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

NAME
     VOP_LOOKUP	-- lookup a component of a pathname

SYNOPSIS
     #include <sys/param.h>
     #include <sys/vnode.h>
     #include <sys/namei.h>

     int
     VOP_LOOKUP(struct vnode *dvp, struct vnode	**vpp,
	 struct	componentname *cnp);

DESCRIPTION
     This entry	point looks up a single	pathname component in a	given direc-
     tory.

     Its arguments are:

     dvp  The locked vnode of the directory to search.

     vpp  The address of a variable where the resulting	locked vnode should be
	  stored.

     cnp  The pathname component to be searched	for.  It is a pointer to a
	  componentname	structure defined as follows:

	  struct componentname {
		  /*
		   * Arguments to lookup.
		   */
		  u_long  cn_nameiop;	  /* namei operation */
		  u_long  cn_flags;	  /* flags to namei */
		  struct  thread *cn_thread;	  /* thread requesting lookup */
		  struct  ucred	*cn_cred; /* credentials */
		  int	  cn_lkflags;	  /* Lock flags	LK_EXCLUSIVE or	LK_SHARED */
		  /*
		   * Shared between lookup and commit routines.
		   */
		  char	  *cn_pnbuf;	  /* pathname buffer */
		  char	  *cn_nameptr;	  /* pointer to	looked up name */
		  long	  cn_namelen;	  /* length of looked up component */
	  };

	  Convert a component of a pathname into a pointer to a	locked vnode.
	  This is a very central and rather complicated	routine.  If the file
	  system is not	maintained in a	strict tree hierarchy, this can	result
	  in a deadlock	situation.

	  The cnp-_cn_nameiop argument is LOOKUP, CREATE, RENAME, or DELETE
	  depending on the intended use	of the object.	When CREATE, RENAME,
	  or DELETE is specified, information usable in	creating, renaming, or
	  deleting a directory entry may be calculated.

	  Overall outline of VOP_LOOKUP:

		Check accessibility of directory.  Look	for name in cache, if
		found, then return name.  Search for name in directory,	goto
		to found or notfound as	appropriate.

	  notfound:

		If creating or renaming	and at end of pathname,	return
		EJUSTRETURN, leaving info on available slots else return
		ENOENT.

	  found:

		If at end of path and deleting,	return information to allow
		delete.	 If at end of path and renaming, lock target inode and
		return info to allow rename.  If not at	end, add name to
		cache; if at end and neither creating nor deleting, add	name
		to cache.

LOCKS
     The directory dvp should be locked	on entry and exit, regardless of error
     condition.	 If an entry is	found in the directory,	it will	be returned
     locked.

RETURN VALUES
     Zero is returned with *vpp	set to the locked vnode	of the file if the
     component is found.  If the component being searched for is ".", then the
     vnode just	has an extra reference added to	it with	vref(9).  The caller
     must take care to release the locks appropriately in this case.

     If	the component is not found and the operation is	CREATE or RENAME, the
     flag ISLASTCN is specified	and the	operation would	succeed, the special
     return value EJUSTRETURN is returned.  Otherwise, an appropriate error
     code is returned.

ERRORS
     [ENOTDIR]		The vnode dvp does not represent a directory.

     [ENOENT]		The component dvp was not found	in this	directory.

     [EACCES]		Access for the specified operation is denied.

     [EJUSTRETURN]	A CREATE or RENAME operation would be successful.

SEE ALSO
     vnode(9), VOP_ACCESS(9), VOP_CREATE(9), VOP_MKDIR(9), VOP_MKNOD(9),
     VOP_RENAME(9), VOP_SYMLINK(9)

HISTORY
     The function VOP_LOOKUP appeared in 4.3BSD.

AUTHORS
     This manual page was written by Doug Rabson, with some text from comments
     in	ufs_lookup.c.

BSD				August 8, 2018				   BSD

NAME | SYNOPSIS | DESCRIPTION | LOCKS | RETURN VALUES | ERRORS | SEE ALSO | HISTORY | AUTHORS

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