[PATCH] net: improve vlan header type alignment

[Morten Brørup]

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.

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 <m...@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