Re: [PATCH v6 4/8] ethdev: add GTP items to support flow API

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

On Thu, Oct 05, 2017 at 08:06:38AM +0000, Wu, Jingjing wrote:
> 
> 
> > -----Original Message-----
> > From: Sean Harte [mailto:seanbh@gmail.com]
> > Sent: Tuesday, October 3, 2017 4:57 PM
> > To: Adrien Mazarguil <adrien.mazarguil@6wind.com>
> > Cc: Xing, Beilei <beilei.xing@intel.com>; Wu, Jingjing <jingjing.wu@intel.com>; Chilikin,
> > Andrey <andrey.chilikin@intel.com>; dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH v6 4/8] ethdev: add GTP items to support flow API
> > 
> > On 2 October 2017 at 13:27, Adrien Mazarguil <adrien.mazarguil@6wind.com> wrote:
> > > On Fri, Sep 29, 2017 at 10:29:55AM +0100, Sean Harte wrote:
> > >> On 29 September 2017 at 09:54, Xing, Beilei <beilei.xing@intel.com> wrote:
> > > <snip>
> > >> >> >  /**
> > >> >> > + * RTE_FLOW_ITEM_TYPE_GTP.
> > >> >> > + *
> > >> >> > + * Matches a GTPv1 header.
> > >> >> > + */
> > >> >> > +struct rte_flow_item_gtp {
> > >> >> > +       /**
> > >> >> > +        * Version (3b), protocol type (1b), reserved (1b),
> > >> >> > +        * Extension header flag (1b),
> > >> >> > +        * Sequence number flag (1b),
> > >> >> > +        * N-PDU number flag (1b).
> > >> >> > +        */
> > >> >> > +       uint8_t v_pt_rsv_flags;
> > >> >> > +       uint8_t msg_type; /**< Message type. */
> > >> >> > +       rte_be16_t msg_len; /**< Message length. */
> > >> >> > +       rte_be32_t teid; /**< Tunnel endpoint identifier. */ };
> > >> >>
> > >> >> In future, you might add support for GTPv2 (which is used since LTE).
> > >> >> Maybe this structure should have v1 in its name to avoid confusion?
> > >> >
> > >> > I considered it before. But I think we can modify it when we support GTPv2 in future,
> > and keep concise 'GTP' currently:)  since I have described it matches v1 header.
> > >> >
> > >>
> > >> You could rename v_pt_rsv_flags to version_flags to avoid some future
> > >> code changes to support GTPv2. There's still the issue that not all
> > >> GTPv2 messages have a TEID though.
> > >
> > > Although they have the same size, the header of these two protocols
> > > obviously differs. My suggestion would be to go with a separate GTPv2
> > > pattern item using its own dedicated structure instead.
> > >
> > > --
> > > Adrien Mazarguil
> > > 6WIND
> > 
> > The 1st four bytes are the same (flags in first byte have different
> > meanings, but the bits indicating the version are in the same
> > location). After that, different fields in each version are optional,
> > and the headers have variable size. A single structure could be used
> > if the first field is renamed to something like "version_flags", and
> > then check that the teid field in item->mask is not set if
> > ((version_flags >> 5 == 2) && ((version_flags >> 4) & 1) == 1). If
> > there's going to be two structures, it would be good to put v1 and v2
> > in the names, in my opinion.
> 
> I think the name GTP is OK for now. Due to v1 and v2 are different, why not rename them
> when the v2 supporting are introduced?

In any case I'd rather avoid renaming and modifying existing items and
structure contents once part of the API to avoid API/ABI breakage that
require deprecation notices, user applications updates and so on; rte_flow
has been created as a kind of append-only API for this reason (of course
there are exceptions, such as a bad design choice for the VLAN item I intend
to fix at some point).

I'm fine with the name "GTP" as defined now and documented as matching
GTPv1. We can add "GTPv2"-themed definitions later when some implementation
provides the ability to match this version. If you want to append the "v1"
suffix right now to be more explicit, I'm also fine with that. Your call.

-- 
Adrien Mazarguil
6WIND