From 715c902eb7571c64f45c975997c5af213fc7a157 Mon Sep 17 00:00:00 2001
From: Harald Welte <laforge@osmocom.org>
Date: Thu, 7 Apr 2022 21:44:43 +0200
Subject: [PATCH] tr-bridge: change bit-order in MAC addresses between TR and
 ETH

---
 tr-bridge.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/tr-bridge.c b/tr-bridge.c
index 8f4062f..240aa26 100644
--- a/tr-bridge.c
+++ b/tr-bridge.c
@@ -34,6 +34,37 @@
 #define	AC		0x10
 #define LLC_FRAME	0x40
 
+/* Copied from libosmocore.git src/bits.c */
+
+/* look-up table for bit-reversal within a byte. Generated using:
+	int i,k;
+        for (i = 0 ; i < 256 ; i++) {
+                uint8_t sample = 0 ;
+                for (k = 0; k<8; k++) {
+                        if ( i & 1 << k ) sample |= 0x80 >>  k;
+                }
+                flip_table[i] = sample;
+        }
+ */
+static const uint8_t flip_table[256] = {
+	0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
+	0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8, 0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
+	0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
+	0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
+	0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2, 0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
+	0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
+	0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
+	0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee, 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
+	0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1, 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
+	0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
+	0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5, 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
+	0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
+	0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
+	0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb, 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
+	0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
+	0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff,
+};
+
 struct tr_hdr {
 	uint8_t ac;
 	uint8_t fc;
@@ -51,6 +82,13 @@ struct bridge_state {
 	} eth;
 };
 
+void osmo_revbytebits_buf(uint8_t *buf, int len)
+{
+	int i;
+
+	for (i = 0; i < len; i++)
+		buf[i] = flip_table[buf[i]];
+}
 
 static int devname2ifindex(const char *ifname)
 {
@@ -179,7 +217,9 @@ static int eth2tr(struct bridge_state *bst)
 	trh.ac = AC;
 	trh.fc = LLC_FRAME;
 	memcpy(&trh.daddr, ethh->h_dest, sizeof(trh.daddr));
+	osmo_revbytebits_buf(trh.daddr, TR_ALEN);
 	memcpy(&trh.saddr, ethh->h_source, sizeof(trh.saddr));
+	osmo_revbytebits_buf(trh.saddr, TR_ALEN);
 
 	return write_tr(bst->tr.socket, &trh, buf + sizeof(*ethh), ethlen - sizeof(*ethh));
 }
@@ -220,7 +260,9 @@ static int tr2eth(struct bridge_state *bst)
 	}
 
 	memcpy(&ethh.h_dest, trh->daddr, sizeof(ethh.h_dest));
+	osmo_revbytebits_buf(ethh.h_dest, TR_ALEN);
 	memcpy(&ethh.h_source, trh->saddr, sizeof(ethh.h_source));
+	osmo_revbytebits_buf(ethh.h_source, TR_ALEN);
 	ethh.h_proto = htons(ETH_P_802_2);
 
 	return write_eth(bst->eth.socket, &ethh, buf + sizeof(*trh), trlen - sizeof(*trh));