Strip the IEC62439-3 PRP trailer if it is present
to support PTP over PRP.
The implementation is very pedantic about
trailing bytes and will indicate bad message if the
PRP trailer bytes are present when parsing the PTP message.
The PRP trailer is normally removed by the PRP implementation
and invisible to the rest of the stack.
If a PRP HW implementation is used the trailer won't be there.
When the SW PRP implementataion introduction in linux kernel 5.9
is used, the trailer will be there.
In short, PRP uses dual lines to send the same information,
LAN A and LAN B, the first arriving packet is handled and
the duplicate from the other interface is dropped.
PTP over PRP can't mix the information from the 2 lines
(path delay might be different) so it is needed to run
a ptp4l instance on each interface instead of on the combined
prp0 interface created by the kernel.
Hence, the PRP trailer will still be there in PTP packages
received directly from the interfaces, the PRP stack hasn't
had the chance to remove it
(which it would if traffic is read from prp0).
Signed-off-by: Magnus Armholt <magnus.armh...@fi.abb.com>
---
raw.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 67 insertions(+), 2 deletions(-)
diff --git a/raw.c b/raw.c
index ce64684..7fa2287 100644
--- a/raw.c
+++ b/raw.c
@@ -23,6 +23,7 @@
#include <net/if.h>
#include <netinet/in.h>
#include <netpacket/packet.h>
+#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -65,6 +66,9 @@ struct raw {
#define N_RAW_FILTER 12
#define RAW_FILTER_TEST 9
+#define PRP_MIN_PACKET_LEN 70
+#define PRP_TRAILER_LEN 6
+
static struct sock_filter raw_filter[N_RAW_FILTER] = {
{OP_LDH, 0, 0, OFF_ETYPE },
{OP_JEQ, 0, 4, ETH_P_8021Q }, /*f goto non-vlan block*/
@@ -206,6 +210,64 @@ static void addr_to_mac(void *mac, struct address *addr)
memcpy(mac, &addr->sll.sll_addr, MAC_LEN);
}
+/* Determines if the packet has Parallel Redundancy Protocol (PRP) trailer. */
+static bool has_prp_trailer(unsigned char *ptr, int cnt, int eth_hlen)
+{
+ unsigned short suffix_id, lane_size_field, lsdu_size;
+ int ptp_msg_len, trailer_start, padding_len;
+ struct ptp_header *hdr;
+
+ /* try to parse like a PTP message to find out the message length */
+ if (cnt < sizeof(struct ptp_header))
+ return false;
+
+ hdr = (struct ptp_header *)ptr;
+ if ((hdr->ver & MAJOR_VERSION_MASK) != PTP_MAJOR_VERSION)
+ return false;
+
+ ptp_msg_len = ntohs(hdr->messageLength);
+
+ /* PRP requires ethernet packets to be minimum 70 bytes, including
trailer */
+ trailer_start = ptp_msg_len;
+ padding_len = 0;
+ if ((eth_hlen + ptp_msg_len + PRP_TRAILER_LEN) < PRP_MIN_PACKET_LEN)
+ {
+ padding_len = PRP_MIN_PACKET_LEN - (eth_hlen + ptp_msg_len +
PRP_TRAILER_LEN);
+ trailer_start += padding_len;
+ }
+
+ if (cnt < (trailer_start + PRP_TRAILER_LEN))
+ return false;
+
+ /* PRP trailer (RCT) consists of 3 uint16.
+ | -------------------------------------------------------- |
+ | SeqNr(0-15) | LanId(0-3) LSDUsize(4-15) | Suffix (0-15) |
+ | -------------------------------------------------------- |
+ - Sequence number is a running number and can't be verified
+ - LanId should be 0x1010 or 0x1011 (but should not be used for
verification)
+ - LSDUsize should match LSDU length
+ (including possible padding and the RCT itself)
+ - Suffix should be 0x88FB
+ */
+
+ /* Verify that the size in the RCT matches.
+ Size is the lower 12 bits
+ */
+ lane_size_field = ntohs(*(unsigned short*)(ptr + trailer_start + 2));
+ lsdu_size = lane_size_field & 0x0FFF;
+ if (lsdu_size != cnt)
+ return false;
+
+ /* Verify the suffix */
+ suffix_id = ntohs(*(unsigned short*)(ptr + trailer_start + 4));
+ if (suffix_id == ETH_P_PRP)
+ {
+ return true;
+ }
+
+ return false;
+}
+
static int raw_open(struct transport *t, struct interface *iface,
struct fdarray *fda, enum timestamp_type ts_type)
{
@@ -266,10 +328,10 @@ no_mac:
static int raw_recv(struct transport *t, int fd, void *buf, int buflen,
struct address *addr, struct hw_timestamp *hwts)
{
- int cnt, hlen;
+ struct raw *raw = container_of(t, struct raw, t);
unsigned char *ptr = buf;
struct eth_hdr *hdr;
- struct raw *raw = container_of(t, struct raw, t);
+ int cnt, hlen;
if (raw->vlan) {
hlen = sizeof(struct vlan_hdr);
@@ -287,6 +349,9 @@ static int raw_recv(struct transport *t, int fd, void *buf,
int buflen,
if (cnt < 0)
return cnt;
+ if (has_prp_trailer(buf, cnt, hlen))
+ cnt -= PRP_TRAILER_LEN;
+
if (raw->vlan) {
if (ETH_P_1588 == ntohs(hdr->type)) {
pr_notice("raw: disabling VLAN mode");
--
2.25.1
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