[dpdk-dev] [PATCH v2 01/22] ethdev: fix MTU size exceeds max rx packet length

[Andrew Rybchenko]

On 12/17/20 12:22 PM, Steve 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: Steve Yang <stevex.yang at intel.com>
> ---
>  lib/librte_ethdev/rte_ethdev.c | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
> index 17ddacc78d..ff6a1e675f 100644
> --- a/lib/librte_ethdev/rte_ethdev.c
> +++ b/lib/librte_ethdev/rte_ethdev.c
> @@ -1292,6 +1292,7 @@ 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;
>  	int diag;
>  	int ret;
>  
> @@ -1323,6 +1324,15 @@ rte_eth_dev_configure(uint16_t port_id, uint16_t nb_rx_q, uint16_t nb_tx_q,
>  	if (ret != 0)
>  		goto rollback;
>  
> +	/* Get the real Ethernet overhead length */
> +	if (dev_info.max_mtu &&

First of all I'm not sure that we need to handle 0 value
separately. Or it should be checked separately and trigger
an error since it is a driver mis-behaviour.

If kept, it should be compared vs 0 explicitly in accordance
with DPDK coding style.

> +	    dev_info.max_mtu != UINT16_MAX &&
> +	    dev_info.max_rx_pktlen &&

It should be compared vs 0 explicitly in accordance
with DPDK coding style.

> +	    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 number of queues specified by application for both Rx and Tx is
>  	 * zero, use driver preferred values. This cannot be done individually
>  	 * as it is valid for either Tx or Rx (but not both) to be zero.
> @@ -1410,13 +1420,18 @@ rte_eth_dev_configure(uint16_t port_id, uint16_t nb_rx_q, uint16_t nb_tx_q,
>  			goto rollback;
>  		}
>  	} else {
> -		if (dev_conf->rxmode.max_rx_pkt_len < RTE_ETHER_MIN_LEN ||
> -			dev_conf->rxmode.max_rx_pkt_len > RTE_ETHER_MAX_LEN)
> +		uint16_t pktlen = dev_conf->rxmode.max_rx_pkt_len;
> +		if (pktlen < RTE_ETHER_MIN_MTU + overhead_len ||
> +			pktlen > RTE_ETHER_MTU + overhead_len)

Alignment looks misleading. Either two tabs or just 4 spaces.

>  			/* Use default value */
>  			dev->data->dev_conf.rxmode.max_rx_pkt_len =
> -							RTE_ETHER_MAX_LEN;
> +						RTE_ETHER_MTU + overhead_len;
>  	}
>  
> +	/* Scale the MTU size to adapt max_rx_pkt_len */
> +	dev->data->mtu = dev->data->dev_conf.rxmode.max_rx_pkt_len -
> +				overhead_len;
> +

Is it expected side effect that re-configure always resets
previously set MTU. I.e.:
   configure -> set_mtu -> start -> stop -> re-configure
and set MTU is lost.

>  	/*
>  	 * If LRO is enabled, check that the maximum aggregated packet
>  	 * size is supported by the configured device.
>