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

[Christoph Paasch <cpaasch at apple.com>]

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On 10/10/18 - 19:47:29, Krystad, Peter wrote:
> 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.

Yes, I think it's a good approach to have a separate struct proto for
subflows.


Christoph

> 
> 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
> > > 
> > > Disclaimer: https://www.tessares.net/mail-disclaimer/
> > > 
> > 
> > --
> > Mat Martineau
> > Intel OTC
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