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Date: Thu, 25 Mar 2021 10:32:06 +0100
From: Florian Westphal <fw@strlen.de>
To: Mat Martineau <mathew.j.martineau@linux.intel.com>
Cc: Florian Westphal <fw@strlen.de>, mptcp@lists.linux.dev,
	mptcp@lists.01.org
Subject: Re: [RFC PATCH mptcp-next v2 5/8] mptcp: setsockopt: add SO_MARK
 support
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References: <20210324131546.13730-1-fw@strlen.de>
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Mat Martineau <mathew.j.martineau@linux.intel.com> wrote:
> On Wed, 24 Mar 2021, Florian Westphal wrote:
> 
> > Value is synced to all subflows.
> > 
> 
> The use case I remember for SO_MARK with MPTCP was to designate different
> interfaces for different subflows:
> 
> https://lore.kernel.org/mptcp/CAKD1Yr2sBCdUO48cp=rZQ6s4v13ytpPd9oPT+U=iYrdXtba5HA@mail.gmail.com/
> 
> 
> Once we have a way to set individual subflow options, it could both be
> useful to set sk_mark on all subflows, and also to not override individual
> settings. The current sync mechanism would overwrite all supported options
> when any single option changes.
> 
> There's no way for these options to diverge yet, so we could wait on solving
> that problem. Do you think it's better to stick with the current syncing
> method for now, or to do more detailed tracking of which options need to be
> synced?

Looks like same issue as with TCP_CONGESTION.
Q is how we can expose the individual subflows.

I see
https://tools.ietf.org/html/draft-hesmans-mptcp-socket-03

Should that be implemented instead of this?