cmdmon: add reset command

The reset command drops all measurements and switches the reference to
the unsynchronised state. This command can help chronyd with recovery
when the measurements are known to be no longer valid or accurate, e.g.
due to moving the computer to a different network, or resuming the
computer from a low-power state (which resets the system clock).

candm.h

@@ -103,7 +103,8 @@
 #define REQ_ONOFFLINE 63
 #define REQ_ADD_SOURCE 64
 #define REQ_NTP_SOURCE_NAME 65
-#define N_REQUEST_TYPES 66
+#define REQ_RESET 66
+#define N_REQUEST_TYPES 67
 
 /* Structure used to exchange timespecs independent of time_t size */
 typedef struct {

client.c

@@ -1269,6 +1269,7 @@ give_help(void)
     "cyclelogs\0Close and re-open log files\0"
     "dump\0Dump all measurements to save files\0"
     "rekey\0Re-read keys from key file\0"
+    "reset\0Drop all measurements\0"
     "shutdown\0Stop daemon\0"
     "\0\0"
     "Client commands:\0\0"
@@ -1315,7 +1316,7 @@ command_name_generator(const char *text, int state)
     "deny", "dns", "dump", "exit", "help", "keygen", "local", "makestep",
     "manual", "maxdelay", "maxdelaydevratio", "maxdelayratio", "maxpoll",
     "maxupdateskew", "minpoll", "minstratum", "ntpdata", "offline", "online", "onoffline",
-    "polltarget", "quit", "refresh", "rekey", "reselect", "reselectdist",
+    "polltarget", "quit", "refresh", "rekey", "reselect", "reselectdist", "reset",
     "retries", "rtcdata", "serverstats", "settime", "shutdown", "smoothing",
     "smoothtime", "sourcename", "sources", "sourcestats",
     "timeout", "tracking", "trimrtc", "waitsync", "writertc",
@@ -2835,6 +2836,14 @@ process_cmd_shutdown(CMD_Request *msg, char *line)
 
 /* ================================================== */
 
+static void
+process_cmd_reset(CMD_Request *msg, char *line)
+{
+  msg->command = htons(REQ_RESET);
+}
+
+/* ================================================== */
+
 static int
 process_cmd_waitsync(char *line)
 {
@@ -3129,6 +3138,8 @@ process_line(char *line)
     process_cmd_reselect(&tx_message, line);
   } else if (!strcmp(command, "reselectdist")) {
     do_normal_submit = process_cmd_reselectdist(&tx_message, line);
+  } else if (!strcmp(command, "reset")) {
+    process_cmd_reset(&tx_message, line);
   } else if (!strcmp(command, "retries")) {
     ret = process_cmd_retries(line);
     do_normal_submit = 0;

cmdmon.c

@@ -134,6 +134,7 @@ static const char permissions[] = {
   PERMIT_AUTH, /* ONOFFLINE */
   PERMIT_AUTH, /* ADD_SOURCE */
   PERMIT_OPEN, /* NTP_SOURCE_NAME */
+  PERMIT_AUTH, /* RESET */
 };
 
 /* ================================================== */
@@ -1218,6 +1219,18 @@ handle_ntp_source_name(CMD_Request *rx_message, CMD_Reply *tx_message)
             sizeof (tx_message->data.ntp_source_name.name));
 }
 
+/* ================================================== */
+
+static void
+handle_reset(CMD_Request *rx_message, CMD_Reply *tx_message)
+{
+  struct timespec cooked_now, now;
+
+  SRC_ResetSources();
+  SCH_GetLastEventTime(&cooked_now, NULL, &now);
+  LCL_NotifyExternalTimeStep(&now, &cooked_now, 0.0, 0.0);
+}
+
 /* ================================================== */
 /* Read a packet and process it */
 
@@ -1595,6 +1608,10 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)
           handle_ntp_source_name(&rx_message, &tx_message);
           break;
 
+        case REQ_RESET:
+          handle_reset(&rx_message, &tx_message);
+          break;
+
         default:
           DEBUG_LOG("Unhandled command %d", rx_command);
           tx_message.status = htons(STT_FAILED);

doc/chronyc.adoc

@@ -1171,6 +1171,13 @@ running.
 The *rekey* command causes *chronyd* to re-read the key file specified in the
 configuration file by the <<chrony.conf.adoc#keyfile,*keyfile*>> directive.
 
+[[reset]]*reset*::
+The *reset* command causes *chronyd* to drop all measurements and switch to the
+unsynchronised state. This command can help *chronyd* with recovery when the
+measurements are known to be no longer valid or accurate, e.g. due to moving
+the computer to a different network, or resuming the computer from a low-power
+state (which resets the system clock).
+
 [[shutdown]]*shutdown*::
 The *shutdown* command causes *chronyd* to exit. This is equivalent to sending
 the process the SIGTERM signal.

pktlength.c

@@ -123,6 +123,7 @@ static const struct request_length request_lengths[] = {
   REQ_LENGTH_ENTRY(ntp_source, null),           /* ADD_SOURCE */
   REQ_LENGTH_ENTRY(ntp_source_name,
                    ntp_source_name),            /* NTP_SOURCE_NAME */
+  REQ_LENGTH_ENTRY(null, null),                 /* RESET */
 };
 
 static const uint16_t reply_lengths[] = {

sources.c

@@ -1252,6 +1252,17 @@ SRC_RemoveDumpFiles(void)
 
 /* ================================================== */
 
+void
+SRC_ResetSources(void)
+{
+  int i;
+
+  for (i = 0; i < n_sources; i++)
+    SRC_ResetInstance(sources[i]);
+}
+
+/* ================================================== */
+
 int
 SRC_IsSyncPeer(SRC_Instance inst)
 {

sources.h

@@ -114,6 +114,8 @@ extern void SRC_DumpSources(void);
 extern void SRC_ReloadSources(void);
 extern void SRC_RemoveDumpFiles(void);
 
+extern void SRC_ResetSources(void);
+
 extern int SRC_IsSyncPeer(SRC_Instance inst);
 extern int SRC_IsReachable(SRC_Instance inst);
 extern int SRC_ReadNumberOfSources(void);

test/simulation/110-chronyc

@@ -138,6 +138,7 @@ for chronyc_conf in \
 	"rekey" \
 	"reselect" \
 	"reselectdist 1e-3" \
+	"reset" \
 	"settime 16:30" \
 	"settime 16:30:05" \
 	"settime Nov 21, 2015 16:30:05" \