pathname translation and lookup operations
, u_long op
, const char *namep
struct thread *td
facility allows the client to
perform pathname translation and lookup operations. The
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
depending on whether the
specified or not. If the Giant
will acquire it if the
caller indicates it is
, in which
case the caller must later release Giant
based on the results of
() function is used to initialize
components. It takes the following
- The struct nameidata to initialize.
- The operation which
perform. The following operations are valid:
RENAME. The latter three are just setup
for those effects; just calling
will not result in
- Operation flags. Several of these can be effective at the same time.
- UIO segment indicator. This indicates if the name of the object is in
UIO_USERSPACE) or in the
kernel address space
- Pointer to the component's pathname buffer (the file or directory name
that will be looked up).
- The thread context to use for
operations and locks.
NAMEI OPERATION FLAGS¶
() function takes the following set
of “operation flags” that influence its operation:
- 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).
- This flag lets the
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
- This flag allows the
to return the parent (directory) vnode in an unlocked state. The parent
vnode must be released separately by using
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.
- 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).
- Do not follow symbolic links (pseudo). This flag is not looked for by the
actual code, which looks for
NOFOLLOW is used to indicate to the
source code reader that symlinks are intentionally not followed.
- Do not free the pathname buffer at the end of the
namei() invocation; instead, free it
NDFREE() so that the caller
may access the pathname buffer. See below for details.
- Retain an additional reference to the parent directory; do not free the
pathname buffer. See below for details.
structure is composed of the
- 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
SAVESTART is set, this is set to the
same as ni_dvp, with an extra
vref(9). To block
NDFREE() from releasing
NDF_NO_STARTDIR_RELE can be set.
- Vnode pointer to directory of the object on which lookup is performed.
This is available on successful return if
WANTPARENT is set. It is locked if
LOCKPARENT is set. Freeing this in
NDFREE() can be inhibited by
NDF_NO_DVP_UNLOCK (with the obvious
- Vnode pointer to the resulting object,
NULL otherwise. The
v_usecount field of this vnode is
LOCKLEAF is set, it is
Freeing this in
NDFREE() can be inhibited
NDF_NO_VP_UNLOCK (with the obvious
- The pathname buffer contains the location of the file or directory that
will be used by the
It is managed by the uma(9) zone allocation
interface. If the
SAVENAME flag is set, then the pathname
buffer is available after calling the
To only deallocate resources used by the pathname buffer,
NDF_ONLY_PNBUF flag can be passed to
NDFREE() function. To keep the
pathname buffer intact, the
NDF_NO_FREE_PNBUF flag can be passed to
() will return 0,
otherwise it will return an error.
() may return:
- A component of the specified pathname is not a directory when a directory
- A component of a pathname exceeded 255 characters, or an entire pathname
exceeded 1023 characters.
- A component of the specified pathname does not exist, or the pathname is
an empty string.
- An attempt is made to access a file in a way forbidden by its file access
- Too many symbolic links were encountered in translating the pathname.
- An attempt is made to open a directory with write mode specified.
- The last component of the pathname specified for a
RENAME operation is
- An attempt is made to modify a file or directory on a read-only file
This manual page was written by Eivind Eklund
⟨eivind@FreeBSD.org⟩ and later significantly revised by
Hiten M. Pandya
flag does not always result in
the parent vnode being locked. This results in complications when the
is used. In order to solve this
for the cases where both
are used, it is necessary to
resort to recursive locking.
Non-MPSAFE file systems exist, requiring callers to conditionally unlock