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DESCRIPTION

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.