RE: [PATCH] net/pcap: support MTU set

From: Ido Goshen <Ido@cgstowernetworks.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: Ferruh Yigit <ferruh.yigit@intel.com>, "dev@dpdk.org" <dev@dpdk.org>
Subject: RE: [PATCH] net/pcap: support MTU set
Date: Thu, 17 Mar 2022 19:11:58 +0000	[thread overview]
Message-ID: <AS4PR09MB552502DDF7E5A4B37052A266D6129@AS4PR09MB5525.eurprd09.prod.outlook.com> (raw)
In-Reply-To: <20220317112047.2d8d4f8a@hermes.local>

As far as I can see the initial device MTU is derived from port *RX* configuration in struct rte_eth_rxmode https://doc.dpdk.org/api-21.11/structrte__eth__rxmode.html
Couple of real NICs I've tested (ixgbe, i40e based) don't allow oversized, tests details can be seen in https://bugs.dpdk.org/show_bug.cgi?id=961

> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Thursday, 17 March 2022 20:21
> To: Ido Goshen <Ido@cgstowernetworks.com>
> Cc: Ferruh Yigit <ferruh.yigit@intel.com>; dev@dpdk.org
> Subject: Re: [PATCH] net/pcap: support MTU set
> 
> On Thu, 17 Mar 2022 19:43:47 +0200
> ido g <ido@cgstowernetworks.com> wrote:
> 
> > +		if (unlikely(header.caplen > dev->data->mtu)) {
> > +			pcap_q->rx_stat.err_pkts++;
> > +			rte_pktmbuf_free(mbuf);
> > +			break;
> > +		}
> 
> MTU should only be enforced on transmit.
> Other real network devices allow oversized packets.
> 
> Since the pcap file is something user provides, if you don't want that then use
> something to filter the file.