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Date: Thu, 17 Jun 2021 08:02:42 -0700
From: Tyler Retzlaff <roretzla@linux.microsoft.com>
To: Gregory Etelson <getelson@nvidia.com>
Cc: dev@dpdk.org, matan@nvidia.com, orika@nvidia.com, rasland@nvidia.com,
 Bernard Iremonger <bernard.iremonger@intel.com>,
 Olivier Matz <olivier.matz@6wind.com>
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Subject: Re: [dpdk-dev] [PATCH] net: introduce IPv4 ihl and version fields
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On Thu, May 27, 2021 at 06:28:58PM +0300, Gregory Etelson wrote:
> diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h
> index 4b728969c1..684bb028b2 100644
> --- a/lib/net/rte_ip.h
> +++ b/lib/net/rte_ip.h
> @@ -38,7 +38,21 @@ extern "C" {
>   * IPv4 Header
>   */
>  struct rte_ipv4_hdr {
> -	uint8_t  version_ihl;		/**< version and header length */
> +	__extension__

this patch reduces compiler portability, though not strictly objecting
so long as the community accepts that it may lead to conditional
compilation having to be introduced in a future change.

please also be mindful of the impact of __attribute__ ((__packed__)) in
the presence of bitfields on gcc when evaluating abi compatibility.

> +	union {
> +		uint8_t version_ihl;    /**< version and header length */
> +		struct {
> +#if RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN
> +			uint8_t ihl:4;
> +			uint8_t version:4;
> +#elif RTE_BYTE_ORDER == RTE_BIG_ENDIAN
> +			uint8_t version:4;
> +			uint8_t ihl:4;
> +#else
> +#error "setup endian definition"
> +#endif
> +		};
> +	};
>  	uint8_t  type_of_service;	/**< type of service */
>  	rte_be16_t total_length;	/**< length of packet */
>  	rte_be16_t packet_id;		/**< packet ID */
> -- 
> 2.31.1