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 ‘.’.

       [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.

Debian                                            May 23, 2015                                          NAMEI(9)