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

 

NAME

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

SYNOPSIS

      #include <sys/param.h>
      #include <sys/proc.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.
      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.
      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.
 

FILES

      src/sys/kern/vfs_lookup.c
      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.
 

Sections

Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.