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

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Gregory Etelson [mailto:getelson@nvidia.com]
> Sent: Tuesday, 18 June 2024 07.18
> 
> 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 patch also preserves existing `vtc_flow` structure member for
> backward compatibility.

Good addition.
I had been wondering why we didn't have this already. :-)

> 
> Signed-off-by: Gregory Etelson <getelson@nvidia.com>
> ---
>  lib/net/rte_ip.h | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h
> index 0d103d4127..26e78a6624 100644
> --- a/lib/net/rte_ip.h
> +++ b/lib/net/rte_ip.h
> @@ -524,7 +524,21 @@ 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.
> */
> +	__extension__
> +	union {
> +		rte_be32_t vtc_flow;        /**< IP version, traffic class & flow
> label. */

The mbuf structure [1] has __extension__ here,
i.e. preceding the structure following the integer field,
instead of preceding the union.

[1]: https://git.dpdk.org/dpdk/tree/lib/mbuf/rte_mbuf_core.h#n520

> +		struct {
> +#if RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN
> +			uint32_t flow_label:24; /**< flow label */

Flow Label is 20 bits, not 24.

> +			uint32_t tc:4;     /**< traffic class */

TC is 8 bits, not 4.

> +			uint32_t version:4; /**< version */
> +#elif RTE_BYTE_ORDER == RTE_BIG_ENDIAN
> +			uint8_t version:4; /**< version */
> +			uint8_t tc:4;     /**< traffic class */

:8, not :4.

> +			uint32_t flow_label:24; /**< flow label */

:20, not :24.

> +#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