Re: [PATCH] app/test-pmd: fix L4 checksum with padding data

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

On 8/4/2023 9:28 AM, Kaiwen Deng wrote:
> IEEE 802 packets may have a minimum size limit. The data fields
> should be padded when necessary. In some cases, the padding data
> is not zero. Testpmd does not trim these IP packets to the true
> length of the frame, so errors will occur when calculating TCP
> or UDP checksum.
> 

Hi Kaiwen,

I am trying to understand the problem, what is the testcase that has
checksum error?

Are the received mbuf data_len & pkt_len wrong? Instead of trying to fix
the mbuf during forwarding, can we fix where packet generated?

> This commit fixes this issue by triming IP packets to the true
> length of the frame in testpmd.
> 
> Fixes: 03d17e4d0179 ("app/testpmd: do not change IP addrs in checksum engine")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Kaiwen Deng <kaiwenx.deng@intel.com>
> ---
>  app/test-pmd/csumonly.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/app/test-pmd/csumonly.c b/app/test-pmd/csumonly.c
> index 7af635e3f7..58b72b714a 100644
> --- a/app/test-pmd/csumonly.c
> +++ b/app/test-pmd/csumonly.c
> @@ -853,12 +853,14 @@ pkt_burst_checksum_forward(struct fwd_stream *fs)
>  	uint16_t nb_rx;
>  	uint16_t nb_prep;
>  	uint16_t i;
> +	uint16_t pad_len;
>  	uint64_t rx_ol_flags, tx_ol_flags;
>  	uint64_t tx_offloads;
>  	uint32_t rx_bad_ip_csum;
>  	uint32_t rx_bad_l4_csum;
>  	uint32_t rx_bad_outer_l4_csum;
>  	uint32_t rx_bad_outer_ip_csum;
> +	uint32_t l3_off;
>  	struct testpmd_offload_info info;
>  
>  	/* receive a burst of packet */
> @@ -980,6 +982,36 @@ pkt_burst_checksum_forward(struct fwd_stream *fs)
>  			l3_hdr = (char *)l3_hdr + info.outer_l3_len + info.l2_len;
>  		}
>  
> +		if (info.is_tunnel) {
> +			l3_off = info.outer_l2_len +
> +					info.outer_l3_len +
> +					info.l2_len;
> +		} else {
> +			l3_off = info.l2_len;
> +		}
> +		switch (info.ethertype) {
> +		case _htons(RTE_ETHER_TYPE_IPV4):
> +			pad_len = rte_pktmbuf_data_len(m) -
> +					(l3_off +
> +					rte_be_to_cpu_16(
> +					((struct rte_ipv4_hdr *)l3_hdr)->total_length));
> +			break;
> +		case _htons(RTE_ETHER_TYPE_IPV6):
> +			pad_len = rte_pktmbuf_data_len(m) -
> +					(l3_off +
> +					rte_be_to_cpu_16(
> +					((struct rte_ipv6_hdr *)l3_hdr)->payload_len));
> +			break;
> +		default:
> +			pad_len = 0;
> +			break;
> +		}
> +
> +		if (pad_len) {
> +			rte_pktmbuf_data_len(m) = rte_pktmbuf_data_len(m) - pad_len;
> +			rte_pktmbuf_pkt_len(m) = rte_pktmbuf_data_len(m);
> +		}
> +
>  		/* step 2: depending on user command line configuration,
>  		 * recompute checksum either in software or flag the
>  		 * mbuf to offload the calculation to the NIC. If TSO