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namei(9)
NAMEI(9) BSD Kernel Developer's Manual NAMEI(9)
NAME
namei, NDINIT, NDFREE, — 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, u_long op, u_long flags,
enum uio_seg segflg, const char *namep, struct thread *td);
void
NDFREE(struct nameidata *ndp, const uint flags);
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 decre‐
mented 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() function is used to initialize namei components. It takes
the following arguments:
ndp The struct nameidata to initialize.
op The operation which namei() will perform. The following opera‐
tions 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. 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).
td The thread context to use for namei operations and locks.
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. The 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 (direc‐
tory) 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. The 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.
SAVENAME Do not free the pathname buffer at the end of the namei()
invocation; instead, free it later in NDFREE() so that the
caller may access the pathname buffer. See below for
details.
SAVESTART Retain an additional reference to the parent directory; do
not free the pathname buffer. See below for details.
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 lookup(), and should
not be considered valid after a call to namei(). If
SAVESTART is set, this is set to the same as ni_dvp,
with an extra vref(9). To block NDFREE() from releasing
ni_startdir, the NDF_NO_STARTDIR_RELE can be set.
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. Freeing this in NDFREE() can be
inhibited by NDF_NO_DVP_RELE, NDF_NO_DVP_PUT, or
NDF_NO_DVP_UNLOCK (with the obvious effects).
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.
Freeing this in NDFREE() can be inhibited by
NDF_NO_VP_RELE, NDF_NO_VP_PUT, or NDF_NO_VP_UNLOCK (with
the obvious effects).
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. If
the SAVESTART or SAVENAME flag is set, then the pathname
buffer is available after calling the namei() function.
To only deallocate resources used by the pathname buf‐
fer, ni_cnd.cn_pnbuf, then NDF_ONLY_PNBUF flag can be
passed to the NDFREE() function. To keep the pathname
buffer intact, the NDF_NO_FREE_PNBUF flag can be passed
to the NDFREE() function.
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 direc‐
tory 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 translat‐
ing 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)
AUTHORS
This manual page was written by Eivind Eklund <eivind@FreeBSD.org> and
later significantly revised by Hiten M. Pandya <hmp@FreeBSD.org>.
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.
BSD May 23, 2015 BSD