netdev - Re: Single socket with TX_RING and RX

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Message-ID: <loom.20130515T152203-727@post.gmane.org>
Date:	Wed, 15 May 2013 13:32:41 +0000 (UTC)
From:	Ricardo Tubío <rtpardavila@...il.com>
To:	netdev@...r.kernel.org
Subject: Re: Single socket with TX_RING and RX_RING

Daniel Borkmann <dborkman <at> redhat.com> writes:

> 
> On 05/15/2013 02:53 PM, Ricardo Tubío wrote:
> > Once I tell kernel to export the TX_RING through setsockopt() (see code
> > below) I always get an error (EBUSY) if i try to tell kernel to export the
> > RX_RING with the same socket descriptor. Therefore, I have to open an
> > additional socket for the RX_RING and I require of two sockets when I though
> > that I would only require of one socket for both TX and RX using mmap()ed
> > memory.
> >
> > Do I need both sockets or am I doing something wrong?
> 
> The second time you call init_ring() in your code e.g. with TX_RING, where
> you have previously set it up for the RX_RING. The kernel will give you
> -EBUSY because the packet socket is already mmap(2)'ed.
> 

Ok, so if I make the following system calls:

void *ring=NULL;
setsockopt(socket_fd, SOL_PACKET, PACKET_RX_RING, p, LEN__TPACKET_REQ);
ring = mmap(NULL, ring_len, ring_access_flags, MAP_SHARED, socket_fd, 0);

Would I be permitted to use the ring map obtained both for RX and for TX? If
so, for me it is confusing to use PACKET_RX_RING if I can also TX data
through that ring...


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