Bug 37719

	we should detail in some relevant man-page the naming scheme
	for vnode operations.  vnode(9) is not quite the place I feel
	but we have no VOP(9) corresponding to VFS(9).

	The functions which can appear in the vnode vectors SHOULD
	follow this naming scheme:

	Methods implemented in a particular filesystem:
		<filesystem>_<vop>
	examples
		msdosfs_read(), devfs_lookup(), ufs_inactive()

	Generic default functions:
		vop_std<vop>
	examples:
		vop_stdinactive(), vop_stdgetpages()

	Generic do-nothing functions:
		vop_null<vop>
	examples:
		vop_nullinactive(), vop_nullread()

	Generic don't-do functions:
		vop_no<vop>
	examples
		vop_noioctl().

	Generic return-error functions:
		vop_<error>
	examples:
		vop_einval(), vop_eopnotsupp()

	The difference between do-nothing and don't-do can be subtle
	and hard to get right.  Be careful.