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NAMEI(9)		 BSD Kernel Developer's Manual		      NAMEI(9)

NAME
     namei, NDINIT, NDFREE, NDHASGIANT — pathname translation and lookup oper‐
     ations

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 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.  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 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.	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 (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).

     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).

     MPSAFE	 With this flag set, namei() will conditionally acquire Giant
		 if it is required by a traversed file system.	MPSAFE callers
		 should pass the results of NDHASGIANT() to VFS_UNLOCK_GIANT
		 in order to conditionally release Giant if necessary.

     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).

     NOOBJ	 Do not call vfs_object_create() for the returned vnode, even
		 though it meets required criteria for VM support.

     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.

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.

     [EROFS]		An attempt is made to modify a file or directory on a
			read-only file system.

FILES
     src/sys/kern/vfs_lookup.c

SEE ALSO
     uio(9), uma(9), VFS(9), VFS_UNLOCK_GIANT(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.

BSD			      September 21, 2005			   BSD
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