def __verifyAcl(self, path, access, parentAcl):
        """Verify one step in the ACL chain"""

        if AclConstants.SUPER_USER_GROUP_NAME in self.__aclIdents: return 1

        if path in self.__aclCache:
            t = self.__aclCache[path].get(access)
            if t == AclConstants.ALLOWED: return
            if t == AclConstants.DENIED:
                raise FtServerServerException(Error.PERMISSION_DENIED,
                                              level=access,
                                              path=path)

        acl,owner = self.__getResourceAcl(PathImp.QuickCreate(path))

        if parentAcl is not None:
            parentAcl.update(acl)
            acl = parentAcl

        if access not in acl and parentAcl is None:
            testPath = path
            while 1:
                if testPath == '/':
                    break

                #Calculate the parent path
                testPath = '/'.join(testPath.split('/')[:-1])
                if not testPath:
                    testPath = '/'
                parentAcl,o = self.__getResourceAcl(PathImp.QuickCreate(testPath))
                parentAcl.update(acl)
                acl = parentAcl
                if access in acl:
                    break

        cur = acl.get(access,{})

        #Resolve any owner ids
        if AclConstants.OWNER in cur and owner not in cur:
            cur[owner] = cur[AclConstants.OWNER]

        #See if we are explicitly disallowed
        for a in self.__aclIdents:
            #'world' is an identifier associated with every user
            if not cur.get(a, 1):
                self.__setCache(path, access, AclConstants.DENIED)
                raise FtServerServerException(Error.PERMISSION_DENIED,
                                              level=access,
                                              path=path)

        #See if we are allowed
        for a in self.__aclIdents:
            if cur.get(a, 0):
                self.__setCache(path, access, AclConstants.ALLOWED)
                return acl
        self.__setCache(path, access, AclConstants.DENIED)
        raise FtServerServerException(Error.PERMISSION_DENIED,
                                      level=access,
                                      path=path)