xen: separate out frontend xenbus

Impact: refactor

Make a distinct frontend xenbus, in preparation for adding a backend xenbus.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
[corresponds to 2fd433a4188f in git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git
 with adjustments to reflect changes in the code which is moved]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

4 files changed, 363 insertions, 305 deletions

diff --git a/drivers/xen/xenbus/Makefile b/drivers/xen/xenbus/Makefile
index 5571f5b84223..33e8cf8149b3 100644
--- a/drivers/xen/xenbus/Makefile
+++ b/drivers/xen/xenbus/Makefile
@@ -5,3 +5,5 @@ xenbus-objs += xenbus_client.o
 xenbus-objs += xenbus_comms.o
 xenbus-objs += xenbus_xs.o
 xenbus-objs += xenbus_probe.o
+
+obj-$(CONFIG_XEN_XENBUS_FRONTEND) += xenbus_probe_frontend.o
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index deb9c4ba3a93..d46205868b88 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -56,7 +56,6 @@
 #include <xen/events.h>
 #include <xen/page.h>
 
-#include <xen/platform_pci.h>
 #include <xen/hvm.h>
 
 #include "xenbus_comms.h"
@@ -73,15 +72,6 @@ static unsigned long xen_store_mfn;
 
 static BLOCKING_NOTIFIER_HEAD(xenstore_chain);
 
-static void wait_for_devices(struct xenbus_driver *xendrv);
-
-static int xenbus_probe_frontend(const char *type, const char *name);
-
-static void xenbus_dev_shutdown(struct device *_dev);
-
-static int xenbus_dev_suspend(struct device *dev, pm_message_t state);
-static int xenbus_dev_resume(struct device *dev);
-
 /* If something in array of ids matches this device, return it. */
 static const struct xenbus_device_id *
 match_device(const struct xenbus_device_id *arr, struct xenbus_device *dev)
@@ -102,8 +92,10 @@ int xenbus_match(struct device *_dev, struct device_driver *_drv)
 
 	return match_device(drv->ids, to_xenbus_device(_dev)) != NULL;
 }
+EXPORT_SYMBOL_GPL(xenbus_match);
+
 
-static int xenbus_uevent(struct device *_dev, struct kobj_uevent_env *env)
+int xenbus_uevent(struct device *_dev, struct kobj_uevent_env *env)
 {
 	struct xenbus_device *dev = to_xenbus_device(_dev);
 
@@ -112,25 +104,7 @@ static int xenbus_uevent(struct device *_dev, struct kobj_uevent_env *env)
 
 	return 0;
 }
-
-/* device/<type>/<id> => <type>-<id> */
-static int frontend_bus_id(char bus_id[XEN_BUS_ID_SIZE], const char *nodename)
-{
-	nodename = strchr(nodename, '/');
-	if (!nodename || strlen(nodename + 1) >= XEN_BUS_ID_SIZE) {
-		printk(KERN_WARNING "XENBUS: bad frontend %s\n", nodename);
-		return -EINVAL;
-	}
-
-	strlcpy(bus_id, nodename + 1, XEN_BUS_ID_SIZE);
-	if (!strchr(bus_id, '/')) {
-		printk(KERN_WARNING "XENBUS: bus_id %s no slash\n", bus_id);
-		return -EINVAL;
-	}
-	*strchr(bus_id, '/') = '-';
-	return 0;
-}
-
+EXPORT_SYMBOL_GPL(xenbus_uevent);
 
 static void free_otherend_details(struct xenbus_device *dev)
 {
@@ -149,7 +123,28 @@ static void free_otherend_watch(struct xenbus_device *dev)
 }
 
 
-int read_otherend_details(struct xenbus_device *xendev,
+static int talk_to_otherend(struct xenbus_device *dev)
+{
+	struct xenbus_driver *drv = to_xenbus_driver(dev->dev.driver);
+
+	free_otherend_watch(dev);
+	free_otherend_details(dev);
+
+	return drv->read_otherend_details(dev);
+}
+
+
+
+static int watch_otherend(struct xenbus_device *dev)
+{
+	struct xen_bus_type *bus = container_of(dev->dev.bus, struct xen_bus_type, bus);
+
+	return xenbus_watch_pathfmt(dev, &dev->otherend_watch, bus->otherend_changed,
+				    "%s/%s", dev->otherend, "state");
+}
+
+
+int xenbus_read_otherend_details(struct xenbus_device *xendev,
 				 char *id_node, char *path_node)
 {
 	int err = xenbus_gather(XBT_NIL, xendev->nodename,
@@ -174,39 +169,11 @@ int read_otherend_details(struct xenbus_device *xendev,
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(xenbus_read_otherend_details);
 
-
-static int read_backend_details(struct xenbus_device *xendev)
-{
-	return read_otherend_details(xendev, "backend-id", "backend");
-}
-
-static struct device_attribute xenbus_dev_attrs[] = {
-	__ATTR_NULL
-};
-
-/* Bus type for frontend drivers. */
-static struct xen_bus_type xenbus_frontend = {
-	.root = "device",
-	.levels = 2, 		/* device/type/<id> */
-	.get_bus_id = frontend_bus_id,
-	.probe = xenbus_probe_frontend,
-	.bus = {
-		.name      = "xen",
-		.match     = xenbus_match,
-		.uevent    = xenbus_uevent,
-		.probe     = xenbus_dev_probe,
-		.remove    = xenbus_dev_remove,
-		.shutdown  = xenbus_dev_shutdown,
-		.dev_attrs = xenbus_dev_attrs,
-
-		.suspend   = xenbus_dev_suspend,
-		.resume    = xenbus_dev_resume,
-	},
-};
-
-static void otherend_changed(struct xenbus_watch *watch,
-			     const char **vec, unsigned int len)
+void xenbus_otherend_changed(struct xenbus_watch *watch,
+			     const char **vec, unsigned int len,
+			     int ignore_on_shutdown)
 {
 	struct xenbus_device *dev =
 		container_of(watch, struct xenbus_device, otherend_watch);
@@ -234,11 +201,7 @@ static void otherend_changed(struct xenbus_watch *watch,
 	 * work that can fail e.g., when the rootfs is gone.
 	 */
 	if (system_state > SYSTEM_RUNNING) {
-		struct xen_bus_type *bus = bus;
-		bus = container_of(dev->dev.bus, struct xen_bus_type, bus);
-		/* If we're frontend, drive the state machine to Closed. */
-		/* This should cause the backend to release our resources. */
-		if ((bus == &xenbus_frontend) && (state == XenbusStateClosing))
+		if (ignore_on_shutdown && (state == XenbusStateClosing))
 			xenbus_frontend_closed(dev);
 		return;
 	}
@@ -246,25 +209,7 @@ static void otherend_changed(struct xenbus_watch *watch,
 	if (drv->otherend_changed)
 		drv->otherend_changed(dev, state);
 }
-
-
-static int talk_to_otherend(struct xenbus_device *dev)
-{
-	struct xenbus_driver *drv = to_xenbus_driver(dev->dev.driver);
-
-	free_otherend_watch(dev);
-	free_otherend_details(dev);
-
-	return drv->read_otherend_details(dev);
-}
-
-
-static int watch_otherend(struct xenbus_device *dev)
-{
-	return xenbus_watch_pathfmt(dev, &dev->otherend_watch, otherend_changed,
-				    "%s/%s", dev->otherend, "state");
-}
-
+EXPORT_SYMBOL_GPL(xenbus_otherend_changed);
 
 int xenbus_dev_probe(struct device *_dev)
 {
@@ -310,6 +255,7 @@ fail:
 	xenbus_switch_state(dev, XenbusStateClosed);
 	return -ENODEV;
 }
+EXPORT_SYMBOL_GPL(xenbus_dev_probe);
 
 int xenbus_dev_remove(struct device *_dev)
 {
@@ -327,8 +273,9 @@ int xenbus_dev_remove(struct device *_dev)
 	xenbus_switch_state(dev, XenbusStateClosed);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(xenbus_dev_remove);
 
-static void xenbus_dev_shutdown(struct device *_dev)
+void xenbus_dev_shutdown(struct device *_dev)
 {
 	struct xenbus_device *dev = to_xenbus_device(_dev);
 	unsigned long timeout = 5*HZ;
@@ -349,6 +296,7 @@ static void xenbus_dev_shutdown(struct device *_dev)
  out:
 	put_device(&dev->dev);
 }
+EXPORT_SYMBOL_GPL(xenbus_dev_shutdown);
 
 int xenbus_register_driver_common(struct xenbus_driver *drv,
 				  struct xen_bus_type *bus,
@@ -362,25 +310,7 @@ int xenbus_register_driver_common(struct xenbus_driver *drv,
 
 	return driver_register(&drv->driver);
 }
-
-int __xenbus_register_frontend(struct xenbus_driver *drv,
-			       struct module *owner, const char *mod_name)
-{
-	int ret;
-
-	drv->read_otherend_details = read_backend_details;
-
-	ret = xenbus_register_driver_common(drv, &xenbus_frontend,
-					    owner, mod_name);
-	if (ret)
-		return ret;
-
-	/* If this driver is loaded as a module wait for devices to attach. */
-	wait_for_devices(drv);
-
-	return 0;
-}
-EXPORT_SYMBOL_GPL(__xenbus_register_frontend);
+EXPORT_SYMBOL_GPL(xenbus_register_driver_common);
 
 void xenbus_unregister_driver(struct xenbus_driver *drv)
 {
@@ -551,24 +481,7 @@ fail:
 	kfree(xendev);
 	return err;
 }
-
-/* device/<typename>/<name> */
-static int xenbus_probe_frontend(const char *type, const char *name)
-{
-	char *nodename;
-	int err;
-
-	nodename = kasprintf(GFP_KERNEL, "%s/%s/%s",
-			     xenbus_frontend.root, type, name);
-	if (!nodename)
-		return -ENOMEM;
-
-	DPRINTK("%s", nodename);
-
-	err = xenbus_probe_node(&xenbus_frontend, type, nodename);
-	kfree(nodename);
-	return err;
-}
+EXPORT_SYMBOL_GPL(xenbus_probe_node);
 
 static int xenbus_probe_device_type(struct xen_bus_type *bus, const char *type)
 {
@@ -577,15 +490,23 @@ static int xenbus_probe_device_type(struct xen_bus_type *bus, const char *type)
 	unsigned int dir_n = 0;
 	int i;
 
+	printk(KERN_CRIT "%s type %s\n", __func__, type);
+
 	dir = xenbus_directory(XBT_NIL, bus->root, type, &dir_n);
-	if (IS_ERR(dir))
+	if (IS_ERR(dir)) {
+		printk(KERN_CRIT "%s failed xenbus_directory\n", __func__);
 		return PTR_ERR(dir);
+	}
 
 	for (i = 0; i < dir_n; i++) {
-		err = bus->probe(type, dir[i]);
-		if (err)
+		printk(KERN_CRIT "%s %d/%d %s\n", __func__, i+1,dir_n, dir[i]);
+		err = bus->probe(bus, type, dir[i]);
+		if (err) {
+			printk(KERN_CRIT "%s failed\n", __func__);
 			break;
+		}
 	}
+	printk("%s done\n", __func__);
 	kfree(dir);
 	return err;
 }
@@ -596,18 +517,27 @@ int xenbus_probe_devices(struct xen_bus_type *bus)
 	char **dir;
 	unsigned int i, dir_n;
 
+	printk(KERN_CRIT "%s %s\n", __func__, bus->root);
+
 	dir = xenbus_directory(XBT_NIL, bus->root, "", &dir_n);
-	if (IS_ERR(dir))
+	if (IS_ERR(dir)) {
+		printk(KERN_CRIT "%s failed xenbus_directory\n", __func__);
 		return PTR_ERR(dir);
+	}
 
 	for (i = 0; i < dir_n; i++) {
+		printk(KERN_CRIT "%s %d/%d %s\n", __func__, i+1,dir_n, dir[i]);
 		err = xenbus_probe_device_type(bus, dir[i]);
-		if (err)
+		if (err) {
+			printk(KERN_CRIT "%s failed\n", __func__);
 			break;
+		}
 	}
+	printk("%s done\n", __func__);
 	kfree(dir);
 	return err;
 }
+EXPORT_SYMBOL_GPL(xenbus_probe_devices);
 
 static unsigned int char_count(const char *str, char c)
 {
@@ -670,32 +600,17 @@ void xenbus_dev_changed(const char *node, struct xen_bus_type *bus)
 }
 EXPORT_SYMBOL_GPL(xenbus_dev_changed);
 
-static void frontend_changed(struct xenbus_watch *watch,
-			     const char **vec, unsigned int len)
-{
-	DPRINTK("");
-
-	xenbus_dev_changed(vec[XS_WATCH_PATH], &xenbus_frontend);
-}
-
-/* We watch for devices appearing and vanishing. */
-static struct xenbus_watch fe_watch = {
-	.node = "device",
-	.callback = frontend_changed,
-};
-
-static int xenbus_dev_suspend(struct device *dev, pm_message_t state)
+int xenbus_dev_suspend(struct device *dev, pm_message_t state)
 {
 	int err = 0;
 	struct xenbus_driver *drv;
-	struct xenbus_device *xdev;
+	struct xenbus_device *xdev = container_of(dev, struct xenbus_device, dev);
 
-	DPRINTK("");
+	DPRINTK("%s", xdev->nodename);
 
 	if (dev->driver == NULL)
 		return 0;
 	drv = to_xenbus_driver(dev->driver);
-	xdev = container_of(dev, struct xenbus_device, dev);
 	if (drv->suspend)
 		err = drv->suspend(xdev, state);
 	if (err)
@@ -703,21 +618,19 @@ static int xenbus_dev_suspend(struct device *dev, pm_message_t state)
 		       "xenbus: suspend %s failed: %i\n", dev_name(dev), err);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(xenbus_dev_suspend);
 
-static int xenbus_dev_resume(struct device *dev)
+int xenbus_dev_resume(struct device *dev)
 {
 	int err;
 	struct xenbus_driver *drv;
-	struct xenbus_device *xdev;
+	struct xenbus_device *xdev = container_of(dev, struct xenbus_device, dev);
 
-	DPRINTK("");
+	DPRINTK("%s", xdev->nodename);
 
 	if (dev->driver == NULL)
 		return 0;
-
 	drv = to_xenbus_driver(dev->driver);
-	xdev = container_of(dev, struct xenbus_device, dev);
-
 	err = talk_to_otherend(xdev);
 	if (err) {
 		printk(KERN_WARNING
@@ -748,6 +661,7 @@ static int xenbus_dev_resume(struct device *dev)
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(xenbus_dev_resume);
 
 /* A flag to determine if xenstored is 'ready' (i.e. has started) */
 int xenstored_ready = 0;
@@ -776,11 +690,6 @@ void xenbus_probe(struct work_struct *unused)
 {
 	xenstored_ready = 1;
 
-	/* Enumerate devices in xenstore and watch for changes. */
-	xenbus_probe_devices(&xenbus_frontend);
-	register_xenbus_watch(&fe_watch);
-	xenbus_backend_probe_and_watch();
-
 	/* Notify others that xenstore is up */
 	blocking_notifier_call_chain(&xenstore_chain, 0, NULL);
 }
@@ -811,15 +720,6 @@ static int __init xenbus_init(void)
 	if (!xen_domain())
 		goto out_error;
 
-	/* Register ourselves with the kernel bus subsystem */
-	err = bus_register(&xenbus_frontend.bus);
-	if (err)
-		goto out_error;
-
-	err = xenbus_backend_bus_register();
-	if (err)
-		goto out_unreg_front;
-
 	/*
 	 * Domain0 doesn't have a store_evtchn or store_mfn yet.
 	 */
@@ -874,7 +774,7 @@ static int __init xenbus_init(void)
 	if (err) {
 		printk(KERN_WARNING
 		       "XENBUS: Error initializing xenstore comms: %i\n", err);
-		goto out_unreg_back;
+		goto out_error;
 	}
 
 #ifdef CONFIG_XEN_COMPAT_XENFS
@@ -885,135 +785,16 @@ static int __init xenbus_init(void)
 	proc_mkdir("xen", NULL);
 #endif
 
+	printk(KERN_CRIT "%s ok\n", __func__);
 	return 0;
 
-  out_unreg_back:
-	xenbus_backend_bus_unregister();
-
-  out_unreg_front:
-	bus_unregister(&xenbus_frontend.bus);
-
   out_error:
 	if (page != 0)
 		free_page(page);
+
 	return err;
 }
 
 postcore_initcall(xenbus_init);
 
 MODULE_LICENSE("GPL");
-
-static int is_device_connecting(struct device *dev, void *data)
-{
-	struct xenbus_device *xendev = to_xenbus_device(dev);
-	struct device_driver *drv = data;
-	struct xenbus_driver *xendrv;
-
-	/*
-	 * A device with no driver will never connect. We care only about
-	 * devices which should currently be in the process of connecting.
-	 */
-	if (!dev->driver)
-		return 0;
-
-	/* Is this search limited to a particular driver? */
-	if (drv && (dev->driver != drv))
-		return 0;
-
-	xendrv = to_xenbus_driver(dev->driver);
-	return (xendev->state < XenbusStateConnected ||
-		(xendev->state == XenbusStateConnected &&
-		 xendrv->is_ready && !xendrv->is_ready(xendev)));
-}
-
-static int exists_connecting_device(struct device_driver *drv)
-{
-	return bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
-				is_device_connecting);
-}
-
-static int print_device_status(struct device *dev, void *data)
-{
-	struct xenbus_device *xendev = to_xenbus_device(dev);
-	struct device_driver *drv = data;
-
-	/* Is this operation limited to a particular driver? */
-	if (drv && (dev->driver != drv))
-		return 0;
-
-	if (!dev->driver) {
-		/* Information only: is this too noisy? */
-		printk(KERN_INFO "XENBUS: Device with no driver: %s\n",
-		       xendev->nodename);
-	} else if (xendev->state < XenbusStateConnected) {
-		enum xenbus_state rstate = XenbusStateUnknown;
-		if (xendev->otherend)
-			rstate = xenbus_read_driver_state(xendev->otherend);
-		printk(KERN_WARNING "XENBUS: Timeout connecting "
-		       "to device: %s (local state %d, remote state %d)\n",
-		       xendev->nodename, xendev->state, rstate);
-	}
-
-	return 0;
-}
-
-/* We only wait for device setup after most initcalls have run. */
-static int ready_to_wait_for_devices;
-
-/*
- * On a 5-minute timeout, wait for all devices currently configured.  We need
- * to do this to guarantee that the filesystems and / or network devices
- * needed for boot are available, before we can allow the boot to proceed.
- *
- * This needs to be on a late_initcall, to happen after the frontend device
- * drivers have been initialised, but before the root fs is mounted.
- *
- * A possible improvement here would be to have the tools add a per-device
- * flag to the store entry, indicating whether it is needed at boot time.
- * This would allow people who knew what they were doing to accelerate their
- * boot slightly, but of course needs tools or manual intervention to set up
- * those flags correctly.
- */
-static void wait_for_devices(struct xenbus_driver *xendrv)
-{
-	unsigned long start = jiffies;
-	struct device_driver *drv = xendrv ? &xendrv->driver : NULL;
-	unsigned int seconds_waited = 0;
-
-	if (!ready_to_wait_for_devices || !xen_domain())
-		return;
-
-	while (exists_connecting_device(drv)) {
-		if (time_after(jiffies, start + (seconds_waited+5)*HZ)) {
-			if (!seconds_waited)
-				printk(KERN_WARNING "XENBUS: Waiting for "
-				       "devices to initialise: ");
-			seconds_waited += 5;
-			printk("%us...", 300 - seconds_waited);
-			if (seconds_waited == 300)
-				break;
-		}
-
-		schedule_timeout_interruptible(HZ/10);
-	}
-
-	if (seconds_waited)
-		printk("\n");
-
-	bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
-			 print_device_status);
-}
-
-#ifndef MODULE
-static int __init boot_wait_for_devices(void)
-{
-	if (xen_hvm_domain() && !xen_platform_pci_unplug)
-		return -ENODEV;
-
-	ready_to_wait_for_devices = 1;
-	wait_for_devices(NULL);
-	return 0;
-}
-
-late_initcall(boot_wait_for_devices);
-#endif
diff --git a/drivers/xen/xenbus/xenbus_probe.h b/drivers/xen/xenbus/xenbus_probe.h
index 6c5e3185a6a2..be390cef329f 100644
--- a/drivers/xen/xenbus/xenbus_probe.h
+++ b/drivers/xen/xenbus/xenbus_probe.h
@@ -36,26 +36,13 @@
 
 #define XEN_BUS_ID_SIZE			20
 
-#ifdef CONFIG_XEN_BACKEND
-extern void xenbus_backend_suspend(int (*fn)(struct device *, void *));
-extern void xenbus_backend_resume(int (*fn)(struct device *, void *));
-extern void xenbus_backend_probe_and_watch(void);
-extern int xenbus_backend_bus_register(void);
-extern void xenbus_backend_bus_unregister(void);
-#else
-static inline void xenbus_backend_suspend(int (*fn)(struct device *, void *)) {}
-static inline void xenbus_backend_resume(int (*fn)(struct device *, void *)) {}
-static inline void xenbus_backend_probe_and_watch(void) {}
-static inline int xenbus_backend_bus_register(void) { return 0; }
-static inline void xenbus_backend_bus_unregister(void) {}
-#endif
-
 struct xen_bus_type
 {
 	char *root;
 	unsigned int levels;
 	int (*get_bus_id)(char bus_id[XEN_BUS_ID_SIZE], const char *nodename);
-	int (*probe)(const char *type, const char *dir);
+	int (*probe)(struct xen_bus_type *bus, const char *type, const char *dir);
+	void (*otherend_changed)(struct xenbus_watch *watch, const char **vec, unsigned int len);
 	struct bus_type bus;
 };
 
@@ -73,4 +60,17 @@ extern int xenbus_probe_devices(struct xen_bus_type *bus);
 
 extern void xenbus_dev_changed(const char *node, struct xen_bus_type *bus);
 
+extern int xenbus_uevent(struct device *_dev, struct kobj_uevent_env *env);
+extern void xenbus_dev_shutdown(struct device *_dev);
+
+extern int xenbus_dev_suspend(struct device *dev, pm_message_t state);
+extern int xenbus_dev_resume(struct device *dev);
+
+extern void xenbus_otherend_changed(struct xenbus_watch *watch,
+				    const char **vec, unsigned int len,
+				    int ignore_on_shutdown);
+
+extern int xenbus_read_otherend_details(struct xenbus_device *xendev,
+					char *id_node, char *path_node);
+
 #endif
diff --git a/drivers/xen/xenbus/xenbus_probe_frontend.c b/drivers/xen/xenbus/xenbus_probe_frontend.c
new file mode 100644
index 000000000000..04c4f0123521
--- /dev/null
+++ b/drivers/xen/xenbus/xenbus_probe_frontend.c
@@ -0,0 +1,275 @@
+#define DPRINTK(fmt, args...)				\
+	pr_debug("xenbus_probe (%s:%d) " fmt ".\n",	\
+		 __func__, __LINE__, ##args)
+
+#include <linux/kernel.h>
+#include <linux/err.h>
+#include <linux/string.h>
+#include <linux/ctype.h>
+#include <linux/fcntl.h>
+#include <linux/mm.h>
+#include <linux/proc_fs.h>
+#include <linux/notifier.h>
+#include <linux/kthread.h>
+#include <linux/mutex.h>
+#include <linux/io.h>
+
+#include <asm/page.h>
+#include <asm/pgtable.h>
+#include <asm/xen/hypervisor.h>
+#include <xen/xenbus.h>
+#include <xen/events.h>
+#include <xen/page.h>
+
+#include <xen/platform_pci.h>
+
+#include "xenbus_comms.h"
+#include "xenbus_probe.h"
+
+
+/* device/<type>/<id> => <type>-<id> */
+static int frontend_bus_id(char bus_id[XEN_BUS_ID_SIZE], const char *nodename)
+{
+	nodename = strchr(nodename, '/');
+	if (!nodename || strlen(nodename + 1) >= XEN_BUS_ID_SIZE) {
+		printk(KERN_WARNING "XENBUS: bad frontend %s\n", nodename);
+		return -EINVAL;
+	}
+
+	strlcpy(bus_id, nodename + 1, XEN_BUS_ID_SIZE);
+	if (!strchr(bus_id, '/')) {
+		printk(KERN_WARNING "XENBUS: bus_id %s no slash\n", bus_id);
+		return -EINVAL;
+	}
+	*strchr(bus_id, '/') = '-';
+	return 0;
+}
+
+/* device/<typename>/<name> */
+static int xenbus_probe_frontend(struct xen_bus_type *bus, const char *type, const char *name)
+{
+	char *nodename;
+	int err;
+
+	nodename = kasprintf(GFP_KERNEL, "%s/%s/%s", bus->root, type, name);
+	if (!nodename)
+		return -ENOMEM;
+
+	DPRINTK("%s", nodename);
+
+	err = xenbus_probe_node(bus, type, nodename);
+	kfree(nodename);
+	return err;
+}
+
+static void backend_changed(struct xenbus_watch *watch,
+			    const char **vec, unsigned int len)
+{
+	xenbus_otherend_changed(watch, vec, len, 1);
+}
+
+static struct device_attribute xenbus_frontend_dev_attrs[] = {
+	__ATTR_NULL
+};
+
+static struct xen_bus_type xenbus_frontend = {
+	.root = "device",
+	.levels = 2, 		/* device/type/<id> */
+	.get_bus_id = frontend_bus_id,
+	.probe = xenbus_probe_frontend,
+	.otherend_changed = backend_changed,
+	.bus = {
+		.name     = "xen",
+		.match    = xenbus_match,
+		.uevent   = xenbus_uevent,
+		.probe    = xenbus_dev_probe,
+		.remove   = xenbus_dev_remove,
+		.shutdown = xenbus_dev_shutdown,
+		.dev_attrs= xenbus_frontend_dev_attrs,
+
+		.suspend  = xenbus_dev_suspend,
+		.resume   = xenbus_dev_resume,
+	},
+};
+
+static void frontend_changed(struct xenbus_watch *watch,
+			     const char **vec, unsigned int len)
+{
+	DPRINTK("");
+
+	xenbus_dev_changed(vec[XS_WATCH_PATH], &xenbus_frontend);
+}
+
+
+/* We watch for devices appearing and vanishing. */
+static struct xenbus_watch fe_watch = {
+	.node = "device",
+	.callback = frontend_changed,
+};
+
+static int read_backend_details(struct xenbus_device *xendev)
+{
+	return xenbus_read_otherend_details(xendev, "backend-id", "backend");
+}
+
+static int is_device_connecting(struct device *dev, void *data)
+{
+	struct xenbus_device *xendev = to_xenbus_device(dev);
+	struct device_driver *drv = data;
+	struct xenbus_driver *xendrv;
+
+	/*
+	 * A device with no driver will never connect. We care only about
+	 * devices which should currently be in the process of connecting.
+	 */
+	if (!dev->driver)
+		return 0;
+
+	/* Is this search limited to a particular driver? */
+	if (drv && (dev->driver != drv))
+		return 0;
+
+	xendrv = to_xenbus_driver(dev->driver);
+	return (xendev->state < XenbusStateConnected ||
+		(xendev->state == XenbusStateConnected &&
+		 xendrv->is_ready && !xendrv->is_ready(xendev)));
+}
+
+static int exists_connecting_device(struct device_driver *drv)
+{
+	return bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
+				is_device_connecting);
+}
+
+static int print_device_status(struct device *dev, void *data)
+{
+	struct xenbus_device *xendev = to_xenbus_device(dev);
+	struct device_driver *drv = data;
+
+	/* Is this operation limited to a particular driver? */
+	if (drv && (dev->driver != drv))
+		return 0;
+
+	if (!dev->driver) {
+		/* Information only: is this too noisy? */
+		printk(KERN_INFO "XENBUS: Device with no driver: %s\n",
+		       xendev->nodename);
+	} else if (xendev->state < XenbusStateConnected) {
+		enum xenbus_state rstate = XenbusStateUnknown;
+		if (xendev->otherend)
+			rstate = xenbus_read_driver_state(xendev->otherend);
+		printk(KERN_WARNING "XENBUS: Timeout connecting "
+		       "to device: %s (local state %d, remote state %d)\n",
+		       xendev->nodename, xendev->state, rstate);
+	}
+
+	return 0;
+}
+
+/* We only wait for device setup after most initcalls have run. */
+static int ready_to_wait_for_devices;
+
+/*
+ * On a 5-minute timeout, wait for all devices currently configured.  We need
+ * to do this to guarantee that the filesystems and / or network devices
+ * needed for boot are available, before we can allow the boot to proceed.
+ *
+ * This needs to be on a late_initcall, to happen after the frontend device
+ * drivers have been initialised, but before the root fs is mounted.
+ *
+ * A possible improvement here would be to have the tools add a per-device
+ * flag to the store entry, indicating whether it is needed at boot time.
+ * This would allow people who knew what they were doing to accelerate their
+ * boot slightly, but of course needs tools or manual intervention to set up
+ * those flags correctly.
+ */
+static void wait_for_devices(struct xenbus_driver *xendrv)
+{
+	unsigned long start = jiffies;
+	struct device_driver *drv = xendrv ? &xendrv->driver : NULL;
+	unsigned int seconds_waited = 0;
+
+	if (!ready_to_wait_for_devices || !xen_domain())
+		return;
+
+	while (exists_connecting_device(drv)) {
+		if (time_after(jiffies, start + (seconds_waited+5)*HZ)) {
+			if (!seconds_waited)
+				printk(KERN_WARNING "XENBUS: Waiting for "
+				       "devices to initialise: ");
+			seconds_waited += 5;
+			printk("%us...", 300 - seconds_waited);
+			if (seconds_waited == 300)
+				break;
+		}
+
+		schedule_timeout_interruptible(HZ/10);
+	}
+
+	if (seconds_waited)
+		printk("\n");
+
+	bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
+			 print_device_status);
+}
+
+int __xenbus_register_frontend(struct xenbus_driver *drv,
+			       struct module *owner, const char *mod_name)
+{
+	int ret;
+
+	drv->read_otherend_details = read_backend_details;
+
+	ret = xenbus_register_driver_common(drv, &xenbus_frontend,
+					    owner, mod_name);
+	if (ret)
+		return ret;
+
+	/* If this driver is loaded as a module wait for devices to attach. */
+	wait_for_devices(drv);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__xenbus_register_frontend);
+
+static int __init xenbus_probe_frontend_init(void)
+{
+	int err;
+
+	DPRINTK("");
+
+	/* Register ourselves with the kernel bus subsystem */
+	err = bus_register(&xenbus_frontend.bus);
+	if (err) {
+		printk(KERN_CRIT "%s didn't register bus!\n", __func__);
+		return err;
+	}
+	printk(KERN_CRIT "%s bus registered ok\n", __func__);
+
+	if (!xen_initial_domain()) {
+		/* Enumerate devices in xenstore and watch for changes. */
+		xenbus_probe_devices(&xenbus_frontend);
+		printk(KERN_CRIT "%s devices probed ok\n", __func__);
+		register_xenbus_watch(&fe_watch);
+		printk(KERN_CRIT "%s watch add ok ok\n", __func__);
+		printk(KERN_CRIT "%s all done\n", __func__);
+	}
+
+	return 0;
+}
+
+module_init(xenbus_probe_frontend_init);
+
+#ifndef MODULE
+static int __init boot_wait_for_devices(void)
+{
+	if (xen_hvm_domain() && !xen_platform_pci_unplug)
+		return -ENODEV;
+
+	ready_to_wait_for_devices = 1;
+	wait_for_devices(NULL);
+	return 0;
+}
+
+late_initcall(boot_wait_for_devices);
+#endif