Re: [dpdk-dev] Segmentation Fault on printf()

[sabu kurian <sabu2kurian@gmail.com>]

Hello chris,

Thanks for your reply. I tried dumping the contents of mbuf as you have
suggested.
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 ?

Regards



On Fri, Mar 14, 2014 at 9:40 PM, Chris Wright <chrisw@redhat.com> wrote:

> * sabu kurian (sabu2kurian@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 = &eth->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
>