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Message-ID: <20230131113029.7647e475@kernel.org>
Date: Tue, 31 Jan 2023 11:30:29 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Chuck Lever III <chuck.lever@...cle.com>
Cc: netdev <netdev@...r.kernel.org>, "hare@...e.com" <hare@...e.com>,
David Howells <dhowells@...hat.com>,
Olga Kornievskaia <kolga@...app.com>,
"jmeneghi@...hat.com" <jmeneghi@...hat.com>,
Benjamin Coddington <bcodding@...hat.com>,
Jeff Layton <jlayton@...hat.com>
Subject: Re: [PATCH v2 2/3] net/handshake: Add support for PF_HANDSHAKE
On Tue, 31 Jan 2023 15:18:02 +0000 Chuck Lever III wrote:
> > On Jan 30, 2023, at 11:35 PM, Jakub Kicinski <kuba@...nel.org> wrote:
> > On Sat, 28 Jan 2023 14:06:49 +0000 Chuck Lever III wrote:
> >> poll/listen/accept is the simplest and most natural way of
> >> materializing a socket endpoint in a process that I can think
> >> of. It's a well-understood building block. What specifically
> >> is troubling you about it?
> >
> > poll/listen/accept yes, but that's not the entire socket interface.
> > Our overall experience with the TCP ULPs is rather painful, proxying
> > all the other callbacks here may add another dimension.
> >
> > Also I have a fear (perhaps unjustified) of reusing constructs which are
> > cornerstones of the networking stack and treating them as abstractions.
>
> OK, then I take this as a NAK for listen/poll/accept in
> any form. I need some finality here because we need to
> move forward.
To be clear - if Paolo, Eric or someone else who knows the socket layer
better than I do thinks that your current implementation is good then
I won't stand in the way.
> > kernel user space
> >
> > notification ---------->
> > (new connection awaits)
> >
> > <----------
> > request (target fd=100)
> >
> > ---------->
> > reply
> > (fd 100 is installed;
> > extra params)
>
> What type of notification do you prefer for this? You've
> said in the past that RT signals are not appropriate. It
> would be easy for user space to simply wait on nlm_recvmsg()
> but I worry that netlink is not a reliable message service.
There are various bits and bobs in netlink which are supposed to help.
A socket which subscribed to notifications should get an error if a
delivery fails (netlink_overrun()). The kernel commonly supports a GET
request which the user space can exercise after missing notifications
to get back in sync.
> And, do you have a preferred mechanism or code sample for
> installing a socket descriptor?
I must admit - I don't.
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