[PATCH] net: improve vlan header type alignment

[Morten Brørup]

> From: Morten Brørup [mailto:mb at smartsharesystems.com]
> Sent: Sunday, 13 October 2024 10.36
> 
> Ethernet packets can be VLAN tagged, i.e. an Ethernet header can have a
> VLAN tag (a.k.a. VLAN header) embedded.
> Since the Ethernet header is 2 byte aligned, and the VLAN tag is
> directly
> related to the Ethernet header, the VLAN tag is also 2 byte aligned, so
> packing the VLAN tag structure is not necessary.

Stephen, Bruce, you missed the VLAN header type in this patch:
https://git.dpdk.org/dpdk/commit/lib/librte_net/rte_ether.h?id=da5350ef29afd35c1adabe76f60832f3092269ad

This patch completes your work.

> 
> Furthermore, the Ethernet header type is implictly 2 byte aligned, so
> removed the superfluous explicit 2 byte alignment.
> 
> Added static_asserts to verify the size and alignment of the various
> Ethernet types.
> 
> Signed-off-by: Morten Brørup <mb at smartsharesystems.com>
> ---
>  lib/net/rte_ether.h | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/net/rte_ether.h b/lib/net/rte_ether.h
> index 403e84f50b..c9a0b536c3 100644
> --- a/lib/net/rte_ether.h
> +++ b/lib/net/rte_ether.h
> @@ -11,6 +11,8 @@
>   * Ethernet Helpers in RTE
>   */
> 
> +#include <assert.h>
> +#include <stdalign.h>
>  #include <stdint.h>
>  #include <stdio.h>
> 
> @@ -75,6 +77,11 @@ struct __rte_aligned(2) rte_ether_addr {
>  	uint8_t addr_bytes[RTE_ETHER_ADDR_LEN]; /**< Addr bytes in tx
> order */
>  };
> 
> +static_assert(sizeof(struct rte_ether_addr) == 6,
> +		"sizeof(struct rte_ether_addr) == 6");
> +static_assert(alignof(struct rte_ether_addr) == 2,
> +		"alignof(struct rte_ether_addr) == 2");
> +
>  #define RTE_ETHER_LOCAL_ADMIN_ADDR 0x02 /**< Locally assigned Eth.
> address. */
>  #define RTE_ETHER_GROUP_ADDR  0x01 /**< Multicast or broadcast Eth.
> address. */
> 
> @@ -290,12 +297,17 @@ rte_ether_unformat_addr(const char *str, struct
> rte_ether_addr *eth_addr);
>   * Ethernet header: Contains the destination address, source address
>   * and frame type.
>   */
> -struct __rte_aligned(2) rte_ether_hdr {
> +struct rte_ether_hdr {
>  	struct rte_ether_addr dst_addr; /**< Destination address. */
>  	struct rte_ether_addr src_addr; /**< Source address. */
>  	rte_be16_t ether_type; /**< Frame type. */
>  };
> 
> +static_assert(sizeof(struct rte_ether_hdr) == 14,
> +		"sizeof(struct rte_ether_hdr) == 14");
> +static_assert(alignof(struct rte_ether_hdr) == 2,
> +		"alignof(struct rte_ether_hdr) == 2");
> +
>  /**
>   * Ethernet VLAN Header.
>   * Contains the 16-bit VLAN Tag Control Identifier and the Ethernet
> type
> @@ -304,7 +316,12 @@ struct __rte_aligned(2) rte_ether_hdr {
>  struct rte_vlan_hdr {
>  	rte_be16_t vlan_tci;  /**< Priority (3) + CFI (1) + Identifier
> Code (12) */
>  	rte_be16_t eth_proto; /**< Ethernet type of encapsulated frame.
> */
> -} __rte_packed;
> +};
> +
> +static_assert(sizeof(struct rte_vlan_hdr) == 4,
> +		"sizeof(struct rte_vlan_hdr) == 4");
> +static_assert(alignof(struct rte_vlan_hdr) == 2,
> +		"alignof(struct rte_vlan_hdr) == 2");
> 
> 
> 
> --
> 2.43.0