net/pcap: truncate packet if it is too large

  From: Zhike Wang <wangzhike@jd.com>

Previously large packet would be dropped, instead now it is better to keep it via truncating it.

Signed-off-by: Zhike Wang <wangzhike@jd.com>
---
 drivers/net/pcap/rte_eth_pcap.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)
  

On 11/8/2019 2:33 AM, Zhike Wang wrote:
> From: Zhike Wang <wangzhike@jd.com>
> 
> Previously large packet would be dropped, instead now it is better to keep it via truncating it.

Looks reasonable, thanks.

cc'ing Cian too, since he did some pcap work recently.

> 
> Signed-off-by: Zhike Wang <wangzhike@jd.com>
> ---
>  drivers/net/pcap/rte_eth_pcap.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/pcap/rte_eth_pcap.c b/drivers/net/pcap/rte_eth_pcap.c
> index 5186d8f..4614239 100644
> --- a/drivers/net/pcap/rte_eth_pcap.c
> +++ b/drivers/net/pcap/rte_eth_pcap.c
> @@ -313,7 +313,7 @@ struct pmd_devargs_all {
>  	struct pcap_pkthdr header;
>  	pcap_dumper_t *dumper;
>  	unsigned char temp_data[RTE_ETH_PCAP_SNAPLEN];
> -	size_t len;
> +	size_t len, caplen;
>  
>  	pp = rte_eth_devices[dumper_q->port_id].process_private;
>  	dumper = pp->tx_dumper[dumper_q->queue_id];
> @@ -328,25 +328,23 @@ struct pmd_devargs_all {
>  		len = rte_pktmbuf_pkt_len(mbuf);
>  		if (unlikely(!rte_pktmbuf_is_contiguous(mbuf) &&
>  				len > sizeof(temp_data))) {
> -			PMD_LOG(ERR,
> -				"Dropping multi segment PCAP packet. Size (%zd) > max size (%zd).",
> -				len, sizeof(temp_data));
> -			rte_pktmbuf_free(mbuf);
> -			continue;
> +			caplen = sizeof(temp_data);
> +		} else {
> +			caplen = len;

No strong opinion, but what do you think removing the else leg by assigning the
'caplen' by default to 'len':
 len = caplen = rte_pktmbuf_pkt_len(mbuf);

>  		}
>  
>  		calculate_timestamp(&header.ts);
>  		header.len = len;
> -		header.caplen = header.len;
> +		header.caplen = caplen;
>  		/* rte_pktmbuf_read() returns a pointer to the data directly
>  		 * in the mbuf (when the mbuf is contiguous) or, otherwise,
>  		 * a pointer to temp_data after copying into it.
>  		 */
>  		pcap_dump((u_char *)dumper, &header,
> -			rte_pktmbuf_read(mbuf, 0, len, temp_data));
> +			rte_pktmbuf_read(mbuf, 0, caplen, temp_data));
>  
>  		num_tx++;
> -		tx_bytes += len;
> +		tx_bytes += caplen;
>  		rte_pktmbuf_free(mbuf);
>  	}
>  
>