Re: [dpdk-dev] [PATCH 2/3] net/pcap: fix transmit return count in error conditions

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

On 7/24/2019 12:54 PM, David Marchand wrote:
> When a packet cannot be transmitted, the driver is supposed to free this
> packet and report it as handled.
> This is to prevent the application from retrying to send the same packet
> and ending up in a liveloop since the driver will never manage to send
> it.
> 
> Fixes: 49a0a2ffd5db ("net/pcap: fix possible mbuf double freeing")
> Fixes: 6db141c91e1f ("pcap: support jumbo frames")
> CC: stable@dpdk.org
> 
> Signed-off-by: David Marchand <david.marchand@redhat.com>
> ---
>  drivers/net/pcap/rte_eth_pcap.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/pcap/rte_eth_pcap.c b/drivers/net/pcap/rte_eth_pcap.c
> index 470867d..5e5aab7 100644
> --- a/drivers/net/pcap/rte_eth_pcap.c
> +++ b/drivers/net/pcap/rte_eth_pcap.c
> @@ -354,7 +354,8 @@ struct pmd_devargs_all {
>  					mbuf->pkt_len,
>  					RTE_ETHER_MAX_JUMBO_FRAME_LEN);
>  
> -				break;
> +				rte_pktmbuf_free(mbuf);
> +				continue;

+1
Very recently 'rte_pktmbuf_free()' was moved because it wasn't compatible with
return value, but this looks better, to free the mbuf and record it as error.

>  			}
>  		}
>  
> @@ -373,7 +374,7 @@ struct pmd_devargs_all {
>  	dumper_q->tx_stat.bytes += tx_bytes;
>  	dumper_q->tx_stat.err_pkts += nb_pkts - num_tx;
>  
> -	return num_tx;
> +	return nb_pkts;
>  }
>  
>  /*
> @@ -439,14 +440,15 @@ struct pmd_devargs_all {
>  					mbuf->pkt_len,
>  					RTE_ETHER_MAX_JUMBO_FRAME_LEN);
>  
> -				break;
> +				rte_pktmbuf_free(mbuf);
> +				continue;
>  			}
>  		}
>  
> -		if (unlikely(ret != 0))
> -			break;
> -		num_tx++;
> -		tx_bytes += mbuf->pkt_len;
> +		if (ret == 0) {
> +			num_tx++;
> +			tx_bytes += mbuf->pkt_len;
> +		}

I don't know this part, this is in 'eth_pcap_tx()' which writes packets to the
interfaces.

if 'pcap_sendpacket()' fails this doesn't mean packet can't be sent and may
cause a liveloop. Why not keep the existing behavior and let application to decide?

>  		rte_pktmbuf_free(mbuf);
>  	}
>  
> @@ -454,7 +456,7 @@ struct pmd_devargs_all {
>  	tx_queue->tx_stat.bytes += tx_bytes;
>  	tx_queue->tx_stat.err_pkts += nb_pkts - num_tx;
>  
> -	return num_tx;
> +	return nb_pkts;
>  }
>  
>  /*
>