fsmonitor--daemon: implement client command options

Implement command options `--stop`, `--is-running`, `--query`,
`--query-index`, and `--flush` to control and query the status of a
`fsmonitor--daemon` server process (and implicitly start a server
process if necessary).

Later commits will implement the actual server and monitor
the file system.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

builtin/fsmonitor--daemon.c

@@ -7,18 +7,144 @@
 #include "khash.h"
 
 static const char * const builtin_fsmonitor__daemon_usage[] = {
+	N_("git fsmonitor--daemon --stop"),
+	N_("git fsmonitor--daemon --is-running"),
+	N_("git fsmonitor--daemon --query <token>"),
+	N_("git fsmonitor--daemon --query-index"),
+	N_("git fsmonitor--daemon --flush"),
 	NULL
 };
 
 #ifdef HAVE_FSMONITOR_DAEMON_BACKEND
+/*
+ * Acting as a CLIENT.
+ *
+ * Send an IPC query to a `git-fsmonitor--daemon` SERVER process and
+ * ask for the changes since the given token.  This will implicitly
+ * start a daemon process if necessary.  The daemon process will
+ * persist after we exit.
+ *
+ * This feature is primarily used by the test suite.
+ */
+static int do_as_client__query_token(const char *token)
+{
+	struct strbuf answer = STRBUF_INIT;
+	int ret;
+
+	ret = fsmonitor_ipc__send_query(token, &answer);
+	if (ret < 0)
+		die(_("could not query fsmonitor--daemon"));
+
+	write_in_full(1, answer.buf, answer.len);
+	strbuf_release(&answer);
+
+	return 0;
+}
+
+/*
+ * Acting as a CLIENT.
+ *
+ * Read the `.git/index` to get the last token written to the FSMonitor index
+ * extension and use that to make a query.
+ *
+ * This feature is primarily used by the test suite.
+ */
+static int do_as_client__query_from_index(void)
+{
+	struct index_state *istate = the_repository->index;
+
+	setup_git_directory();
+	if (do_read_index(istate, the_repository->index_file, 0) < 0)
+		die("unable to read index file");
+	if (!istate->fsmonitor_last_update)
+		die("index file does not have fsmonitor extension");
+
+	return do_as_client__query_token(istate->fsmonitor_last_update);
+}
+
+/*
+ * Acting as a CLIENT.
+ *
+ * Send a "quit" command to the `git-fsmonitor--daemon` (if running)
+ * and wait for it to shutdown.
+ */
+static int do_as_client__send_stop(void)
+{
+	struct strbuf answer = STRBUF_INIT;
+	int ret;
+
+	ret = fsmonitor_ipc__send_command("quit", &answer);
+
+	/* The quit command does not return any response data. */
+	strbuf_release(&answer);
+
+	if (ret)
+		return ret;
+
+	trace2_region_enter("fsm_client", "polling-for-daemon-exit", NULL);
+	while (fsmonitor_ipc__get_state() == IPC_STATE__LISTENING)
+		sleep_millisec(50);
+	trace2_region_leave("fsm_client", "polling-for-daemon-exit", NULL);
+
+	return 0;
+}
+
+/*
+ * Acting as a CLIENT.
+ *
+ * Send a "flush" command to the `git-fsmonitor--daemon` (if running)
+ * and tell it to flush its cache.
+ *
+ * This feature is primarily used by the test suite to simulate a loss of
+ * sync with the filesystem where we miss kernel events.
+ */
+static int do_as_client__send_flush(void)
+{
+	struct strbuf answer = STRBUF_INIT;
+	int ret;
+
+	ret = fsmonitor_ipc__send_command("flush", &answer);
+	if (ret)
+		return ret;
+
+	write_in_full(1, answer.buf, answer.len);
+	strbuf_release(&answer);
+
+	return 0;
+}
+
+static int is_ipc_daemon_listening(void)
+{
+	return fsmonitor_ipc__get_state() == IPC_STATE__LISTENING;
+}
 
 int cmd_fsmonitor__daemon(int argc, const char **argv, const char *prefix)
 {
 	enum daemon_mode {
 		UNDEFINED_MODE,
+		STOP,
+		IS_RUNNING,
+		QUERY,
+		QUERY_INDEX,
+		FLUSH,
 	} mode = UNDEFINED_MODE;
 
 	struct option options[] = {
+		OPT_CMDMODE(0, "stop", &mode, N_("stop the running daemon"),
+			    STOP),
+
+		OPT_CMDMODE(0, "is-running", &mode,
+			    N_("test whether the daemon is running"),
+			    IS_RUNNING),
+
+		OPT_CMDMODE(0, "query", &mode,
+			    N_("query the daemon (starting if necessary)"),
+			    QUERY),
+		OPT_CMDMODE(0, "query-index", &mode,
+			    N_("query the daemon (starting if necessary) using token from index"),
+			    QUERY_INDEX),
+		OPT_CMDMODE(0, "flush", &mode, N_("flush cached filesystem events"),
+			    FLUSH),
 		OPT_END()
 	};
 
@@ -31,6 +157,24 @@ int cmd_fsmonitor__daemon(int argc, const char **argv, const char *prefix)
 			     builtin_fsmonitor__daemon_usage, 0);
 
 	switch (mode) {
+	case STOP:
+		return !!do_as_client__send_stop();
+
+	case IS_RUNNING:
+		return !is_ipc_daemon_listening();
+
+	case QUERY:
+		if (argc != 1)
+			usage_with_options(builtin_fsmonitor__daemon_usage,
+					   options);
+		return !!do_as_client__query_token(argv[0]);
+
+	case QUERY_INDEX:
+		return !!do_as_client__query_from_index();
+
+	case FLUSH:
+		return !!do_as_client__send_flush();
+
 	case UNDEFINED_MODE:
 	default:
 		die(_("Unhandled command mode %d"), mode);