Re: [RFC PATCH 15/16] gtp: add ability to send GTP controls headers

[Pravin Shelar <pravin.ovn@gmail.com>]

On Mon, Jan 25, 2021 at 9:52 AM Harald Welte <laforge@gnumonks.org> wrote:
>
> Hi Jonas,
>

> On Sun, Jan 24, 2021 at 03:21:21PM +0100, Jonas Bonn wrote:
> > struct gtpu_metadata {
> >         __u8    ver;
> >         __u8    flags;
> >         __u8    type;
> > };
> >
> > Here ver is the version of the metadata structure itself, which is fine.
> > 'flags' corresponds to the 3 flag bits of GTP header's first byte:  E, S,
> > and PN.
> > 'type' corresponds to the 'message type' field of the GTP header.
>
> One more comment on the 'type': Of how much use is it?  After all, the
> GTP-U kernel driver only handles a single message type at all (G-PDU /
> 255 - the only message type that encapsulates user IP data), while all
> other message types are always processed in userland via the UDP socket.
>
There is NO userland UDP socket for the LWT tunnel. All UDP traffic is
terminated in kernel space. userland only sets rules over LTW tunnel
device to handle traffic. This is how OVS/eBPF handles other UDP based
LWT tunnel devices.


> Side-note: 3GPP TS 29.060 lists 5 other message types that can happen in
> GTP-U:
> * Echo Request
> * Echo Response
> * Error Indication
> * Supported Extension Headers Notification
> * End Marker
>
> It would be interesting to understand how the new flow-based tunnel would
> treat those, if those
>
Current code does handle Echo Request, Response and End marker.