[dpdk-dev] Segmentation Fault on printf()
daniel.kaminsky at infinitelocality.com
Mon Mar 17 20:45:48 CET 2014
I think that in this case the packet length is zero which will result in
nothing from mtod.
On Sun, Mar 16, 2014 at 3:03 PM, sabu kurian <sabu2kurian at gmail.com> wrote:
> Hello chris,
> Thanks for your reply. I tried dumping the contents of mbuf as you have
> This is what I get:
> dump mbuf at 0x0x6c7620, phys=7f34d91eba28, buf_len=59488
> pkt_len=0, ol_flags=0, nb_segs=0, in_port=0
> and soon after that I get a segmentation fault. Do you have any idea on
> what could be causing it ?
> On Fri, Mar 14, 2014 at 9:40 PM, Chris Wright <chrisw at redhat.com> wrote:
> > * sabu kurian (sabu2kurian at gmail.com) wrote:
> > > Hello friends,
> > >
> > > I'm trying to print the ether_type for a packet that I captured from a
> > port
> > > on my machine. Suppose 'm' holds the packet. 'm' is of type 'struct
> > > rte_mbuf'. Intels API reference for DPDK says 'ether_type' is of
> > uint16_t.
> > > I used the following code to retrieve ether_type.
> > >
> > > void * eth_type;
> > > struct ether_hdr *eth;
> > >
> > > eth = rte_pktmbuf_mtod(m, struct ether_hdr *);
> > > eth_type = ð->ether_type;
> > >
> > > printf("\n Type is %" PRIu16 , *((uint16_t *)eth_type));
> > Looks ok, albeit slightly overly complicated.
> > struct ether_hdr *eth;
> > uint16_t eth_type;
> > eth = rte_pktmbuf_mtod(m, struct ether_hdr *);
> > eth_type = eth->ether_type;
> > printf("\n Type is %" PRIu16 , eth_type));
> > This would remove all the extra casting. Perhaps the mbuf is the problem
> > here. And if so, the above snippet would segfault on eth->ether_type
> > showing you that mbuf is invalid.
> > You could try to (above mtod):
> > rte_pktmbuf_dump(m, sizeof(struct ether_hdr));
> > as that will show key contents of mbuf and packet data (and do some
> > basic validation along the way).
> > thanks,
> > -chris
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