On Thu, Jul 6, 2023 at 10:00 AM Dave Thaler <dthaler=40microsoft.com@xxxxxxxxxxxxxx> wrote: > > The charter for the newly formed IETF BPF WG includes: > > “The BPF working group is initially tasked with … creating a clear process for extensions, …” > > > > I wanted to kick off a discussion of this topic in preparation for discussion > at IETF 117. > > > > Once the BPF ISA is published in an RFC, we expect more instructions may be > added over time. It seems undesirable to delay use such additions until > > another RFC can be published, although having them appear in an RFC > would be a good thing in my view. > > > > Personally, I envision such additions to appear in an RFC per extension > > (i.e., set of additions) rather than obsoleting the original ISA RFC. So > I would propose the ability to reference another document (e.g., one > in the Linux kernel tree) in the meantime. > > > > For comparison, the IANA registry for URI schemes at > https://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml > defines status values for “Permanent” and “Provisional” with different > registration policies for each of those two statuses. > > > > Similarly, I would propose as a strawman using an IANA registry (as most > IETF standards do) that requires say an IETF Standards Track RFC for > > “Permanent” status, and “Specification required” (a public specification > reviewed by a designated expert) for “Provisional” registrations. > So updating a document in say the Linux kernel tree would be sufficient > for Provisional registration, and the status of an instruction would change > to Permanent once it appears in an RFC. The definition of status and the semantics make sense, but I suspect to implement them via full IANA would require to list every instruction encoding in the registry and that's where IANA key/value mapping won't work. 8-bit opcode is often not enough to denote an instruction. All of v1,v2,v3,v4 existing extensions to BPF ISA happened by a combination of new 8-bit opcodes and using reserved bits in other parts of 64-bit insn. Now we pretty much ran out of 8-bit opcodes. So there is really nothing the IANA registry can help with.
