RE: [PATCH dpdk v2 03/16] net: add structure for ipv6 addresses

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

+to: Various CPU architecture maintainers
+to: Stephen (already participating in this discussion)
+cc: x86 CPU architecture maintainers

> From: Robin Jarry [mailto:rjarry@redhat.com]
> Sent: Tuesday, 1 October 2024 10.17
> 
> There is currently no structure defined for IPv6 addresses. Introduce
> one that is simply a uint8_t array of 16 elements without any union.
> The
> idea is to ensure this structure alignment is 1 so that it can be
> mapped
> directly on unaligned packet memory.
> 
> Signed-off-by: Robin Jarry <rjarry@redhat.com>
> ---
>  lib/net/rte_ip6.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/lib/net/rte_ip6.h b/lib/net/rte_ip6.h
> index 5ad1dd25db08..52c41088681e 100644
> --- a/lib/net/rte_ip6.h
> +++ b/lib/net/rte_ip6.h
> @@ -35,6 +35,16 @@
>  extern "C" {
>  #endif
> 
> +#define RTE_IPV6_ADDR_SIZE 16
> +#define RTE_IPV6_MAX_DEPTH 128
> +
> +/**
> + * IPv6 Address
> + */
> +struct rte_ipv6_addr {
> +	unsigned char a[RTE_IPV6_ADDR_SIZE];
> +};

This has been discussed before, but I want to double check...

If - sometime in the future - we want to add a union to offer a 2-byte access variant and make the structure to 2-byte aligned (which is the common case in Ethernet packets), it will break both API and ABI. This seems unlikely to get accepted at a later time, so I think we are - right now - in a situation where it's now or never:

struct rte_ipv6_addr {
	__extension__
	union {
		unsigned char a[RTE_IPV6_ADDR_SIZE];
		uint16_t      w[RTE_IPV6_ADDR_SIZE / 2];
	};
};

Unless some of the CPU folks want the 2-byte aligned variant, stick with what you offered.