375 lines
9.0 KiB
Groff
375 lines
9.0 KiB
Groff
.\"
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.\" Copyright (c) 1998, 1999 Eivind Eklund
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.\" Copyright (c) 2003 Hiten M. Pandya
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.\" Copyright (c) 2005 Robert N. M. Watson
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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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.\"
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.\" If you integrate this manpage in another OS, I'd appreciate a note
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.\" - eivind@FreeBSD.org
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.\"
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.\" $FreeBSD$
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.\"
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.Dd September 21, 2005
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.Dt NAMEI 9
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.Os
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.Sh NAME
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.Nm namei ,
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.Nm NDINIT ,
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.Nm NDFREE ,
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.Nm NDHASGIANT
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.Nd pathname translation and lookup operations
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/fcntl.h
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.In sys/namei.h
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.Ft int
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.Fn namei "struct nameidata *ndp"
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.Ft void
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.Fo NDINIT
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.Fa "struct nameidata *ndp" "u_long op" "u_long flags"
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.Fa "enum uio_seg segflg" "const char *namep" "struct thread *td"
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.Fc
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.Ft void
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.Fn NDFREE "struct nameidata *ndp" "const uint flags"
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.Ft int
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.Fn NDHASGIANT "struct nameidata *ndp"
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.Sh DESCRIPTION
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The
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.Nm
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facility allows the client to perform pathname translation and lookup
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operations.
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The
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.Nm
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functions will increment the reference count for the vnode in question.
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The reference count has to be decremented after use of the vnode, by
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using either
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.Xr vrele 9
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or
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.Xr vput 9 ,
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depending on whether the
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.Dv LOCKLEAF
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flag was specified or not.
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If the
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.Va Giant
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lock is required,
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.Nm
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will acquire it if the caller indicates it is
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.Dv MPSAFE ,
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in which case the caller must later release
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.Va Giant
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based on the results of
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.Fn NDHASGIANT .
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.Pp
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The
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.Fn NDINIT
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function is used to initialize
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.Nm
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components.
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It takes the following arguments:
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.Bl -tag -width ".Fa segflg"
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.It Fa ndp
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The
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.Vt "struct nameidata"
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to initialize.
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.It Fa op
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The operation which
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.Fn namei
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will perform.
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The following operations are valid:
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.Dv LOOKUP , CREATE , DELETE ,
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and
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.Dv RENAME .
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The latter three are just setup for those
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effects; just calling
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.Fn namei
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will not result in
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.Fn VOP_RENAME
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being called.
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.It Fa flags
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Operation flags.
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Several of these can be effective at the same time.
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.It Fa segflg
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UIO segment indicator.
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This indicates if the name of the object is in userspace
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.Pq Dv UIO_USERSPACE
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or in the kernel address space
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.Pq Dv UIO_SYSSPACE .
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.It Fa namep
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Pointer to the component's pathname buffer
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(the file or directory name that will be looked up).
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.It Fa td
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The thread context to use for
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.Nm
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operations and locks.
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.El
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.Sh NAMEI OPERATION FLAGS
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The
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.Fn namei
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function takes the following set of
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.Dq "operation flags"
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that influence its operation:
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.Bl -tag -width ".Dv WANTPARENT"
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.It Dv LOCKLEAF
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Lock vnode on return.
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This is a full lock of the vnode; the
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.Xr VOP_UNLOCK 9
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should be used
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to release the lock (or
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.Xr vput 9
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which is equivalent to calling
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.Xr VOP_UNLOCK 9
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followed by
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.Xr vrele 9 ,
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all in one).
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.It Dv LOCKPARENT
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This flag lets the
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.Fn namei
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function return the parent (directory) vnode,
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.Va ni_dvp
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in locked state, unless it is identical to
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.Va ni_vp ,
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in which case
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.Va ni_dvp
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is not locked per se (but may be locked due to
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.Dv LOCKLEAF ) .
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If a lock is enforced, it should be released using
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.Xr vput 9
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or
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.Xr VOP_UNLOCK 9
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and
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.Xr vrele 9 .
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.It Dv WANTPARENT
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This flag allows the
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.Fn namei
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function to return the parent (directory) vnode in an unlocked state.
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The parent vnode must be released separately by using
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.Xr vrele 9 .
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.It Dv MPSAFE
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With this flag set,
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.Fn namei
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will conditionally acquire
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.Va Giant
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if it is required by a traversed file system.
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MPSAFE callers should pass the results of
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.Fn NDHASGIANT
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to
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.Xr VFS_UNLOCK_GIANT
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in order to conditionally release
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.Va Giant
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if necessary.
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.It Dv NOCACHE
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Avoid
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.Fn namei
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creating this entry in the namecache if it is not
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already present.
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Normally,
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.Fn namei
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will add entries to the name cache
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if they are not already there.
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.It Dv FOLLOW
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With this flag,
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.Fn namei
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will follow the symbolic link if the last part
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of the path supplied is a symbolic link (i.e., it will return a vnode
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for whatever the link points at, instead for the link itself).
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.It Dv NOFOLLOW
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Do not follow symbolic links (pseudo).
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This flag is not looked for by the actual code, which looks for
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.Dv FOLLOW .
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.Dv NOFOLLOW
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is used to indicate to the source code reader that symlinks
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are intentionally not followed.
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.It Dv SAVENAME
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Do not free the pathname buffer at the end of the
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.Fn namei
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invocation; instead, free it later in
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.Fn NDFREE
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so that the caller may access the pathname buffer.
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See below for details.
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.It Dv SAVESTART
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Retain an additional reference to the parent directory; do not free
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the pathname buffer.
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See below for details.
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.El
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.Sh ALLOCATED ELEMENTS
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The
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.Vt nameidata
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structure is composed of the following fields:
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.Bl -tag -width ".Va ni_cnd.cn_pnbuf"
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.It Va ni_startdir
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In the normal case, this is either the current directory or the root.
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It is the current directory if the name passed in does not start with
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.Ql /
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and we have not gone through any symlinks with an absolute path, and
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the root otherwise.
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.Pp
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In this case, it is only used by
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.Fn lookup ,
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and should not be
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considered valid after a call to
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.Fn namei .
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If
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.Dv SAVESTART
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is set, this is set to the same as
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.Va ni_dvp ,
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with an extra
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.Xr vref 9 .
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To block
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.Fn NDFREE
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from releasing
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.Va ni_startdir ,
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the
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.Dv NDF_NO_STARTDIR_RELE
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can be set.
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.It Va ni_dvp
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Vnode pointer to directory of the object on which lookup is performed.
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This is available on successful return if
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.Dv LOCKPARENT
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or
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.Dv WANTPARENT
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is set.
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It is locked if
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.Dv LOCKPARENT
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is set.
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Freeing this in
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.Fn NDFREE
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can be inhibited by
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.Dv NDF_NO_DVP_RELE , NDF_NO_DVP_PUT ,
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or
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.Dv NDF_NO_DVP_UNLOCK
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(with the obvious effects).
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.It Va ni_vp
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Vnode pointer to the resulting object,
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.Dv NULL
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otherwise.
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The
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.Va v_usecount
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field of this vnode is incremented.
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If
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.Dv LOCKLEAF
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is set, it is also locked.
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.Pp
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Freeing this in
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.Fn NDFREE
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can be inhibited by
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.Dv NDF_NO_VP_RELE , NDF_NO_VP_PUT ,
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or
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.Dv NDF_NO_VP_UNLOCK
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(with the obvious effects).
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.It Va ni_cnd.cn_pnbuf
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The pathname buffer contains the location of the file or directory
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that will be used by the
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.Nm
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operations.
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It is managed by the
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.Xr uma 9
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zone allocation interface.
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If the
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.Dv SAVESTART
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or
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.Dv SAVENAME
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flag is set, then the pathname buffer is available
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after calling the
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.Fn namei
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function.
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.Pp
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To only deallocate resources used by the pathname buffer,
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.Va ni_cnd.cn_pnbuf ,
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then
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.Dv NDF_ONLY_PNBUF
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flag can be passed to the
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.Fn NDFREE
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function.
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To keep the pathname buffer intact,
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the
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.Dv NDF_NO_FREE_PNBUF
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flag can be passed to the
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.Fn NDFREE
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function.
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.El
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.Sh RETURN VALUES
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If successful,
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.Fn namei
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will return 0, otherwise it will return an error.
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.Sh FILES
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.Bl -tag
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.It Pa src/sys/kern/vfs_lookup.c
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.El
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.Sh ERRORS
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Errors which
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.Fn namei
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may return:
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.Bl -tag -width Er
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.It Bq Er ENOTDIR
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A component of the specified pathname is not a directory when a directory is
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expected.
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded 255 characters,
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or an entire pathname exceeded 1023 characters.
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.It Bq Er ENOENT
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A component of the specified pathname does not exist,
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or the pathname is an empty string.
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.It Bq Er EACCES
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An attempt is made to access a file in a way forbidden by its file access
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permissions.
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating the pathname.
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.It Bq Er EISDIR
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An attempt is made to open a directory with write mode specified.
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.It Bq Er EROFS
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An attempt is made to modify a file or directory on a read-only file system.
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.El
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.Sh SEE ALSO
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.Xr uio 9 ,
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.Xr uma 9 ,
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.Xr VFS 9 ,
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.Xr VFS_UNLOCK_GIANT 9 ,
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.Xr vnode 9 ,
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.Xr vput 9 ,
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.Xr vref 9
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.Sh AUTHORS
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.An -nosplit
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This manual page was written by
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.An Eivind Eklund Aq eivind@FreeBSD.org
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and later significantly revised by
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.An Hiten M. Pandya Aq hmp@FreeBSD.org .
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.Sh BUGS
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The
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.Dv LOCKPARENT
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flag does not always result in the parent vnode being locked.
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This results in complications when the
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.Dv LOCKPARENT
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is used.
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In order to solve this for the cases where both
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.Dv LOCKPARENT
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and
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.Dv LOCKLEAF
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are used, it is necessary to resort to recursive locking.
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.Pp
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Non-MPSAFE file systems exist, requiring callers to conditionally unlock
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.Va Giant .
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