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 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. 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.