NDFREE(9) manual page

Manual Pages — NAMEI

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 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() 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 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 (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`. 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 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 ‘`amp;.`’.
[`EROFS`]
	An attempt is made to modify a file or directory on a read-only file system.

AUTHORS

This manual page was written by Eivind Eklund <Mt eivind@FreeBSD.org> and later significantly revised by Hiten M. Pandya <Mt 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.

NAMEI (9)

May 23, 2015

Please direct any comments about this manual page service to Ben Bullock. Privacy policy.

“	UNIX has been evolving feverishly for close to 30 years, sort of like bacteria in a cesspool — only not as attractive	”
— John Levine, "Unix for Dummies"