Re: Packet crafting....

Thanks on the reply Richardson. You did mention something like "Don't
forget that when you get the mbuf from rte_pktmbuf_alloc, you also need to
set the length value to the appropriate size." .

 Like I'm allocating the mbuf using rte_mbuf . The rte_mempool_create has
already set the maximum packet size for a mbuf and the number of mbuf's and
all. So do I really need to use rte_pktmbuf_alloc ?


On Fri, Mar 14, 2014 at 4:38 PM, Richardson, Bruce <
bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:

quoted

From: sabu kurian [mailto:sabu2kurian-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org]
Sent: Friday, March 14, 2014 10:09 AM
To: Richardson, Bruce
Cc: dev-VfR2kkLFssw@public.gmane.org
Subject: Re: [dpdk-dev] Packet crafting....

Thank you very much Richardson for your valuable reply. But is there

another way of doing it using the rte_pktmbuf_append / rte_pktmbuf_prepend
? Can you please tell me on how to do that ?

You could use pktmbuf_append and pktmbuf_prepend, but they are primarily
designed to add headers/footers on to an existing packet that already has
headers, so that you don't need to move the existing data. In the case of
having to craft a packet from scratch, there is no existing data in the
mbuf, so the whole packet can just be filled in sequentially. [Don't forget
that when you get the mbuf from rte_pktmbuf_alloc, you also need to set the
length value to the appropriate size.]

However, if you first write the data to the mbuf and then want to add the
headers in order, like a packet moving down through layers of a stack,  you
can use prepend to add udp, then ip, then your ethernet header, but this
will be no faster than just writing the data directly to the mbuf space,
and may be slightly slower as each prepend call has to just the length
values and data pointer values in the mbuf. Each header prepended also uses
up headroom in the mbuf, so you can only add 128-bytes of headers by
default to each packet.

In short, if you are creating a single packet, I'd recommend just getting
the data pointer from the returned mbuf and writing directly to that.

Regards,
/Bruce