e1_input: Use osmo_pcap_lapd if using software LAPD

The e1_input code for PCAP writing uses the Layer3 RSL/OML message and
prepends a fake LAPD header.  This means that all frames look like UI
frames in wireshark.  In case we use in-kernel LAPD of mISDN, this is
the best we can do.  However, in case of software (libosmocore) LAPD,
we can do better, by dumping the real LAPD frames at the interface
between LAPD code and the physical layer.

Related: OS#1763
Change-Id: Id0815690b5bc0a9b7f29f5cfde9d2f24c4f88ee5

1 files changed, 24 insertions, 4 deletions

diff --git a/src/e1_input.c b/src/e1_input.c
index c454b4a..4ba991e 100644
--- a/src/e1_input.c
+++ b/src/e1_input.c
@@ -249,8 +249,14 @@ int abis_sendmsg(struct msgb *msg)
 	}
 	msgb_enqueue(&sign_link->tx_list, msg);
 
-	/* dump it */
-	write_pcap_packet(PCAP_OUTPUT, sign_link->sapi, sign_link->tei, msg);
+	/* we only need to write a 'Fake LAPD' packet here, if the
+	 * underlying driver hides LAPD from us.  If we use the
+	 * libosmocore LAPD implementation, it will take care of writing
+	 * the _actual_ LAPD packet */
+	if (!e1i_ts->lapd) {
+		write_pcap_packet(PCAP_OUTPUT, sign_link->sapi,
+				  sign_link->tei, msg);
+	}
 
 	return 0;
 }
@@ -499,8 +505,13 @@ int e1inp_rx_ts(struct e1inp_ts *ts, struct msgb *msg,
 
 	switch (ts->type) {
 	case E1INP_TS_TYPE_SIGN:
+		/* we only need to write a 'Fake LAPD' packet here, if
+		 * the underlying driver hides LAPD from us.  If we use
+		 * the libosmocore LAPD implementation, it will take
+		 * care of writing the _actual_ LAPD packet */
+		if (!ts->lapd)
+			write_pcap_packet(PCAP_INPUT, sapi, tei, msg);
 		/* consult the list of signalling links */
-		write_pcap_packet(PCAP_INPUT, sapi, tei, msg);
 		link = e1inp_lookup_sign_link(ts, tei, sapi);
 		if (!link) {
 			LOGP(DLMI, LOGL_ERROR, "didn't find signalling link for "
@@ -712,7 +723,7 @@ struct e1inp_driver *e1inp_driver_find(const char *name)
 int e1inp_line_update(struct e1inp_line *line)
 {
 	struct input_signal_data isd;
-	int rc;
+	int i, rc;
 
 	e1inp_line_get(line);
 
@@ -721,6 +732,15 @@ int e1inp_line_update(struct e1inp_line *line)
 	} else
 		rc = 0;
 
+	/* Set the PCAP file descriptor for all timeslots that have
+	 * software LAPD instances, to ensure the osmo_lapd_pcap code is
+	 * used to write PCAP files (if requested) */
+	for (i = 0; i < ARRAY_SIZE(line->ts); i++) {
+		struct e1inp_ts *e1i_ts = &line->ts[i];
+		if (e1i_ts->lapd)
+			e1i_ts->lapd->pcap_fd = pcap_fd;
+	}
+
 	/* Send a signal to anyone who is interested in new lines being
 	 * configured */
 	memset(&isd, 0, sizeof(isd));