Tagging Data in the Network Stack: mbuf_tags

Abstract

We describe the mbuf_tag API, a mechanism for tagging data as they flow through the network stack. Originally introduced in OpenBSD, mbuf_tags were initially intended for use by the IPsec stack. The API has matured enough to be used by several other kernel components, and formed the basis for the FreeBSD mbuf_tags. We present the API, discuss its various uses in the OpenBSD network stack, and describe some plans for future work. Our goal is to demonstrate the flexibility of this relatively simple mechanism and expose it to other kernel developers.