NAME¶
namei
,
NDINIT
,
NDFREE
,
NDHASGIANT
—
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);
int
NDHASGIANT
(
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. If the
Giant lock is
required,
namei
will acquire it if the
caller indicates it is
MPSAFE
, in which
case the caller must later release
Giant
based on the results of
NDHASGIANT
().
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 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. 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. This is a full lock of the vnode; 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 (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).
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 buffer,
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 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)
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.
Non-MPSAFE file systems exist, requiring callers to conditionally unlock
Giant.