snoopy: add "ippkt" protocol to demux ip packet interfaces without media header.

When using a packet interface, such as /net/ipifc/x as the
packet-soucre, there is no media header and the ip protocol
version has to be determined from the first byte.

The ippkt protocol solves this, allowing one to decode
both ipv4 and ipv6, such as:

snoopy -h ippkt /net/ipifc/2

2 files changed, 83 insertions, 0 deletions

diff --git a/sys/src/cmd/ip/snoopy/ippkt.c b/sys/src/cmd/ip/snoopy/ippkt.c
new file mode 100644
index 000000000..c87d0e9f2
--- /dev/null
+++ b/sys/src/cmd/ip/snoopy/ippkt.c
@@ -0,0 +1,82 @@
+#include <u.h>
+#include <libc.h>
+#include <ip.h>
+#include "dat.h"
+#include "protos.h"
+
+static Mux p_mux[] =
+{
+	{"ip",		0x40, },
+	{"ip6", 	0x60, },
+	{0}
+};
+
+enum
+{
+	Ot,	/* ip type */
+};
+
+static Field p_fields[] =
+{
+	{"t",	Fnum,	Ot,	"ip type" },
+	{0}
+};
+
+static void
+p_compile(Filter *f)
+{
+	Mux *m;
+
+	if(f->op == '='){
+		compile_cmp(ippkt.name, f, p_fields);
+		return;
+	}
+	for(m = p_mux; m->name != nil; m++)
+		if(strcmp(f->s, m->name) == 0){
+			f->pr = m->pr;
+			f->ulv = m->val;
+			f->subop = Ot;
+			return;
+		}
+	sysfatal("unknown ippkt field or protocol: %s", f->s);
+}
+
+static int
+p_filter(Filter *f, Msg *m)
+{
+	if(m->ps >= m->pe)
+		return 0;
+
+	switch(f->subop){
+	case Ot:
+		return (m->ps[0]&0xF0) == f->ulv;
+	}
+	return 0;
+}
+
+static int
+p_seprint(Msg *m)
+{
+	uint t;
+
+	if(m->ps >= m->pe)
+		return -1;
+
+	t = m->ps[0]&0xF0;
+	demux(p_mux, t, t, m, &dump);
+
+	m->p = seprint(m->p, m->e, "t=%2.2ux", t);
+	return 0;
+}
+
+Proto ippkt =
+{
+	"ippkt",
+	p_compile,
+	p_filter,
+	p_seprint,
+	p_mux,
+	"%#.2lux",
+	p_fields,
+	defaultframer
+};
diff --git a/sys/src/cmd/ip/snoopy/mkfile b/sys/src/cmd/ip/snoopy/mkfile
index c4d42bb82..00d901de0 100644
--- a/sys/src/cmd/ip/snoopy/mkfile
+++ b/sys/src/cmd/ip/snoopy/mkfile
@@ -20,6 +20,7 @@ PROTOS=\
 	eapol_key\
 	ether\
 	ipmux\
+	ippkt\
 	gre\
 	hdlc\
 	icmp6\