[MirageOS-devel] Thoughts on the STACKV4 interface

[Nicolas Ojeda Bar <no263@xxxxxxxxxxxxxxx>]

Hi list,

TL;DR- With the addition of IPv6 the interface V1.STACKV4 (renamed
NETSTACK) looks like an overgrown garden of weed and grass. I propose
(see below) to completely eliminate this interface and to shift its
role to the existing Udp & Tcp signatures/implementations.

Right now STACKV4 performs two roles:

1) Keeps track of open ports for Tcp & Udp
2) Connects together the whole stack of TCP/UDP over IP, ARP over
ETHIF over NETIF.

Remarks:

- 1) this can be done independently for Tcp and Udp and there doesn't
seem to be a problem keeping the `port -> callback` table in those
modules directly.

- 2) boils down to calling `Ethif.input`, `Ipv{4,6}.input` with
arguments specifying the callbacks for each protocol.  With the
current signatures one needs to have all the callback functions "at
once".  It is not possible to register, say, the `tcp` callback
independently of the `udp` callback or the `ipv4` callback
independently of the `ipv6` one.  But this is easily solved by making
the implementations keep a table `protocol -> callback` and exposing a
function in the signatures to register such a callback.

- STACKV4 is neither a good low-level nor a good high-level
abstraction to the network stack.  We should let the existing
ETHIF/IP/TCP/UDP provide a low-level interface and start thinking how
to make a good high-level interface (maybe in the style of `launchd`
or `systemd`) to all network services (and maybe other Mirage
services?) that hides these modules.

If we make the above changes then there is no more a raison d'etre for
STACKV4 and we can eliminate it altogether.  The current unikernels
that depend on stackv4 will instead depend on a subset of {udp,tcp} x
{ipv4,ipv6}. Instead of having a DIRECT/SOCKET network stack we would
have DIRECT/SOCKET UDP & TCP implementations.

Thoughts ?

Cheers,
Nicolas

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