[PATCH v2] net: add bit fields to IPv6 header definition

[Morten Brørup]

> From: Gregory Etelson [mailto:getelson at nvidia.com]
> Sent: Tuesday, 18 June 2024 09.58
> 
> DPDK IPv6 header definition combined the `version`, `traffic class`
> and `flow label` header fields into a single 32 bits structure member
> `vtc_flow`.
> 
> The patch expands IPv6 header definition with dedicated structure
> members for the `version`, `traffic class` and `flow label` fields.
> The `traffic class` is also separated into DS and ECN fields.
> 
> The patch also preserves existing `vtc_flow` structure member for
> backward compatibility.
> 
> Signed-off-by: Gregory Etelson <getelson at nvidia.com>
> ---
> v2:
> Replace uint32_t with rte_be32_t.
> Split traffic_class into DS and ECN bits.
> ---
>  lib/net/rte_ip.h | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h
> index 0d103d4127..fe1d596054 100644
> --- a/lib/net/rte_ip.h
> +++ b/lib/net/rte_ip.h
> @@ -524,7 +524,23 @@ rte_ipv4_udptcp_cksum_mbuf_verify(const struct rte_mbuf
> *m,
>   * IPv6 Header
>   */
>  struct rte_ipv6_hdr {
> -	rte_be32_t vtc_flow;	/**< IP version, traffic class & flow label.
> */
> +	union {
> +		rte_be32_t vtc_flow;        /**< IP version, traffic class & flow
> label. */
> +		__extension__
> +		struct {
> +#if RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN
> +			rte_be32_t flow_label:20; /**< flow label */

I don't know if sub-unions of bitfields are possible and/or require special magic for packing the bits.
If possible, expanding the 8 bit "tc" field like this would be nice:

+ union {
+ 	rte_be32_t tc:8;
+ 	__extension__
+ 	struct {

> +			rte_be32_t ecn:2; /**< ECN */
> +			rte_be32_t ds:6;     /**< differentiated services */

+ 	};
+ };

> +			rte_be32_t version:4; /**< version */
> +#elif RTE_BYTE_ORDER == RTE_BIG_ENDIAN
> +			rte_be32_t version:4; /**< version */
> +			rte_be32_t ds:6;     /**< differentiated services */
> +			rte_be32_t ecn:2; /**< ECN */
> +			rte_be32_t flow_label:20; /**< flow label */
> +#endif
> +		};
> +	};
>  	rte_be16_t payload_len;	/**< IP payload size, including ext. headers
> */
>  	uint8_t  proto;		/**< Protocol, next header. */
>  	uint8_t  hop_limits;	/**< Hop limits. */
> --
> 2.43.0

Without the suggested addition,
Reviewed-by: Morten Brørup <mb at smartsharesystems.com>

With the suggested addition,
Acked-by: Morten Brørup <mb at smartsharesystems.com>