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Date:   Tue, 8 Jun 2021 15:33:49 -0700
From:   Stephen Hemminger <stephen@networkplumber.org>
To:     Alexander Aring <aahringo@redhat.com>
Cc:     Stefan Metzmacher <metze@samba.org>,
        Steve French <smfrench@gmail.com>,
        =?UTF-8?B?QXVyw6lsaWVu?= Aptel <aaptel@suse.com>,
        Network Development <netdev@vger.kernel.org>,
        linux-nfs <linux-nfs@vger.kernel.org>,
        CIFS <linux-cifs@vger.kernel.org>,
        Leif Sahlberg <lsahlber@redhat.com>,
        Steven Whitehouse <swhiteho@redhat.com>
Subject: Re: quic in-kernel implementation?
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On Tue, 8 Jun 2021 17:03:16 -0400
Alexander Aring <aahringo@redhat.com> wrote:

> Hi,
> 
> On Tue, Jun 8, 2021 at 3:36 AM Stefan Metzmacher <metze@samba.org> wrote:
> ...
> >  
> > > 2) then switch focus to porting a smaller C userspace implementation of
> > > QUIC to Linux (probably not msquic since it is larger and doesn't
> > > follow kernel style)
> > > to kernel in fs/cifs  (since currently SMB3.1.1 is the only protocol
> > > that uses QUIC,
> > > and the Windows server target is quite stable and can be used to test against)> 3) use the userspace upcall example from step 1 for
> > > comparison/testing/debugging etc.
> > > since we know the userspace version is stable  
> >
> > With having the fuse-like socket before it should be trivial to switch
> > between the implementations.  
> 
> So a good starting point would be to have such a "fuse-like socket"
> component? What about having a simple example for that at first
> without having quic involved. The kernel calls some POSIX-like socket
> interface which triggers a communication to a user space application.
> This user space application will then map everything to a user space
> generated socket. This would be a map from socket struct
> "proto/proto_ops" to user space and vice versa. The kernel application
> probably can use the kernel_FOO() (e.g. kernel_recvmsg()) socket api
> directly then. Exactly like "fuse" as you mentioned just for sockets.
> 
> I think two veth interfaces can help to test something like that,
> either with a "fuse-like socket" on the other end or an user space
> application. Just doing a ping-pong example.
> 
> Afterwards we can look at how to replace the user generated socket
> application with any $LIBQUIC e.g. msquic implementation as second
> step.
> 
> - Alex
> 

Socket state management is complex and timers etc in userspace are hard.