text: /*
   * CDDL HEADER START
   *
   * The contents of this file are subject to the terms of the
   * Common Development and Distribution License (the "License").
   * You may not use this file except in compliance with the License.
   *
   * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   * or http://www.opensolaris.org/os/licensing.
   * See the License for the specific language governing permissions
   * and limitations under the License.
   *
   * When distributing Covered Code, include this CDDL HEADER in each
   * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
   * If applicable, add the following below this CDDL HEADER, with the
   * fields enclosed by brackets "[]" replaced with your own identifying
   * information: Portions Copyright [yyyy] [name of copyright owner]
   *
   * CDDL HEADER END
   */
  
  /*
   * Copyright 2015 Nexenta Systems, Inc.  All rights reserved.
   * Copyright (c) 1988, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright 2016 Joyent, Inc.
   */
  
  /*	Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T	*/
  /*	  All Rights Reserved  	*/
  
  /*
   * University Copyright- Copyright (c) 1982, 1986, 1988
   * The Regents of the University of California
   * All Rights Reserved
   *
   * University Acknowledgment- Portions of this document are derived from
   * software developed by the University of California, Berkeley, and its
   * contributors.
   */
  
  #include <sys/types.h>
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/cpuvar.h>
  #include <sys/errno.h>
  #include <sys/cred.h>
  #include <sys/user.h>
  #include <sys/uio.h>
  #include <sys/vfs.h>
  #include <sys/vnode.h>
  #include <sys/pathname.h>
  #include <sys/proc.h>
  #include <sys/vtrace.h>
  #include <sys/sysmacros.h>
  #include <sys/debug.h>
  #include <sys/dirent.h>
  #include <c2/audit.h>
  #include <sys/zone.h>
  #include <sys/dnlc.h>
  #include <sys/fs/snode.h>
  
  /* Controls whether paths are stored with vnodes. */
  int vfs_vnode_path = 1;
  
  int
  lookupname(
  	char *fnamep,
  	enum uio_seg seg,
  	int followlink,
  	vnode_t **dirvpp,
  	vnode_t **compvpp)
  {
  	return (lookupnameatcred(fnamep, seg, followlink, dirvpp, compvpp, NULL,
  	    CRED()));
  }
  
  /*
   * Lookup the user file name,
   * Handle allocation and freeing of pathname buffer, return error.
   */
  int
  lookupnameatcred(
  	char *fnamep,			/* user pathname */
  	enum uio_seg seg,		/* addr space that name is in */
  	int followlink,			/* follow sym links */
  	vnode_t **dirvpp,		/* ret for ptr to parent dir vnode */
  	vnode_t **compvpp,		/* ret for ptr to component vnode */
  	vnode_t *startvp,		/* start path search from vp */
  	cred_t *cr)			/* credential */
  {
  	char namebuf[TYPICALMAXPATHLEN];
  	struct pathname lookpn;
  	int error;
  
  	error = pn_get_buf(fnamep, seg, &lookpn, namebuf, sizeof (namebuf));
  	if (error == 0) {
  		error = lookuppnatcred(&lookpn, NULL, followlink,
  		    dirvpp, compvpp, startvp, cr);
  	}
  	if (error == ENAMETOOLONG) {
  		/*
  		 * This thread used a pathname > TYPICALMAXPATHLEN bytes long.
  		 */
  		if (error = pn_get(fnamep, seg, &lookpn))
  			return (error);
  		error = lookuppnatcred(&lookpn, NULL, followlink,
  		    dirvpp, compvpp, startvp, cr);
  		pn_free(&lookpn);
  	}
  
  	return (error);
  }
  
  int
  lookupnameat(char *fnamep, enum uio_seg seg, int followlink,
      vnode_t **dirvpp, vnode_t **compvpp, vnode_t *startvp)
  {
  	return (lookupnameatcred(fnamep, seg, followlink, dirvpp, compvpp,
  	    startvp, CRED()));
  }
  
  int
  lookuppn(
  	struct pathname *pnp,
  	struct pathname *rpnp,
  	int followlink,
  	vnode_t **dirvpp,
  	vnode_t **compvpp)
  {
  	return (lookuppnatcred(pnp, rpnp, followlink, dirvpp, compvpp, NULL,
  	    CRED()));
  }
  
  /*
   * Lookup the user file name from a given vp, using a specific credential.
   */
  int
  lookuppnatcred(
  	struct pathname *pnp,		/* pathname to lookup */
  	struct pathname *rpnp,		/* if non-NULL, return resolved path */
  	int followlink,			/* (don't) follow sym links */
  	vnode_t **dirvpp,		/* ptr for parent vnode */
  	vnode_t **compvpp,		/* ptr for entry vnode */
  	vnode_t *startvp,		/* start search from this vp */
  	cred_t *cr)			/* user credential */
  {
  	vnode_t *vp;	/* current directory vp */
  	vnode_t *rootvp;
  	proc_t *p = curproc;
  
  	if (pnp->pn_pathlen == 0)
  		return (ENOENT);
  
  	mutex_enter(&p->p_lock);	/* for u_rdir and u_cdir */
  	if ((rootvp = PTOU(p)->u_rdir) == NULL)
  		rootvp = rootdir;
  	else if (rootvp != rootdir)	/* no need to VN_HOLD rootdir */
  		VN_HOLD(rootvp);
  
  	if (pnp->pn_path[0] == '/') {
  		vp = rootvp;
  	} else {
  		vp = (startvp == NULL) ? PTOU(p)->u_cdir : startvp;
  	}
  	VN_HOLD(vp);
  	mutex_exit(&p->p_lock);
  
  	/*
  	 * Skip over leading slashes
  	 */
  	if (pnp->pn_path[0] == '/') {
  		do {
  			pnp->pn_path++;
  			pnp->pn_pathlen--;
  		} while (pnp->pn_path[0] == '/');
  	}
  
  	return (lookuppnvp(pnp, rpnp, followlink, dirvpp,
  	    compvpp, rootvp, vp, cr));
  }
  
  int
  lookuppnat(struct pathname *pnp, struct pathname *rpnp,
      int followlink, vnode_t **dirvpp, vnode_t **compvpp,
      vnode_t *startvp)
  {
  	return (lookuppnatcred(pnp, rpnp, followlink, dirvpp, compvpp, startvp,
  	    CRED()));
  }
  
  /* Private flag to do our getcwd() dirty work */
  #define	LOOKUP_CHECKREAD	0x10
  #define	LOOKUP_MASK		(~LOOKUP_CHECKREAD)
  
  /*
   * Starting at current directory, translate pathname pnp to end.
   * Leave pathname of final component in pnp, return the vnode
   * for the final component in *compvpp, and return the vnode
   * for the parent of the final component in dirvpp.
   *
   * This is the central routine in pathname translation and handles
   * multiple components in pathnames, separating them at /'s.  It also
   * implements mounted file systems and processes symbolic links.
   *
   * vp is the vnode where the directory search should start.
   *
   * Reference counts: vp must be held prior to calling this function.  rootvp
   * should only be held if rootvp != rootdir.
   */
  int
  lookuppnvp(
  	struct pathname *pnp,		/* pathname to lookup */
  	struct pathname *rpnp,		/* if non-NULL, return resolved path */
  	int flags,			/* follow symlinks */
  	vnode_t **dirvpp,		/* ptr for parent vnode */
  	vnode_t **compvpp,		/* ptr for entry vnode */
  	vnode_t *rootvp,		/* rootvp */
  	vnode_t *vp,			/* directory to start search at */
  	cred_t *cr)			/* user's credential */
  {
  	vnode_t *cvp;	/* current component vp */
  	char component[MAXNAMELEN];	/* buffer for component (incl null) */
  	int error;
  	int nlink;
  	int lookup_flags;
  	struct pathname presrvd; /* case preserved name */
  	struct pathname *pp = NULL;
  	vnode_t *startvp;
  	vnode_t *zonevp = curproc->p_zone->zone_rootvp;		/* zone root */
  	int must_be_directory = 0;
  	boolean_t retry_with_kcred;
  	uint32_t auditing = AU_AUDITING();
  
  	CPU_STATS_ADDQ(CPU, sys, namei, 1);
  	nlink = 0;
  	cvp = NULL;
  	if (rpnp)
  		rpnp->pn_pathlen = 0;
  
  	lookup_flags = dirvpp ? LOOKUP_DIR : 0;
  	if (flags & FIGNORECASE) {
  		lookup_flags |= FIGNORECASE;
  		pn_alloc(&presrvd);
  		pp = &presrvd;
  	}
  
  	if (auditing)
  		audit_anchorpath(pnp, vp == rootvp);
  
  	/*
  	 * Eliminate any trailing slashes in the pathname.
  	 * If there are any, we must follow all symlinks.
  	 * Also, we must guarantee that the last component is a directory.
  	 */
  	if (pn_fixslash(pnp)) {
  		flags |= FOLLOW;
  		must_be_directory = 1;
  	}
  
  	startvp = vp;
  next:
  	retry_with_kcred = B_FALSE;
  
  	/*
  	 * Make sure we have a directory.
  	 */
  	if (vp->v_type != VDIR) {
  		error = ENOTDIR;
  		goto bad;
  	}
  
  	if (rpnp && VN_CMP(vp, rootvp))
  		(void) pn_set(rpnp, "/");
  
  	/*
  	 * Process the next component of the pathname.
  	 */
  	if (error = pn_getcomponent(pnp, component)) {
  		goto bad;
  	}
  
  	/*
  	 * Handle "..": two special cases.
  	 * 1. If we're at the root directory (e.g. after chroot or
  	 *    zone_enter) then change ".." to "." so we can't get
  	 *    out of this subtree.
  	 * 2. If this vnode is the root of a mounted file system,
  	 *    then replace it with the vnode that was mounted on
  	 *    so that we take the ".." in the other file system.
  	 */
  	if (component[0] == '.' && component[1] == '.' && component[2] == 0) {
  checkforroot:
  		if (VN_CMP(vp, rootvp) || VN_CMP(vp, zonevp)) {
  			component[1] = '\0';
  		} else if (vp->v_flag & VROOT) {
  			vfs_t *vfsp;
  			cvp = vp;
  
  			/*
  			 * While we deal with the vfs pointer from the vnode
  			 * the filesystem could have been forcefully unmounted
  			 * and the vnode's v_vfsp could have been invalidated
  			 * by VFS_UNMOUNT. Hence, we cache v_vfsp and use it
  			 * with vfs_rlock_wait/vfs_unlock.
  			 * It is safe to use the v_vfsp even it is freed by
  			 * VFS_UNMOUNT because vfs_rlock_wait/vfs_unlock
  			 * do not dereference v_vfsp. It is just used as a
  			 * magic cookie.
  			 * One more corner case here is the memory getting
  			 * reused for another vfs structure. In this case
  			 * lookuppnvp's vfs_rlock_wait will succeed, domount's
  			 * vfs_lock will fail and domount will bail out with an
  			 * error (EBUSY).
  			 */
  			vfsp = cvp->v_vfsp;
  
  			/*
  			 * This lock is used to synchronize
  			 * mounts/unmounts and lookups.
  			 * Threads doing mounts/unmounts hold the
  			 * writers version vfs_lock_wait().
  			 */
  
  			vfs_rlock_wait(vfsp);
  
  			/*
  			 * If this vnode is on a file system that
  			 * has been forcibly unmounted,
  			 * we can't proceed. Cancel this operation
  			 * and return EIO.
  			 *
  			 * vfs_vnodecovered is NULL if unmounted.
  			 * Currently, nfs uses VFS_UNMOUNTED to
  			 * check if it's a forced-umount. Keep the
  			 * same checking here as well even though it
  			 * may not be needed.
  			 */
  			if (((vp = cvp->v_vfsp->vfs_vnodecovered) == NULL) ||
  			    (cvp->v_vfsp->vfs_flag & VFS_UNMOUNTED)) {
  				vfs_unlock(vfsp);
  				VN_RELE(cvp);
  				if (pp)
  					pn_free(pp);
  				return (EIO);
  			}
  			VN_HOLD(vp);
  			vfs_unlock(vfsp);
  			VN_RELE(cvp);
  			cvp = NULL;
  			/*
  			 * Crossing mount points. For eg: We are doing
  			 * a lookup of ".." for file systems root vnode
  			 * mounted here, and VOP_LOOKUP() (with covered vnode)
  			 * will be on underlying file systems mount point
  			 * vnode. Set retry_with_kcred flag as we might end
  			 * up doing VOP_LOOKUP() with kcred if required.
  			 */
  			retry_with_kcred = B_TRUE;
  			goto checkforroot;
  		}
  	}
  
  	/*
  	 * LOOKUP_CHECKREAD is a private flag used by vnodetopath() to indicate
  	 * that we need to have read permission on every directory in the entire
  	 * path.  This is used to ensure that a forward-lookup of a cached value
  	 * has the same effect as a reverse-lookup when the cached value cannot
  	 * be found.
  	 */
  	if ((flags & LOOKUP_CHECKREAD) &&
  	    (error = VOP_ACCESS(vp, VREAD, 0, cr, NULL)) != 0)
  		goto bad;
  
  	/*
  	 * Perform a lookup in the current directory.
  	 */
  	error = VOP_LOOKUP(vp, component, &cvp, pnp, lookup_flags,
  	    rootvp, cr, NULL, NULL, pp);
  
  	/*
  	 * Retry with kcred - If crossing mount points & error is EACCES.
  	 *
  	 * If we are crossing mount points here and doing ".." lookup,
  	 * VOP_LOOKUP() might fail if the underlying file systems
  	 * mount point has no execute permission. In cases like these,
  	 * we retry VOP_LOOKUP() by giving as much privilage as possible
  	 * by passing kcred credentials.
  	 *
  	 * In case of hierarchical file systems, passing kcred still may
  	 * or may not work.
  	 * For eg: UFS FS --> Mount NFS FS --> Again mount UFS on some
  	 *			directory inside NFS FS.
  	 */
  	if ((error == EACCES) && retry_with_kcred)
  		error = VOP_LOOKUP(vp, component, &cvp, pnp, lookup_flags,
  		    rootvp, zone_kcred(), NULL, NULL, pp);
  
  	if (error) {
  		cvp = NULL;
  		/*
  		 * On error, return hard error if
  		 * (a) we're not at the end of the pathname yet, or
  		 * (b) the caller didn't want the parent directory, or
  		 * (c) we failed for some reason other than a missing entry.
  		 */
  		if (pn_pathleft(pnp) || dirvpp == NULL || error != ENOENT)
  			goto bad;
  		if (auditing) {	/* directory access */
  			if (error = audit_savepath(pnp, vp, vp, error, cr))
  				goto bad_noaudit;
  		}
  
  		pn_setlast(pnp);
  		/*
  		 * We inform the caller that the desired entry must be
  		 * a directory by adding a '/' to the component name.
  		 */
  		if (must_be_directory && (error = pn_addslash(pnp)) != 0)
  			goto bad;
  		*dirvpp = vp;
  		if (compvpp != NULL)
  			*compvpp = NULL;
  		if (rootvp != rootdir)
  			VN_RELE(rootvp);
  		if (pp)
  			pn_free(pp);
  		return (0);
  	}
  
  	/*
  	 * Traverse mount points.
  	 * XXX why don't we need to hold a read lock here (call vn_vfsrlock)?
  	 * What prevents a concurrent update to v_vfsmountedhere?
  	 * 	Possible answer: if mounting, we might not see the mount
  	 *	if it is concurrently coming into existence, but that's
  	 *	really not much different from the thread running a bit slower.
  	 *	If unmounting, we may get into traverse() when we shouldn't,
  	 *	but traverse() will catch this case for us.
  	 *	(For this to work, fetching v_vfsmountedhere had better
  	 *	be atomic!)
  	 */
  	if (vn_mountedvfs(cvp) != NULL) {
  		if ((error = traverse(&cvp)) != 0)
  			goto bad;
  	}
  
  	/*
  	 * If we hit a symbolic link and there is more path to be
  	 * translated or this operation does not wish to apply
  	 * to a link, then place the contents of the link at the
  	 * front of the remaining pathname.
  	 */
  	if (cvp->v_type == VLNK && ((flags & FOLLOW) || pn_pathleft(pnp))) {
  		struct pathname linkpath;
  
  		if (++nlink > MAXSYMLINKS) {
  			error = ELOOP;
  			goto bad;
  		}
  		pn_alloc(&linkpath);
  		if (error = pn_getsymlink(cvp, &linkpath, cr)) {
  			pn_free(&linkpath);
  			goto bad;
  		}
  
  		if (auditing)
  			audit_symlink(pnp, &linkpath);
  
  		if (pn_pathleft(&linkpath) == 0)
  			(void) pn_set(&linkpath, ".");
  		error = pn_insert(pnp, &linkpath, strlen(component));
  		pn_free(&linkpath);
  		if (error)
  			goto bad;
  		VN_RELE(cvp);
  		cvp = NULL;
  		if (pnp->pn_pathlen == 0) {
  			error = ENOENT;
  			goto bad;
  		}
  		if (pnp->pn_path[0] == '/') {
  			do {
  				pnp->pn_path++;
  				pnp->pn_pathlen--;
  			} while (pnp->pn_path[0] == '/');
  			VN_RELE(vp);
  			vp = rootvp;
  			VN_HOLD(vp);
  		}
  		if (auditing)
  			audit_anchorpath(pnp, vp == rootvp);
  		if (pn_fixslash(pnp)) {
  			flags |= FOLLOW;
  			must_be_directory = 1;
  		}
  		goto next;
  	}
  
  	/*
  	 * If rpnp is non-NULL, remember the resolved path name therein.
  	 * Do not include "." components.  Collapse occurrences of
  	 * "previous/..", so long as "previous" is not itself "..".
  	 * Exhausting rpnp results in error ENAMETOOLONG.
  	 */
  	if (rpnp && strcmp(component, ".") != 0) {
  		size_t len;
  
  		if (strcmp(component, "..") == 0 &&
  		    rpnp->pn_pathlen != 0 &&
  		    !((rpnp->pn_pathlen > 2 &&
  		    strncmp(rpnp->pn_path+rpnp->pn_pathlen-3, "/..", 3) == 0) ||
  		    (rpnp->pn_pathlen == 2 &&
  		    strncmp(rpnp->pn_path, "..", 2) == 0))) {
  			while (rpnp->pn_pathlen &&
  			    rpnp->pn_path[rpnp->pn_pathlen-1] != '/')
  				rpnp->pn_pathlen--;
  			if (rpnp->pn_pathlen > 1)
  				rpnp->pn_pathlen--;
  			rpnp->pn_path[rpnp->pn_pathlen] = '\0';
  		} else {
  			if (rpnp->pn_pathlen != 0 &&
  			    rpnp->pn_path[rpnp->pn_pathlen-1] != '/')
  				rpnp->pn_path[rpnp->pn_pathlen++] = '/';
  			if (flags & FIGNORECASE) {
  				/*
  				 * Return the case-preserved name
  				 * within the resolved path.
  				 */
  				error = copystr(pp->pn_buf,
  				    rpnp->pn_path + rpnp->pn_pathlen,
  				    rpnp->pn_bufsize - rpnp->pn_pathlen, &len);
  			} else {
  				error = copystr(component,
  				    rpnp->pn_path + rpnp->pn_pathlen,
  				    rpnp->pn_bufsize - rpnp->pn_pathlen, &len);
  			}
  			if (error)	/* copystr() returns ENAMETOOLONG */
  				goto bad;
  			rpnp->pn_pathlen += (len - 1);
  			ASSERT(rpnp->pn_bufsize > rpnp->pn_pathlen);
  		}
  	}
  
  	/*
  	 * If no more components, return last directory (if wanted) and
  	 * last component (if wanted).
  	 */
  	if (pn_pathleft(pnp) == 0) {
  		/*
  		 * If there was a trailing slash in the pathname,
  		 * make sure the last component is a directory.
  		 */
  		if (must_be_directory && cvp->v_type != VDIR) {
  			error = ENOTDIR;
  			goto bad;
  		}
  		if (dirvpp != NULL) {
  			/*
  			 * Check that we have the real parent and not
  			 * an alias of the last component.
  			 */
  			if (vn_compare(vp, cvp)) {
  				if (auditing)
  					(void) audit_savepath(pnp, cvp, vp,
  					    EINVAL, cr);
  				pn_setlast(pnp);
  				VN_RELE(vp);
  				VN_RELE(cvp);
  				if (rootvp != rootdir)
  					VN_RELE(rootvp);
  				if (pp)
  					pn_free(pp);
  				return (EINVAL);
  			}
  			*dirvpp = vp;
  		} else
  			VN_RELE(vp);
  		if (auditing)
  			(void) audit_savepath(pnp, cvp, vp, 0, cr);
  		if (pnp->pn_path == pnp->pn_buf)
  			(void) pn_set(pnp, ".");
  		else
  			pn_setlast(pnp);
  		if (rpnp) {
  			if (VN_CMP(cvp, rootvp))
  				(void) pn_set(rpnp, "/");
  			else if (rpnp->pn_pathlen == 0)
  				(void) pn_set(rpnp, ".");
  		}
  
  		if (compvpp != NULL)
  			*compvpp = cvp;
  		else
  			VN_RELE(cvp);
  		if (rootvp != rootdir)
  			VN_RELE(rootvp);
  		if (pp)
  			pn_free(pp);
  		return (0);
  	}
  
  	/*
  	 * Skip over slashes from end of last component.
  	 */
  	while (pnp->pn_path[0] == '/') {
  		pnp->pn_path++;
  		pnp->pn_pathlen--;
  	}
  
  	/*
  	 * Searched through another level of directory:
  	 * release previous directory handle and save new (result
  	 * of lookup) as current directory.
  	 */
  	VN_RELE(vp);
  	vp = cvp;
  	cvp = NULL;
  	goto next;
  
  bad:
  	if (auditing)	/* reached end of path */
  		(void) audit_savepath(pnp, cvp, vp, error, cr);
  bad_noaudit:
  	/*
  	 * Error.  Release vnodes and return.
  	 */
  	if (cvp)
  		VN_RELE(cvp);
  	/*
  	 * If the error was ESTALE and the current directory to look in
  	 * was the root for this lookup, the root for a mounted file
  	 * system, or the starting directory for lookups, then
  	 * return ENOENT instead of ESTALE.  In this case, no recovery
  	 * is possible by the higher level.  If ESTALE was returned for
  	 * some intermediate directory along the path, then recovery
  	 * is potentially possible and retrying from the higher level
  	 * will either correct the situation by purging stale cache
  	 * entries or eventually get back to the point where no recovery
  	 * is possible.
  	 */
  	if (error == ESTALE &&
  	    (VN_CMP(vp, rootvp) || (vp->v_flag & VROOT) || vp == startvp))
  		error = ENOENT;
  	VN_RELE(vp);
  	if (rootvp != rootdir)
  		VN_RELE(rootvp);
  	if (pp)
  		pn_free(pp);
  	return (error);
  }
  
  /*
   * Traverse a mount point.  Routine accepts a vnode pointer as a reference
   * parameter and performs the indirection, releasing the original vnode.
   */
  int
  traverse(vnode_t **cvpp)
  {
  	int error = 0;
  	vnode_t *cvp;
  	vnode_t *tvp;
  	vfs_t *vfsp;
  
  	cvp = *cvpp;
  
  	/*
  	 * If this vnode is mounted on, then we transparently indirect
  	 * to the vnode which is the root of the mounted file system.
  	 * Before we do this we must check that an unmount is not in
  	 * progress on this vnode.
  	 */
  
  	for (;;) {
  		/*
  		 * Try to read lock the vnode.  If this fails because
  		 * the vnode is already write locked, then check to
  		 * see whether it is the current thread which locked
  		 * the vnode.  If it is not, then read lock the vnode
  		 * by waiting to acquire the lock.
  		 *
  		 * The code path in domount() is an example of support
  		 * which needs to look up two pathnames and locks one
  		 * of them in between the two lookups.
  		 */
  		error = vn_vfsrlock(cvp);
  		if (error) {
  			if (!vn_vfswlock_held(cvp))
  				error = vn_vfsrlock_wait(cvp);
  			if (error != 0) {
  				/*
  				 * lookuppn() expects a held vnode to be
  				 * returned because it promptly calls
  				 * VN_RELE after the error return
  				 */
  				*cvpp = cvp;
  				return (error);
  			}
  		}
  
  		/*
  		 * Reached the end of the mount chain?
  		 */
  		vfsp = vn_mountedvfs(cvp);
  		if (vfsp == NULL) {
  			vn_vfsunlock(cvp);
  			break;
  		}
  
  		/*
  		 * The read lock must be held across the call to VFS_ROOT() to
  		 * prevent a concurrent unmount from destroying the vfs.
  		 */
  		error = VFS_ROOT(vfsp, &tvp);
  		vn_vfsunlock(cvp);
  
  		if (error)
  			break;
  
  		VN_RELE(cvp);
  
  		cvp = tvp;
  	}
  
  	*cvpp = cvp;
  	return (error);
  }
  
  /*
   * Return the lowermost vnode if this is a mountpoint.
   */
  static vnode_t *
  vn_under(vnode_t *vp)
  {
  	vnode_t *uvp;
  	vfs_t *vfsp;
  
  	while (vp->v_flag & VROOT) {
  
  		vfsp = vp->v_vfsp;
  		vfs_rlock_wait(vfsp);
  		if ((uvp = vfsp->vfs_vnodecovered) == NULL ||
  		    (vfsp->vfs_flag & VFS_UNMOUNTED)) {
  			vfs_unlock(vfsp);
  			break;
  		}
  		VN_HOLD(uvp);
  		vfs_unlock(vfsp);
  		VN_RELE(vp);
  		vp = uvp;
  	}
  
  	return (vp);
  }
  
  static int
  vnode_match(vnode_t *v1, vnode_t *v2, cred_t *cr)
  {
  	vattr_t	v1attr, v2attr;
  
  	/*
  	 * If we have a device file, check to see if is a cloned open of the
  	 * same device.  For self-cloning devices, the major numbers will match.
  	 * For devices cloned through the 'clone' driver, the minor number of
  	 * the source device will be the same as the major number of the cloned
  	 * device.
  	 */
  	if ((v1->v_type == VCHR || v1->v_type == VBLK) &&
  	    v1->v_type == v2->v_type) {
  		if ((spec_is_selfclone(v1) || spec_is_selfclone(v2)) &&
  		    getmajor(v1->v_rdev) == getmajor(v2->v_rdev))
  			return (1);
  
  		if (spec_is_clone(v1) &&
  		    getmajor(v1->v_rdev) == getminor(v2->v_rdev))
  			return (1);
  
  		if (spec_is_clone(v2) &&
  		    getmajor(v2->v_rdev) == getminor(v1->v_rdev))
  			return (1);
  	}
  
  	v1attr.va_mask = v2attr.va_mask = AT_TYPE;
  
  	/*
  	 * This check for symbolic links handles the pseudo-symlinks in procfs.
  	 * These particular links have v_type of VDIR, but the attributes have a
  	 * type of VLNK.  We need to avoid these links because otherwise if we
  	 * are currently in '/proc/self/fd', then '/proc/self/cwd' will compare
  	 * as the same vnode.
  	 */
  	if (VOP_GETATTR(v1, &v1attr, 0, cr, NULL) != 0 ||
  	    VOP_GETATTR(v2, &v2attr, 0, cr, NULL) != 0 ||
  	    v1attr.va_type == VLNK || v2attr.va_type == VLNK)
  		return (0);
  
  	v1attr.va_mask = v2attr.va_mask = AT_TYPE | AT_FSID | AT_NODEID;
  
  	if (VOP_GETATTR(v1, &v1attr, ATTR_REAL, cr, NULL) != 0 ||
  	    VOP_GETATTR(v2, &v2attr, ATTR_REAL, cr, NULL) != 0)
  		return (0);
  
  	return (v1attr.va_fsid == v2attr.va_fsid &&
  	    v1attr.va_nodeid == v2attr.va_nodeid);
  }
  
  
  /*
   * Find the entry in the directory corresponding to the target vnode.
   */
  int
  dirfindvp(vnode_t *vrootp, vnode_t *dvp, vnode_t *tvp, cred_t *cr, char *dbuf,
      size_t dlen, dirent64_t **rdp)
  {
  	size_t dbuflen;
  	struct iovec iov;
  	struct uio uio;
  	int error;
  	int eof;
  	vnode_t *cmpvp;
  	struct dirent64 *dp;
  	pathname_t pnp;
  
  	ASSERT(dvp->v_type == VDIR);
  
  	/*
  	 * This is necessary because of the strange semantics of VOP_LOOKUP().
  	 */
  	bzero(&pnp, sizeof (pnp));
  
  	uio.uio_iov = &iov;
  	uio.uio_iovcnt = 1;
  	uio.uio_segflg = UIO_SYSSPACE;
  	uio.uio_fmode = 0;
  	uio.uio_extflg = UIO_COPY_CACHED;
  	uio.uio_loffset = 0;
  
  	if ((error = VOP_ACCESS(dvp, VREAD, 0, cr, NULL)) != 0)
  		return (error);
  
  	dp = NULL;
  	eof = 0;
  
  	while (!eof) {
  		uio.uio_resid = dlen;
  		iov.iov_base = dbuf;
  		iov.iov_len = dlen;
  
  		(void) VOP_RWLOCK(dvp, V_WRITELOCK_FALSE, NULL);
  		error = VOP_READDIR(dvp, &uio, cr, &eof, NULL, 0);
  		VOP_RWUNLOCK(dvp, V_WRITELOCK_FALSE, NULL);
  
  		dbuflen = dlen - uio.uio_resid;
  
  		if (error || dbuflen == 0)
  			break;
  
  		dp = (dirent64_t *)dbuf;
  		while ((intptr_t)dp < (intptr_t)dbuf + dbuflen) {
  			/*
  			 * Ignore '.' and '..' entries
  			 */
  			if (strcmp(dp->d_name, ".") == 0 ||
  			    strcmp(dp->d_name, "..") == 0) {
  				dp = (dirent64_t *)((intptr_t)dp +
  				    dp->d_reclen);
  				continue;
  			}
  
  			error = VOP_LOOKUP(dvp, dp->d_name, &cmpvp, &pnp, 0,
  			    vrootp, cr, NULL, NULL, NULL);
  
  			/*
  			 * We only want to bail out if there was an error other
  			 * than ENOENT.  Otherwise, it could be that someone
  			 * just removed an entry since the readdir() call, and
  			 * the entry we want is further on in the directory.
  			 */
  			if (error == 0) {
  				if (vnode_match(tvp, cmpvp, cr)) {
  					VN_RELE(cmpvp);
  					*rdp = dp;
  					return (0);
  				}
  
  				VN_RELE(cmpvp);
  			} else if (error != ENOENT) {
  				return (error);
  			}
  
  			dp = (dirent64_t *)((intptr_t)dp + dp->d_reclen);
  		}
  	}
  
  	/*
  	 * Something strange has happened, this directory does not contain the
  	 * specified vnode.  This should never happen in the normal case, since
  	 * we ensured that dvp is the parent of vp.  This is possible in some
  	 * rare conditions (races and the special .zfs directory).
  	 */
  	if (error == 0) {
  		error = VOP_LOOKUP(dvp, ".zfs", &cmpvp, &pnp, 0, vrootp, cr,
  		    NULL, NULL, NULL);
  		if (error == 0) {
  			if (vnode_match(tvp, cmpvp, cr)) {
  				(void) strcpy(dp->d_name, ".zfs");
  				dp->d_reclen = strlen(".zfs");
  				dp->d_off = 2;
  				dp->d_ino = 1;
  				*rdp = dp;
  			} else {
  				error = ENOENT;
  			}
  			VN_RELE(cmpvp);
  		}
  	}
  
  	return (error);
  }
  
  /*
   * Given a global path (from rootdir), and a vnode that is the current root,
   * return the portion of the path that is beneath the current root or NULL on
   * failure.  The path MUST be a resolved path (no '..' entries or symlinks),
   * otherwise this function will fail.
   */
  static char *
  localpath(char *path, struct vnode *vrootp, cred_t *cr)
  {
  	vnode_t *vp;
  	vnode_t *cvp;
  	char component[MAXNAMELEN];
  	char *ret = NULL;
  	pathname_t pn;
  
  	/*
  	 * We use vn_compare() instead of VN_CMP() in order to detect lofs
  	 * mounts and stacked vnodes.
  	 */
  	if (vn_compare(vrootp, rootdir))
  		return (path);
  
  	if (pn_get(path, UIO_SYSSPACE, &pn) != 0)
  		return (NULL);
  
  	vp = rootdir;
  	VN_HOLD(vp);
  
  	if (vn_ismntpt(vp) && traverse(&vp) != 0) {
  		VN_RELE(vp);
  		pn_free(&pn);
  		return (NULL);
  	}
  
  	while (pn_pathleft(&pn)) {
  		pn_skipslash(&pn);
  
  		if (pn_getcomponent(&pn, component) != 0)
  			break;
  
  		if (VOP_LOOKUP(vp, component, &cvp, &pn, 0, rootdir, cr,
  		    NULL, NULL, NULL) != 0)
  			break;
  		VN_RELE(vp);
  		vp = cvp;
  
  		if (vn_ismntpt(vp) && traverse(&vp) != 0)
  			break;
  
  		if (vn_compare(vp, vrootp)) {
  			ret = path + (pn.pn_path - pn.pn_buf);
  			break;
  		}
  	}
  
  	VN_RELE(vp);
  	pn_free(&pn);
  
  	return (ret);
  }
  
  /*
   * Clean a stale v_path from a vnode.  This is only performed if the v_path has
   * not been altered since it was found to be stale
   */
  static void
  vnode_clear_vpath(vnode_t *vp, char *vpath_old)
  {
  	mutex_enter(&vp->v_lock);
  	if (vp->v_path != vn_vpath_empty && vp->v_path == vpath_old) {
  		vp->v_path = vn_vpath_empty;
  		mutex_exit(&vp->v_lock);
  		kmem_free(vpath_old, strlen(vpath_old) + 1);
  	} else {
  		mutex_exit(&vp->v_lock);
  	}
  }
  
  /*
   * Validate that a pathname refers to a given vnode.
   */
  static int
  vnode_valid_pn(vnode_t *vp, vnode_t *vrootp, pathname_t *pn, pathname_t *rpn,
      int flags, cred_t *cr)
  {
  	vnode_t *compvp;
  	/*
  	 * If we are in a zone or a chroot environment, then we have to
  	 * take additional steps, since the path to the root might not
  	 * be readable with the current credentials, even though the
  	 * process can legitmately access the file.  In this case, we
  	 * do the following:
  	 *
  	 * lookuppnvp() with all privileges to get the resolved path.
  	 * call localpath() to get the local portion of the path, and
  	 * continue as normal.
  	 *
  	 * If the the conversion to a local path fails, then we continue
  	 * as normal.  This is a heuristic to make process object file
  	 * paths available from within a zone.  Because lofs doesn't
  	 * support page operations, the vnode stored in the seg_t is
  	 * actually the underlying real vnode, not the lofs node itself.
  	 * Most of the time, the lofs path is the same as the underlying
  	 * vnode (for example, /usr/lib/libc.so.1).
  	 */
  	if (vrootp != rootdir) {
  		char *local = NULL;
  
  		VN_HOLD(rootdir);
  		if (lookuppnvp(pn, rpn, FOLLOW, NULL, &compvp, rootdir,
  		    rootdir, kcred) == 0) {
  			local = localpath(rpn->pn_path, vrootp, kcred);
  			VN_RELE(compvp);
  		}
  
  		/*
  		 * The original pn was changed through lookuppnvp().
  		 * Set it to local for next validation attempt.
  		 */
  		if (local) {
  			(void) pn_set(pn, local);
  		} else {
  			return (1);
  		}
  	}
  
  	/*
  	 * We should have a local path at this point, so start the search from
  	 * the root of the current process.
  	 */
  	VN_HOLD(vrootp);
  	if (vrootp != rootdir)
  		VN_HOLD(vrootp);
  	if (lookuppnvp(pn, rpn, FOLLOW | flags, NULL, &compvp, vrootp, vrootp,
  	    cr) == 0) {
  		/*
  		 * Check to see if the returned vnode is the same as the one we
  		 * expect.
  		 */
  		if (vn_compare(vp, compvp) ||
  		    vnode_match(vp, compvp, cr)) {
  			VN_RELE(compvp);
  			return (0);
  		} else {
  			VN_RELE(compvp);
  		}
  	}
  
  	return (1);
  }
  
  /*
   * Struct for tracking vnodes with invalidated v_path entries during a
   * dirtopath reverse lookup.  By keeping adequate state, those vnodes can be
   * revisted to populate v_path.
   */
  struct dirpath_walk {
  	struct dirpath_walk	*dw_next;
  	vnode_t			*dw_vnode;
  	vnode_t			*dw_pvnode;
  	size_t			dw_len;
  	char			*dw_name;
  };
  
  /*
   * Given a directory, return the full, resolved path.  This looks up "..",
   * searches for the given vnode in the parent, appends the component, etc.  It
   * is used to implement vnodetopath() and getcwd() when the cached path fails.
   */
  static int
  dirtopath(vnode_t *vrootp, vnode_t *vp, char *buf, size_t buflen, int flags,
      cred_t *cr)
  {
  	pathname_t	pn, rpn, emptypn;
  	vnode_t		*pvp = NULL, *startvp = vp;
  	int		err = 0;
  	size_t		complen;
  	dirent64_t	*dp;
  	char		*bufloc, *dbuf;
  	const size_t	dlen = DIRENT64_RECLEN(MAXPATHLEN);
  	struct dirpath_walk *dw_chain = NULL, *dw_entry;
  
  	/* Operation only allowed on directories */
  	ASSERT(vp->v_type == VDIR);
  
  	/* We must have at least enough space for "/" */
  	if (buflen < 2)
  		return (ENAMETOOLONG);
  
  	/* Start at end of string with terminating null */
  	bufloc = &buf[buflen - 1];
  	*bufloc = '\0';
  
  	pn_alloc(&pn);
  	pn_alloc(&rpn);
  	dbuf = kmem_alloc(dlen, KM_SLEEP);
  	bzero(&emptypn, sizeof (emptypn));
  
  	/*
  	 * Begin with an additional reference on vp.  This will be decremented
  	 * during the loop.
  	 */
  	VN_HOLD(vp);
  
  	for (;;) {
  		int vprivs;
  		hrtime_t cached_stamp;
  
  		/*
  		 * Return if we've reached the root.  If the buffer is empty,
  		 * return '/'.  We explicitly don't use vn_compare(), since it
  		 * compares the real vnodes.  A lofs mount of '/' would produce
  		 * incorrect results otherwise.
  		 */
  		if (VN_CMP(vrootp, vp)) {
  			if (*bufloc == '\0')
  				*--bufloc = '/';
  			break;
  		}
  
  		/*
  		 * If we've reached the VFS root, something has gone wrong.  We
  		 * should have reached the root in the above check.  The only
  		 * explantation is that 'vp' is not contained withing the given
  		 * root, in which case we return EPERM.
  		 */
  		if (VN_CMP(rootdir, vp)) {
  			err = EPERM;
  			goto out;
  		}
  
  		/*
  		 * Shortcut: see if this vnode has correct v_path. If so,
  		 * we have the work done.
  		 */
  		mutex_enter(&vp->v_lock);
  		if (vp->v_path != vn_vpath_empty &&
  		    pn_set(&pn, vp->v_path) == 0) {
  			cached_stamp = vp->v_path_stamp;
  			mutex_exit(&vp->v_lock);
  			rpn.pn_path = rpn.pn_buf;
  
  			/* Ensure the v_path pointing to correct vnode */
  			if (vnode_valid_pn(vp, vrootp, &pn, &rpn, flags,
  			    cr) == 0) {
  				complen = strlen(rpn.pn_path);
  				bufloc -= complen;
  				if (bufloc < buf) {
  					err = ERANGE;
  					goto out;
  				}
  				bcopy(rpn.pn_path, bufloc, complen);
  				break;
  			} else {
  				/*
  				 * Immediately nuke cached v_path entries known
  				 * to be invalid.
  				 */
  				vn_clearpath(vp, cached_stamp);
  			}
  		} else {
  			mutex_exit(&vp->v_lock);
  		}
  
  		/*
  		 * Shortcuts failed, search for this vnode in its parent.  If
  		 * this is a mountpoint, then get the vnode underneath.
  		 */
  		if (vp->v_flag & VROOT)
  			vp = vn_under(vp);
  		if ((err = VOP_LOOKUP(vp, "..", &pvp, &emptypn, 0, vrootp, cr,
  		    NULL, NULL, NULL)) != 0)
  			goto out;
  
  		/*
  		 * With extended attributes, it's possible for a directory to
  		 * have a parent that is a regular file.  Check for that here.
  		 */
  		if (pvp->v_type != VDIR) {
  			err = ENOTDIR;
  			goto out;
  		}
  
  		/*
  		 * If this is true, something strange has happened.  This is
  		 * only true if we are the root of a filesystem, which should
  		 * have been caught by the check above.
  		 */
  		if (VN_CMP(pvp, vp)) {
  			err = ENOENT;
  			goto out;
  		}
  
  		/*
  		 * Check if we have read and search privilege so, that
  		 * we can lookup the path in the directory
  		 */
  		vprivs = (flags & LOOKUP_CHECKREAD) ? VREAD | VEXEC : VEXEC;
  		if ((err = VOP_ACCESS(pvp, vprivs, 0, cr, NULL)) != 0) {
  			goto out;
  		}
  
  		/*
  		 * Search the parent directory for the entry corresponding to
  		 * this vnode.
  		 */
  		if ((err = dirfindvp(vrootp, pvp, vp, cr, dbuf, dlen, &dp))
  		    != 0)
  			goto out;
  		complen = strlen(dp->d_name);
  		bufloc -= complen;
  		if (bufloc <= buf) {
  			err = ENAMETOOLONG;
  			goto out;
  		}
  		bcopy(dp->d_name, bufloc, complen);
  
  		/* Prepend a slash to the current path.  */
  		*--bufloc = '/';
  
  		/*
  		 * Record the name and directory for later reconstruction and
  		 * link it up with the others.
  		 */
  		dw_entry = kmem_alloc(sizeof (*dw_entry), KM_SLEEP);
  		dw_entry->dw_name = kmem_alloc(complen + 1, KM_SLEEP);
  		VN_HOLD(dw_entry->dw_vnode = vp);
  		VN_HOLD(dw_entry->dw_pvnode = pvp);
  		bcopy(dp->d_name, dw_entry->dw_name, complen + 1);
  		dw_entry->dw_len = complen;
  		dw_entry->dw_next = dw_chain;
  		dw_chain = dw_entry;
  
  		/* And continue with the next component */
  		VN_RELE(vp);
  		vp = pvp;
  		pvp = NULL;
  	}
  
  	/*
  	 * Place the path at the beginning of the buffer.
  	 */
  	if (bufloc != buf)
  		ovbcopy(bufloc, buf, buflen - (bufloc - buf));
  
  out:
  	/*
  	 * Walk over encountered directory entries which were afflicted with a
  	 * stale or absent v_path.  If the dirtopath was successful, we should
  	 * possess the necessary information to populate all of them with a
  	 * valid v_path.
  	 *
  	 * While processing this list, it is safe to call vn_setpath despite
  	 * the fact that racing vnode actions may have altered v_path entries
  	 * while the above loopwas still executing.  Any updated entries will
  	 * have a newer v_path_stamp value which prevents an invalid overwrite.
  	 *
  	 * If an error was encountered during the search, freeing the chain is
  	 * still required.
  	 */
  	dw_entry = dw_chain;
  	while (dw_entry != NULL) {
  		struct dirpath_walk *next = dw_entry->dw_next;
  
  		if (err == 0) {
  			vn_setpath(NULL, dw_entry->dw_pvnode,
  			    dw_entry->dw_vnode, dw_entry->dw_name,
  			    dw_entry->dw_len);
  		}
  
  		VN_RELE(dw_entry->dw_vnode);
  		VN_RELE(dw_entry->dw_pvnode);
  		kmem_free(dw_entry->dw_name, dw_entry->dw_len + 1);
  		kmem_free(dw_entry, sizeof (*dw_entry));
  		dw_entry = next;
  	}
  
  	/*
  	 * If the error was ESTALE and the current directory to look in
  	 * was the root for this lookup, the root for a mounted file
  	 * system, or the starting directory for lookups, then
  	 * return ENOENT instead of ESTALE.  In this case, no recovery
  	 * is possible by the higher level.  If ESTALE was returned for
  	 * some intermediate directory along the path, then recovery
  	 * is potentially possible and retrying from the higher level
  	 * will either correct the situation by purging stale cache
  	 * entries or eventually get back to the point where no recovery
  	 * is possible.
  	 */
  	if (err == ESTALE &&
  	    (VN_CMP(vp, vrootp) || (vp->v_flag & VROOT) || vp == startvp))
  		err = ENOENT;
  
  	kmem_free(dbuf, dlen);
  	VN_RELE(vp);
  	if (pvp)
  		VN_RELE(pvp);
  	pn_free(&pn);
  	pn_free(&rpn);
  
  	return (err);
  }
  
  /*
   * The additional flag, LOOKUP_CHECKREAD, is used to enforce artificial
   * constraints in order to be standards compliant.  For example, if we have
   * the cached path of '/foo/bar', and '/foo' has permissions 100 (execute
   * only), then we can legitimately look up the path to the current working
   * directory without needing read permission.  Existing standards tests,
   * however, assume that we are determining the path by repeatedly looking up
   * "..".  We need to keep this behavior in order to maintain backwards
   * compatibility.
   */
  static int
  vnodetopath_common(vnode_t *vrootp, vnode_t *vp, char *buf, size_t buflen,
      cred_t *cr, int flags)
  {
  	pathname_t pn;
  	int ret = 0;
  	vnode_t *realvp;
  	boolean_t doclose = B_FALSE;
  
  	/*
  	 * If vrootp is NULL, get the root for curproc.  Callers with any other
  	 * requirements should pass in a different vrootp.
  	 */
  	if (vrootp == NULL) {
  		proc_t *p = curproc;
  
  		mutex_enter(&p->p_lock);
  		if ((vrootp = PTOU(p)->u_rdir) == NULL)
  			vrootp = rootdir;
  		VN_HOLD(vrootp);
  		mutex_exit(&p->p_lock);
  	} else {
  		VN_HOLD(vrootp);
  	}
  
  	/*
  	 * This is to get around an annoying artifact of the /proc filesystem,
  	 * which is the behavior of {cwd/root}.  Trying to resolve this path
  	 * will result in /proc/pid/cwd instead of whatever the real working
  	 * directory is.  We can't rely on VOP_REALVP(), since that will break
  	 * lofs.  The only difference between procfs and lofs is that opening
  	 * the file will return the underling vnode in the case of procfs.
  	 */
  	if (vp->v_type == VDIR && VOP_REALVP(vp, &realvp, NULL) == 0 &&
  	    realvp != vp) {
  		VN_HOLD(vp);
  		if (VOP_OPEN(&vp, FREAD, cr, NULL) == 0)
  			doclose = B_TRUE;
  		else
  			VN_RELE(vp);
  	}
  
  	/*
  	 * Check to see if we have a valid cached path in the vnode.
  	 */
  	pn_alloc(&pn);
  	mutex_enter(&vp->v_lock);
  	if (vp->v_path != vn_vpath_empty) {
  		hrtime_t cached_stamp;
  		pathname_t rpn;
  
  		cached_stamp = vp->v_path_stamp;
  		(void) pn_set(&pn, vp->v_path);
  		mutex_exit(&vp->v_lock);
  
  		/* We should only cache absolute paths */
  		ASSERT(pn.pn_buf[0] == '/');
  
  		pn_alloc(&rpn);
  		if (vnode_valid_pn(vp, vrootp, &pn, &rpn, flags, cr) == 0) {
  			/* Return the result, if we're able. */
  			if (buflen > rpn.pn_pathlen) {
  				bcopy(rpn.pn_path, buf, rpn.pn_pathlen + 1);
  			} else {
  				ret = ENAMETOOLONG;
  			}
  			pn_free(&pn);
  			pn_free(&rpn);
  			goto out;
  		}
  		pn_free(&rpn);
  		vn_clearpath(vp, cached_stamp);
  	} else {
  		mutex_exit(&vp->v_lock);
  	}
  	pn_free(&pn);
  
  	if (vp->v_type != VDIR) {
  		/*
  		 * The reverse lookup tricks used by dirtopath aren't possible
  		 * for non-directory entries.  The best which can be done is
  		 * clearing any stale v_path so later lookups can potentially
  		 * repopulate it with a valid path.
  		 */
  		ret = ENOENT;
  	} else {
  		ret = dirtopath(vrootp, vp, buf, buflen, flags, cr);
  	}
  
  out:
  	VN_RELE(vrootp);
  	if (doclose) {
  		(void) VOP_CLOSE(vp, FREAD, 1, 0, cr, NULL);
  		VN_RELE(vp);
  	}
  
  	return (ret);
  }
  
  int
  vnodetopath(vnode_t *vrootp, vnode_t *vp, char *buf, size_t buflen, cred_t *cr)
  {
  	return (vnodetopath_common(vrootp, vp, buf, buflen, cr, 0));
  }
  
  int
  dogetcwd(char *buf, size_t buflen)
  {
  	int ret;
  	vnode_t *vp;
  	vnode_t *compvp;
  	refstr_t *cwd, *oldcwd;
  	const char *value;
  	pathname_t rpnp, pnp;
  	proc_t *p = curproc;
  
  	/*
  	 * Check to see if there is a cached version of the cwd.  If so, lookup
  	 * the cached value and make sure it is the same vnode.
  	 */
  	mutex_enter(&p->p_lock);
  	if ((cwd = PTOU(p)->u_cwd) != NULL)
  		refstr_hold(cwd);
  	vp = PTOU(p)->u_cdir;
  	VN_HOLD(vp);
  	mutex_exit(&p->p_lock);
  
  	/*
  	 * Make sure we have permission to access the current directory.
  	 */
  	if ((ret = VOP_ACCESS(vp, VEXEC, 0, CRED(), NULL)) != 0) {
  		if (cwd != NULL)
  			refstr_rele(cwd);
  		VN_RELE(vp);
  		return (ret);
  	}
  
  	if (cwd) {
  		value = refstr_value(cwd);
  		if ((ret = pn_get((char *)value, UIO_SYSSPACE, &pnp)) != 0) {
  			refstr_rele(cwd);
  			VN_RELE(vp);
  			return (ret);
  		}
  
  		pn_alloc(&rpnp);
  
  		if (lookuppn(&pnp, &rpnp, NO_FOLLOW, NULL, &compvp) == 0) {
  
  			if (VN_CMP(vp, compvp) &&
  			    strcmp(value, rpnp.pn_path) == 0) {
  				VN_RELE(compvp);
  				VN_RELE(vp);
  				pn_free(&pnp);
  				pn_free(&rpnp);
  				if (strlen(value) + 1 > buflen) {
  					refstr_rele(cwd);
  					return (ENAMETOOLONG);
  				}
  				bcopy(value, buf, strlen(value) + 1);
  				refstr_rele(cwd);
  				return (0);
  			}
  
  			VN_RELE(compvp);
  		}
  
  		pn_free(&rpnp);
  		pn_free(&pnp);
  
  		refstr_rele(cwd);
  	}
  
  	ret = vnodetopath_common(NULL, vp, buf, buflen, CRED(),
  	    LOOKUP_CHECKREAD);
  
  	VN_RELE(vp);
  
  	/*
  	 * Store the new cwd and replace the existing cached copy.
  	 */
  	if (ret == 0)
  		cwd = refstr_alloc(buf);
  	else
  		cwd = NULL;
  
  	mutex_enter(&p->p_lock);
  	oldcwd = PTOU(p)->u_cwd;
  	PTOU(p)->u_cwd = cwd;
  	mutex_exit(&p->p_lock);
  
  	if (oldcwd)
  		refstr_rele(oldcwd);
  
  	return (ret);
  }
  