xenbus: advertise control feature flags

The Xen docs specify several flags which a guest can set to advertise
which values of the xenstore control/shutdown key it will recognize.
This patch adds code to write all the relevant feature-flag keys.
Based-on-patch-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

drivers/xen/manage.c

@@ -168,7 +168,9 @@ static void do_suspend(void)
 #endif	/* CONFIG_HIBERNATE_CALLBACKS */
 
 struct shutdown_handler {
-	const char *command;
+#define SHUTDOWN_CMD_SIZE 11
+	const char command[SHUTDOWN_CMD_SIZE];
+	bool flag;
 	void (*cb)(void);
 };
 
@@ -206,22 +208,22 @@ static void do_reboot(void)
 	ctrl_alt_del();
 }
 
+static struct shutdown_handler shutdown_handlers[] = {
+	{ "poweroff",	true,	do_poweroff },
+	{ "halt",	false,	do_poweroff },
+	{ "reboot",	true,	do_reboot   },
+#ifdef CONFIG_HIBERNATE_CALLBACKS
+	{ "suspend",	true,	do_suspend  },
+#endif
+};
+
 static void shutdown_handler(struct xenbus_watch *watch,
 			     const char **vec, unsigned int len)
 {
 	char *str;
 	struct xenbus_transaction xbt;
 	int err;
-	static struct shutdown_handler handlers[] = {
-		{ "poweroff",	do_poweroff },
-		{ "halt",	do_poweroff },
-		{ "reboot",	do_reboot   },
-#ifdef CONFIG_HIBERNATE_CALLBACKS
-		{ "suspend",	do_suspend  },
-#endif
-		{NULL, NULL},
-	};
-	static struct shutdown_handler *handler;
+	int idx;
 
 	if (shutting_down != SHUTDOWN_INVALID)
 		return;
@@ -238,13 +240,13 @@ static void shutdown_handler(struct xenbus_watch *watch,
 		return;
 	}
 
-	for (handler = &handlers[0]; handler->command; handler++) {
-		if (strcmp(str, handler->command) == 0)
+	for (idx = 0; idx < ARRAY_SIZE(shutdown_handlers); idx++) {
+		if (strcmp(str, shutdown_handlers[idx].command) == 0)
 			break;
 	}
 
 	/* Only acknowledge commands which we are prepared to handle. */
-	if (handler->cb)
+	if (idx < ARRAY_SIZE(shutdown_handlers))
 		xenbus_write(xbt, "control", "shutdown", "");
 
 	err = xenbus_transaction_end(xbt, 0);
@@ -253,8 +255,8 @@ static void shutdown_handler(struct xenbus_watch *watch,
 		goto again;
 	}
 
-	if (handler->cb) {
-		handler->cb();
+	if (idx < ARRAY_SIZE(shutdown_handlers)) {
+		shutdown_handlers[idx].cb();
 	} else {
 		pr_info("Ignoring shutdown request: %s\n", str);
 		shutting_down = SHUTDOWN_INVALID;
@@ -310,6 +312,9 @@ static struct notifier_block xen_reboot_nb = {
 static int setup_shutdown_watcher(void)
 {
 	int err;
+	int idx;
+#define FEATURE_PATH_SIZE (SHUTDOWN_CMD_SIZE + sizeof("feature-"))
+	char node[FEATURE_PATH_SIZE];
 
 	err = register_xenbus_watch(&shutdown_watch);
 	if (err) {
@@ -326,6 +331,14 @@ static int setup_shutdown_watcher(void)
 	}
 #endif
 
+	for (idx = 0; idx < ARRAY_SIZE(shutdown_handlers); idx++) {
+		if (!shutdown_handlers[idx].flag)
+			continue;
+		snprintf(node, FEATURE_PATH_SIZE, "feature-%s",
+			 shutdown_handlers[idx].command);
+		xenbus_printf(XBT_NIL, "control", node, "%u", 1);
+	}
+
 	return 0;
 }