags & LOCKLEAF))
                        VOP_UNLOCK(dp, 0, p);
                *vpp = dp;
                if (cnp->cn_flags & SAVESTART)
                        panic("lookup: SAVESTART");
                return (0);
        }

        if (cnp->cn_flags & ISDOTDOT)
                panic ("relookup: lookup on dot-dot");

        /*
         * We now have a segment name to search for, and a directory to search.
         */
        if (error = VOP_LOOKUP(dp, vpp, cnp)) {
#if DIAGNOSTIC
                if (*vpp != NULL)
                        panic("leaf should be empty");
#endif
                if (error != EJUSTRETURN)
                        goto bad;
                /*
                 * If creating and at end of pathname, then can consider
                 * allowing file to be created.
                 */
                if (rdonly) {
                        error = EROFS;
                        goto bad;
                }
                /* ASSERT(dvp == ndp->ni_startdir) */
                if (cnp->cn_flags & SAVESTART)
                        VREF(dvp);
                /*
                 * We return with ni_vp NULL to indicate that the entry
                 * doesn't currently exist, leaving a pointer to the
                 * (possibly locked) directory inode in ndp->ni_dvp.
                 */
                return (0);
        }
        dp = *vpp;

#if DIAGNOSTIC
        /*
         * Check for symbolic link
         */
        if (dp->v_type == VLNK && (cnp->cn_flags & FOLLOW))
                panic ("relookup: symlink found.\n");
#endif

        /*
         * Disallow directory write attempts on read-only file systems.
         */
        if (rdonly &&
            (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
                error = EROFS;
                goto bad2;
        }
        /* ASSERT(dvp == ndp->ni_startdir) */
        if (cnp->cn_flags & SAVESTART)
                VREF(dvp);
        
        if (!wantparent)
                vrele(dvp);
        if ((cnp->cn_flags & LOCKLEAF) == 0)
                VOP_UNLOCK(dp, 0, p);
        return (0);

bad2:
        if ((cnp->cn_flags & LOCKPARENT) && (cnp->cn_flags & ISLASTCN))
                VOP_UNLOCK(dvp, 0, p);
        vrele(dvp);
bad:
        vput(dp);
        *vpp = NULL;
        return (error);
}


#define NUMPARMS 23

kdebug_lookup(dp, cnp)
        struct vnode *dp;
        struct componentname *cnp;
{
        register int i, n;
        register int dbg_namelen;
        register int save_dbg_namelen;
        register char *dbg_nameptr;
        long dbg_parms[NUMPARMS];
        char dbg_buf[4];
        static char *dbg_filler = ">>>>";

        /* Collect the pathname for tracing */
        dbg_namelen = (cnp->cn_nameptr - cnp->cn_pnbuf) + cnp->cn_namelen;
        dbg_nameptr = cnp->cn_nameptr + cnp->cn_namelen;

        if (dbg_namelen > sizeof(dbg_parms))
            dbg_namelen = sizeof(dbg_parms);
        dbg_nameptr -= dbg_namelen;
        save_dbg_namelen = dbg_namelen;

        i = 0;

        while (dbg_namelen > 0) {
            if (dbg_namelen >= 4) {
                dbg_parms[i++] = *(long *)dbg_nameptr;
                dbg_nameptr += sizeof(long);
                dbg_namelen -= sizeof(long);
            } else {
                for (n = 0; n < dbg_namelen; n++)
                    dbg_buf[n] = *dbg_nameptr++;
                while (n <= 3) {
                    if (*dbg_nameptr)
                        dbg_buf[n++] = '>';
                    else
                        dbg_buf[n++] = 0;
                }
                dbg_parms[i++] = *(long *)&dbg_buf[0];

                break;
            }
        }
        while (i < NUMPARMS) {
            if (*dbg_nameptr)
                dbg_parms[i++] = *(long *)dbg_filler;
            else
                dbg_parms[i++] = 0;
        }

        /*
          In the event that we collect multiple, consecutive pathname
          entries, we must mark the start of the path's string.
        */
        KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_FSRW,36)) | DBG_FUNC_START,
                              dp, dbg_parms[0], dbg_parms[1], dbg_parms[2], 0);

        for (dbg_namelen = save_dbg_namelen-12, i=3;
             dbg_namelen > 0;
             dbg_namelen -=(4 * sizeof(long)), i+= 4)
          {
            KERNEL_DEBUG_CONSTANT((FSDBG_CODE(DBG_FSRW,36)) | DBG_FUNC_NONE,
                                  dbg_parms[i], dbg_parms[i+1], dbg_parms[i+2], dbg_parms[i+3], 0);
          }
}