From 3dc9f1ff9271bdc7d82d67362de5dfd42dd79212 Mon Sep 17 00:00:00 2001
From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Tue, 8 Aug 2023 15:44:25 +0200
Subject: [PATCH] ntp: don't require previous HW TX timestamp to wait for
 another

Clients sockets are closed immediately after receiving valid response.
Don't wait for the first early HW TX timestamp to enable waiting for
late timestamps. It may take a long time or never come if the HW/driver
is consistently slow. It's a chicken and egg problem.

Instead, simply check if HW timestamping is enabled on at least one
interface. Responses from NTP sources on other interfaces will always be
saved (for 1 millisecond by default).
---
 ntp_core.c           |  9 +--------
 ntp_io.c             | 12 ++++++++++++
 ntp_io.h             |  3 +++
 ntp_io_linux.c       |  8 ++++++++
 ntp_io_linux.h       |  2 ++
 test/unit/ntp_core.c |  7 ++-----
 6 files changed, 28 insertions(+), 13 deletions(-)

diff --git a/ntp_core.c b/ntp_core.c
index 73519a3..22cab43 100644
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -215,9 +215,6 @@ struct NCR_Instance_Record {
   SPF_Instance filter;
   int filter_count;
 
-  /* Flag indicating HW transmit timestamps are expected */
-  int had_hw_tx_timestamp;
-
   /* Response waiting for a HW transmit timestamp of the request */
   struct SavedResponse *saved_response;
 
@@ -794,8 +791,6 @@ NCR_ResetInstance(NCR_Instance instance)
   if (instance->filter)
     SPF_DropSamples(instance->filter);
   instance->filter_count = 0;
-
-  instance->had_hw_tx_timestamp = 0;
 }
 
 /* ================================================== */
@@ -1966,7 +1961,7 @@ process_response(NCR_Instance inst, int saved, NTP_Local_Address *local_addr,
      response to the request, when at least one good response has already been
      accepted to avoid incorrectly confirming a tentative source. */
   if (valid_packet && synced_packet && !saved && !inst->valid_rx &&
-      inst->had_hw_tx_timestamp && inst->local_tx.source != NTP_TS_HARDWARE &&
+      NIO_IsHwTsEnabled() && inst->local_tx.source != NTP_TS_HARDWARE &&
       inst->report.total_good_count > 0) {
     if (save_response(inst, local_addr, rx_ts, message, info))
       return 1;
@@ -2692,8 +2687,6 @@ NCR_ProcessTxKnown(NCR_Instance inst, NTP_Local_Address *local_addr,
                       message);
 
   if (tx_ts->source == NTP_TS_HARDWARE) {
-    inst->had_hw_tx_timestamp = 1;
-
     if (has_saved_response(inst))
       process_saved_response(inst);
   }
diff --git a/ntp_io.c b/ntp_io.c
index deb8e25..fce7b17 100644
--- a/ntp_io.c
+++ b/ntp_io.c
@@ -278,6 +278,18 @@ NIO_Finalise(void)
 
 /* ================================================== */
 
+int
+NIO_IsHwTsEnabled(void)
+{
+#ifdef HAVE_LINUX_TIMESTAMPING
+  return NIO_Linux_IsHwTsEnabled();
+#else
+  return 0;
+#endif
+}
+
+/* ================================================== */
+
 int
 NIO_OpenClientSocket(NTP_Remote_Address *remote_addr)
 {
diff --git a/ntp_io.h b/ntp_io.h
index 19ffeed..427bd96 100644
--- a/ntp_io.h
+++ b/ntp_io.h
@@ -39,6 +39,9 @@ extern void NIO_Initialise(void);
 /* Function to finalise the module */
 extern void NIO_Finalise(void);
 
+/* Function to check if HW timestamping is enabled on any interface */
+extern int NIO_IsHwTsEnabled(void);
+
 /* Function to obtain a socket for sending client packets */
 extern int NIO_OpenClientSocket(NTP_Remote_Address *remote_addr);
 
diff --git a/ntp_io_linux.c b/ntp_io_linux.c
index 6988a28..8f93f59 100644
--- a/ntp_io_linux.c
+++ b/ntp_io_linux.c
@@ -439,6 +439,14 @@ NIO_Linux_Finalise(void)
 
 /* ================================================== */
 
+int
+NIO_Linux_IsHwTsEnabled(void)
+{
+  return ARR_GetSize(interfaces) > 0;
+}
+
+/* ================================================== */
+
 int
 NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events)
 {
diff --git a/ntp_io_linux.h b/ntp_io_linux.h
index 089d4a1..7978889 100644
--- a/ntp_io_linux.h
+++ b/ntp_io_linux.h
@@ -33,6 +33,8 @@ extern void NIO_Linux_Initialise(void);
 
 extern void NIO_Linux_Finalise(void);
 
+extern int NIO_Linux_IsHwTsEnabled(void);
+
 extern int NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events);
 
 extern int NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
diff --git a/test/unit/ntp_core.c b/test/unit/ntp_core.c
index 7d64986..08a1532 100644
--- a/test/unit/ntp_core.c
+++ b/test/unit/ntp_core.c
@@ -35,6 +35,7 @@ static struct timespec current_time;
 static NTP_Packet req_buffer, res_buffer;
 static int req_length, res_length;
 
+#define NIO_IsHwTsEnabled() 1
 #define NIO_OpenServerSocket(addr) ((addr)->ip_addr.family != IPADDR_UNSPEC ? 100 : 0)
 #define NIO_CloseServerSocket(fd) assert(fd == 100)
 #define NIO_OpenClientSocket(addr) ((addr)->ip_addr.family != IPADDR_UNSPEC ? 101 : 0)
@@ -106,13 +107,9 @@ send_request(NCR_Instance inst, int late_hwts)
   }
 
   if (late_hwts) {
-    inst->had_hw_tx_timestamp = 1;
     inst->report.total_good_count++;
   } else {
-    if (random() % 2)
-      inst->had_hw_tx_timestamp = 0;
-    else
-      inst->report.total_good_count = 0;
+    inst->report.total_good_count = 0;
   }
 }