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

     namei, NDINIT, NDFREE, NDHASGIANT - pathname translation and lookup

     #include <sys/param.h>
     #include <sys/fcntl.h>
     #include <sys/namei.h>

     namei(struct nameidata *ndp);

     NDINIT(struct nameidata *ndp, u_long op, u_long flags,
         enum uio_seg segflg, const char *namep, struct thread *td);

     NDFREE(struct nameidata *ndp, const uint flags);

     NDHASGIANT(struct nameidata *ndp);

     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.

     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

     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

     SAVESTART       Retain an additional reference to the parent directory;
                     do not free the pathname buffer.  See below for details.

     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.

     If successful, namei() will return 0, otherwise it will return an error.


     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

     [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.

     uio(9), uma(9), VFS(9), VFS_UNLOCK_GIANT(9), vnode(9), vput(9), vref(9)

     This manual page was written by Eivind Eklund <> and
     later significantly revised by Hiten M. Pandya <>.

     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

FreeBSD 11.0-PRERELEASE          March 1, 2012         FreeBSD 11.0-PRERELEASE


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