Re: [PATCH v2 2/3] net/handshake: Add support for PF_HANDSHAKE

[Jakub Kicinski <kuba@kernel.org>]

On Sat, 28 Jan 2023 14:06:49 +0000 Chuck Lever III wrote:
> > On Jan 28, 2023, at 3:32 AM, Jakub Kicinski <kuba@kernel.org> wrote:
> > On Thu, 26 Jan 2023 11:02:22 -0500 Chuck Lever wrote:  
> >> I've designed a way to pass a connected kernel socket endpoint to
> >> user space using the traditional listen/accept mechanism. accept(2)
> >> gives us a well-worn building block that can materialize a connected
> >> socket endpoint as a file descriptor in a specific user space
> >> process. Like any open socket descriptor, the accepted FD can then
> >> be passed to a library such as GnuTLS to perform a TLS handshake.  
> > 
> > I can't bring myself to like the new socket family layer.  
> 
> 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.

> > I'd like a second opinion on that, if anyone within netdev
> > is willing to share..  
> 
> Hopefully that opinion comes with an alternative way of getting
> a connected kernel socket endpoint up to user space without
> race issues.

If the user application decides the fd, wouldn't that solve the problem
in netlink?

  kernel                          user space

   notification     ---------->
 (new connection awaits)

                    <----------
                                  request (target fd=100)

                    ---------->
   reply
 (fd 100 is installed;
  extra params)

> We need to make some progress on this. If you don't have a
> technical objection, I think we should go with this with the
> idea that eventually something more palatable will come along
> to replace it.