[dpdk-dev] [PATCH] pcap: fix captured frame length

[Dror Birkman]

Hi Nicolas,

Thanks.
I tried to test my application with a pcap file I had, but got weird
results, so I wrote back the rte_mbufs in pcap format and hex compared it
to my input pcap. Only then I noticed that my original pcap had frames that
were captured with a length smaller than the frame length.

I guess you can call it pure (bad) luck :)


Dror

On Thu, Jan 28, 2016 at 8:00 PM, Nicolas Pernas Maradei <
nicolas.pernas.maradei at emutex.com> wrote:

> Hi Dror,
>
> Good catch. What you are saying makes sense and it is also explained in
> pcap's documentation. Was your setup unusual though?
> This might sound like a silly question but I don't remember seeing that
> issue and I should have since your fix is correct.
>
> Nico.
>
> On 28/01/16 08:09, Dror Birkman wrote:
>
> The actual captured length is header.caplen, whereas header.len is
> the original length on the wire.
>
> Signed-off-by: Dror Birkman <dror.birkman at lightcyber.com> <dror.birkman at lightcyber.com>
> ---
>
>
> Without this fix, if the captured length is smaller than the original
> length on the wire, mbuf will contain incorrect data.
>
>
>  drivers/net/pcap/rte_eth_pcap.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/pcap/rte_eth_pcap.c b/drivers/net/pcap/rte_eth_pcap.c
> index f9230eb..1d121f8 100644
> --- a/drivers/net/pcap/rte_eth_pcap.c
> +++ b/drivers/net/pcap/rte_eth_pcap.c
> @@ -220,25 +220,25 @@ eth_pcap_rx(void *queue,
>  		buf_size = (uint16_t)(rte_pktmbuf_data_room_size(pcap_q->mb_pool) -
>  				RTE_PKTMBUF_HEADROOM);
>
> -		if (header.len <= buf_size) {
> +		if (header.caplen <= buf_size) {
>  			/* pcap packet will fit in the mbuf, go ahead and copy */
>  			rte_memcpy(rte_pktmbuf_mtod(mbuf, void *), packet,
> -					header.len);
> -			mbuf->data_len = (uint16_t)header.len;
> +					header.caplen);
> +			mbuf->data_len = (uint16_t)header.caplen;
>  		} else {
>  			/* Try read jumbo frame into multi mbufs. */
>  			if (unlikely(eth_pcap_rx_jumbo(pcap_q->mb_pool,
>  						       mbuf,
>  						       packet,
> -						       header.len) == -1))
> +						       header.caplen) == -1))
>  				break;
>  		}
>
> -		mbuf->pkt_len = (uint16_t)header.len;
> +		mbuf->pkt_len = (uint16_t)header.caplen;
>  		mbuf->port = pcap_q->in_port;
>  		bufs[num_rx] = mbuf;
>  		num_rx++;
> -		rx_bytes += header.len;
> +		rx_bytes += header.caplen;
>  	}
>  	pcap_q->rx_pkts += num_rx;
>  	pcap_q->rx_bytes += rx_bytes;
>
>
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