Exemple #1
0
/*
 * Rename system call.
 * 	rename("foo", "bar");
 * is essentially
 *	unlink("bar");
 *	link("foo", "bar");
 *	unlink("foo");
 * but ``atomically''.  Can't do full commit without saving state in the
 * inode on disk which isn't feasible at this time.  Best we can do is
 * always guarantee the target exists.
 *
 * Basic algorithm is:
 *
 * 1) Bump link count on source while we're linking it to the
 *    target.  This also ensure the inode won't be deleted out
 *    from underneath us while we work (it may be truncated by
 *    a concurrent `trunc' or `open' for creation).
 * 2) Link source to destination.  If destination already exists,
 *    delete it first.
 * 3) Unlink source reference to inode if still around. If a
 *    directory was moved and the parent of the destination
 *    is different from the source, patch the ".." entry in the
 *    directory.
 */
static int
ext2_rename(struct vop_rename_args *ap)
{
	struct vnode *tvp = ap->a_tvp;
	struct vnode *tdvp = ap->a_tdvp;
	struct vnode *fvp = ap->a_fvp;
	struct vnode *fdvp = ap->a_fdvp;
	struct componentname *tcnp = ap->a_tcnp;
	struct componentname *fcnp = ap->a_fcnp;
	struct inode *ip, *xp, *dp;
	struct dirtemplate dirbuf;
	int doingdirectory = 0, oldparent = 0, newparent = 0;
	int error = 0;
	u_char namlen;

#ifdef DIAGNOSTIC
	if ((tcnp->cn_flags & HASBUF) == 0 ||
	    (fcnp->cn_flags & HASBUF) == 0)
		panic("ext2_rename: no name");
#endif
	/*
	 * Check for cross-device rename.
	 */
	if ((fvp->v_mount != tdvp->v_mount) ||
	    (tvp && (fvp->v_mount != tvp->v_mount))) {
		error = EXDEV;
abortit:
		if (tdvp == tvp)
			vrele(tdvp);
		else
			vput(tdvp);
		if (tvp)
			vput(tvp);
		vrele(fdvp);
		vrele(fvp);
		return (error);
	}

	if (tvp && ((VTOI(tvp)->i_flags & (NOUNLINK | IMMUTABLE | APPEND)) ||
	    (VTOI(tdvp)->i_flags & APPEND))) {
		error = EPERM;
		goto abortit;
	}

	/*
	 * Renaming a file to itself has no effect.  The upper layers should
	 * not call us in that case.  Temporarily just warn if they do.
	 */
	if (fvp == tvp) {
		printf("ext2_rename: fvp == tvp (can't happen)\n");
		error = 0;
		goto abortit;
	}

	if ((error = vn_lock(fvp, LK_EXCLUSIVE)) != 0)
		goto abortit;
	dp = VTOI(fdvp);
	ip = VTOI(fvp);
	if (ip->i_nlink >= EXT2_LINK_MAX) {
 		VOP_UNLOCK(fvp, 0);
 		error = EMLINK;
 		goto abortit;
 	}
	if ((ip->i_flags & (NOUNLINK | IMMUTABLE | APPEND))
	    || (dp->i_flags & APPEND)) {
		VOP_UNLOCK(fvp, 0);
		error = EPERM;
		goto abortit;
	}
	if ((ip->i_mode & IFMT) == IFDIR) {
		/*
		 * Avoid ".", "..", and aliases of "." for obvious reasons.
		 */
		if ((fcnp->cn_namelen == 1 && fcnp->cn_nameptr[0] == '.') ||
		    dp == ip || (fcnp->cn_flags | tcnp->cn_flags) & ISDOTDOT ||
		    (ip->i_flag & IN_RENAME)) {
			VOP_UNLOCK(fvp, 0);
			error = EINVAL;
			goto abortit;
		}
		ip->i_flag |= IN_RENAME;
		oldparent = dp->i_number;
		doingdirectory++;
	}
	vrele(fdvp);

	/*
	 * When the target exists, both the directory
	 * and target vnodes are returned locked.
	 */
	dp = VTOI(tdvp);
	xp = NULL;
	if (tvp)
		xp = VTOI(tvp);

	/*
	 * 1) Bump link count while we're moving stuff
	 *    around.  If we crash somewhere before
	 *    completing our work, the link count
	 *    may be wrong, but correctable.
	 */
	ip->i_nlink++;
	ip->i_flag |= IN_CHANGE;
	if ((error = ext2_update(fvp, !DOINGASYNC(fvp))) != 0) {
		VOP_UNLOCK(fvp, 0);
		goto bad;
	}

	/*
	 * If ".." must be changed (ie the directory gets a new
	 * parent) then the source directory must not be in the
	 * directory hierarchy above the target, as this would
	 * orphan everything below the source directory. Also
	 * the user must have write permission in the source so
	 * as to be able to change "..". We must repeat the call
	 * to namei, as the parent directory is unlocked by the
	 * call to checkpath().
	 */
	error = VOP_ACCESS(fvp, VWRITE, tcnp->cn_cred, tcnp->cn_thread);
	VOP_UNLOCK(fvp, 0);
	if (oldparent != dp->i_number)
		newparent = dp->i_number;
	if (doingdirectory && newparent) {
		if (error)	/* write access check above */
			goto bad;
		if (xp != NULL)
			vput(tvp);
		error = ext2_checkpath(ip, dp, tcnp->cn_cred);
		if (error)
			goto out;
		VREF(tdvp);
		error = relookup(tdvp, &tvp, tcnp);
		if (error)
			goto out;
		vrele(tdvp);
		dp = VTOI(tdvp);
		xp = NULL;
		if (tvp)
			xp = VTOI(tvp);
	}
	/*
	 * 2) If target doesn't exist, link the target
	 *    to the source and unlink the source.
	 *    Otherwise, rewrite the target directory
	 *    entry to reference the source inode and
	 *    expunge the original entry's existence.
	 */
	if (xp == NULL) {
		if (dp->i_devvp != ip->i_devvp)
			panic("ext2_rename: EXDEV");
		/*
		 * Account for ".." in new directory.
		 * When source and destination have the same
		 * parent we don't fool with the link count.
		 */
		if (doingdirectory && newparent) {
			if ((nlink_t)dp->i_nlink >= EXT2_LINK_MAX) {
				error = EMLINK;
				goto bad;
			}
			dp->i_nlink++;
			dp->i_flag |= IN_CHANGE;
			error = ext2_update(tdvp, !DOINGASYNC(tdvp));
			if (error)
				goto bad;
		}
		error = ext2_direnter(ip, tdvp, tcnp);
		if (error) {
			if (doingdirectory && newparent) {
				dp->i_nlink--;
				dp->i_flag |= IN_CHANGE;
				(void)ext2_update(tdvp, 1);
			}
			goto bad;
		}
		vput(tdvp);
	} else {
		if (xp->i_devvp != dp->i_devvp || xp->i_devvp != ip->i_devvp)
		       panic("ext2_rename: EXDEV");
		/*
		 * Short circuit rename(foo, foo).
		 */
		if (xp->i_number == ip->i_number)
			panic("ext2_rename: same file");
		/*
		 * If the parent directory is "sticky", then the user must
		 * own the parent directory, or the destination of the rename,
		 * otherwise the destination may not be changed (except by
		 * root). This implements append-only directories.
		 */
		if ((dp->i_mode & S_ISTXT) && tcnp->cn_cred->cr_uid != 0 &&
		    tcnp->cn_cred->cr_uid != dp->i_uid &&
		    xp->i_uid != tcnp->cn_cred->cr_uid) {
			error = EPERM;
			goto bad;
		}
		/*
		 * Target must be empty if a directory and have no links
		 * to it. Also, ensure source and target are compatible
		 * (both directories, or both not directories).
		 */
		if ((xp->i_mode&IFMT) == IFDIR) {
			if (! ext2_dirempty(xp, dp->i_number, tcnp->cn_cred) || 
			    xp->i_nlink > 2) {
				error = ENOTEMPTY;
				goto bad;
			}
			if (!doingdirectory) {
				error = ENOTDIR;
				goto bad;
			}
			cache_purge(tdvp);
		} else if (doingdirectory) {
			error = EISDIR;
			goto bad;
		}
		error = ext2_dirrewrite(dp, ip, tcnp);
		if (error)
			goto bad;
		/*
		 * If the target directory is in the same
		 * directory as the source directory,
		 * decrement the link count on the parent
		 * of the target directory.
		 */
		if (doingdirectory && !newparent) {
		       dp->i_nlink--;
		       dp->i_flag |= IN_CHANGE;
		}
		vput(tdvp);
		/*
		 * Adjust the link count of the target to
		 * reflect the dirrewrite above.  If this is
		 * a directory it is empty and there are
		 * no links to it, so we can squash the inode and
		 * any space associated with it.  We disallowed
		 * renaming over top of a directory with links to
		 * it above, as the remaining link would point to
		 * a directory without "." or ".." entries.
		 */
		xp->i_nlink--;
		if (doingdirectory) {
			if (--xp->i_nlink != 0)
				panic("ext2_rename: linked directory");
			error = ext2_truncate(tvp, (off_t)0, IO_SYNC,
			    tcnp->cn_cred, tcnp->cn_thread);
		}
		xp->i_flag |= IN_CHANGE;
		vput(tvp);
		xp = NULL;
	}

	/*
	 * 3) Unlink the source.
	 */
	fcnp->cn_flags &= ~MODMASK;
	fcnp->cn_flags |= LOCKPARENT | LOCKLEAF;
	VREF(fdvp);
	error = relookup(fdvp, &fvp, fcnp);
	if (error == 0)
		vrele(fdvp);
	if (fvp != NULL) {
		xp = VTOI(fvp);
		dp = VTOI(fdvp);
	} else {
		/*
		 * From name has disappeared.
		 */
		if (doingdirectory)
			panic("ext2_rename: lost dir entry");
		vrele(ap->a_fvp);
		return (0);
	}
	/*
	 * Ensure that the directory entry still exists and has not
	 * changed while the new name has been entered. If the source is
	 * a file then the entry may have been unlinked or renamed. In
	 * either case there is no further work to be done. If the source
	 * is a directory then it cannot have been rmdir'ed; its link
	 * count of three would cause a rmdir to fail with ENOTEMPTY.
	 * The IN_RENAME flag ensures that it cannot be moved by another
	 * rename.
	 */
	if (xp != ip) {
		if (doingdirectory)
			panic("ext2_rename: lost dir entry");
	} else {
		/*
		 * If the source is a directory with a
		 * new parent, the link count of the old
		 * parent directory must be decremented
		 * and ".." set to point to the new parent.
		 */
		if (doingdirectory && newparent) {
			dp->i_nlink--;
			dp->i_flag |= IN_CHANGE;
			error = vn_rdwr(UIO_READ, fvp, (caddr_t)&dirbuf,
				sizeof(struct dirtemplate), (off_t)0,
				UIO_SYSSPACE, IO_NODELOCKED | IO_NOMACCHECK,
				tcnp->cn_cred, NOCRED, NULL, NULL);
			if (error == 0) {
				/* Like ufs little-endian: */
				namlen = dirbuf.dotdot_type;
				if (namlen != 2 ||
				    dirbuf.dotdot_name[0] != '.' ||
				    dirbuf.dotdot_name[1] != '.') {
					ext2_dirbad(xp, (doff_t)12,
					    "rename: mangled dir");
				} else {
					dirbuf.dotdot_ino = newparent;
					(void) vn_rdwr(UIO_WRITE, fvp,
					    (caddr_t)&dirbuf,
					    sizeof(struct dirtemplate),
					    (off_t)0, UIO_SYSSPACE,
					    IO_NODELOCKED | IO_SYNC |
					    IO_NOMACCHECK, tcnp->cn_cred,
					    NOCRED, NULL, NULL);
					cache_purge(fdvp);
				}
			}
		}
		error = ext2_dirremove(fdvp, fcnp);
		if (!error) {
			xp->i_nlink--;
			xp->i_flag |= IN_CHANGE;
		}
		xp->i_flag &= ~IN_RENAME;
	}
	if (dp)
		vput(fdvp);
	if (xp)
		vput(fvp);
	vrele(ap->a_fvp);
	return (error);

bad:
	if (xp)
		vput(ITOV(xp));
	vput(ITOV(dp));
out:
	if (doingdirectory)
		ip->i_flag &= ~IN_RENAME;
	if (vn_lock(fvp, LK_EXCLUSIVE) == 0) {
		ip->i_nlink--;
		ip->i_flag |= IN_CHANGE;
		ip->i_flag &= ~IN_RENAME;
		vput(fvp);
	} else
		vrele(fvp);
	return (error);
}
Exemple #2
0
/*
 * Convert a component of a pathname into a pointer to a locked inode.
 * This is a very central and rather complicated routine.
 * If the file system is not maintained in a strict tree hierarchy,
 * this can result in a deadlock situation (see comments in code below).
 *
 * The cnp->cn_nameiop argument is LOOKUP, CREATE, RENAME, or DELETE depending
 * on whether the name is to be looked up, created, renamed, or deleted.
 * When CREATE, RENAME, or DELETE is specified, information usable in
 * creating, renaming, or deleting a directory entry may be calculated.
 * If flag has LOCKPARENT or'ed into it and the target of the pathname
 * exists, lookup returns both the target and its parent directory locked.
 * When creating or renaming and LOCKPARENT is specified, the target may
 * not be ".".  When deleting and LOCKPARENT is specified, the target may
 * be "."., but the caller must check to ensure it does an vrele and vput
 * instead of two vputs.
 *
 * Overall outline of ufs_lookup:
 *
 *	search for name in directory, to found or notfound
 * notfound:
 *	if creating, return locked directory, leaving info on available slots
 *	else return error
 * found:
 *	if at end of path and deleting, return information to allow delete
 *	if at end of path and rewriting (RENAME and LOCKPARENT), lock target
 *	  inode and return info to allow rewrite
 *	if not at end, add name to cache; if at end and neither creating
 *	  nor deleting, add name to cache
 *
 * ext2_lookup(struct vnode *a_dvp, struct vnode **a_vpp,
 *	       struct componentname *a_cnp)
 */
int
ext2_lookup(struct vop_old_lookup_args *ap)
{
	struct vnode *vdp;	/* vnode for directory being searched */
	struct inode *dp;	/* inode for directory being searched */
	struct buf *bp;			/* a buffer of directory entries */
	struct ext2_dir_entry_2 *ep; /* the current directory entry */
	int entryoffsetinblock;		/* offset of ep in bp's buffer */
	enum {NONE, COMPACT, FOUND} slotstatus;
	doff_t slotoffset;		/* offset of area with free space */
	int slotsize;			/* size of area at slotoffset */
	int slotfreespace;		/* amount of space free in slot */
	int slotneeded;			/* size of the entry we're seeking */
	int numdirpasses;		/* strategy for directory search */
	doff_t endsearch;		/* offset to end directory search */
	doff_t prevoff;			/* prev entry dp->i_offset */
	struct vnode *pdp;		/* saved dp during symlink work */
	struct vnode *tdp;		/* returned by VFS_VGET */
	doff_t enduseful;		/* pointer past last used dir slot */
	u_long bmask;			/* block offset mask */
	int lockparent;			/* 1 => lockparent flag is set */
	int wantparent;			/* 1 => wantparent or lockparent flag */
	int namlen, error;
	struct vnode **vpp = ap->a_vpp;
	struct componentname *cnp = ap->a_cnp;
	struct ucred *cred = cnp->cn_cred;
	int flags = cnp->cn_flags;
	int nameiop = cnp->cn_nameiop;

	int	DIRBLKSIZ = VTOI(ap->a_dvp)->i_e2fs->s_blocksize;

	bp = NULL;
	slotoffset = -1;
	*vpp = NULL;
	vdp = ap->a_dvp;
	dp = VTOI(vdp);
	lockparent = flags & CNP_LOCKPARENT;
	wantparent = flags & (CNP_LOCKPARENT|CNP_WANTPARENT);

	/*
	 * We now have a segment name to search for, and a directory to search.
	 */

	/*
	 * Suppress search for slots unless creating
	 * file and at end of pathname, in which case
	 * we watch for a place to put the new file in
	 * case it doesn't already exist.
	 */
	slotstatus = FOUND;
	slotfreespace = slotsize = slotneeded = 0;
	if (nameiop == NAMEI_CREATE || nameiop == NAMEI_RENAME) {
		slotstatus = NONE;
		slotneeded = EXT2_DIR_REC_LEN(cnp->cn_namelen);
		/* was
		slotneeded = (sizeof(struct direct) - MAXNAMLEN +
			cnp->cn_namelen + 3) &~ 3; */
	}

	/*
	 * If there is cached information on a previous search of
	 * this directory, pick up where we last left off.
	 * We cache only lookups as these are the most common
	 * and have the greatest payoff. Caching CREATE has little
	 * benefit as it usually must search the entire directory
	 * to determine that the entry does not exist. Caching the
	 * location of the last DELETE or RENAME has not reduced
	 * profiling time and hence has been removed in the interest
	 * of simplicity.
	 */
	bmask = VFSTOEXT2(vdp->v_mount)->um_mountp->mnt_stat.f_iosize - 1;
	if (nameiop != NAMEI_LOOKUP || dp->i_diroff == 0 ||
	    dp->i_diroff > dp->i_size) {
		entryoffsetinblock = 0;
		dp->i_offset = 0;
		numdirpasses = 1;
	} else {
		dp->i_offset = dp->i_diroff;
		if ((entryoffsetinblock = dp->i_offset & bmask) &&
		    (error = EXT2_BLKATOFF(vdp, (off_t)dp->i_offset, NULL, &bp)))
			return (error);
		numdirpasses = 2;
	}
	prevoff = dp->i_offset;
	endsearch = roundup(dp->i_size, DIRBLKSIZ);
	enduseful = 0;

searchloop:
	while (dp->i_offset < endsearch) {
		/*
		 * If necessary, get the next directory block.
		 */
		if ((dp->i_offset & bmask) == 0) {
			if (bp != NULL)
				brelse(bp);
			if ((error =
			    EXT2_BLKATOFF(vdp, (off_t)dp->i_offset, NULL, &bp)) != 0)
				return (error);
			entryoffsetinblock = 0;
		}
		/*
		 * If still looking for a slot, and at a DIRBLKSIZE
		 * boundary, have to start looking for free space again.
		 */
		if (slotstatus == NONE &&
		    (entryoffsetinblock & (DIRBLKSIZ - 1)) == 0) {
			slotoffset = -1;
			slotfreespace = 0;
		}
		/*
		 * Get pointer to next entry.
		 * Full validation checks are slow, so we only check
		 * enough to insure forward progress through the
		 * directory. Complete checks can be run by patching
		 * "dirchk" to be true.
		 */
		ep = (struct ext2_dir_entry_2 *)
			((char *)bp->b_data + entryoffsetinblock);
		if (ep->rec_len == 0 ||
		    (dirchk && ext2_dirbadentry(vdp, ep, entryoffsetinblock))) {
			int i;
			ext2_dirbad(dp, dp->i_offset, "mangled entry");
			i = DIRBLKSIZ - (entryoffsetinblock & (DIRBLKSIZ - 1));
			dp->i_offset += i;
			entryoffsetinblock += i;
			continue;
		}

		/*
		 * If an appropriate sized slot has not yet been found,
		 * check to see if one is available. Also accumulate space
		 * in the current block so that we can determine if
		 * compaction is viable.
		 */
		if (slotstatus != FOUND) {
			int size = ep->rec_len;

			if (ep->inode != 0)
				size -= EXT2_DIR_REC_LEN(ep->name_len);
			if (size > 0) {
				if (size >= slotneeded) {
					slotstatus = FOUND;
					slotoffset = dp->i_offset;
					slotsize = ep->rec_len;
				} else if (slotstatus == NONE) {
					slotfreespace += size;
					if (slotoffset == -1)
						slotoffset = dp->i_offset;
					if (slotfreespace >= slotneeded) {
						slotstatus = COMPACT;
						slotsize = dp->i_offset +
						      ep->rec_len - slotoffset;
					}
				}
			}
		}

		/*
		 * Check for a name match.
		 */
		if (ep->inode) {
			namlen = ep->name_len;
			if (namlen == cnp->cn_namelen &&
			    !bcmp(cnp->cn_nameptr, ep->name,
				(unsigned)namlen)) {
				/*
				 * Save directory entry's inode number and
				 * reclen in ndp->ni_ufs area, and release
				 * directory buffer.
				 */
				dp->i_ino = ep->inode;
				dp->i_reclen = ep->rec_len;
				goto found;
			}
		}
		prevoff = dp->i_offset;
		dp->i_offset += ep->rec_len;
		entryoffsetinblock += ep->rec_len;
		if (ep->inode)
			enduseful = dp->i_offset;
	}
/* notfound: */
	/*
	 * If we started in the middle of the directory and failed
	 * to find our target, we must check the beginning as well.
	 */
	if (numdirpasses == 2) {
		numdirpasses--;
		dp->i_offset = 0;
		endsearch = dp->i_diroff;
		goto searchloop;
	}
	if (bp != NULL)
		brelse(bp);
	/*
	 * If creating, and at end of pathname and current
	 * directory has not been removed, then can consider
	 * allowing file to be created.
	 */
	if ((nameiop == NAMEI_CREATE || nameiop == NAMEI_RENAME) &&
	    dp->i_nlink != 0) {
		/*
		 * Access for write is interpreted as allowing
		 * creation of files in the directory.
		 */
		if ((error = VOP_EACCESS(vdp, VWRITE, cred)) != 0)
			return (error);
		/*
		 * Return an indication of where the new directory
		 * entry should be put.  If we didn't find a slot,
		 * then set dp->i_count to 0 indicating
		 * that the new slot belongs at the end of the
		 * directory. If we found a slot, then the new entry
		 * can be put in the range from dp->i_offset to
		 * dp->i_offset + dp->i_count.
		 */
		if (slotstatus == NONE) {
			dp->i_offset = roundup(dp->i_size, DIRBLKSIZ);
			dp->i_count = 0;
			enduseful = dp->i_offset;
		} else {
			dp->i_offset = slotoffset;
			dp->i_count = slotsize;
			if (enduseful < slotoffset + slotsize)
				enduseful = slotoffset + slotsize;
		}
		dp->i_endoff = roundup(enduseful, DIRBLKSIZ);
		dp->i_flag |= IN_CHANGE | IN_UPDATE;
		/*
		 * We return with the directory locked, so that
		 * the parameters we set up above will still be
		 * valid if we actually decide to do a direnter().
		 * We return ni_vp == NULL to indicate that the entry
		 * does not currently exist; we leave a pointer to
		 * the (locked) directory inode in ndp->ni_dvp.
		 * The pathname buffer is saved so that the name
		 * can be obtained later.
		 *
		 * NB - if the directory is unlocked, then this
		 * information cannot be used.
		 */
		if (!lockparent)
			vn_unlock(vdp);
		return (EJUSTRETURN);
	}
	return (ENOENT);

found:
	/*
	 * Check that directory length properly reflects presence
	 * of this entry.
	 */
	if (entryoffsetinblock + EXT2_DIR_REC_LEN(ep->name_len)
		> dp->i_size) {
		ext2_dirbad(dp, dp->i_offset, "i_size too small");
		dp->i_size = entryoffsetinblock+EXT2_DIR_REC_LEN(ep->name_len);
		dp->i_flag |= IN_CHANGE | IN_UPDATE;
	}
	brelse(bp);

	/*
	 * Found component in pathname.
	 * If the final component of path name, save information
	 * in the cache as to where the entry was found.
	 */
	if (nameiop == NAMEI_LOOKUP)
		dp->i_diroff = dp->i_offset &~ (DIRBLKSIZ - 1);

	/*
	 * If deleting, and at end of pathname, return
	 * parameters which can be used to remove file.
	 * If the wantparent flag isn't set, we return only
	 * the directory (in ndp->ni_dvp), otherwise we go
	 * on and lock the inode, being careful with ".".
	 */
	if (nameiop == NAMEI_DELETE) {
		/*
		 * Write access to directory required to delete files.
		 */
		if ((error = VOP_EACCESS(vdp, VWRITE, cred)) != 0)
			return (error);
		/*
		 * Return pointer to current entry in dp->i_offset,
		 * and distance past previous entry (if there
		 * is a previous entry in this block) in dp->i_count.
		 * Save directory inode pointer in ndp->ni_dvp for dirremove().
		 */
		if ((dp->i_offset & (DIRBLKSIZ - 1)) == 0)
			dp->i_count = 0;
		else
			dp->i_count = dp->i_offset - prevoff;
		if (dp->i_number == dp->i_ino) {
			vref(vdp);
			*vpp = vdp;
			return (0);
		}
		if ((error = VFS_VGET(vdp->v_mount, NULL, dp->i_ino, &tdp)) != 0)
			return (error);
		/*
		 * If directory is "sticky", then user must own
		 * the directory, or the file in it, else she
		 * may not delete it (unless she's root). This
		 * implements append-only directories.
		 */
		if ((dp->i_mode & ISVTX) &&
		    cred->cr_uid != 0 &&
		    cred->cr_uid != dp->i_uid &&
		    VTOI(tdp)->i_uid != cred->cr_uid) {
			vput(tdp);
			return (EPERM);
		}
		*vpp = tdp;
		if (!lockparent)
			vn_unlock(vdp);
		return (0);
	}

	/*
	 * If rewriting (RENAME), return the inode and the
	 * information required to rewrite the present directory
	 * Must get inode of directory entry to verify it's a
	 * regular file, or empty directory.
	 */
	if (nameiop == NAMEI_RENAME && wantparent) {
		if ((error = VOP_EACCESS(vdp, VWRITE, cred)) != 0)
			return (error);
		/*
		 * Careful about locking second inode.
		 * This can only occur if the target is ".".
		 */
		if (dp->i_number == dp->i_ino)
			return (EISDIR);
		if ((error = VFS_VGET(vdp->v_mount, NULL, dp->i_ino, &tdp)) != 0)
			return (error);
		*vpp = tdp;
		if (!lockparent)
			vn_unlock(vdp);
		return (0);
	}

	/*
	 * Step through the translation in the name.  We do not `vput' the
	 * directory because we may need it again if a symbolic link
	 * is relative to the current directory.  Instead we save it
	 * unlocked as "pdp".  We must get the target inode before unlocking
	 * the directory to insure that the inode will not be removed
	 * before we get it.  We prevent deadlock by always fetching
	 * inodes from the root, moving down the directory tree. Thus
	 * when following backward pointers ".." we must unlock the
	 * parent directory before getting the requested directory.
	 * There is a potential race condition here if both the current
	 * and parent directories are removed before the VFS_VGET for the
	 * inode associated with ".." returns.  We hope that this occurs
	 * infrequently since we cannot avoid this race condition without
	 * implementing a sophisticated deadlock detection algorithm.
	 * Note also that this simple deadlock detection scheme will not
	 * work if the file system has any hard links other than ".."
	 * that point backwards in the directory structure.
	 */
	pdp = vdp;
	if (flags & CNP_ISDOTDOT) {
		vn_unlock(pdp);	/* race to get the inode */
		if ((error = VFS_VGET(vdp->v_mount, NULL, dp->i_ino, &tdp)) != 0) {
			vn_lock(pdp, LK_EXCLUSIVE | LK_RETRY);
			return (error);
		}
		if (lockparent && (error = vn_lock(pdp, LK_EXCLUSIVE))) {
			vput(tdp);
			return (error);
		}
		*vpp = tdp;
	} else if (dp->i_number == dp->i_ino) {
		vref(vdp);	/* we want ourself, ie "." */
		*vpp = vdp;
	} else {
		if ((error = VFS_VGET(vdp->v_mount, NULL, dp->i_ino, &tdp)) != 0)
			return (error);
		if (!lockparent)
			vn_unlock(pdp);
		*vpp = tdp;
	}
	return (0);
}