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VOP_LOOKUP(9)	       FreeBSD 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.

     Cnp 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 */
	     /*
	      *	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 */
	     u_long  cn_hash;	     /*	hash value of looked up	name */
	     long    cn_consume;     /*	chars to consume in lookup() */
     };

     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 depend-
     ing on the	intended use of	the object.  When CREATE, RENAME, or DELETE is
     specified,	information usable in creating,	renaming, or deleting a	direc-
     tory 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.  If an error	(note: the
     return value EJUSTRETURN is not considered	an error) is detected, it will
     be	returned locked.  Otherwise, it	will be	unlocked unless	both
     LOCKPARENT	and ISLASTCN are specified in cnp-_cn_flags.  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.

FreeBSD	10.1		       November	24, 1997		  FreeBSD 10.1

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

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