From f3e51aa390e7df8081984bd1c7f7d9911dffb12d Mon Sep 17 00:00:00 2001
From: dlg <dlg@openbsd.org>
Date: Thu, 1 Feb 2018 12:10:27 +0000
Subject: [PATCH] add bpf_tap_hdr(), for handling a buffer (not an mbuf) with a
 header.

internally it uses mbufs to handle the chain of buffers, but the
caller doesnt have to deal with that or allocate a temporary buffer
with the header attached.

ok mpi@
---
 sys/net/bpf.c | 41 ++++++++++++++++++++++++++++++++++++++++-
 sys/net/bpf.h |  3 ++-
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/sys/net/bpf.c b/sys/net/bpf.c
index 2d3795199f0..af7406e1d00 100644
--- a/sys/net/bpf.c
+++ b/sys/net/bpf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: bpf.c,v 1.166 2018/01/24 00:25:17 dlg Exp $	*/
+/*	$OpenBSD: bpf.c,v 1.167 2018/02/01 12:10:27 dlg Exp $	*/
 /*	$NetBSD: bpf.c,v 1.33 1997/02/21 23:59:35 thorpej Exp $	*/
 
 /*
@@ -1290,6 +1290,45 @@ _bpf_mtap(caddr_t arg, const struct mbuf *m, u_int direction,
 	return (drop);
 }
 
+/*
+ * Incoming linkage from device drivers, where a data buffer should be
+ * prepended by an arbitrary header. In this situation we already have a
+ * way of representing a chain of memory buffers, ie, mbufs, so reuse
+ * the existing functionality by attaching the buffers to mbufs.
+ *
+ * Con up a minimal mbuf chain to pacify bpf by allocating (only) a
+ * struct m_hdr each for the header and data on the stack.
+ */
+int
+bpf_tap_hdr(caddr_t arg, const void *hdr, unsigned int hdrlen,
+    const void *buf, unsigned int buflen, u_int direction)
+{
+	struct m_hdr mh, md;
+	struct mbuf *m0 = NULL;
+	struct mbuf **mp = &m0;
+
+	if (hdr != NULL) {
+		mh.mh_flags = 0;
+		mh.mh_next = NULL;
+		mh.mh_len = hdrlen;
+		mh.mh_data = (void *)hdr;
+
+		*mp = (struct mbuf *)&mh;
+		mp = &mh.mh_next;
+	}
+
+	if (buf != NULL) {
+		md.mh_flags = 0;
+		md.mh_next = NULL;
+		md.mh_len = buflen;
+		md.mh_data = (void *)buf;
+
+		*mp = (struct mbuf *)&md;
+	}
+
+	return _bpf_mtap(arg, m0, direction, bpf_mcopy);
+}
+
 /*
  * Incoming linkage from device drivers, when packet is in an mbuf chain.
  */
diff --git a/sys/net/bpf.h b/sys/net/bpf.h
index 98afe4f4f60..cb713eef697 100644
--- a/sys/net/bpf.h
+++ b/sys/net/bpf.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: bpf.h,v 1.63 2018/01/24 00:25:17 dlg Exp $	*/
+/*	$OpenBSD: bpf.h,v 1.64 2018/02/01 12:10:27 dlg Exp $	*/
 /*	$NetBSD: bpf.h,v 1.15 1996/12/13 07:57:33 mikel Exp $	*/
 
 /*
@@ -311,6 +311,7 @@ int	 bpf_mtap_hdr(caddr_t, caddr_t, u_int, const struct mbuf *, u_int,
 	    void (*)(const void *, void *, size_t));
 int	 bpf_mtap_af(caddr_t, u_int32_t, const struct mbuf *, u_int);
 int	 bpf_mtap_ether(caddr_t, const struct mbuf *, u_int);
+int	 bpf_tap_hdr(caddr_t, const void *, u_int, const void *, u_int, u_int);
 void	 bpfattach(caddr_t *, struct ifnet *, u_int, u_int);
 void	 bpfdetach(struct ifnet *);
 void	*bpfsattach(caddr_t *, const char *, u_int, u_int);
-- 
2.20.1