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 directory.

     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 sys-
     tem 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.  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 spe-
     cial 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
								 November 24, 1997							       BSD