RE: Query regarding pf_packet sockets

[Prashant Batra (prbatra)]

That’s look good

Thanks.

-----Original Message-----
From: Eric Dumazet [mailto:eric.d...@gmail.com]
Sent: Thursday, March 22, 2012 9:59 AM
To: Prashant Batra (prbatra)
Cc: net...@vger.kernel.org
Subject: Re: Query regarding pf_packet sockets

On Thu, 2012-03-22 at 08:52 +0530, Prashant Batra (prbatra) wrote:
> Hi ,
>
> I am trying to use PF_PACKET socket along with filters applied on the socket through setsockopt, SO_ATTACH_FILTER.
> Now as I create this socket, any packet coming to the kernel would be copied into the socket buffer for this socket.
>
> So, even if I apply the filter, first few packets would always be those which do not match the filter.
>
> Is there a way (some socket option), to make socket passive and active, so that I will set the socket in passive mode after creation,
> and then set it as active, after I apply the filter, so that I only receive the filtered packet in user space.
>
> Thanks,
> Prashant
>
1) open PF_PACKET
2) Install a "deny all packets" filter
3) read all packets that might have been captured right before 2)
4) Install your filter

This is what is done by libpcap