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Date:   Sun, 13 Nov 2022 18:10:39 +0100
From:   Andrew Lunn <andrew@lunn.ch>
To:     John Ousterhout <ouster@cs.stanford.edu>
Cc:     Jiri Pirko <jiri@resnulli.us>,
        Stephen Hemminger <stephen@networkplumber.org>,
        netdev@vger.kernel.org
Subject: Re: Upstream Homa?
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> 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.

	  Andrew