netdev - Re: [PATCH net-next 0/6] kcm: Kernel Connection Multiplexor (KCM)

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Message-ID: <20151124162515.GA22266@breakpoint.cc>
Date:	Tue, 24 Nov 2015 17:25:15 +0100
From:	Florian Westphal <fw@...len.de>
To:	David Miller <davem@...emloft.net>
Cc:	fw@...len.de, tom@...bertland.com, hannes@...essinduktion.org,
	netdev@...r.kernel.org, kernel-team@...com, davejwatson@...com,
	alexei.starovoitov@...il.com
Subject: Re: [PATCH net-next 0/6] kcm: Kernel Connection Multiplexor (KCM)

David Miller <davem@...emloft.net> wrote:
> From: Florian Westphal <fw@...len.de>
> Date: Tue, 24 Nov 2015 16:27:44 +0100
> 
> > Aside from Hannes comment -- KCM seems to be tied to the TLS work, i.e.
> > I have the impression that KCM without ability to do TLS in the kernel
> > is pretty much useless for whatever use case Tom has in mind.
> 
> I do not get this impression at all.
> 
> Tom's design document in the final patch looks legitimately what the
> core use case is.

You mean
https://patchwork.ozlabs.org/patch/547054/ ?

Its a well-written document, but I don't see how moving the burden of
locking a single logical tcp connection (to prevent threads from
reading a partial record) from userspace to kernel is an improvement.

If you really have 100 threads and must use a single tcp connection
to multiplex some arbitrarily complex record-format in atomic fashion,
then your requirements suck.

Now, arguably, maybe the requirements of Toms use case are restricted
/cannot be avoided.

But that still begs the question: Why should mainline care?

Once its in, next step will be 'my single tcp connection that I use
for multiplexing via KCM now has requirement to use TLS'.

How far are you willing to take the KCM concept?
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