NAMEI(9) BSD Kernel Manual NAMEI(9)
namei, lookup, relookup, NDINIT - pathname lookup
#include <sys/param.h>
#include <sys/namei.h>
int
namei(struct nameidata *ndp);
int
lookup(struct nameidata *ndp);
int
relookup(struct vnode *dvp, struct vnode **vpp,
struct componentname *cnp);
void
NDINIT(struct nameidata *ndp, u_long op, u_long flags,
enum uio_seg segflg, const char *namep, struct proc *p);
The namei interface is used to convert pathnames to filesystem vnodes.
The name of the interface is actually a contraction of the words name and
inode for name-to-inode conversion, in the days before the vfs(9) inter-
face was implemented.
The arguments passed to the functions are encapsulated in the nameidata
structure. It has the following structure:
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;
};
The namei interface accesses vnode operations by passing arguments in the
partially initialised componentname structure ni_cnd. This structure
describes the subset of information from the nameidata structure that is
passed through to the vnode operations. See VOP_LOOKUP(9) for more infor-
mation. The details of the componentname structure are not absolutely
necessary since the members are initialised by the helper macro NDINIT().
It is useful to know the operations and flags as specified in
VOP_LOOKUP(9).
The namei interface overloads ni_cnd.cn_flags with some additional flags.
These flags should be specific to the namei interface and ignored by
vnode operations. However, due to the historic close relationship between
the namei interface and the vnode operations, these flags are sometimes
used (and set) by vnode operations, particularly VOP_LOOKUP(). The addi-
tional flags are:
NOCROSSMOUNT do not cross mount points
RDONLY lookup with read-only semantics
HASBUF caller has allocated pathname buffer ni_cnd.cn_pnbuf
SAVENAME save pathname buffer
SAVESTART save starting directory
ISDOTDOT current pathname component is ..
MAKEENTRY add entry to the name cache
ISLASTCN this is last component of pathname
ISSYMLINK symlink needs interpretation
ISWHITEOUT found whiteout
DOWHITEOUT do whiteouts
REQUIREDIR must be a directory
PDIRUNLOCK vfs_lookup() unlocked parent dir
If the caller of namei() sets the SAVENAME flag, then it must free the
buffer. If VOP_LOOKUP() sets the flag, then the buffer must be freed by
either the commit routine or the VOP_ABORT() routine. The SAVESTART flag
is set only by the callers of namei(). It implies SAVENAME plus the addi-
tion of saving the parent directory that contains the name in
ni_startdir. It allows repeated calls to lookup() for the name being
sought. The caller is responsible for releasing the buffer and for invok-
ing vrele() on ni_startdir.
All access to the namei interface must be in process context. Pathname
lookups cannot be done in interrupt context.
namei(ndp)
Convert a pathname into a pointer to a locked inode. The path-
name is specified by ndp->ni_dirp and is of length ndp-
>ni_pathlen. The ndp->segflg flags defines whether the name in
ndp->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 ndp->ni_vp.
If ndp->ni_cnd.cn_flags has the FOLLOW flag set then symbolic
links are followed when they occur at the end of the name trans-
lation process. Symbolic links are always followed for all other
pathname components other than the last.
lookup(ndp)
Search for a pathname. This is a very central and rather compli-
cated routine.
The pathname is specified by ndp->ni_dirp and is of length ndp-
>ni_pathlen. The starting directory is taken from ndp-
>ni_startdir. The pathname is descended until done, or a symbol-
ic link is encountered.
The semantics of lookup() are altered by the operation specified
by ndp->ni_cnd.cn_nameiop. When CREATE, RENAME, or DELETE is
specified, information usable in creating, renaming, or deleting
a directory entry may be calculated.
If ndp->ci_cnd.cn_flags has LOCKPARENT set, the parent directory
is returned locked in ndp->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 ndp-
>ni_vp, otherwise it is returned unlocked.
relookup(dvp, vpp, cnp)
Reacquire a path name component is a directory. This is a quick-
er way to lookup a pathname component when the parent directory
is known. The unlocked parent directory vnode is specified by
dvp and the pathname component by cnp. The vnode of the pathname
is returned in the address specified by vpp.
NDINIT(ndp, op, flags, segflg, namep, p)
Initialise a nameidata structure pointed to by ndp for use by
the namei interface. It saves having to deal with the com-
ponentname structure inside ndp. The operation and flags are
specified by op and flags respectively. These are the values to
which ndp->ni_cnd.cn_nameiop and ndp->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 segflg. The argument namep is a pointer to the
pathname that ndp->ni_dirp is set to and p is the calling pro-
cess.
The name lookup subsystem is implemented within the file
sys/kern/vfs_lookup.c.
intro(9), vfs(9), vnode(9), VOP_LOOKUP(9)
It is unfortunate that much of the namei interface makes assumptions on
the underlying vnode operations. These assumptions are an artefact of the
introduction of the vfs interface to split a filesystem interface which
was historically designed as a tightly coupled module.
MirBSD #10-current October 13, 2001 2