NAMEI(9) FreeBSD Kernel Developer's Manual NAMEI(9)
NAME
namei, NDINIT, NDINIT_AT, NDFREE_PNBUF - pathname translation and lookup
operations
SYNOPSIS
#include <sys/param.h>
#include <sys/fcntl.h>
#include <sys/namei.h>
int
namei(struct nameidata *ndp);
void
NDINIT(struct nameidata *ndp, enum nameiop op, u_int64_t flags,
enum uio_seg segflg, const char *namep);
void
NDINIT_AT(struct nameidata *ndp, enum nameiop op, u_int64_t flags,
enum uio_seg segflg, const char *namep, int dirfd);
void
NDFREE_PNBUF(struct nameidata *ndp);
DESCRIPTION
The namei facility allows the client to perform pathname translation and
lookup operations. The namei functions will increment the reference
count for the vnode in question. The reference count has to be
decremented after use of the vnode, by using either vrele(9) or vput(9),
depending on whether the LOCKLEAF flag was specified or not.
The NDINIT() macro is used to initialize namei components. It takes the
following arguments:
ndp A pointer to the struct nameidata to initialize.
op The operation which namei() will perform. The following
operations are valid: LOOKUP, CREATE, DELETE, and RENAME. The
latter three are just setup for those effects; just calling
namei() will not result in VOP_RENAME() being called.
flags Operation flags, described in the next section. Several of these
can be effective at the same time.
segflg UIO segment indicator. This indicates if the name of the object
is in userspace (UIO_USERSPACE) or in the kernel address space
(UIO_SYSSPACE).
namep Pointer to the component's pathname buffer (the file or directory
name that will be looked up).
The NDINIT_AT() macro is similar to NDINIT(), but takes one extra
argument:
dirfd File descriptor referencing a directory, or the special value
AT_FDCWD meaning the calling thread's current working directory.
Lookups will be performed relative to this directory.
The NDFREE_PNBUF() macro is used to free the pathname buffer. It must be
called exactly once for each successful namei() call. It takes the
following argument:
ndp A pointer to a struct nameidata that was used in a successful
namei() call.
NAMEI OPERATION FLAGS
The namei() function takes the following set of "operation flags" that
influence its operation:
LOCKLEAF Lock vnode on return with LK_EXCLUSIVE unless LOCKSHARED is
also set. VOP_UNLOCK(9) should be used to release the lock
(or vput(9) which is equivalent to calling VOP_UNLOCK(9)
followed by vrele(9), all in one).
LOCKPARENT This flag lets the namei() function return the parent
(directory) vnode, ni_dvp in locked state, unless it is
identical to ni_vp, in which case ni_dvp is not locked per se
(but may be locked due to LOCKLEAF). If a lock is enforced,
it should be released using vput(9) or VOP_UNLOCK(9) and
vrele(9).
LOCKSHARED Lock vnode on return with LK_SHARED, if permitted by the file
system that owns the vnode. The file system must explicitly
permit this by setting MNTK_LOOKUP_SHARED in
mp->mnt_kern_flag during mount and by calling
VN_LOCK_ASHARE() when allocating the vnode. If LOCKLEAF is
specified but shared locking is not permitted, then the vnode
will be returned with LK_EXCLUSIVE. VOP_UNLOCK(9) should be
used to release the lock (or vput(9) which is equivalent to
calling VOP_UNLOCK(9) followed by vrele(9), all in one).
WANTPARENT This flag allows the namei() function to return the parent
(directory) vnode in an unlocked state. The parent vnode
must be released separately by using vrele(9).
NOCACHE Avoid namei() creating this entry in the namecache if it is
not already present. Normally, namei() will add entries to
the name cache if they are not already there.
FOLLOW With this flag, namei() will follow the symbolic link if the
last part of the path supplied is a symbolic link (i.e., it
will return a vnode for whatever the link points at, instead
for the link itself).
NOFOLLOW Do not follow symbolic links (pseudo). This flag is not
looked for by the actual code, which looks for FOLLOW.
NOFOLLOW is used to indicate to the source code reader that
symlinks are intentionally not followed.
ALLOCATED ELEMENTS
The nameidata structure is composed of the following fields:
ni_startdir In the normal case, this is either the current directory
or the root. It is the current directory if the name
passed in does not start with `/' and we have not gone
through any symlinks with an absolute path, and the root
otherwise.
In this case, it is only used by vfs_lookup(), and
should not be considered valid after a call to namei().
ni_dvp Vnode pointer to directory of the object on which lookup
is performed. This is available on successful return if
LOCKPARENT or WANTPARENT is set. It is locked if
LOCKPARENT is set.
ni_vp Vnode pointer to the resulting object, NULL otherwise.
The v_usecount field of this vnode is incremented. If
LOCKLEAF is set, it is also locked.
ni_cnd.cn_pnbuf The pathname buffer contains the location of the file or
directory that will be used by the namei operations. It
is managed by the uma(9) zone allocation interface.
RETURN VALUES
If successful, namei() will return 0, otherwise it will return an error.
FILES
src/sys/kern/vfs_lookup.c
ERRORS
Errors which namei() may return:
[ENOTDIR] A component of the specified pathname is not a
directory when a directory is expected.
[ENAMETOOLONG] A component of a pathname exceeded 255 characters, or
an entire pathname exceeded 1023 characters.
[ENOENT] A component of the specified pathname does not exist,
or the pathname is an empty string.
[EACCES] An attempt is made to access a file in a way forbidden
by its file access permissions.
[ELOOP] Too many symbolic links were encountered in
translating the pathname.
[EISDIR] An attempt is made to open a directory with write mode
specified.
[EINVAL] The last component of the pathname specified for a
DELETE or RENAME operation is `.'.
[EROFS] An attempt is made to modify a file or directory on a
read-only file system.
SEE ALSO
uio(9), uma(9), VFS(9), vnode(9), vput(9), vref(9), vrele(9)
AUTHORS
This manual page was written by Eivind Eklund <
[email protected]> and
later significantly revised by Hiten M. Pandya <
[email protected]>.
BUGS
The LOCKPARENT flag does not always result in the parent vnode being
locked. This results in complications when the LOCKPARENT is used. In
order to solve this for the cases where both LOCKPARENT and LOCKLEAF are
used, it is necessary to resort to recursive locking.
FreeBSD 14.1-RELEASE-p8 May 16, 2025 FreeBSD 14.1-RELEASE-p8