NAMEI(9) | Kernel Developer's Manual | NAMEI(9) |
namei
, vfs_lookup
,
vfs_relookup
, NDINIT
,
NDINITAT
— pathname
lookup
#include
<sys/param.h>
#include <sys/namei.h>
int
namei
(struct
nameidata *ndp);
int
vfs_lookup
(struct
nameidata *ndp);
int
vfs_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);
void
NDINITAT
(struct
nameidata *ndp, u_long
op, u_long flags,
enum uio_seg segflg,
int dirfd,
const char *namep,
struct proc *p);
The
namei
()
function converts a pathname to a
vnode(9). It uses the
following structure:
struct nameidata { /* * Arguments to namei/lookup. */ const char *ni_dirp; /* pathname pointer */ int ni_dirfd; /* AT_FDCWD or fd of base of */ /* relative paths */ 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
()
function 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
information. The details of the componentname structure are not absolutely
necessary since the members are initialised by the helper macros
NDINIT
()
and NDINITAT
(). It is useful to know the operations
and flags as specified in
VOP_LOOKUP(9).
The
namei
()
function overloads
ni_cnd.cn_flags
with some additional flags. These flags should be specific to
namei
() and ignored by vnode operations. However,
due to the historic close relationship between
namei
() and the vnode operations, these flags are
sometimes used (and set) by vnode operations, particularly
VOP_LOOKUP
(). The additional flags are:
VOP_LOOKUP
()
unlocked parent dirIf 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 addition of
saving the parent directory that contains the name in
ni_startdir. It allows repeated calls to
vfs_lookup
() for the name being sought. The caller
is responsible for releasing the buffer and for invoking
vrele
()
on ni_startdir.
All access to
namei
(),
vfs_lookup
(), and
vfs_relookup
() must be in process context. Pathname
lookups cannot be done in interrupt context.
namei
(ndp)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 translation process. Symbolic links are always followed for all other pathname components other than the last.
If the LOCKLEAF flag is set, a locked vnode is returned.
vfs_lookup
(ndp)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 symbolic link is encountered.
The semantics of
vfs_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.
vfs_relookup
(dvp,
vpp, cnp)NDINITAT
(ndp,
op, flags,
segflg, dirfd,
namep, p)namei
interfaces. It saves having
to deal with the componentname 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 flag, which defines whether the pathname is in kernel address
space or user address space, is specified by segflg.
The directory from which relative pathnames will be looked up is specified
by dirfd, with AT_FDCWD
specifying use of the current working directory of process
p. The argument namep is a
pointer to the pathname that ndp->ni_dirp is set to
and p is the calling process.NDINIT
(ndp,
op, flags,
segflg, namep,
p)NDINITAT
(ndp,
op, flags,
segflg, AT_FDCWD,
namep, p).The name lookup subsystem is implemented within the file sys/kern/vfs_lookup.c.
The namei
() function first appeared in
Version 4 AT&T UNIX. Its name is an
abbreviation for the name-to-inode conversion which it performed before the
appearance of vfs(9) in
4.3BSD-Reno.
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 file system interface which was historically designed as a tightly
coupled module.
September 30, 2019 | OpenBSD-6.9 |