.\" $OpenBSD: namei.9,v 1.9 2004/03/09 18:31:15 tedu Exp $ .\" $NetBSD: namei.9,v 1.9 2003/05/06 10:46:44 jmmv Exp $ .\" .\" Copyright (c) 2001 The NetBSD Foundation, Inc. .\" All rights reserved. .\" .\" This code is derived from software contributed to The NetBSD Foundation .\" by Gregory McGarry. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the NetBSD .\" Foundation, Inc. and its contributors. .\" 4. Neither the name of The NetBSD Foundation nor the names of its .\" contributors may be used to endorse or promote products derived .\" from this software without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS .\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED .\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS .\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS .\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN .\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGE. .\" .Dd October 13, 2001 .Dt NAMEI 9 .Os .Sh NAME .Nm namei , .Nm lookup , .Nm relookup , .Nm NDINIT .Nd pathname lookup .Sh SYNOPSIS .Fd #include .Fd #include .Ft int .Fn namei "struct nameidata *ndp" .Ft int .Fn lookup "struct nameidata *ndp" .Ft int .Fn relookup "struct vnode *dvp" "struct vnode **vpp" \ "struct componentname *cnp" .Ft void .Fn NDINIT "struct nameidata *ndp" "u_long op" "u_long flags" \ "enum uio_seg segflg" "const char *namep" "struct proc *p" .Sh DESCRIPTION The .Nm interface is used to convert pathnames to file system vnodes. The name of the interface is actually a contraction of the words .Em name and .Em inode for name-to-inode conversion, in the days before the .Xr vfs 9 interface was implemented. .Pp The arguments passed to the functions are encapsulated in the .Em nameidata structure. It has the following structure: .Bd -literal struct nameidata { /* * Arguments to namei/lookup. */ const char *ni_dirp; /* pathname pointer */ enum uio_seg ni_segflg; /* location of pathname */ /* * Arguments to lookup. */ struct vnode *ni_startdir; /* starting directory */ struct vnode *ni_rootdir; /* logical root directory */ /* * Results: returned from/manipulated by lookup */ struct vnode *ni_vp; /* vnode of result */ struct vnode *ni_dvp; /* vnode of intermediate dir */ /* * Shared between namei and lookup/commit routines. */ size_t ni_pathlen; /* remaining chars in path */ const char *ni_next; /* next location in pathname */ u_long ni_loopcnt; /* count of symlinks encountered */ /* * Lookup parameters */ struct componentname ni_cnd; }; .Ed .Pp The .Nm interface accesses vnode operations by passing arguments in the partially initialised .Em componentname structure .Em ni_cnd . This structure describes the subset of information from the nameidata structure that is passed through to the vnode operations. See .Xr VOP_LOOKUP 9 for more information. The details of the componentname structure are not absolutely necessary since the members are initialised by the helper macro .Fn NDINIT . It is useful to know the operations and flags as specified in .Xr VOP_LOOKUP 9 . .Pp The .Nm interface overloads .Em ni_cnd.cn_flags with some additional flags. These flags should be specific to the .Nm interface and ignored by vnode operations. However, due to the historic close relationship between the .Nm interface and the vnode operations, these flags are sometimes used (and set) by vnode operations, particularly .Fn VOP_LOOKUP . The additional flags are: .Pp .Bl -tag -offset indent -width NOCROSSMOUNT -compact .It NOCROSSMOUNT do not cross mount points .It RDONLY lookup with read-only semantics .It HASBUF caller has allocated pathname buffer .Em ni_cnd.cn_pnbuf .It SAVENAME save pathname buffer .It SAVESTART save starting directory .It ISDOTDOT current pathname component is .. .It MAKEENTRY add entry to the name cache .It ISLASTCN this is last component of pathname .It ISSYMLINK symlink needs interpretation .It ISWHITEOUT found whiteout .It DOWHITEOUT do whiteouts .It REQUIREDIR must be a directory .It PDIRUNLOCK vfs_lookup() unlocked parent dir .El .Pp If the caller of .Fn namei sets the SAVENAME flag, then it must free the buffer. If .Fn VOP_LOOKUP sets the flag, then the buffer must be freed by either the commit routine or the .Fn VOP_ABORT routine. The SAVESTART flag is set only by the callers of .Fn namei . It implies SAVENAME plus the addition of saving the parent directory that contains the name in .Em ni_startdir . It allows repeated calls to .Fn lookup for the name being sought. The caller is responsible for releasing the buffer and for invoking .Fn vrele on .Em ni_startdir . .Pp All access to the .Nm interface must be in process context. Pathname lookups cannot be done in interrupt context. .Sh FUNCTIONS .Bl -tag -width compact .It Fn namei "ndp" Convert a pathname into a pointer to a locked inode. The pathname is specified by .Em ndp-\*[Gt]ni_dirp and is of length .Em ndp-\*[Gt]ni_pathlen . The .Em ndp-\*[Gt]segflg flags defines whether the name in .Em ndp-\*[Gt]ni_dirp is an address in kernel space (UIO_SYSSPACE) or an address in user space (UIO_USERSPACE). The locked vnode for the pathname is referenced and returned in .Em ndp-\*[Gt]ni_vp . .Pp If .Em ndp-\*[Gt]ni_cnd.cn_flags has the FOLLOW flag set then symbolic links are followed when they occur at the end of the name translation process. Symbolic links are always followed for all other pathname components other than the last. .It Fn lookup "ndp" Search for a pathname. This is a very central and rather complicated routine. .Pp The pathname is specified by .Em ndp-\*[Gt]ni_dirp and is of length .Em ndp-\*[Gt]ni_pathlen . The starting directory is taken from .Em ndp-\*[Gt]ni_startdir . The pathname is descended until done, or a symbolic link is encountered. .Pp The semantics of .Fn lookup are altered by the operation specified by .Em ndp-\*[Gt]ni_cnd.cn_nameiop . When CREATE, RENAME, or DELETE is specified, information usable in creating, renaming, or deleting a directory entry may be calculated. .Pp If .Em ndp-\*[Gt]ci_cnd.cn_flags has LOCKPARENT set, the parent directory is returned locked in .Em ndp-\*[Gt]ni_dvp . If WANTPARENT is set, the parent directory is returned unlocked. Otherwise the parent directory is not returned. If the target of the pathname exists and LOCKLEAF is set, the target is returned locked in .Em ndp-\*[Gt]ni_vp , otherwise it is returned unlocked. .It Fn relookup "dvp" "vpp" "cnp" Reacquire a path name component is a directory. This is a quicker way to lookup a pathname component when the parent directory is known. The unlocked parent directory vnode is specified by .Fa dvp and the pathname component by .Fa cnp . The vnode of the pathname is returned in the address specified by .Fa vpp . .It Fn NDINIT "ndp" "op" "flags" "segflg" "namep" "p" Initialise a nameidata structure pointed to by .Fa ndp for use by the .Nm interface. It saves having to deal with the componentname structure inside .Fa ndp . The operation and flags are specified by .Fa op and .Fa flags respectively. These are the values to which .Em ndp-\*[Gt]ni_cnd.cn_nameiop and .Em ndp-\*[Gt]ni_cnd.cn_flags are respectively set. The segment flags which defines whether the pathname is in kernel address space or user address space is specified by .Fa segflg . The argument .Fa namep is a pointer to the pathname that .Em ndp-\*[Gt]ni_dirp is set to and .Fa p is the calling process. .El .Sh CODE REFERENCES The name lookup subsystem is implemented within the file .Pa sys/kern/vfs_lookup.c . .Sh SEE ALSO .Xr intro 9 , .\" .Xr namecache 9 , .Xr vfs 9 , .Xr vnode 9 , .Xr VOP_LOOKUP 9 .Sh BUGS It is unfortunate that much of the .Nm interface makes assumptions on the underlying vnode operations. These assumptions are an artefact of the introduction of the vfs interface to split a file system interface which was historically designed as a tightly coupled module.