452 lines
11 KiB
Groff
452 lines
11 KiB
Groff
.\" -*- nroff -*-
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.\"
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.\" Copyright (c) 1996 Doug Rabson
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.\"
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.\" All rights reserved.
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.\"
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.\" This program is free software.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd November 24, 1997
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.Os FreeBSD
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.Dt VOP_LOOKUP 9
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.Sh NAME
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.Nm VOP_LOOKUP
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.Nd lookup a component of a pathname
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.Sh SYNOPSIS
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.Fd #include <sys/param.h>
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.Fd #include <sys/vnode.h>
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.Fd #include <sys/namei.h>
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.Ft int
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.Fn VOP_LOOKUP "struct vnode *dvp" "struct vnode **vpp" "struct componentname *cnp"
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.Sh DESCRIPTION
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This VFS entry point looks up a single pathname component in a given directory.
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.Pp
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Its arguments are:
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.Bl -tag -width vpp
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.It Ar dvp
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the locked vnode of the directory to search
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.It Ar vpp
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the address of a variable where the resulting locked vnode should be stored
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.It Ar cnp
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the pathname component to be searched for
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.El
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.Pp
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.Fa Cnp
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is a pointer to a componentname structure defined as follows:
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.Bd -literal
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struct componentname {
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/*
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* Arguments to lookup.
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*/
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u_long cn_nameiop; /* namei operation */
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u_long cn_flags; /* flags to namei */
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struct proc *cn_proc; /* process requesting lookup */
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struct ucred *cn_cred; /* credentials */
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/*
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* Shared between lookup and commit routines.
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*/
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char *cn_pnbuf; /* pathname buffer */
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char *cn_nameptr; /* pointer to looked up name */
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long cn_namelen; /* length of looked up component */
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u_long cn_hash; /* hash value of looked up name */
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long cn_consume; /* chars to consume in lookup() */
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};
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.Ed
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.Pp
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Convert a component of a pathname into a pointer to a locked vnode.
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This is a very central and rather complicated routine.
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If the file system is not maintained in a strict tree hierarchy,
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this can result in a deadlock situation.
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.Pp
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The
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.Fa cnp->cn_nameiop
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argument is
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.Dv LOOKUP ,
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.Dv CREATE ,
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.Dv RENAME ,
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or
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.Dv DELETE
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depending on the intended use of the object.
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When
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.Dv CREATE ,
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.Dv RENAME ,
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or
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.Dv DELETE
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is specified, information usable in
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creating, renaming, or deleting a directory entry may be calculated.
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.Pp
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Overall outline of VOP_LOOKUP:
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.Bd -filled -offset indent
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Check accessibility of directory.
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Look for name in cache, if found, then return name.
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Search for name in directory, goto to found or notfound as appropriate.
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.Ed
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.Pp
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notfound:
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.Bd -filled -offset indent
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If creating or renaming and at end of pathname,
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return
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.Dv EJUSTRETURN ,
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leaving info on available slots else return
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.Dv ENOENT .
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.Ed
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.Pp
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found:
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.Bd -filled -offset indent
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If at end of path and deleting, return information to allow delete.
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If at end of path and renaming, lock target
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inode and return info to allow rename.
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If not at end, add name to cache; if at end and neither creating
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nor deleting, add name to cache.
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.Ed
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.Sh LOCKS
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The directory,
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.Fa dvp
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should be locked on entry.
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If an error (note: the return value
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.Dv EJUSTRETURN
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is not considered an error)
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is detected, it will be returned locked.
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Otherwise, it will be unlocked unless both
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.Dv LOCKPARENT
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and
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.Dv ISLASTCN
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are specified in
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.Fa cnp->cn_flags .
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If an entry is found in the directory, it will be returned locked.
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.Sh RETURN VALUES
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Zero is returned with
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.Fa *vpp
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set to the locked vnode of the file if the component is found.
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If the component being searched for is ".", then the vnode just has
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an extra reference added to it with
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.Xr vref 9 .
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The caller must take care to release the locks appropriately in this
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case.
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.Pp
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If the component is not found and the operation is
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.Dv CREATE
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or
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.Dv RENAME ,
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the flag
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.Dv ISLASTCN
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is specified and the operation would succeed, the special return value
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.Dv EJUSTRETURN
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is returned.
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Otherwise, an appropriate error code is returned.
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.Sh PSEUDOCODE
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.Bd -literal
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int
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vop_lookup(struct vnode *dvp,
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struct vnode **vpp,
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struct componentname *cnp)
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{
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int error;
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int nameiop = cnp->cn_nameiop;
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int flags = cnp->cn_flags;
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int lockparent = flags & LOCKPARENT;
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int islastcn = flags & ISLASTCN;
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struct vnode *vp = NULL;
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/*
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* Check accessibility of directory.
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*/
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if (dvp->v_type != VDIR)
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return ENOTDIR;
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error = VOP_ACCESS(dvp, VEXEC, cred, cnp->cn_proc);
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if (error)
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return (error);
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if (islastcn && (dvp->v_mount->mnt_flag & MNT_RDONLY) &&
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(cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME))
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return (EROFS);
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/*
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* Check name cache for directory/name pair. This returns ENOENT
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* if the name is known not to exist, -1 if the name was found, or
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* zero if not.
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*/
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error = cache_lookup(dvp, vpp, cnp);
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if (error) {
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int vpid;
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if (error = ENOENT)
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return error;
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vp = *vpp;
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if (dvp == vp) { /* lookup on "." */
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VREF(vp);
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error = 0;
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} else if (flags & ISDOTDOT) {
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/*
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* We need to unlock the directory before getting
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* the locked vnode for ".." to avoid deadlocks.
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*/
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VOP_UNLOCK(dvp);
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error = vget(vp, 1);
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if (!error) {
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if (lockparent && islastcn)
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error = VOP_LOCK(dvp);
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}
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} else {
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error = vget(vp, 1);
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if (error || !(lockparent && islastcn)) {
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VOP_UNLOCK(dvp);
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}
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}
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/*
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* Check that the capability number did not change
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* while we were waiting for the lock.
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*/
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if (!error) {
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if (vpid == vp->v_id) {
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/*
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* dvp is locked if lockparent && islastcn.
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* vp is locked.
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*/
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return (0);
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}
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vput(vp);
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if (dvp != vp && lockparent && islastcn)
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VOP_UNLOCK(pdp);
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}
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/*
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* Re-lock dvp for the directory search below.
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*/
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error = VOP_LOCK(dvp);
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if (error) {
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return (error);
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}
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*vpp = NULL;
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}
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/*
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* Search dvp for the component cnp->cn_nameptr.
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*/
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...;
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if (!found) {
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if ((nameiop == CREATE || nameiop == RENAME)
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&& islastcn
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&& directory dvp has not been removed) {
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/*
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* Check for write access on directory.
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*/
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/*
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* Possibly record the position of a slot in the directory
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* large enough for the new component name. This can be
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* recorded in the vnode private data for dvp.
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* Set the SAVENAME flag to hold onto the pathname for use
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* later in VOP_CREATE or VOP_RENAME.
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*/
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cnp->cn_flags |= SAVENAME;
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if (!lockparent)
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/*
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* Note that the extra data recorded above is only
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* useful if lockparent is specified.
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*/
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VOP_UNLOCK(dvp);
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return EJUSTRETURN;
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}
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/*
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* Consider inserting name into cache.
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*/
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if ((cnp->cn_flags & MAKEENTRY) && nameiop != CREATE)
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cache_enter(dvp, NULL, cnp);
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return ENOENT;
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} else {
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/*
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* If deleting, and at end of pathname, return parameters
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* which can be used to remove file. If the wantparent flag
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* isn't set, we return only the directory, otherwise we go on
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* and lock the inode, being careful with ".".
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*/
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if (nameiop == DELETE && islastcn) {
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/*
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* Check for write access on directory.
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*/
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error = VOP_ACCESS(dvp, VWRITE, cred, cnp->cn_proc);
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if (error)
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return (error);
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if (found entry is same as dvp) {
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VREF(dvp);
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*vpp = dvp;
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return 0;
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}
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error = VFS_VGET(dvp->v_mount, ..., &vp);
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if (error)
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return error;
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if (directory is sticky
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&& cred->cr_uid != 0
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&& cred->cr_uid != owner of dvp
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&& owner of vp != cred->cr_uid) {
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vput(vp);
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return EPERM;
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}
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*vpp = vp;
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if (!lockparent)
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VOP_UNLOCK(dvp);
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return 0;
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}
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/*
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* If rewriting (RENAME), return the inode and the
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* information required to rewrite the present directory
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* Must get inode of directory entry to verify it's a
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* regular file, or empty directory.
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*/
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if (nameiop == RENAME && wantparent && islastcn) {
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error = VOP_ACCESS(dvp, VWRITE, cred, cnp->cn_proc);
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if (error)
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return (error);
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/*
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* Check for "."
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*/
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if (found entry is same as dvp)
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return EISDIR;
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error = VFS_VGET(dvp->v_mount, ..., &vp);
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if (error)
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return error;
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*vpp = vp;
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/*
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* Save the name for use in VOP_RENAME later.
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*/
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cnp->cn_flags |= SAVENAME;
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if (!lockparent)
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VOP_UNLOCK(dvp);
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return 0;
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}
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/*
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* Step through the translation in the name. We do not `vput' the
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* directory because we may need it again if a symbolic link
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* is relative to the current directory. Instead we save it
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* unlocked as "pdp". We must get the target inode before unlocking
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* the directory to insure that the inode will not be removed
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* before we get it. We prevent deadlock by always fetching
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* inodes from the root, moving down the directory tree. Thus
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* when following backward pointers ".." we must unlock the
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* parent directory before getting the requested directory.
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* There is a potential race condition here if both the current
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* and parent directories are removed before the VFS_VGET for the
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* inode associated with ".." returns. We hope that this occurs
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* infrequently since we cannot avoid this race condition without
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* implementing a sophisticated deadlock detection algorithm.
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* Note also that this simple deadlock detection scheme will not
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* work if the file system has any hard links other than ".."
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* that point backwards in the directory structure.
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*/
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if (flags & ISDOTDOT) {
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VOP_UNLOCK(dvp); /* race to get the inode */
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error = VFS_VGET(dvp->v_mount, ..., &vp);
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if (error) {
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VOP_LOCK(dvp);
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return (error);
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}
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if (lockparent && islastcn) {
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error = VOP_LOCK(dvp);
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if (error) {
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vput(vp);
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return error;
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}
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}
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*vpp = vp;
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} else if (found entry is same as dvp) {
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VREF(dvp); /* we want ourself, ie "." */
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*vpp = dvp;
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} else {
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error = VFS_VGET(dvp->v_mount, ..., &vp);
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if (error)
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return (error);
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if (!lockparent || !islastcn)
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VOP_UNLOCK(dvp);
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*vpp = vp;
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}
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/*
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* Insert name into cache if appropriate.
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*/
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if (cnp->cn_flags & MAKEENTRY)
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cache_enter(dvp, *vpp, cnp);
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return (0);
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}
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}
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.Ed
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er ENOTDIR
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The vnode
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.Fa dvp
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does not represent a directory.
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.It Bq Er ENOENT
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The component
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.Fa dvp
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was not found in this directory.
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.It Bq Er EACCES
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access for the specified operation is denied.
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.It Bq Er EJUSTRETURN
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a
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.Dv CREATE
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or
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.Dv RENAME
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operation would be successful
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.El
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.Sh SEE ALSO
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.Xr VOP_ABORTOP 9 ,
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.Xr VOP_ACCESS 9 ,
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.Xr VOP_CREATE 9 ,
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.Xr VOP_MKDIR 9 ,
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.Xr VOP_MKNOD 9 ,
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.Xr VOP_RENAME 9 ,
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.Xr VOP_SYMLINK 9
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.Sh HISTORY
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The function
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.Nm
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appeared in
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.Bx 4.3 .
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.Sh SEE ALSO
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.Xr vnode 9
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.Sh AUTHORS
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This man page was written by
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.An Doug Rabson ,
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with some text from comments in
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.Pa ufs_lookup.c .
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