2 files changed, 34 insertions, 0 deletions
diff --git a/builtin/fsmonitor--daemon.c b/builtin/fsmonitor--daemon.c
index 46be55a461..66b78a0353 100644
--- a/builtin/fsmonitor--daemon.c
+++ b/builtin/fsmonitor--daemon.c
@@ -1423,6 +1423,7 @@ static int try_to_start_background_daemon(void)
 int cmd_fsmonitor__daemon(int argc, const char **argv, const char *prefix)
 {
 	const char *subcmd;
+	enum fsmonitor_reason reason;
 	int detach_console = 0;
 
 	struct option options[] = {
@@ -1449,6 +1450,23 @@ int cmd_fsmonitor__daemon(int argc, const char **argv, const char *prefix)
 		die(_("invalid 'ipc-threads' value (%d)"),
 		    fsmonitor__ipc_threads);
 
+	prepare_repo_settings(the_repository);
+	/*
+	 * If the repo is fsmonitor-compatible, explicitly set IPC-mode
+	 * (without bothering to load the `core.fsmonitor` config settings).
+	 *
+	 * If the repo is not compatible, the repo-settings will be set to
+	 * incompatible rather than IPC, so we can use one of the __get
+	 * routines to detect the discrepancy.
+	 */
+	fsm_settings__set_ipc(the_repository);
+
+	reason = fsm_settings__get_reason(the_repository);
+	if (reason > FSMONITOR_REASON_OK)
+		die("%s",
+		    fsm_settings__get_incompatible_msg(the_repository,
+						       reason));
+
 	if (!strcmp(subcmd, "start"))
 		return !!try_to_start_background_daemon();
 
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 876112abb2..01ed4c4976 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -1237,6 +1237,22 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 
 	if (fsmonitor > 0) {
 		enum fsmonitor_mode fsm_mode = fsm_settings__get_mode(r);
+		enum fsmonitor_reason reason = fsm_settings__get_reason(r);
+
+		/*
+		 * The user wants to turn on FSMonitor using the command
+		 * line argument.  (We don't know (or care) whether that
+		 * is the IPC or HOOK version.)
+		 *
+		 * Use one of the __get routines to force load the FSMonitor
+		 * config settings into the repo-settings.  That will detect
+		 * whether the file system is compatible so that we can stop
+		 * here with a nice error message.
+		 */
+		if (reason > FSMONITOR_REASON_OK)
+			die("%s",
+			    fsm_settings__get_incompatible_msg(r, reason));
+
 		if (fsm_mode == FSMONITOR_MODE_DISABLED) {
 			warning(_("core.fsmonitor is unset; "
 				"set it if you really want to "