Re: [DO_NOT_APPLY v3 3/3] docs/architecture: add paragraph about networking

[Alyssa Ross <hi@alyssa.is>]

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Yureka Lilian <yureka@cyberchaos.dev> writes:

> ---
>  Documentation/about/architecture.adoc | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)

Reviewed-by: Alyssa Ross <hi@alyssa.is>

(I'll make some minor copyediting changes when it's ready to be applied,
but won't trouble you with those.)

When I get around to it, I'll probably rename netvm to "driver VM" or
something, BTW, since given we don't control the IOMMU groups, we'll
have to be prepared to drive multiple kinds of devices from one VM,
assuming we ever manage to move anything aside from network devices out
of the host.

> diff --git a/Documentation/about/architecture.adoc b/Documentation/about/architecture.adoc
> index e32ab27..2b86616 100644
> --- a/Documentation/about/architecture.adoc
> +++ b/Documentation/about/architecture.adoc
> @@ -68,3 +68,23 @@ nix-build img/live --no-out-link | xargs -o nix-tree
>  
>  See the https://diode.zone/w/8DBDQ6HQUe5UUdLkpDuL35[video] of Spectrum live
>  image interactive analysis with nix-tree.
> +
> +== Networking
> +
> +The net-vm's purpose is running the Linux drivers for any physical
> +interfaces on the spectrum system.
> +
> +A net-vm (there could be multiple, one per IOMMU-group) will load the
> +xdp-forwarder XDP programs on the passed-through physical interfaces as well
> +as the downstream virtio interface going into the router (recognized by
> +its special MAC address) using mdev events.
> +
> +The net-vm needs to multiplex between the physical interfaces, as there
> +might be several interfaces in the same IOMMU-group.
> +
> +For this, the xdp-forwarder applies a
> +VLAN tag corresponding to the interface id, and redirects the packets to
> +the router interface (identified by the router_iface bpf map).
> +In the other direction the XDP program loaded on the router interface
> +removes one layer of VLAN tagging, and redirects the packets to the
> +interface read from the VLAN tag.
> -- 
> 2.50.1

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