int myfilter_insert(FilterLayer *layer, pblock *pb) { if (pblock_findval("dont-insert-filter", pb)) return REQ_NOACTION; return REQ_PROCEED; } ... FilterMethods myfilter_methods = FILTER_METHODS_INITIALIZER; const Filter *myfilter; myfilter_methods.insert = &myfilter_insert; myfilter = filter_create("myfilter", &myfilter_methods); ...