[dpdk-dev] [PATCH v6 2/2] librte_ethdev: fix MTU size exceeds max rx packet length

[Ferruh Yigit]

On 10/22/2020 9:48 AM, SteveX Yang wrote:
> If max rx packet length is smaller then MTU + Ether overhead, that will
> drop all MTU size packets.
> 
> Update the MTU size according to the max rx packet and Ether overhead.
> 
> Fixes: 59d0ecdbf0e1 ("ethdev: MTU accessors")
> 
> Signed-off-by: SteveX Yang <stevex.yang at intel.com>
> ---
>   lib/librte_ethdev/rte_ethdev.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
> 
> diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
> index b12bb3854..17f1c33ac 100644
> --- a/lib/librte_ethdev/rte_ethdev.c
> +++ b/lib/librte_ethdev/rte_ethdev.c
> @@ -1290,6 +1290,8 @@ rte_eth_dev_configure(uint16_t port_id, uint16_t nb_rx_q, uint16_t nb_tx_q,
>   	struct rte_eth_dev *dev;
>   	struct rte_eth_dev_info dev_info;
>   	struct rte_eth_conf orig_conf;
> +	uint16_t overhead_len;
> +	uint16_t max_rx_pktlen;
>   	int diag;
>   	int ret;
>   
> @@ -1415,6 +1417,18 @@ rte_eth_dev_configure(uint16_t port_id, uint16_t nb_rx_q, uint16_t nb_tx_q,
>   							RTE_ETHER_MAX_LEN;
>   	}
>   
> +	/*
> +	 * Update MTU value if MTU + OVERHEAD exceeds the max_rx_pkt_len
> +	 */

I am not sure this conditional update is required, the target is keep 
'max_rx_pktlen' & 'mtu' in sync.

So why not just:
dev->data->mtu = max_rx_pktlen - overhead_len;


> +	max_rx_pktlen = dev->data->dev_conf.rxmode.max_rx_pkt_len;
> +	if (dev_info.max_rx_pktlen && dev_info.max_mtu)
> +		overhead_len = dev_info.max_rx_pktlen - dev_info.max_mtu;
> +	else
> +		overhead_len = RTE_ETHER_HDR_LEN + RTE_ETHER_CRC_LEN;
> +
> +	if (max_rx_pktlen < dev->data->mtu + overhead_len)
> +		dev->data->mtu = max_rx_pktlen - overhead_len;
> +
>   	/*
>   	 * If LRO is enabled, check that the maximum aggregated packet
>   	 * size is supported by the configured device.
>