Re: [MPTCP] [RFC PATCH v3 05/16] tcp: Add IPPROTO_SUBFLOW

[Krystad, Peter <peter.krystad at intel.com>]

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On Tue, 2018-10-09 at 20:35 -0700, Mat Martineau wrote:
> On Tue, 9 Oct 2018, Matthieu Baerts wrote:
> 
> > On Sat, Oct 6, 2018 at 1:04 AM Mat Martineau
> > <mathew.j.martineau(a)linux.intel.com> wrote:
> > > 
> > > From: Peter Krystad <peter.krystad(a)intel.com>
> > > 
> > > IANA protocol numbers fit in a single byte, however the protocol field
> > > of struct inet_protosw is an unsigned short so defining IPPROTO_SUBFLOW
> > > as a 16-bit value greater than 0xFF with the same LSB as IPPROTO_TCP is
> > > convenient for registering a unique protocol with inet_register_protosw()
> > > that still transmits packets with IPPROTO_TCP as the protocol number.
> > 
> > Should we then call it IPPROTO_TCP_SUBFLOW? :)
> > 
> 
> Hopefully we won't need a special IPPROTO_ for the subflows in the long 
> run. It could be defined internally for kernel code with some checks to 
> prevent userspace-owned sockets of this type. Since the MPTCP kernel code 
> has complete control over the subflow sockets, maybe we could create 
> regular TCP sockets and modify them before using them (kind of like ULP 
> does, but without using the ULP infrastructure between an MPTCP socket and 
> its subflows).
> 
> Mat
> 
The purpose of my approach with IPPROTO_SUBFLOW was it reduced a lot of
impacts to the TCP code by allowing overriding all the 'struct proto'
routines, and defining the sock structure size as the size of
subflow_sock. Tradeoff would be more "if (sk->is_mptcp)" hooks in TCP
code.

Peter.

> 
> > > 
> > > Signed-off-by: Peter Krystad <peter.krystad(a)intel.com>
> > > ---
> > >  include/uapi/linux/in.h | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h
> > > index f65975c801e5..6986aecd0f46 100644
> > > --- a/include/uapi/linux/in.h
> > > +++ b/include/uapi/linux/in.h
> > > @@ -78,6 +78,8 @@ enum {
> > >  #define IPPROTO_MPLS           IPPROTO_MPLS
> > >    IPPROTO_RAW = 255,           /* Raw IP packets                       */
> > >  #define IPPROTO_RAW            IPPROTO_RAW
> > > +  IPPROTO_SUBFLOW = 262,       /* Multipath TCP (IPPROTO_TCP | 0x100)  */
> > > +#define IPPROTO_SUBFLOW                IPPROTO_SUBFLOW
> > >    IPPROTO_MAX
> > >  };
> > >  #endif
> > > --
> > > 2.19.1
> > > 
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> > 
> > 
> > -- 
> > Matthieu Baerts | R&D Engineer
> > matthieu.baerts(a)tessares.net
> > Tessares SA | Hybrid Access Solutions
> > www.tessares.net
> > 1 Avenue Jean Monnet, 1348 Louvain-la-Neuve, Belgium
> > 
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> 
> --
> Mat Martineau
> Intel OTC
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