diff -up chrony-3.2/configure.timestamping chrony-3.2/configure

--- chrony-3.2/configure.timestamping	2017-09-19 13:58:21.093194558 +0200

+++ chrony-3.2/configure	2017-09-19 13:57:56.109116276 +0200

@@ -683,15 +683,15 @@ if [ $feat_timestamping = "1" ] && [ $tr

   test_code 'SW/HW timestamping' 'sys/types.h sys/socket.h linux/net_tstamp.h

                                   linux/errqueue.h linux/ptp_clock.h' '' '' '

     int val = SOF_TIMESTAMPING_SOFTWARE | SOF_TIMESTAMPING_RX_SOFTWARE |

-              SOF_TIMESTAMPING_RAW_HARDWARE | SOF_TIMESTAMPING_OPT_CMSG;

-    return sizeof (struct scm_timestamping) + SCM_TSTAMP_SND + PTP_SYS_OFFSET +

+              SOF_TIMESTAMPING_RAW_HARDWARE | 1;

+    return 3 * sizeof (struct timespec) + 0 + PTP_SYS_OFFSET +

            setsockopt(0, SOL_SOCKET, SO_SELECT_ERR_QUEUE + SO_TIMESTAMPING,

                       &val, sizeof (val));'

 then

   add_def HAVE_LINUX_TIMESTAMPING

   EXTRA_OBJECTS="$EXTRA_OBJECTS hwclock.o ntp_io_linux.o"

-  if test_code 'other timestamping options' \

+  if true || test_code 'other timestamping options' \

     'sys/types.h sys/socket.h linux/net_tstamp.h' '' '' '

     struct scm_ts_pktinfo pktinfo;

     pktinfo.if_index = pktinfo.pkt_length = 0;

diff -up chrony-3.2/doc/chrony.conf.man.in.timestamping chrony-3.2/doc/chrony.conf.man.in

--- chrony-3.2/doc/chrony.conf.man.in.timestamping	2017-09-15 10:17:41.000000000 +0200

+++ chrony-3.2/doc/chrony.conf.man.in	2017-09-19 13:52:59.544187046 +0200

@@ -3201,13 +3201,12 @@ timestamping. If the server or peer supp

 be enabled by the \fBxleave\fP option in the \fBserver\fP or the

 \fBpeer\fP directive.

 .sp

-This directive is supported on Linux 3.19 and newer. The NIC must support HW

+This directive is supported on Linux. The NIC must support HW

 timestamping, which can be verified with the \fBethtool \-T\fP command. The list of

 capabilities should include \fISOF_TIMESTAMPING_RAW_HARDWARE\fP,

 \fISOF_TIMESTAMPING_TX_HARDWARE\fP, and \fISOF_TIMESTAMPING_RX_HARDWARE\fP. Receive

 filter \fIHWTSTAMP_FILTER_ALL\fP, or \fIHWTSTAMP_FILTER_NTP_ALL\fP, is necessary for

-timestamping of received packets. Timestamping of packets received from bridged

-and bonded interfaces is supported on Linux 4.13 and newer. When \fBchronyd\fP is

+timestamping of received packets. When \fBchronyd\fP is

 running, no other process (e.g. a PTP daemon) should be working with the NIC

 clock.

 .sp

diff -up chrony-3.2/ntp_io_linux.c.timestamping chrony-3.2/ntp_io_linux.c

--- chrony-3.2/ntp_io_linux.c.timestamping	2017-09-15 08:32:09.000000000 +0200

+++ chrony-3.2/ntp_io_linux.c	2017-09-19 13:52:59.544187046 +0200

@@ -35,6 +35,16 @@

 #include <linux/sockios.h>

 #include <net/if.h>

+/* Missing in older kernel headers */

+#define SOF_TIMESTAMPING_OPT_CMSG (1<<10)

+#define SOF_TIMESTAMPING_OPT_PKTINFO (1<<13)

+#define SOF_TIMESTAMPING_OPT_TX_SWHW (1<<14)

+#define SCM_TSTAMP_SND 0

+#define HWTSTAMP_FILTER_NTP_ALL 15

+#ifndef SCM_TIMESTAMPING_PKTINFO

+#define SCM_TIMESTAMPING_PKTINFO 58

+#endif

+

 #include "array.h"

 #include "conf.h"

 #include "hwclock.h"

@@ -94,6 +104,10 @@ static int ts_tx_flags;

 /* Flag indicating the socket options can't be changed in control messages */

 static int permanent_ts_options;

+/* Index of a HW-timestamping interface, but only if the machine has not more

+   than one */

+static int single_hwts_if_index;

+

 /* ================================================== */

 static int

@@ -278,7 +292,7 @@ update_interface_speed(struct Interface

 /* ================================================== */

-#if defined(HAVE_LINUX_TIMESTAMPING_OPT_PKTINFO) || defined(HAVE_LINUX_TIMESTAMPING_OPT_TX_SWHW)

+#if 1

 static int

 check_timestamping_option(int option)

 {

@@ -301,6 +315,61 @@ check_timestamping_option(int option)

 /* ================================================== */

+static int

+get_single_hwts_index()

+{

+  struct ifaddrs *ifaddr, *ifa;

+  struct ethtool_ts_info ts_info;

+  struct ifreq req;

+  int sock_fd, if_index, hwts_if_index = INVALID_IF_INDEX;

+

+  sock_fd = socket(AF_INET, SOCK_DGRAM, 0);

+  if (sock_fd < 0)

+    return INVALID_IF_INDEX;

+

+  if (getifaddrs(&ifaddr)) {

+    DEBUG_LOG("getifaddrs() failed : %s", strerror(errno));

+    close(sock_fd);

+    return INVALID_IF_INDEX;

+  }

+

+  for (ifa = ifaddr; ifa; ifa = ifa->ifa_next) {

+    memset(&req, 0, sizeof (req));

+    memset(&ts_info, 0, sizeof (ts_info));

+

+    if (snprintf(req.ifr_name, sizeof (req.ifr_name), "%s", ifa->ifa_name) >=

+        sizeof (req.ifr_name))

+      break;

+

+    if (ioctl(sock_fd, SIOCGIFINDEX, &req))

+      break;

+

+    if_index = req.ifr_ifindex;

+    ts_info.cmd = ETHTOOL_GET_TS_INFO;

+    req.ifr_data = (char *)&ts_info;

+

+    if (ioctl(sock_fd, SIOCETHTOOL, &req))

+      break;

+

+    if (ts_info.phc_index < 0)

+      continue;

+

+    if (hwts_if_index != INVALID_IF_INDEX && hwts_if_index != if_index)

+      break;

+

+    hwts_if_index = if_index;

+  }

+

+  close(sock_fd);

+  freeifaddrs(ifaddr);

+

+  if (ifa)

+    return INVALID_IF_INDEX;

+

+  return hwts_if_index;

+}

+

+/* ================================================== */

 void

 NIO_Linux_Initialise(void)

 {

@@ -345,8 +414,20 @@ NIO_Linux_Initialise(void)

 #endif

   }

-  /* Enable IP_PKTINFO in messages looped back to the error queue */

-  ts_flags |= SOF_TIMESTAMPING_OPT_CMSG;

+  single_hwts_if_index = INVALID_IF_INDEX;

+

+  /* Enable IP_PKTINFO in messages looped back to the error queue if possible.

+     If not, HW timestamping of IPv4 packets can be supported only with one

+     interface capable of HW timestamping. */

+  if (check_timestamping_option(SOF_TIMESTAMPING_OPT_CMSG)) {

+    ts_flags |= SOF_TIMESTAMPING_OPT_CMSG;

+  } else if (ARR_GetSize(interfaces) > 0) {

+    single_hwts_if_index = get_single_hwts_index();

+    if (single_hwts_if_index == INVALID_IF_INDEX)

+      LOG(LOGS_WARN, "Missing SOF_TIMESTAMPING_OPT_CMSG option for HW timestamping with multiple HW-timestamping interfaces");

+    else

+      LOG(LOGS_INFO, "Enabled single-interface HW-timestamping mode");

+  }

   /* Kernels before 4.7 ignore timestamping flags set in control messages */

   permanent_ts_options = !SYS_Linux_CheckKernelVersion(4, 7);

@@ -590,7 +671,11 @@ NIO_Linux_ProcessMessage(NTP_Remote_Addr

   for (cmsg = CMSG_FIRSTHDR(hdr); cmsg; cmsg = CMSG_NXTHDR(hdr, cmsg)) {

 #ifdef HAVE_LINUX_TIMESTAMPING_OPT_PKTINFO

     if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_TIMESTAMPING_PKTINFO) {

-      struct scm_ts_pktinfo ts_pktinfo;

+      struct {

+	      __u32 if_index;

+	      __u32 pkt_length;

+	      __u32 reserved[2];

+      } ts_pktinfo;

       memcpy(&ts_pktinfo, CMSG_DATA(cmsg), sizeof (ts_pktinfo));

@@ -602,11 +687,16 @@ NIO_Linux_ProcessMessage(NTP_Remote_Addr

 #endif

     if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_TIMESTAMPING) {

-      struct scm_timestamping ts3;

+      struct {

+        struct timespec ts[3];

+      } ts3;

       memcpy(&ts3, CMSG_DATA(cmsg), sizeof (ts3));

       if (!UTI_IsZeroTimespec(&ts3.ts[2])) {

+        if (ts_if_index == INVALID_IF_INDEX)

+          ts_if_index = single_hwts_if_index;

+

         iface = get_interface(ts_if_index);

         if (iface) {

           process_hw_timestamp(iface, &ts3.ts[2], local_ts, !is_tx ? length : 0,