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

/*
 * Copyright (c) 2000-2015 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The 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, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_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
 */
/*
 * NOTICE: This file was modified by SPARTA, Inc. in 2005 to introduce
 * support for mandatory and extensible security protections.  This notice
 * is included in support of clause 2.2 (b) of the Apple Public License,
 * Version 2.0.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/syslimits.h>
#include <sys/time.h>
#include <sys/namei.h>
#include <sys/vm.h>
#include <sys/vnode_internal.h>
#include <sys/mount_internal.h>
#include <sys/errno.h>
#include <sys/malloc.h>
#include <sys/filedesc.h>
#include <sys/proc_internal.h>
#include <sys/kdebug.h>
#include <sys/unistd.h>         /* For _PC_NAME_MAX */
#include <sys/uio_internal.h>
#include <sys/kauth.h>
#include <kern/kalloc.h>
#include <security/audit/audit.h>
#include <sys/dtrace.h>        /* to get the prototype for strstr() in sys/dtrace_glue.h */
#if CONFIG_MACF
#include <security/mac_framework.h>
#endif

#if NAMEDRSRCFORK
#include <sys/xattr.h>
#endif
/*
 * The minimum volfs-style pathname is 9.
 * Example:  "/.vol/1/2"
 */
#define VOLFS_MIN_PATH_LEN  9


#if CONFIG_VOLFS
static int vfs_getrealpath(const char * path, char * realpath, size_t bufsize, vfs_context_t ctx);
#define MAX_VOLFS_RESTARTS 5
#endif

static int              lookup_traverse_mountpoints(struct nameidata *ndp, struct componentname *cnp, vnode_t dp, int vbusyflags, vfs_context_t ctx);
static int              lookup_handle_symlink(struct nameidata *ndp, vnode_t *new_dp, vfs_context_t ctx);
static int              lookup_authorize_search(vnode_t dp, struct componentname *cnp, int dp_authorized_in_cache, vfs_context_t ctx);
static void             lookup_consider_update_cache(vnode_t dvp, vnode_t vp, struct componentname *cnp, int nc_generation);
static int              lookup_handle_found_vnode(struct nameidata *ndp, struct componentname *cnp, int rdonly,
    int vbusyflags, int *keep_going, int nc_generation,
    int wantparent, int atroot, vfs_context_t ctx);
static int              lookup_handle_emptyname(struct nameidata *ndp, struct componentname *cnp, int wantparent);

#if NAMEDRSRCFORK
static int              lookup_handle_rsrc_fork(vnode_t dp, struct nameidata *ndp, struct componentname *cnp, int wantparent, vfs_context_t ctx);
#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
 *      }
 *
 * Returns:     0                       Success
 *              ENOENT                  No such file or directory
 *              ELOOP                   Too many levels of symbolic links
 *              ENAMETOOLONG            Filename too long
 *              copyinstr:EFAULT        Bad address
 *              copyinstr:ENAMETOOLONG  Filename too long
 *              lookup:EBADF            Bad file descriptor
 *              lookup:EROFS
 *              lookup:EACCES
 *              lookup:EPERM
 *              lookup:ERECYCLE  vnode was recycled from underneath us in lookup.
 *                                               This means we should re-drive lookup from this point.
 *              lookup: ???
 *              VNOP_READLINK:???
 */
int
namei(struct nameidata *ndp)
{
        struct filedesc *fdp;   /* pointer to file descriptor state */
        struct vnode *dp;       /* the directory we are searching */
        struct vnode *usedvp = ndp->ni_dvp;  /* store pointer to vp in case we must loop due to
                                              *                                          heavy vnode pressure */
        u_long cnpflags = ndp->ni_cnd.cn_flags; /* store in case we have to restore after loop */
        int error;
        struct componentname *cnp = &ndp->ni_cnd;
        vfs_context_t ctx = cnp->cn_context;
        proc_t p = vfs_context_proc(ctx);
#if CONFIG_AUDIT
/* XXX ut should be from context */
        uthread_t ut = (struct uthread *)get_bsdthread_info(current_thread());
#endif

#if CONFIG_VOLFS
        int volfs_restarts = 0;
#endif
        size_t bytes_copied = 0;

        fdp = p->p_fd;

#if DIAGNOSTIC
        if (!vfs_context_ucred(ctx) || !p) {
                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

        /*
         * A compound VNOP found something that needs further processing:
         * either a trigger vnode, a covered directory, or a symlink.
         */
        if (ndp->ni_flag & NAMEI_CONTLOOKUP) {
                int rdonly, vbusyflags, keep_going, wantparent;

                rdonly = cnp->cn_flags & RDONLY;
                vbusyflags = ((cnp->cn_flags & CN_NBMOUNTLOOK) != 0) ? LK_NOWAIT : 0;
                keep_going = 0;
                wantparent = cnp->cn_flags & (LOCKPARENT | WANTPARENT);

                ndp->ni_flag &= ~(NAMEI_CONTLOOKUP);

                error = lookup_handle_found_vnode(ndp, &ndp->ni_cnd, rdonly, vbusyflags,
                    &keep_going, ndp->ni_ncgeneration, wantparent, 0, ctx);
                if (error) {
                        goto out_drop;
                }
                if (keep_going) {
                        if ((cnp->cn_flags & ISSYMLINK) == 0) {
                                panic("We need to keep going on a continued lookup, but for vp type %d (tag %d)\n", ndp->ni_vp->v_type, ndp->ni_vp->v_tag);
                        }
                        goto continue_symlink;
                }

                return 0;
        }

vnode_recycled:

        /*
         * Get a buffer for the name to be translated, and copy the
         * name into the buffer.
         */
        if ((cnp->cn_flags & HASBUF) == 0) {
                cnp->cn_pnbuf = ndp->ni_pathbuf;
                cnp->cn_pnlen = PATHBUFLEN;
        }
#if LP64_DEBUG
        if ((UIO_SEG_IS_USER_SPACE(ndp->ni_segflg) == 0)
            && (ndp->ni_segflg != UIO_SYSSPACE)
            && (ndp->ni_segflg != UIO_SYSSPACE32)) {
                panic("%s :%d - invalid ni_segflg\n", __FILE__, __LINE__);
        }
#endif /* LP64_DEBUG */

retry_copy:
        if (UIO_SEG_IS_USER_SPACE(ndp->ni_segflg)) {
                error = copyinstr(ndp->ni_dirp, cnp->cn_pnbuf,
                    cnp->cn_pnlen, &bytes_copied);
        } else {
                error = copystr(CAST_DOWN(void *, ndp->ni_dirp), cnp->cn_pnbuf,
                    cnp->cn_pnlen, &bytes_copied);
        }
        if (error == ENAMETOOLONG && !(cnp->cn_flags & HASBUF)) {
                MALLOC_ZONE(cnp->cn_pnbuf, caddr_t, MAXPATHLEN, M_NAMEI, M_WAITOK);
                if (cnp->cn_pnbuf == NULL) {
                        error = ENOMEM;
                        goto error_out;
                }

                cnp->cn_flags |= HASBUF;
                cnp->cn_pnlen = MAXPATHLEN;
                bytes_copied = 0;

                goto retry_copy;
        }
        if (error) {
                goto error_out;
        }
        ndp->ni_pathlen = bytes_copied;
        bytes_copied = 0;

        /*
         * Since the name cache may contain positive entries of
         * the incorrect case, force lookup() to bypass the cache
         * and call directly into the filesystem for each path
         * component. Note: the FS may still consult the cache,
         * but can apply rules to validate the results.
         */
        if (proc_is_forcing_hfs_case_sensitivity(p)) {
                cnp->cn_flags |= CN_SKIPNAMECACHE;
        }

#if CONFIG_VOLFS
        /*
         * Check for legacy volfs style pathnames.
         *
         * For compatibility reasons we currently allow these paths,
         * but future versions of the OS may not support them.
         */
        if (ndp->ni_pathlen >= VOLFS_MIN_PATH_LEN &&
            cnp->cn_pnbuf[0] == '/' &&
            cnp->cn_pnbuf[1] == '.' &&
            cnp->cn_pnbuf[2] == 'v' &&
            cnp->cn_pnbuf[3] == 'o' &&
            cnp->cn_pnbuf[4] == 'l' &&
            cnp->cn_pnbuf[5] == '/') {
                char * realpath;
                int realpath_err;
                /* Attempt to resolve a legacy volfs style pathname. */
                MALLOC_ZONE(realpath, caddr_t, MAXPATHLEN, M_NAMEI, M_WAITOK);
                if (realpath) {
                        /*
                         * We only error out on the ENAMETOOLONG cases where we know that
                         * vfs_getrealpath translation succeeded but the path could not fit into
                         * MAXPATHLEN characters.  In other failure cases, we may be dealing with a path
                         * that legitimately looks like /.vol/1234/567 and is not meant to be translated
                         */
                        if ((realpath_err = vfs_getrealpath(&cnp->cn_pnbuf[6], realpath, MAXPATHLEN, ctx))) {
                                FREE_ZONE(realpath, MAXPATHLEN, M_NAMEI);
                                if (realpath_err == ENOSPC || realpath_err == ENAMETOOLONG) {
                                        error = ENAMETOOLONG;
                                        goto error_out;
                                }
                        } else {
                                if (cnp->cn_flags & HASBUF) {
                                        FREE_ZONE(cnp->cn_pnbuf, cnp->cn_pnlen, M_NAMEI);
                                }
                                cnp->cn_pnbuf = realpath;
                                cnp->cn_pnlen = MAXPATHLEN;
                                ndp->ni_pathlen = strlen(realpath) + 1;
                                cnp->cn_flags |= HASBUF | CN_VOLFSPATH;
                        }
                }
        }
#endif /* CONFIG_VOLFS */

#if CONFIG_AUDIT
        /* If we are auditing the kernel pathname, save the user pathname */
        if (cnp->cn_flags & AUDITVNPATH1) {
                AUDIT_ARG(upath, ut->uu_cdir, cnp->cn_pnbuf, ARG_UPATH1);
        }
        if (cnp->cn_flags & AUDITVNPATH2) {
                AUDIT_ARG(upath, ut->uu_cdir, cnp->cn_pnbuf, ARG_UPATH2);
        }
#endif /* CONFIG_AUDIT */

        /*
         * Do not allow empty pathnames
         */
        if (*cnp->cn_pnbuf == '\0') {
                error = ENOENT;
                goto error_out;
        }
        ndp->ni_loopcnt = 0;

        /*
         * determine the starting point for the translation.
         */
        if ((ndp->ni_rootdir = fdp->fd_rdir) == NULLVP) {
                if (!(fdp->fd_flags & FD_CHROOT)) {
                        ndp->ni_rootdir = rootvnode;
                }
        }
        cnp->cn_nameptr = cnp->cn_pnbuf;

        ndp->ni_usedvp = NULLVP;

        if (*(cnp->cn_nameptr) == '/') {
                while (*(cnp->cn_nameptr) == '/') {
                        cnp->cn_nameptr++;
                        ndp->ni_pathlen--;
                }
                dp = ndp->ni_rootdir;
        } else if (cnp->cn_flags & USEDVP) {
                dp = ndp->ni_dvp;
                ndp->ni_usedvp = dp;
        } else {
                dp = vfs_context_cwd(ctx);
        }

        if (dp == NULLVP || (dp->v_lflag & VL_DEAD)) {
                error = ENOENT;
                goto error_out;
        }
        ndp->ni_dvp = NULLVP;
        ndp->ni_vp  = NULLVP;

        for (;;) {
#if CONFIG_MACF
                /*
                 * Give MACF policies a chance to reject the lookup
                 * before performing any filesystem operations.
                 * This hook is called before resolving the path and
                 * again each time a symlink is encountered.
                 * NB: policies receive path information as supplied
                 *     by the caller and thus cannot be trusted.
                 */
                error = mac_vnode_check_lookup_preflight(ctx, dp, cnp->cn_nameptr, cnp->cn_namelen);
                if (error) {
                        goto error_out;
                }
#endif

                ndp->ni_startdir = dp;

                if ((error = lookup(ndp))) {
                        goto error_out;
                }

                /*
                 * Check for symbolic link
                 */
                if ((cnp->cn_flags & ISSYMLINK) == 0) {
                        return 0;
                }

continue_symlink:
                /* Gives us a new path to process, and a starting dir */
                error = lookup_handle_symlink(ndp, &dp, ctx);
                if (error != 0) {
                        break;
                }
        }
        /*
         * only come here if we fail to handle a SYMLINK...
         * if either ni_dvp or ni_vp is non-NULL, then
         * we need to drop the iocount that was picked
         * up in the lookup routine
         */
out_drop:
        if (ndp->ni_dvp) {
                vnode_put(ndp->ni_dvp);
        }
        if (ndp->ni_vp) {
                vnode_put(ndp->ni_vp);
        }
error_out:
        if ((cnp->cn_flags & HASBUF)) {
                cnp->cn_flags &= ~HASBUF;
                FREE_ZONE(cnp->cn_pnbuf, cnp->cn_pnlen, M_NAMEI);
        }
        cnp->cn_pnbuf = NULL;
        ndp->ni_vp = NULLVP;
        ndp->ni_dvp = NULLVP;

#if CONFIG_VOLFS
        /*
         * Deal with volfs fallout.
         *
         * At this point, if we were originally given a volfs path that
         * looks like /.vol/123/456, then we would have had to convert it into
         * a full path.  Assuming that part worked properly, we will now attempt
         * to conduct a lookup of the item in the namespace.  Under normal
         * circumstances, if a user looked up /tmp/foo and it was not there, it
         * would be permissible to return ENOENT.
         *
         * However, we may not want to do that here.  Specifically, the volfs path
         * uniquely identifies a certain item in the namespace regardless of where it
         * lives.  If the item has moved in between the time we constructed the
         * path and now, when we're trying to do a lookup/authorization on the full
         * path, we may have gotten an ENOENT.
         *
         * At this point we can no longer tell if the path no longer exists
         * or if the item in question no longer exists. It could have been renamed
         * away, in which case the /.vol identifier is still valid.
         *
         * Do this dance a maximum of MAX_VOLFS_RESTARTS times.
         */
        if ((error == ENOENT) && (ndp->ni_cnd.cn_flags & CN_VOLFSPATH)) {
                if (volfs_restarts < MAX_VOLFS_RESTARTS) {
                        volfs_restarts++;
                        goto vnode_recycled;
                }
        }
#endif

        if (error == ERECYCLE) {
                /* vnode was recycled underneath us. re-drive lookup to start at
                 *  the beginning again, since recycling invalidated last lookup*/
                ndp->ni_cnd.cn_flags = cnpflags;
                ndp->ni_dvp = usedvp;
                goto vnode_recycled;
        }


        return error;
}

int
namei_compound_available(vnode_t dp, struct nameidata *ndp)
{
        if ((ndp->ni_flag & NAMEI_COMPOUNDOPEN) != 0) {
                return vnode_compound_open_available(dp);
        }

        return 0;
}

static int
lookup_authorize_search(vnode_t dp, struct componentname *cnp, int dp_authorized_in_cache, vfs_context_t ctx)
{
#if !CONFIG_MACF
#pragma unused(cnp)
#endif

        int error;

        if (!dp_authorized_in_cache) {
                error = vnode_authorize(dp, NULL, KAUTH_VNODE_SEARCH, ctx);
                if (error) {
                        return error;
                }
        }
#if CONFIG_MACF
        error = mac_vnode_check_lookup(ctx, dp, cnp);
        if (error) {
                return error;
        }
#endif /* CONFIG_MACF */

        return 0;
}

static void
lookup_consider_update_cache(vnode_t dvp, vnode_t vp, struct componentname *cnp, int nc_generation)
{
        int isdot_or_dotdot;
        isdot_or_dotdot = (cnp->cn_namelen == 1 && cnp->cn_nameptr[0] == '.') || (cnp->cn_flags & ISDOTDOT);

        if (vp->v_name == NULL || vp->v_parent == NULLVP) {
                int  update_flags = 0;

                if (isdot_or_dotdot == 0) {
                        if (vp->v_name == NULL) {
                                update_flags |= VNODE_UPDATE_NAME;
                        }
                        if (dvp != NULLVP && vp->v_parent == NULLVP) {
                                update_flags |= VNODE_UPDATE_PARENT;
                        }

                        if (update_flags) {
                                vnode_update_identity(vp, dvp, cnp->cn_nameptr, cnp->cn_namelen, cnp->cn_hash, update_flags);
                        }
                }
        }
        if ((cnp->cn_flags & MAKEENTRY) && (vp->v_flag & VNCACHEABLE) && LIST_FIRST(&vp->v_nclinks) == NULL) {
                /*
                 * missing from name cache, but should
                 * be in it... this can happen if volfs
                 * causes the vnode to be created or the
                 * name cache entry got recycled but the
                 * vnode didn't...
                 * check to make sure that ni_dvp is valid
                 * cache_lookup_path may return a NULL
                 * do a quick check to see if the generation of the
                 * directory matches our snapshot... this will get
                 * rechecked behind the name cache lock, but if it
                 * already fails to match, no need to go any further
                 */
                if (dvp != NULLVP && (nc_generation == dvp->v_nc_generation) && (!isdot_or_dotdot)) {
                        cache_enter_with_gen(dvp, vp, cnp, nc_generation);
                }
        }
}

#if NAMEDRSRCFORK
/*
 * Can change ni_dvp and ni_vp.  On success, returns with iocounts on stream vnode (always) and
 * data fork if requested.  On failure, returns with iocount data fork (always) and its parent directory
 * (if one was provided).
 */
static int
lookup_handle_rsrc_fork(vnode_t dp, struct nameidata *ndp, struct componentname *cnp, int wantparent, vfs_context_t ctx)
{
        vnode_t svp = NULLVP;
        enum nsoperation nsop;
        int nsflags;
        int error;

        if (dp->v_type != VREG) {
                error = ENOENT;
                goto out;
        }
        switch (cnp->cn_nameiop) {
        case DELETE:
                if (cnp->cn_flags & CN_ALLOWRSRCFORK) {
                        nsop = NS_DELETE;
                } else {
                        error = EPERM;
                        goto out;
                }
                break;
        case CREATE:
                if (cnp->cn_flags & CN_ALLOWRSRCFORK) {
                        nsop = NS_CREATE;
                } else {
                        error = EPERM;
                        goto out;
                }
                break;
        case LOOKUP:
                /* Make sure our lookup of "/..namedfork/rsrc" is allowed. */
                if (cnp->cn_flags & CN_ALLOWRSRCFORK) {
                        nsop = NS_OPEN;
                } else {
                        error = EPERM;
                        goto out;
                }
                break;
        default:
                error = EPERM;
                goto out;
        }

        nsflags = 0;
        if (cnp->cn_flags & CN_RAW_ENCRYPTED) {
                nsflags |= NS_GETRAWENCRYPTED;
        }

        /* Ask the file system for the resource fork. */
        error = vnode_getnamedstream(dp, &svp, XATTR_RESOURCEFORK_NAME, nsop, nsflags, ctx);

        /* During a create, it OK for stream vnode to be missing. */
        if (error == ENOATTR || error == ENOENT) {
                error = (nsop == NS_CREATE) ? 0 : ENOENT;
        }
        if (error) {
                goto out;
        }
        /* The "parent" of the stream is the file. */
        if (wantparent) {
                if (ndp->ni_dvp) {
                        vnode_put(ndp->ni_dvp);
                }
                ndp->ni_dvp = dp;
        } else {
                vnode_put(dp);
        }
        ndp->ni_vp = svp;  /* on create this may be null */

        /* Restore the truncated pathname buffer (for audits). */
        if (ndp->ni_pathlen == 1 && ndp->ni_next[0] == '\0') {
                ndp->ni_next[0] = '/';
        }
        cnp->cn_flags  &= ~MAKEENTRY;

        return 0;
out:
        return error;
}
#endif /* NAMEDRSRCFORK */

/*
 * iocounts in:
 *      --One on ni_vp.  One on ni_dvp if there is more path, or we didn't come through the
 *      cache, or we came through the cache and the caller doesn't want the parent.
 *
 * iocounts out:
 *      --Leaves us in the correct state for the next step, whatever that might be.
 *      --If we find a symlink, returns with iocounts on both ni_vp and ni_dvp.
 *      --If we are to look up another component, then we have an iocount on ni_vp and
 *      nothing else.
 *      --If we are done, returns an iocount on ni_vp, and possibly on ni_dvp depending on nameidata flags.
 *      --In the event of an error, may return with ni_dvp NULL'ed out (in which case, iocount
 *      was dropped).
 */
static int
lookup_handle_found_vnode(struct nameidata *ndp, struct componentname *cnp, int rdonly,
    int vbusyflags, int *keep_going, int nc_generation,
    int wantparent, int atroot, vfs_context_t ctx)
{
        vnode_t dp;
        int error;
        char *cp;

        dp = ndp->ni_vp;
        *keep_going = 0;

        if (ndp->ni_vp == NULLVP) {
                panic("NULL ni_vp in %s\n", __FUNCTION__);
        }

        if (atroot) {
                goto nextname;
        }

        /*
         * 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;
        } else {
                lookup_consider_update_cache(ndp->ni_dvp, dp, cnp, nc_generation);
        }

        /*
         * Check to see if the vnode has been mounted on...
         * if so find the root of the mounted file system.
         * Updates ndp->ni_vp.
         */
        error = lookup_traverse_mountpoints(ndp, cnp, dp, vbusyflags, ctx);
        dp = ndp->ni_vp;
        if (error) {
                goto out;
        }

#if CONFIG_MACF
        if (vfs_flags(vnode_mount(dp)) & MNT_MULTILABEL) {
                error = vnode_label(vnode_mount(dp), NULL, dp, NULL, 0, ctx);
                if (error) {
                        goto out;
                }
        }
#endif

        /*
         * Check for symbolic link
         */
        if ((dp->v_type == VLNK) &&
            ((cnp->cn_flags & FOLLOW) || (ndp->ni_flag & NAMEI_TRAILINGSLASH) || *ndp->ni_next == '/')) {
                cnp->cn_flags |= ISSYMLINK;
                *keep_going = 1;
                return 0;
        }

        /*
         * Check for bogus trailing slashes.
         */
        if ((ndp->ni_flag & NAMEI_TRAILINGSLASH)) {
                if (dp->v_type != VDIR) {
                        error = ENOTDIR;
                        goto out;
                }
                ndp->ni_flag &= ~(NAMEI_TRAILINGSLASH);
        }

#if NAMEDSTREAMS
        /*
         * Deny namei/lookup requests to resolve paths that point to shadow files.
         * Access to shadow files must be conducted by explicit calls to VNOP_LOOKUP
         * directly, and not use lookup/namei
         */
        if (vnode_isshadow(dp)) {
                error = ENOENT;
                goto out;
        }
#endif

nextname:
        /*
         * Not a symbolic link.  If more pathname,
         * continue at next component, else return.
         *
         * Definitely have a dvp if there's another slash
         */
        if (*ndp->ni_next == '/') {
                cnp->cn_nameptr = ndp->ni_next + 1;
                ndp->ni_pathlen--;
                while (*cnp->cn_nameptr == '/') {
                        cnp->cn_nameptr++;
                        ndp->ni_pathlen--;
                }

                cp = cnp->cn_nameptr;
                vnode_put(ndp->ni_dvp);
                ndp->ni_dvp = NULLVP;

                if (*cp == '\0') {
                        goto emptyname;
                }

                *keep_going = 1;
                return 0;
        }

        /*
         * Disallow directory write attempts on read-only file systems.
         */
        if (rdonly &&
            (cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME)) {
                error = EROFS;
                goto out;
        }

        /* If SAVESTART is set, we should have a dvp */
        if (cnp->cn_flags & SAVESTART) {
                /*
                 * note that we already hold a reference
                 * on both dp and ni_dvp, but for some reason
                 * can't get another one... in this case we
                 * need to do vnode_put on dp in 'bad2'
                 */
                if ((vnode_get(ndp->ni_dvp))) {
                        error = ENOENT;
                        goto out;
                }
                ndp->ni_startdir = ndp->ni_dvp;
        }
        if (!wantparent && ndp->ni_dvp) {
                vnode_put(ndp->ni_dvp);
                ndp->ni_dvp = NULLVP;
        }

        if (cnp->cn_flags & AUDITVNPATH1) {
                AUDIT_ARG(vnpath, dp, ARG_VNODE1);
        } else if (cnp->cn_flags & AUDITVNPATH2) {
                AUDIT_ARG(vnpath, dp, ARG_VNODE2);
        }

#if NAMEDRSRCFORK
        /*
         * Caller wants the resource fork.
         */
        if ((cnp->cn_flags & CN_WANTSRSRCFORK) && (dp != NULLVP)) {
                error = lookup_handle_rsrc_fork(dp, ndp, cnp, wantparent, ctx);
                if (error != 0) {
                        goto out;
                }

                dp = ndp->ni_vp;
        }
#endif
        if (kdebug_enable) {
                kdebug_lookup(ndp->ni_vp, cnp);
        }

        return 0;

emptyname:
        error = lookup_handle_emptyname(ndp, cnp, wantparent);
        if (error != 0) {
                goto out;
        }

        return 0;
out:
        return error;
}

/*
 * Comes in iocount on ni_vp.  May overwrite ni_dvp, but doesn't interpret incoming value.
 */
static int
lookup_handle_emptyname(struct nameidata *ndp, struct componentname *cnp, int wantparent)
{
        vnode_t dp;
        int error = 0;

        dp = ndp->ni_vp;
        cnp->cn_namelen = 0;
        /*
         * A degenerate name (e.g. / or "") which is a way of
         * talking about a directory, e.g. like "/." or ".".
         */
        if (dp->v_type != VDIR) {
                error = ENOTDIR;
                goto out;
        }
        if (cnp->cn_nameiop != LOOKUP) {
                error = EISDIR;
                goto out;
        }
        if (wantparent) {
                /*
                 * note that we already hold a reference
                 * on dp, but for some reason can't
                 * get another one... in this case we
                 * need to do vnode_put on dp in 'bad'
                 */
                if ((vnode_get(dp))) {
                        error = ENOENT;
                        goto out;
                }
                ndp->ni_dvp = dp;
        }
        cnp->cn_flags &= ~ISDOTDOT;
        cnp->cn_flags |= ISLASTCN;
        ndp->ni_next = cnp->cn_nameptr;
        ndp->ni_vp = dp;

        if (cnp->cn_flags & AUDITVNPATH1) {
                AUDIT_ARG(vnpath, dp, ARG_VNODE1);
        } else if (cnp->cn_flags & AUDITVNPATH2) {
                AUDIT_ARG(vnpath, dp, ARG_VNODE2);
        }
        if (cnp->cn_flags & SAVESTART) {
                panic("lookup: SAVESTART");
        }

        return 0;
out:
        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 VNOP_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
 *
 * Returns:     0                       Success
 *              ENOENT                  No such file or directory
 *              EBADF                   Bad file descriptor
 *              ENOTDIR                 Not a directory
 *              EROFS                   Read-only file system [CREATE]
 *              EISDIR                  Is a directory [CREATE]
 *              cache_lookup_path:ERECYCLE  (vnode was recycled from underneath us, redrive lookup again)
 *              vnode_authorize:EROFS
 *              vnode_authorize:EACCES
 *              vnode_authorize:EPERM
 *              vnode_authorize:???
 *              VNOP_LOOKUP:ENOENT      No such file or directory
 *              VNOP_LOOKUP:EJUSTRETURN Restart system call (INTERNAL)
 *              VNOP_LOOKUP:???
 *              VFS_ROOT:ENOTSUP
 *              VFS_ROOT:ENOENT
 *              VFS_ROOT:???
 */
int
lookup(struct nameidata *ndp)
{
        char    *cp;            /* pointer into pathname argument */
        vnode_t         tdp;            /* saved dp */
        vnode_t         dp;             /* the directory we are searching */
        int docache = 1;                /* == 0 do not cache last component */
        int wantparent;                 /* 1 => wantparent or lockparent flag */
        int rdonly;                     /* lookup read-only flag bit */
        int dp_authorized = 0;
        int error = 0;
        struct componentname *cnp = &ndp->ni_cnd;
        vfs_context_t ctx = cnp->cn_context;
        int vbusyflags = 0;
        int nc_generation = 0;
        vnode_t last_dp = NULLVP;
        int keep_going;
        int atroot;

        /*
         * Setup: break out flag bits into variables.
         */
        if (cnp->cn_flags & NOCACHE) {
                docache = 0;
        }
        wantparent = cnp->cn_flags & (LOCKPARENT | WANTPARENT);
        rdonly = cnp->cn_flags & RDONLY;
        cnp->cn_flags &= ~ISSYMLINK;
        cnp->cn_consume = 0;

        dp = ndp->ni_startdir;
        ndp->ni_startdir = NULLVP;

        if ((cnp->cn_flags & CN_NBMOUNTLOOK) != 0) {
                vbusyflags = LK_NOWAIT;
        }
        cp = cnp->cn_nameptr;

        if (*cp == '\0') {
                if ((vnode_getwithref(dp))) {
                        dp = NULLVP;
                        error = ENOENT;
                        goto bad;
                }
                ndp->ni_vp = dp;
                error = lookup_handle_emptyname(ndp, cnp, wantparent);
                if (error) {
                        goto bad;
                }

                return 0;
        }
dirloop:
        atroot = 0;
        ndp->ni_vp = NULLVP;

        if ((error = cache_lookup_path(ndp, cnp, dp, ctx, &dp_authorized, last_dp))) {
                dp = NULLVP;
                goto bad;
        }
        if ((cnp->cn_flags & ISLASTCN)) {
                if (docache) {
                        cnp->cn_flags |= MAKEENTRY;
                }
        } else {
                cnp->cn_flags |= MAKEENTRY;
        }

        dp = ndp->ni_dvp;

        if (ndp->ni_vp != NULLVP) {
                /*
                 * cache_lookup_path returned a non-NULL ni_vp then,
                 * we're guaranteed that the dp is a VDIR, it's
                 * been authorized, and vp is not ".."
                 *
                 * make sure we don't try to enter the name back into
                 * the cache if this vp is purged before we get to that
                 * check since we won't have serialized behind whatever
                 * activity is occurring in the FS that caused the purge
                 */
                if (dp != NULLVP) {
                        nc_generation = dp->v_nc_generation - 1;
                }

                goto returned_from_lookup_path;
        }

        /*
         * 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)) {
                /*
                 * if this is a chroot'ed process, check if the current
                 * directory is still a subdirectory of the process's
                 * root directory.
                 */
                if (ndp->ni_rootdir && (ndp->ni_rootdir != rootvnode) &&
                    dp != ndp->ni_rootdir) {
                        int sdir_error;
                        int is_subdir = FALSE;

                        sdir_error = vnode_issubdir(dp, ndp->ni_rootdir,
                            &is_subdir, vfs_context_kernel());

                        /*
                         * If we couldn't determine if dp is a subdirectory of
                         * ndp->ni_rootdir (sdir_error != 0), we let the request
                         * proceed.
                         */
                        if (!sdir_error && !is_subdir) {
                                vnode_put(dp);
                                dp = ndp->ni_rootdir;
                                /*
                                 * There's a ref on the process's root directory
                                 * but we can't use vnode_getwithref here as
                                 * there is nothing preventing that ref being
                                 * released by another thread.
                                 */
                                if (vnode_get(dp)) {
                                        error = ENOENT;
                                        goto bad;
                                }
                        }
                }

                for (;;) {
                        if (dp == ndp->ni_rootdir || dp == rootvnode) {
                                ndp->ni_dvp = dp;
                                ndp->ni_vp = dp;
                                /*
                                 * we're pinned at the root
                                 * we've already got one reference on 'dp'
                                 * courtesy of cache_lookup_path... take
                                 * another one for the ".."
                                 * if we fail to get the new reference, we'll
                                 * drop our original down in 'bad'
                                 */
                                if ((vnode_get(dp))) {
                                        error = ENOENT;
                                        goto bad;
                                }
                                atroot = 1;
                                goto returned_from_lookup_path;
                        }
                        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 = tdp->v_mount->mnt_vnodecovered;

                        vnode_put(tdp);

                        if ((vnode_getwithref(dp))) {
                                dp = NULLVP;
                                error = ENOENT;
                                goto bad;
                        }
                        ndp->ni_dvp = dp;
                        dp_authorized = 0;
                }
        }

        /*
         * We now have a segment name to search for, and a directory to search.
         */
unionlookup:
        ndp->ni_vp = NULLVP;

        if (dp->v_type != VDIR) {
                error = ENOTDIR;
                goto lookup_error;
        }
        if ((cnp->cn_flags & DONOTAUTH) != DONOTAUTH) {
                error = lookup_authorize_search(dp, cnp, dp_authorized, ctx);
                if (error) {
                        goto lookup_error;
                }
        }

        /*
         * Now that we've authorized a lookup, can bail out if the filesystem
         * will be doing a batched operation.  Return an iocount on dvp.
         */
#if NAMEDRSRCFORK
        if ((cnp->cn_flags & ISLASTCN) && namei_compound_available(dp, ndp) && !(cnp->cn_flags & CN_WANTSRSRCFORK)) {
#else
        if ((cnp->cn_flags & ISLASTCN) && namei_compound_available(dp, ndp)) {
#endif /* NAMEDRSRCFORK */
                ndp->ni_flag |= NAMEI_UNFINISHED;
                ndp->ni_ncgeneration = dp->v_nc_generation;
                return 0;
        }

        nc_generation = dp->v_nc_generation;

        /*
         * Note:
         * Filesystems that support hardlinks may want to call vnode_update_identity
         * if the lookup operation below will modify the in-core vnode to belong to a new point
         * in the namespace.  VFS cannot infer whether or not the look up operation makes the vnode
         * name change or change parents.  Without this, the lookup may make update
         * filesystem-specific in-core metadata but fail to update the v_parent or v_name
         * fields in the vnode.  If VFS were to do this, it would be necessary to call
         * vnode_update_identity on every lookup operation -- expensive!
         *
         * However, even with this in place, multiple lookups may occur in between this lookup
         * and the subsequent vnop, so, at best, we could only guarantee that you would get a
         * valid path back, and not necessarily the one that you wanted.
         *
         * Example:
         * /tmp/a == /foo/b
         *
         * If you are now looking up /foo/b and the vnode for this link represents /tmp/a,
         * vnode_update_identity will fix the parentage so that you can get /foo/b back
         * through the v_parent chain (preventing you from getting /tmp/b back). It would
         * not fix whether or not you should or should not get /tmp/a vs. /foo/b.
         */

        error = VNOP_LOOKUP(dp, &ndp->ni_vp, cnp, ctx);

        if (error) {
lookup_error:
                if ((error == ENOENT) &&
                    (dp->v_mount != NULL) &&
                    (dp->v_mount->mnt_flag & MNT_UNION)) {
                        tdp = dp;
                        error = lookup_traverse_union(tdp, &dp, ctx);
                        vnode_put(tdp);
                        if (error) {
                                dp = NULLVP;
                                goto bad;
                        }

                        ndp->ni_dvp = dp;
                        dp_authorized = 0;
                        goto unionlookup;
                }

                if (error != EJUSTRETURN) {
                        goto bad;
                }

                if (ndp->ni_vp != NULLVP) {
                        panic("leaf should be empty");
                }

#if NAMEDRSRCFORK
                /*
                 * At this point, error should be EJUSTRETURN.
                 *
                 * If CN_WANTSRSRCFORK is set, that implies that the
                 * underlying filesystem could not find the "parent" of the
                 * resource fork (the data fork), and we are doing a lookup
                 * for a CREATE event.
                 *
                 * However, this should be converted to an error, as the
                 * failure to find this parent should disallow further
                 * progress to try and acquire a resource fork vnode.
                 */
                if (cnp->cn_flags & CN_WANTSRSRCFORK) {
                        error = ENOENT;
                        goto bad;
                }
#endif

                error = lookup_validate_creation_path(ndp);
                if (error) {
                        goto bad;
                }
                /*
                 * We return with ni_vp NULL to indicate that the entry
                 * doesn't currently exist, leaving a pointer to the
                 * referenced directory vnode in ndp->ni_dvp.
                 */
                if (cnp->cn_flags & SAVESTART) {
                        if ((vnode_get(ndp->ni_dvp))) {
                                error = ENOENT;
                                goto bad;
                        }
                        ndp->ni_startdir = ndp->ni_dvp;
                }
                if (!wantparent) {
                        vnode_put(ndp->ni_dvp);
                }

                if (kdebug_enable) {
                        kdebug_lookup(ndp->ni_dvp, cnp);
                }
                return 0;
        }
returned_from_lookup_path:
        /* We'll always have an iocount on ni_vp when this finishes. */
        error = lookup_handle_found_vnode(ndp, cnp, rdonly, vbusyflags, &keep_going, nc_generation, wantparent, atroot, ctx);
        if (error != 0) {
                goto bad2;
        }

        if (keep_going) {
                dp = ndp->ni_vp;

                /* namei() will handle symlinks */
                if ((dp->v_type == VLNK) &&
                    ((cnp->cn_flags & FOLLOW) || (ndp->ni_flag & NAMEI_TRAILINGSLASH) || *ndp->ni_next == '/')) {
                        return 0;
                }

                /*
                 * Otherwise, there's more path to process.
                 * cache_lookup_path is now responsible for dropping io ref on dp
                 * when it is called again in the dirloop.  This ensures we hold
                 * a ref on dp until we complete the next round of lookup.
                 */
                last_dp = dp;

                goto dirloop;
        }

        return 0;
bad2:
        if (ndp->ni_dvp) {
                vnode_put(ndp->ni_dvp);
        }

        vnode_put(ndp->ni_vp);
        ndp->ni_vp = NULLVP;

        if (kdebug_enable) {
                kdebug_lookup(dp, cnp);
        }
        return error;

bad:
        if (dp) {
                vnode_put(dp);
        }
        ndp->ni_vp = NULLVP;

        if (kdebug_enable) {
                kdebug_lookup(dp, cnp);
        }
        return error;
}

/*
 * Given a vnode in a union mount, traverse to the equivalent
 * vnode in the underlying mount.
 */
int
lookup_traverse_union(vnode_t dvp, vnode_t *new_dvp, vfs_context_t ctx)
{
        char *path = NULL, *pp;
        const char *name, *np;
        int len;
        int error = 0;
        struct nameidata nd;
        vnode_t vp = dvp;

        *new_dvp = NULL;

        if (vp && vp->v_flag & VROOT) {
                *new_dvp = vp->v_mount->mnt_vnodecovered;
                if (vnode_getwithref(*new_dvp)) {
                        return ENOENT;
                }
                return 0;
        }

        path = (char *) kalloc(MAXPATHLEN);
        if (path == NULL) {
                error = ENOMEM;
                goto done;
        }

        /*
         * Walk back up to the mountpoint following the
         * v_parent chain and build a slash-separated path.
         * Then lookup that path starting with the covered vnode.
         */
        pp = path + (MAXPATHLEN - 1);
        *pp = '\0';

        while (1) {
                name = vnode_getname(vp);
                if (name == NULL) {
                        printf("lookup_traverse_union: null parent name: .%s\n", pp);
                        error = ENOENT;
                        goto done;
                }
                len = strlen(name);
                if ((len + 1) > (pp - path)) {          // Enough space for this name ?
                        error = ENAMETOOLONG;
                        vnode_putname(name);
                        goto done;
                }
                for (np = name + len; len > 0; len--) { // Copy name backwards
                        *--pp = *--np;
                }
                vnode_putname(name);
                vp = vp->v_parent;
                if (vp == NULLVP || vp->v_flag & VROOT) {
                        break;
                }
                *--pp = '/';
        }

        /* Evaluate the path in the underlying mount */
        NDINIT(&nd, LOOKUP, OP_LOOKUP, USEDVP, UIO_SYSSPACE, CAST_USER_ADDR_T(pp), ctx);
        nd.ni_dvp = dvp->v_mount->mnt_vnodecovered;
        error = namei(&nd);
        if (error == 0) {
                *new_dvp = nd.ni_vp;
        }
        nameidone(&nd);
done:
        if (path) {
                kfree(path, MAXPATHLEN);
        }
        return error;
}

int
lookup_validate_creation_path(struct nameidata *ndp)
{
        struct componentname *cnp = &ndp->ni_cnd;

        /*
         * If creating and at end of pathname, then can consider
         * allowing file to be created.
         */
        if (cnp->cn_flags & RDONLY) {
                return EROFS;
        }
        if ((cnp->cn_flags & ISLASTCN) && (ndp->ni_flag & NAMEI_TRAILINGSLASH) && !(cnp->cn_flags & WILLBEDIR)) {
                return ENOENT;
        }

        return 0;
}

/*
 * Modifies only ni_vp.  Always returns with ni_vp still valid (iocount held).
 */
static int
lookup_traverse_mountpoints(struct nameidata *ndp, struct componentname *cnp, vnode_t dp,
    int vbusyflags, vfs_context_t ctx)
{
        mount_t mp;
        vnode_t tdp;
        int error = 0;
        uint32_t depth = 0;
        vnode_t mounted_on_dp;
        int current_mount_generation = 0;
#if CONFIG_TRIGGERS
        vnode_t triggered_dp = NULLVP;
        int retry_cnt = 0;
#define MAX_TRIGGER_RETRIES 1
#endif

        if (dp->v_type != VDIR || cnp->cn_flags & NOCROSSMOUNT) {
                return 0;
        }

        mounted_on_dp = dp;
#if CONFIG_TRIGGERS
restart:
#endif
        current_mount_generation = mount_generation;

        while (dp->v_mountedhere) {
                vnode_lock_spin(dp);
                if ((mp = dp->v_mountedhere)) {
                        mp->mnt_crossref++;
                        vnode_unlock(dp);
                } else {
                        vnode_unlock(dp);
                        break;
                }

                if (ISSET(mp->mnt_lflag, MNT_LFORCE)) {
                        mount_dropcrossref(mp, dp, 0);
                        break;  // don't traverse into a forced unmount
                }


                if (vfs_busy(mp, vbusyflags)) {
                        mount_dropcrossref(mp, dp, 0);
                        if (vbusyflags == LK_NOWAIT) {
                                error = ENOENT;
                                goto out;
                        }

                        continue;
                }

                error = VFS_ROOT(mp, &tdp, ctx);

                mount_dropcrossref(mp, dp, 0);
                vfs_unbusy(mp);

                if (error) {
                        goto out;
                }

                vnode_put(dp);
                ndp->ni_vp = dp = tdp;
                if (dp->v_type != VDIR) {
#if DEVELOPMENT || DEBUG
                        panic("%s : Root of filesystem not a directory\n",
                            __FUNCTION__);
#else
                        break;
#endif
                }
                depth++;
        }

#if CONFIG_TRIGGERS
        /*
         * The triggered_dp check here is required but is susceptible to a
         * (unlikely) race in which trigger mount is done from here and is
         * unmounted before we get past vfs_busy above. We retry to deal with
         * that case but it has the side effect of unwanted retries for
         * "special" processes which don't want to trigger mounts.
         */
        if (dp->v_resolve && retry_cnt < MAX_TRIGGER_RETRIES) {
                error = vnode_trigger_resolve(dp, ndp, ctx);
                if (error) {
                        goto out;
                }
                if (dp == triggered_dp) {
                        retry_cnt += 1;
                } else {
                        retry_cnt = 0;
                }
                triggered_dp = dp;
                goto restart;
        }
#endif /* CONFIG_TRIGGERS */

        if (depth) {
                mp = mounted_on_dp->v_mountedhere;

                if (mp) {
                        mount_lock_spin(mp);
                        mp->mnt_realrootvp_vid = dp->v_id;
                        mp->mnt_realrootvp = dp;
                        mp->mnt_generation = current_mount_generation;
                        mount_unlock(mp);
                }
        }

        return 0;

out:
        return error;
}

/*
 * Takes ni_vp and ni_dvp non-NULL.  Returns with *new_dp set to the location
 * at which to start a lookup with a resolved path, and all other iocounts dropped.
 */
static int
lookup_handle_symlink(struct nameidata *ndp, vnode_t *new_dp, vfs_context_t ctx)
{
        int error;
        char *cp;               /* pointer into pathname argument */
        uio_t auio;
        union {
                union {
                        struct user_iovec s_uiovec;
                        struct kern_iovec s_kiovec;
                } u_iovec;
                struct uio s_uio;
                char uio_buf[UIO_SIZEOF(1)];
        } u_uio_buf; /* union only for aligning uio_buf correctly */
        int need_newpathbuf;
        u_int linklen;
        struct componentname *cnp = &ndp->ni_cnd;
        vnode_t dp;
        char *tmppn;

        if (ndp->ni_loopcnt++ >= MAXSYMLINKS) {
                return ELOOP;
        }
#if CONFIG_MACF
        if ((error = mac_vnode_check_readlink(ctx, ndp->ni_vp)) != 0) {
                return error;
        }
#endif /* MAC */
        if (ndp->ni_pathlen > 1 || !(cnp->cn_flags & HASBUF)) {
                need_newpathbuf = 1;
        } else {
                need_newpathbuf = 0;
        }

        if (need_newpathbuf) {
                MALLOC_ZONE(cp, char *, MAXPATHLEN, M_NAMEI, M_WAITOK);
                if (cp == NULL) {
                        return ENOMEM;
                }
        } else {
                cp = cnp->cn_pnbuf;
        }
        auio = uio_createwithbuffer(1, 0, UIO_SYSSPACE, UIO_READ,
            &u_uio_buf.uio_buf[0], sizeof(u_uio_buf.uio_buf));

        uio_addiov(auio, CAST_USER_ADDR_T(cp), MAXPATHLEN);

        error = VNOP_READLINK(ndp->ni_vp, auio, ctx);
        if (error) {
                if (need_newpathbuf) {
                        FREE_ZONE(cp, MAXPATHLEN, M_NAMEI);
                }
                return error;
        }

        /*
         * Safe to set unsigned with a [larger] signed type here
         * because 0 <= uio_resid <= MAXPATHLEN and MAXPATHLEN
         * is only 1024.
         */
        linklen = MAXPATHLEN - (u_int)uio_resid(auio);
        if (linklen + ndp->ni_pathlen > MAXPATHLEN) {
                if (need_newpathbuf) {
                        FREE_ZONE(cp, MAXPATHLEN, M_NAMEI);
                }

                return ENAMETOOLONG;
        }
        if (need_newpathbuf) {
                long len = cnp->cn_pnlen;

                tmppn = cnp->cn_pnbuf;
                bcopy(ndp->ni_next, cp + linklen, ndp->ni_pathlen);
                cnp->cn_pnbuf = cp;
                cnp->cn_pnlen = MAXPATHLEN;

                if ((cnp->cn_flags & HASBUF)) {
                        FREE_ZONE(tmppn, len, M_NAMEI);
                } else {
                        cnp->cn_flags |= HASBUF;
                }
        } else {
                cnp->cn_pnbuf[linklen] = '\0';
        }

        ndp->ni_pathlen += linklen;
        cnp->cn_nameptr = cnp->cn_pnbuf;

        /*
         * starting point for 'relative'
         * symbolic link path
         */
        dp = ndp->ni_dvp;

        /*
         * get rid of references returned via 'lookup'
         */
        vnode_put(ndp->ni_vp);
        vnode_put(ndp->ni_dvp); /* ALWAYS have a dvp for a symlink */

        ndp->ni_vp = NULLVP;
        ndp->ni_dvp = NULLVP;

        /*
         * Check if symbolic link restarts us at the root
         */
        if (*(cnp->cn_nameptr) == '/') {
                while (*(cnp->cn_nameptr) == '/') {
                        cnp->cn_nameptr++;
                        ndp->ni_pathlen--;
                }
                if ((dp = ndp->ni_rootdir) == NULLVP) {
                        return ENOENT;
                }
        }

        *new_dp = dp;

        return 0;
}

/*
 * relookup - lookup a path name component
 *    Used by lookup to re-aquire things.
 */
int
relookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
{
        struct vnode *dp = NULL;                /* the directory we are searching */
        int wantparent;                 /* 1 => wantparent or lockparent flag */
        int rdonly;                     /* lookup read-only flag bit */
        int error = 0;
#ifdef NAMEI_DIAGNOSTIC
        int i, newhash;                 /* DEBUG: check name hash */
        char *cp;                       /* DEBUG: check name ptr/len */
#endif
        vfs_context_t ctx = cnp->cn_context;;

        /*
         * Setup: break out flag bits into variables.
         */
        wantparent = cnp->cn_flags & (LOCKPARENT | WANTPARENT);
        rdonly = cnp->cn_flags & RDONLY;
        cnp->cn_flags &= ~ISSYMLINK;

        if (cnp->cn_flags & NOCACHE) {
                cnp->cn_flags &= ~MAKEENTRY;
        } else {
                cnp->cn_flags |= MAKEENTRY;
        }

        dp = dvp;

        /*
         * 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 ((vnode_get(dp))) {
                        error = ENOENT;
                        goto bad;
                }
                *vpp = dp;

                if (cnp->cn_flags & SAVESTART) {
                        panic("lookup: SAVESTART");
                }
                return 0;
        }
        /*
         * We now have a segment name to search for, and a directory to search.
         */
        if ((error = VNOP_LOOKUP(dp, vpp, cnp, ctx))) {
                if (error != EJUSTRETURN) {
                        goto bad;
                }
#if DIAGNOSTIC
                if (*vpp != NULL) {
                        panic("leaf should be empty");
                }
#endif
                /*
                 * If creating and at end of pathname, then can consider
                 * allowing file to be created.
                 */
                if (rdonly) {
                        error = EROFS;
                        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.
                 */
                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) */

        return 0;

bad2:
        vnode_put(dp);
bad:
        *vpp = NULL;

        return error;
}

/*
 * Free pathname buffer
 */
void
nameidone(struct nameidata *ndp)
{
        if (ndp->ni_cnd.cn_flags & HASBUF) {
                char *tmp = ndp->ni_cnd.cn_pnbuf;

                ndp->ni_cnd.cn_pnbuf = NULL;
                ndp->ni_cnd.cn_flags &= ~HASBUF;
                FREE_ZONE(tmp, ndp->ni_cnd.cn_pnlen, M_NAMEI);
        }
}


/*
 * Log (part of) a pathname using the KERNEL_DEBUG_CONSTANT mechanism, as used
 * by fs_usage.  The path up to and including the current component name are
 * logged.  Up to NUMPARMS*4 bytes of pathname will be logged.  If the path
 * to be logged is longer than that, then the last NUMPARMS*4 bytes are logged.
 * That is, the truncation removes the leading portion of the path.
 *
 * The logging is done via multiple KERNEL_DEBUG_CONSTANT calls.  The first one
 * is marked with DBG_FUNC_START.  The last one is marked with DBG_FUNC_END
 * (in addition to DBG_FUNC_START if it is also the first).  There may be
 * intermediate ones with neither DBG_FUNC_START nor DBG_FUNC_END.
 *
 * The first KERNEL_DEBUG_CONSTANT passes the vnode pointer and 12 bytes of
 * pathname.  The remaining KERNEL_DEBUG_CONSTANT calls add 16 bytes of pathname
 * each.  The minimum number of KERNEL_DEBUG_CONSTANT calls required to pass
 * the path are used.  Any excess padding in the final KERNEL_DEBUG_CONSTANT
 * (because not all of the 12 or 16 bytes are needed for the remainder of the
 * path) is set to zero bytes, or '>' if there is more path beyond the
 * current component name (usually because an intermediate component was not
 * found).
 *
 * NOTE: If the path length is greater than NUMPARMS*4, or is not of the form
 * 12+N*16, there will be no padding.
 *
 * TODO: If there is more path beyond the current component name, should we
 * force some padding?  For example, a lookup for /foo_bar_baz/spam that
 * fails because /foo_bar_baz is not found will only log "/foo_bar_baz", with
 * no '>' padding.  But /foo_bar/spam would log "/foo_bar>>>>".
 */
#if (KDEBUG_LEVEL >= KDEBUG_LEVEL_IST)

void
kdebug_vfs_lookup(long *dbg_parms, int dbg_namelen, void *dp, uint32_t flags)
{
        int code;
        unsigned int i;
        bool lookup = flags & KDBG_VFS_LOOKUP_FLAG_LOOKUP;
        bool noprocfilt = flags & KDBG_VFS_LOOKUP_FLAG_NOPROCFILT;

        /*
         * In the event that we collect multiple, consecutive pathname
         * entries, we must mark the start of the path's string and the end.
         */
        if (lookup) {
                code = VFS_LOOKUP | DBG_FUNC_START;
        } else {
                code = VFS_LOOKUP_DONE | DBG_FUNC_START;
        }

        if (dbg_namelen <= (int)(3 * sizeof(long))) {
                code |= DBG_FUNC_END;
        }

        if (noprocfilt) {
                KDBG_RELEASE_NOPROCFILT(code, kdebug_vnode(dp), dbg_parms[0],
                    dbg_parms[1], dbg_parms[2]);
        } else {
                KDBG_RELEASE(code, kdebug_vnode(dp), dbg_parms[0], dbg_parms[1],
                    dbg_parms[2]);
        }

        code &= ~DBG_FUNC_START;

        for (i = 3, dbg_namelen -= (3 * sizeof(long)); dbg_namelen > 0; i += 4, dbg_namelen -= (4 * sizeof(long))) {
                if (dbg_namelen <= (int)(4 * sizeof(long))) {
                        code |= DBG_FUNC_END;
                }

                if (noprocfilt) {
                        KDBG_RELEASE_NOPROCFILT(code, dbg_parms[i], dbg_parms[i + 1],
                            dbg_parms[i + 2], dbg_parms[i + 3]);
                } else {
                        KDBG_RELEASE(code, dbg_parms[i], dbg_parms[i + 1], dbg_parms[i + 2],
                            dbg_parms[i + 3]);
                }
        }
}

void
kdebug_lookup_gen_events(long *dbg_parms, int dbg_namelen, void *dp,
    boolean_t lookup)
{
        kdebug_vfs_lookup(dbg_parms, dbg_namelen, dp,
            lookup ? KDBG_VFS_LOOKUP_FLAG_LOOKUP : 0);
}

void
kdebug_lookup(vnode_t dp, struct componentname *cnp)
{
        int dbg_namelen;
        char *dbg_nameptr;
        long dbg_parms[NUMPARMS];

        /* 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 > (int)sizeof(dbg_parms)) {
                dbg_namelen = sizeof(dbg_parms);
        }
        dbg_nameptr -= dbg_namelen;

        /* Copy the (possibly truncated) path itself */
        memcpy(dbg_parms, dbg_nameptr, dbg_namelen);

        /* Pad with '\0' or '>' */
        if (dbg_namelen < (int)sizeof(dbg_parms)) {
                memset((char *)dbg_parms + dbg_namelen,
                    *(cnp->cn_nameptr + cnp->cn_namelen) ? '>' : 0,
                    sizeof(dbg_parms) - dbg_namelen);
        }
        kdebug_vfs_lookup(dbg_parms, dbg_namelen, (void *)dp,
            KDBG_VFS_LOOKUP_FLAG_LOOKUP);
}

#else /* (KDEBUG_LEVEL >= KDEBUG_LEVEL_IST) */

void
kdebug_vfs_lookup(long *dbg_parms __unused, int dbg_namelen __unused,
    void *dp __unused, __unused uint32_t flags)
{
}

static void
kdebug_lookup(struct vnode *dp __unused, struct componentname *cnp __unused)
{
}
#endif /* (KDEBUG_LEVEL >= KDEBUG_LEVEL_IST) */

int
vfs_getbyid(fsid_t *fsid, ino64_t ino, vnode_t *vpp, vfs_context_t ctx)
{
        mount_t mp;
        int error;

        mp = mount_lookupby_volfsid(fsid->val[0], 1);
        if (mp == NULL) {
                return EINVAL;
        }

        /* Get the target vnode. */
        if (ino == 2) {
                error = VFS_ROOT(mp, vpp, ctx);
        } else {
                error = VFS_VGET(mp, ino, vpp, ctx);
        }

        vfs_unbusy(mp);
        return error;
}
/*
 * Obtain the real path from a legacy volfs style path.
 *
 * Valid formats of input path:
 *
 *      "555/@"
 *      "555/2"
 *      "555/123456"
 *      "555/123456/foobar"
 *
 * Where:
 *      555 represents the volfs file system id
 *      '@' and '2' are aliases to the root of a file system
 *      123456 represents a file id
 *      "foobar" represents a file name
 */
#if CONFIG_VOLFS
static int
vfs_getrealpath(const char * path, char * realpath, size_t bufsize, vfs_context_t ctx)
{
        vnode_t vp;
        struct mount *mp = NULL;
        char  *str;
        char ch;
        uint32_t  id;
        ino64_t ino;
        int error;
        int length;

        /* Get file system id and move str to next component. */
        id = strtoul(path, &str, 10);
        if (id == 0 || str[0] != '/') {
                return EINVAL;
        }
        while (*str == '/') {
                str++;
        }
        ch = *str;

        mp = mount_lookupby_volfsid(id, 1);
        if (mp == NULL) {
                return EINVAL;  /* unexpected failure */
        }
        /* Check for an alias to a file system root. */
        if (ch == '@' && str[1] == '\0') {
                ino = 2;
                str++;
        } else {
                /* Get file id and move str to next component. */
                ino = strtouq(str, &str, 10);
        }

        /* Get the target vnode. */
        if (ino == 2) {
                error = VFS_ROOT(mp, &vp, ctx);
        } else {
                error = VFS_VGET(mp, ino, &vp, ctx);
        }
        vfs_unbusy(mp);
        if (error) {
                goto out;
        }
        realpath[0] = '\0';

        /* Get the absolute path to this vnode. */
        error = build_path(vp, realpath, bufsize, &length, 0, ctx);
        vnode_put(vp);

        if (error == 0 && *str != '\0') {
                int attempt = strlcat(realpath, str, MAXPATHLEN);
                if (attempt > MAXPATHLEN) {
                        error = ENAMETOOLONG;
                }
        }
out:
        return error;
}
#endif

void
lookup_compound_vnop_post_hook(int error, vnode_t dvp, vnode_t vp, struct nameidata *ndp, int did_create)
{
        if (error == 0 && vp == NULLVP) {
                panic("NULL vp with error == 0.\n");
        }

        /*
         * We don't want to do any of this if we didn't use the compound vnop
         * to perform the lookup... i.e. if we're allowing and using the legacy pattern,
         * where we did a full lookup.
         */
        if ((ndp->ni_flag & NAMEI_COMPOUND_OP_MASK) == 0) {
                return;
        }

        /*
         * If we're going to continue the lookup, we'll handle
         * all lookup-related updates at that time.
         */
        if (error == EKEEPLOOKING) {
                return;
        }

        /*
         * Only audit or update cache for *found* vnodes.  For creation
         * neither would happen in the non-compound-vnop case.
         */
        if ((vp != NULLVP) && !did_create) {
                /*
                 * If MAKEENTRY isn't set, and we've done a successful compound VNOP,
                 * then we certainly don't want to update cache or identity.
                 */
                if ((error != 0) || (ndp->ni_cnd.cn_flags & MAKEENTRY)) {
                        lookup_consider_update_cache(dvp, vp, &ndp->ni_cnd, ndp->ni_ncgeneration);
                }
                if (ndp->ni_cnd.cn_flags & AUDITVNPATH1) {
                        AUDIT_ARG(vnpath, vp, ARG_VNODE1);
                } else if (ndp->ni_cnd.cn_flags & AUDITVNPATH2) {
                        AUDIT_ARG(vnpath, vp, ARG_VNODE2);
                }
        }

        /*
         * If you created (whether you opened or not), cut a lookup tracepoint
         * for the parent dir (as would happen without a compound vnop).  Note: we may need
         * a vnode despite failure in this case!
         *
         * If you did not create:
         *      Found child (succeeded or not): cut a tracepoint for the child.
         *      Did not find child: cut a tracepoint with the parent.
         */
        if (kdebug_enable) {
                kdebug_lookup(vp ? vp : dvp, &ndp->ni_cnd);
        }
}