Re: [dpdk-dev] [PATCH v4 1/2] ethdev: add new ext hdr for gtp psc

[Olivier Matz <olivier.matz@6wind.com>]

On Thu, Apr 08, 2021 at 12:37:27PM +0000, Raslan Darawsheh wrote:
> Hi Olivier,
> 
> > -----Original Message-----
> > From: Olivier Matz <olivier.matz@6wind.com>
> > Sent: Thursday, April 8, 2021 3:30 PM
> > To: Raslan Darawsheh <rasland@nvidia.com>
> > Cc: dev@dpdk.org; ferruh.yigit@intel.com; Ori Kam <orika@nvidia.com>;
> > andrew.rybchenko@oktetlabs.ru; ivan.malov@oktetlabs.ru;
> > ying.a.wang@intel.com; Slava Ovsiienko <viacheslavo@nvidia.com>; Shiri
> > Kuzin <shirik@nvidia.com>
> > Subject: Re: [PATCH v4 1/2] ethdev: add new ext hdr for gtp psc
> > 
> > Hi Raslan,
> > 
> > On Sun, Apr 04, 2021 at 10:45:51AM +0300, Raslan Darawsheh wrote:
> > > Define new rte header for gtp PDU session container
> > > based on RFC 38415-g30
> > 
> > Do you have a link to this RFC?
> Yes sure,
> https://www.3gpp.org/ftp/Specs/archive/38_series/38.415/38415-g30.zip
> 
> > 
> > > Signed-off-by: Raslan Darawsheh <rasland@nvidia.com>
> > > ---
> > >  lib/librte_net/rte_gtp.h | 34 ++++++++++++++++++++++++++++++++++
> > >  1 file changed, 34 insertions(+)
> > >
> > > diff --git a/lib/librte_net/rte_gtp.h b/lib/librte_net/rte_gtp.h
> > > index 6a6f9b238d..088b0b5a53 100644
> > > --- a/lib/librte_net/rte_gtp.h
> > > +++ b/lib/librte_net/rte_gtp.h
> > > @@ -61,6 +61,40 @@ struct rte_gtp_hdr_ext_word {
> > >  	uint8_t next_ext;     /**< Next Extension Header Type. */
> > >  }  __rte_packed;
> > >
> > > +/**
> > > + * Optional extension for GTP with next_ext set to 0x85
> > > + * defined based on RFC 38415-g30.
> > > + */
> > > +__extension__
> > > +struct rte_gtp_psc_hdr {
> > > +	uint8_t ext_hdr_len; /**< PDU ext hdr len in multiples of 4 bytes */
> > > +	uint8_t type:4; /**< PDU type */
> > > +	uint8_t qmp:1; /**< Qos Monitoring Packet */
> > > +	union {
> > > +		struct {
> > > +			uint8_t snp:1; /**< Sequence number presence */
> > > +			uint8_t spare_dl1:2; /**< spare down link bits */
> > > +		};
> > > +		struct {
> > > +			uint8_t dl_delay_ind:1; /**< dl delay result presence
> > */
> > > +			uint8_t ul_delay_ind:1; /**< ul delay result presence
> > */
> > > +			uint8_t snp_ul1:1; /**< Sequence number presence
> > ul */
> > > +		};
> > > +	};
> > > +	union {
> > > +		struct {
> > > +			uint8_t ppp:1; /**< Paging policy presence */
> > > +			uint8_t rqi:1; /**< Reflective Qos Indicator */
> > > +		};
> > > +		struct {
> > > +			uint8_t n_delay_ind:1; /**< N3/N9 delay result
> > presence */
> > > +			uint8_t spare_ul2:1; /**< spare up link bits */
> > > +		};
> > > +	};
> > > +	uint8_t qfi:6; /**< Qos Flow Identifier */
> > > +	uint8_t data[0]; /**< data feilds */
> > > +} __rte_packed;
> > 
> > With this header, sizeof(rte_gtp_psc_hdr) = 5, is it really expected?
> The data[0] is variable length data, I guess I should send another version to mention that in the comment maybe.
> The header size according to the spec should be 4 octets aligned in general.

What I wanted to highlight is that using union of structs containing
bitfields does not work as you expect: each union is at least 1 byte.
This results in a structure that does not match the expected header.

> > 
> > It would help to see the specification to have a better idea of how to
> Sure, I've just posted the link above, please let me know of any suggestion that you have, and I'll be glad to do accordingly.
> 
> > split, but a possible solution is to do something like this:
> > 
> > struct rte_gtp_psc_generic_hdr {
> > 	uint8_t ext_hdr_len;
> > 	uint8_t type:4
> > 	uint8_t qmp:1;
> > 	uint8_t pad:3;
> > };
> > 
> > struct rte_gtp_psc_<name1>_hdr {
> > 	uint8_t ext_hdr_len;
> > 	uint8_t type:4
> > 	uint8_t qmp:1;
> > 	uint8_t uint8_t snp:1;
> > 	uint8_t spare_dl1:2;
> > 	...
> > };
> > 
> > ...
> > 
> > struct rte_gtp_psc_hdr {
> > 	union {
> > 		struct rte_gtp_psc_generic_hdr generic;
> > 		struct rte_gtp_psc_<name1>_hdr <name1>;
> > 		struct rte_gtp_psc_<name2>_hdr <name2>;
> > 	};
> > };

From what I see in the documation, I think this approach should
work. From afar, I suggest:

struct rte_gtp_psc_generic_hdr {
#if big endian
	uint8_t type:4
	uint8_t qmp:1;
	uint8_t pad:3;
#else
	uint8_t pad:3;
	uint8_t qmp:1;
	uint8_t type:4
#endif
};

struct rte_gtp_psc_type0_hdr {
#if big endian
	uint8_t type:4
	uint8_t qmp:1;
	uint8_t snp:1;
	uint8_t spare:2;

	uint8_t ppp:1;
	...
#else
	uint8_t pad:3;
	uint8_t qmp:1;
	uint8_t type:4
	uint8_t spare:2;
	uint8_t snp:1;

	...
#endif
	uint8_t data[0]; /* for variable fields */
};

struct rte_gtp_psc_type1_hdr {
	... same for fixed fields of type1


	uint8_t data[0]; /* for variable fields */
};

I don't see in the spec where is the reference to ext_hdr_len.

Regards,
Olivier