Patch from Ian Lance Taylor <ian@airs.com>:

   From: Eric Norum <eric@skatter.usask.ca>
   Date: Sat,  5 Dec 98 13:20:51 -0600

   What do you think of this patch?  It implements your `tap'
   suggestion in a way that adds support for all ethernet devices with
   no driver modifications.  I also added a return value from the tap
   function.  If the return value is zero, the packet will be passed up
   the chain as usual.  If the return value is non-zero the mbuf holding
   the packet will be freed and the packet will be dropped.

   If you like it, please submit it to Joel.

   I guess there needs to be an addition to the network documentation
   describing the additional ioctl's -- and a big warning that the tap
   function is called from a context that holds the network semaphore.

   Here is Eric's patch.  I've tested it a bit, and made a couple of
   trivial changes.  This is certainly better than mine: it should work
   for all Ethernet drivers.
   ==================================================

   The only concern I have about this patch is that the tap function may
   want to fiddle with the mbuf, calling functions like m_pullup and the
   like.  If those force the networking code to rearrange the mbuf
   structure, then the caller's call to m_freem may crash.  I don't know
   if this is a realistic concern--I don't know enough about the mbuf
   layer.

1 files changed, 9 insertions, 0 deletions

diff --git a/cpukit/libnetworking/net/if_ethersubr.c b/cpukit/libnetworking/net/if_ethersubr.c
index 4d1675ca3c..2a6446ebb6 100644
--- a/cpukit/libnetworking/net/if_ethersubr.c
+++ b/cpukit/libnetworking/net/if_ethersubr.c
@@ -483,6 +483,15 @@ ether_input(ifp, eh, m)
 	if (m->m_flags & (M_BCAST|M_MCAST))
 		ifp->if_imcasts++;
 
+	/*
+	 * RTEMS addition -- allow application to `tap into'
+	 * the incoming packet stream.
+	 */
+	if (ifp->if_tap && (*ifp->if_tap)(ifp, eh, m)) {
+		m_freem(m);
+		return;
+	}
+
 	ether_type = ntohs(eh->ether_type);
 
 	switch (ether_type) {