netdev - Re: Upstream Homa?

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Date:   Sun, 13 Nov 2022 12:10:22 -0800
From:   John Ousterhout <ouster@...stanford.edu>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Jiri Pirko <jiri@...nulli.us>,
        Stephen Hemminger <stephen@...workplumber.org>,
        netdev@...r.kernel.org
Subject: Re: Upstream Homa?

On Sun, Nov 13, 2022 at 9:10 AM Andrew Lunn <andrew@...n.ch> wrote:
>
> > Homa implements RPCs rather than streams like TCP or messages like
> > UDP. An RPC consists of a request message sent from client to server,
> > followed by a response message from server back to client. This requires
> > additional information in the API beyond what is provided in the arguments to
> > sendto and recvfrom. For example, when sending a request message, the
> > kernel returns an RPC identifier back to the application; when waiting for
> > a response, the application can specify that it wants to receive the reply for
> > a specific RPC identifier (or, it can specify that it will accept any
> > reply, or any
> > request, or both).
>
> This sounds like the ancillary data you can pass to sendmsg(). I've
> not checked the code, it might be the current plumbing is only into to
> the kernel, but i don't see why you cannot extend it to also allow
> data to be passed back to user space. If this is new functionality,
> maybe add a new flags argument to control it.
>
> recvmsg() also has ancillary data.

Whoah! I'd never noticed the msg_control and msg_controllen fields before.
These may be sufficient to do everything Homa needs. Thanks for pointing
this out.

-John-