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.

c/src/exec/libcsupport/include/sys/sockio.h

@@ -83,4 +83,11 @@
 #define	SIOCSIFMEDIA	_IOWR('i', 55, struct ifreq)	/* set net media */
 #define	SIOCGIFMEDIA	_IOWR('i', 56, struct ifmediareq) /* get net media */
 
+
+/*
+ * RTEMS additions for setting/getting `tap' function on incoming packets.
+ */
+#define SIOCSIFTAP	 _IOW('i', 80, struct ifreq)	/* set tap function */
+#define SIOCGIFTAP	_IOWR('i', 81, struct ifreq)	/* get tap function */
+
 #endif /* !_SYS_SOCKIO_H_ */

c/src/exec/libnetworking/net/if.c

@@ -664,6 +664,17 @@ ifioctl(so, cmd, data, p)
 
 	    }
 #endif
+
+	/*
+	 * RTEMS additions for setting/getting `tap' function
+	 */
+	case SIOCSIFTAP:
+		ifp->if_tap = ifr->ifr_tap;
+		return 0;
+
+	case SIOCGIFTAP:
+		ifr->ifr_tap = ifp->if_tap;
+		return 0;
 	}
 	return (0);
 }

c/src/exec/libnetworking/net/if.h

@@ -162,6 +162,8 @@ struct ifnet {
 		__P((struct ifnet *, struct mbuf *));
 	void	(*if_init)		/* Init routine */
 		__P((void *));
+	int	(*if_tap)		/* Packet filter routine */
+		(struct ifnet *, struct ether_header *, struct mbuf *);
 	struct	ifqueue if_snd;		/* output queue */
 	struct	ifqueue *if_poll_slowq;	/* input queue for slow devices */
 };
@@ -369,6 +371,7 @@ struct	ifreq {
 		int	ifru_phys;
 		int	ifru_media;
 		caddr_t	ifru_data;
+		int	(*ifru_tap)(struct ifnet *, struct ether_header *, struct mbuf *);
 	} ifr_ifru;
 #define	ifr_addr	ifr_ifru.ifru_addr	/* address */
 #define	ifr_dstaddr	ifr_ifru.ifru_dstaddr	/* other end of p-to-p link */
@@ -379,6 +382,7 @@ struct	ifreq {
 #define ifr_phys	ifr_ifru.ifru_phys	/* physical wire */
 #define ifr_media	ifr_ifru.ifru_media	/* physical media */
 #define	ifr_data	ifr_ifru.ifru_data	/* for use by interface */
+#define ifr_tap		ifr_ifru.ifru_tap	/* tap function */
 };
 
 struct ifaliasreq {

c/src/exec/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) {

c/src/lib/include/sys/sockio.h

@@ -83,4 +83,11 @@
 #define	SIOCSIFMEDIA	_IOWR('i', 55, struct ifreq)	/* set net media */
 #define	SIOCGIFMEDIA	_IOWR('i', 56, struct ifmediareq) /* get net media */
 
+
+/*
+ * RTEMS additions for setting/getting `tap' function on incoming packets.
+ */
+#define SIOCSIFTAP	 _IOW('i', 80, struct ifreq)	/* set tap function */
+#define SIOCGIFTAP	_IOWR('i', 81, struct ifreq)	/* get tap function */
+
 #endif /* !_SYS_SOCKIO_H_ */

c/src/lib/libnetworking/net/if.c

@@ -664,6 +664,17 @@ ifioctl(so, cmd, data, p)
 
 	    }
 #endif
+
+	/*
+	 * RTEMS additions for setting/getting `tap' function
+	 */
+	case SIOCSIFTAP:
+		ifp->if_tap = ifr->ifr_tap;
+		return 0;
+
+	case SIOCGIFTAP:
+		ifr->ifr_tap = ifp->if_tap;
+		return 0;
 	}
 	return (0);
 }

c/src/lib/libnetworking/net/if.h

@@ -162,6 +162,8 @@ struct ifnet {
 		__P((struct ifnet *, struct mbuf *));
 	void	(*if_init)		/* Init routine */
 		__P((void *));
+	int	(*if_tap)		/* Packet filter routine */
+		(struct ifnet *, struct ether_header *, struct mbuf *);
 	struct	ifqueue if_snd;		/* output queue */
 	struct	ifqueue *if_poll_slowq;	/* input queue for slow devices */
 };
@@ -369,6 +371,7 @@ struct	ifreq {
 		int	ifru_phys;
 		int	ifru_media;
 		caddr_t	ifru_data;
+		int	(*ifru_tap)(struct ifnet *, struct ether_header *, struct mbuf *);
 	} ifr_ifru;
 #define	ifr_addr	ifr_ifru.ifru_addr	/* address */
 #define	ifr_dstaddr	ifr_ifru.ifru_dstaddr	/* other end of p-to-p link */
@@ -379,6 +382,7 @@ struct	ifreq {
 #define ifr_phys	ifr_ifru.ifru_phys	/* physical wire */
 #define ifr_media	ifr_ifru.ifru_media	/* physical media */
 #define	ifr_data	ifr_ifru.ifru_data	/* for use by interface */
+#define ifr_tap		ifr_ifru.ifru_tap	/* tap function */
 };
 
 struct ifaliasreq {

c/src/lib/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) {

c/src/lib/libnetworking/sys/sockio.h

@@ -83,4 +83,11 @@
 #define	SIOCSIFMEDIA	_IOWR('i', 55, struct ifreq)	/* set net media */
 #define	SIOCGIFMEDIA	_IOWR('i', 56, struct ifmediareq) /* get net media */
 
+
+/*
+ * RTEMS additions for setting/getting `tap' function on incoming packets.
+ */
+#define SIOCSIFTAP	 _IOW('i', 80, struct ifreq)	/* set tap function */
+#define SIOCGIFTAP	_IOWR('i', 81, struct ifreq)	/* get tap function */
+
 #endif /* !_SYS_SOCKIO_H_ */

c/src/libnetworking/net/if.c

@@ -664,6 +664,17 @@ ifioctl(so, cmd, data, p)
 
 	    }
 #endif
+
+	/*
+	 * RTEMS additions for setting/getting `tap' function
+	 */
+	case SIOCSIFTAP:
+		ifp->if_tap = ifr->ifr_tap;
+		return 0;
+
+	case SIOCGIFTAP:
+		ifr->ifr_tap = ifp->if_tap;
+		return 0;
 	}
 	return (0);
 }

c/src/libnetworking/net/if.h

@@ -162,6 +162,8 @@ struct ifnet {
 		__P((struct ifnet *, struct mbuf *));
 	void	(*if_init)		/* Init routine */
 		__P((void *));
+	int	(*if_tap)		/* Packet filter routine */
+		(struct ifnet *, struct ether_header *, struct mbuf *);
 	struct	ifqueue if_snd;		/* output queue */
 	struct	ifqueue *if_poll_slowq;	/* input queue for slow devices */
 };
@@ -369,6 +371,7 @@ struct	ifreq {
 		int	ifru_phys;
 		int	ifru_media;
 		caddr_t	ifru_data;
+		int	(*ifru_tap)(struct ifnet *, struct ether_header *, struct mbuf *);
 	} ifr_ifru;
 #define	ifr_addr	ifr_ifru.ifru_addr	/* address */
 #define	ifr_dstaddr	ifr_ifru.ifru_dstaddr	/* other end of p-to-p link */
@@ -379,6 +382,7 @@ struct	ifreq {
 #define ifr_phys	ifr_ifru.ifru_phys	/* physical wire */
 #define ifr_media	ifr_ifru.ifru_media	/* physical media */
 #define	ifr_data	ifr_ifru.ifru_data	/* for use by interface */
+#define ifr_tap		ifr_ifru.ifru_tap	/* tap function */
 };
 
 struct ifaliasreq {

c/src/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) {

c/src/libnetworking/sys/sockio.h

@@ -83,4 +83,11 @@
 #define	SIOCSIFMEDIA	_IOWR('i', 55, struct ifreq)	/* set net media */
 #define	SIOCGIFMEDIA	_IOWR('i', 56, struct ifmediareq) /* get net media */
 
+
+/*
+ * RTEMS additions for setting/getting `tap' function on incoming packets.
+ */
+#define SIOCSIFTAP	 _IOW('i', 80, struct ifreq)	/* set tap function */
+#define SIOCGIFTAP	_IOWR('i', 81, struct ifreq)	/* get tap function */
+
 #endif /* !_SYS_SOCKIO_H_ */

cpukit/libcsupport/include/sys/sockio.h

@@ -83,4 +83,11 @@
 #define	SIOCSIFMEDIA	_IOWR('i', 55, struct ifreq)	/* set net media */
 #define	SIOCGIFMEDIA	_IOWR('i', 56, struct ifmediareq) /* get net media */
 
+
+/*
+ * RTEMS additions for setting/getting `tap' function on incoming packets.
+ */
+#define SIOCSIFTAP	 _IOW('i', 80, struct ifreq)	/* set tap function */
+#define SIOCGIFTAP	_IOWR('i', 81, struct ifreq)	/* get tap function */
+
 #endif /* !_SYS_SOCKIO_H_ */

cpukit/libnetworking/net/if.c

@@ -664,6 +664,17 @@ ifioctl(so, cmd, data, p)
 
 	    }
 #endif
+
+	/*
+	 * RTEMS additions for setting/getting `tap' function
+	 */
+	case SIOCSIFTAP:
+		ifp->if_tap = ifr->ifr_tap;
+		return 0;
+
+	case SIOCGIFTAP:
+		ifr->ifr_tap = ifp->if_tap;
+		return 0;
 	}
 	return (0);
 }

cpukit/libnetworking/net/if.h

@@ -162,6 +162,8 @@ struct ifnet {
 		__P((struct ifnet *, struct mbuf *));
 	void	(*if_init)		/* Init routine */
 		__P((void *));
+	int	(*if_tap)		/* Packet filter routine */
+		(struct ifnet *, struct ether_header *, struct mbuf *);
 	struct	ifqueue if_snd;		/* output queue */
 	struct	ifqueue *if_poll_slowq;	/* input queue for slow devices */
 };
@@ -369,6 +371,7 @@ struct	ifreq {
 		int	ifru_phys;
 		int	ifru_media;
 		caddr_t	ifru_data;
+		int	(*ifru_tap)(struct ifnet *, struct ether_header *, struct mbuf *);
 	} ifr_ifru;
 #define	ifr_addr	ifr_ifru.ifru_addr	/* address */
 #define	ifr_dstaddr	ifr_ifru.ifru_dstaddr	/* other end of p-to-p link */
@@ -379,6 +382,7 @@ struct	ifreq {
 #define ifr_phys	ifr_ifru.ifru_phys	/* physical wire */
 #define ifr_media	ifr_ifru.ifru_media	/* physical media */
 #define	ifr_data	ifr_ifru.ifru_data	/* for use by interface */
+#define ifr_tap		ifr_ifru.ifru_tap	/* tap function */
 };
 
 struct ifaliasreq {

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) {