Re: [dpdk-dev] [PATCH 4/5] net/iavf: fix protocol size for virtchnl copy

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 11/16/2020 7:55 AM, Xiaoyu Min wrote:
> From: Xiaoyu Min <jackmin@nvidia.com>
> 
> The rte_flow_item_vlan items are refined.
> The structs do not exactly represent the packet bits captured on the
> wire anymore so should only copy real header instead of the whole struct.
> 
> Replace the rte_flow_item_* with the existing corresponding rte_*_hdr.
> 
> Fixes: 09315fc83861 ("ethdev: add VLAN attributes to ethernet and VLAN items")
> 
> Signed-off-by: Xiaoyu Min <jackmin@nvidia.com>
> ---
>   drivers/net/iavf/iavf_fdir.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/iavf/iavf_fdir.c b/drivers/net/iavf/iavf_fdir.c
> index d683a468c1..7054bde0b9 100644
> --- a/drivers/net/iavf/iavf_fdir.c
> +++ b/drivers/net/iavf/iavf_fdir.c
> @@ -541,7 +541,7 @@ iavf_fdir_parse_pattern(__rte_unused struct iavf_adapter *ad,
>   				VIRTCHNL_ADD_PROTO_HDR_FIELD_BIT(hdr, ETH, ETHERTYPE);
>   
>   				rte_memcpy(hdr->buffer,
> -					eth_spec, sizeof(*eth_spec));
> +					eth_spec, sizeof(struct rte_ether_hdr));

This requires 'struct rte_flow_item_eth' should have 'struct rte_ether_hdr' as 
first element, and I suspect this usage exists in a few more locations, but I 
wonder if this assumption is real and documented in somewhere?
I am not just talking about 'struct rte_flow_item_eth', but for all 
'rte_flow_item_*'...



btw, while checking for the 'struct rte_flow_item_eth', pahole shows it is using 
20 bytes, and I suspect this is not the intention with the reserved field:

struct rte_flow_item_eth {
	struct rte_ether_addr      dst;                  /*     0     6 */
	struct rte_ether_addr      src;                  /*     6     6 */
	uint16_t                   type;                 /*    12     2 */

	/* Bitfield combined with previous fields */

	uint32_t                   has_vlan:1;           /*    12:15  4 */

	/* XXX 31 bits hole, try to pack */

	uint32_t                   reserved:31;          /*    16: 1  4 */

	/* size: 20, cachelines: 1, members: 5 */
	/* bit holes: 1, sum bit holes: 31 bits */
	/* bit_padding: 1 bits */
	/* last cacheline: 20 bytes */
};

'has_vlan' seems combined with previous field to make together 32 bits. So the 
'reserved' field is occupying a new 32 bits all by itself.

What about changing the struct as following, while we can change the ABI:
struct rte_flow_item_eth {
	struct rte_ether_addr      dst;                  /*     0     6 */
	struct rte_ether_addr      src;                  /*     6     6 */
	uint16_t                   type;                 /*    12     2 */
	uint16_t                   has_vlan:1;           /*    14:15  2 */
	uint16_t                   reserved:15;          /*    14: 0  2 */

	/* size: 16, cachelines: 1, members: 5 */
	/* last cacheline: 16 bytes */
};