[PATCH] xenbus: advertize control feature flags

[Paul Durrant <paul.durrant@citrix.com>]

The Xen docs specify several flags which a guest can set to advertize
which values of the xenstore control/shutdown key it will recognize.
This patch adds code to write all the relevant feature-flag keys.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Juergen Gross <jgross@suse.com>
---
 drivers/xen/manage.c | 45 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 10 deletions(-)

diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index e12bd36..86cf57c 100644
--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -170,6 +170,7 @@ out:
 struct shutdown_handler {
 	const char *command;
 	void (*cb)(void);
+	bool flag;
 };
 
 static int poweroff_nb(struct notifier_block *cb, unsigned long code, void *unused)
@@ -206,21 +207,22 @@ static void do_reboot(void)
 	ctrl_alt_del();
 }
 
+static struct shutdown_handler shutdown_handlers[] = {
+	{ "poweroff", do_poweroff, true },
+	{ "halt", do_poweroff, true },
+	{ "reboot", do_reboot, false },
+#ifdef CONFIG_HIBERNATE_CALLBACKS
+	{ "suspend", do_suspend, true },
+#endif
+	{NULL, NULL, false },
+};
+
 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;
 
 	if (shutting_down != SHUTDOWN_INVALID)
@@ -238,7 +240,7 @@ static void shutdown_handler(struct xenbus_watch *watch,
 		return;
 	}
 
-	for (handler = &handlers[0]; handler->command; handler++) {
+	for (handler = &shutdown_handlers[0]; handler->command; handler++) {
 		if (strcmp(str, handler->command) == 0)
 			break;
 	}
@@ -309,8 +311,31 @@ static struct notifier_block xen_reboot_nb = {
 
 static int setup_shutdown_watcher(void)
 {
+	static struct shutdown_handler *handler;
 	int err;
 
+	for (handler = &shutdown_handlers[0]; handler->command; handler++) {
+		const char *fmt = "feature-%s";
+		int size;
+		char *node;
+
+		if (!handler->flag)
+			continue;
+
+		size = snprintf(NULL, 0, fmt, handler->command);
+
+		node = kmalloc(++size, GFP_KERNEL);
+		if (!node) {
+			pr_err("Failed to allocate feature flag\n");
+			return -ENOMEM;
+		}
+
+		(void) snprintf(node, size, fmt, handler->command);
+		xenbus_printf(XBT_NIL, "control", node, "%u", 1);
+
+		kfree(node);
+	}
+
 	err = register_xenbus_watch(&shutdown_watch);
 	if (err) {
 		pr_err("Failed to set shutdown watcher\n");
-- 
2.1.4