xen: add the Xenbus sysfs and virtual device hotplug driver

This communicates with the machine control software via a registry
residing in a controlling virtual machine. This allows dynamic
creation, destruction and modification of virtual device
configurations (network devices, block devices and CPUS, to name some
examples).

[ Greg, would you mind giving this a review?  Thanks -J ]

Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Greg KH <greg@kroah.com>

1 files changed, 935 insertions, 0 deletions

diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
new file mode 100644
index 000000000000..0b769f7c4a48
--- /dev/null
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -0,0 +1,935 @@
+/******************************************************************************
+ * Talks to Xen Store to figure out what devices we have.
+ *
+ * Copyright (C) 2005 Rusty Russell, IBM Corporation
+ * Copyright (C) 2005 Mike Wray, Hewlett-Packard
+ * Copyright (C) 2005, 2006 XenSource Ltd
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#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/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 "xenbus_comms.h"
+#include "xenbus_probe.h"
+
+int xen_store_evtchn;
+struct xenstore_domain_interface *xen_store_interface;
+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);
+
+/* 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)
+{
+        for (; *arr->devicetype != '\0'; arr++) {
+                if (!strcmp(arr->devicetype, dev->devicetype))
+                        return arr;
+        }
+        return NULL;
+}
+
+int xenbus_match(struct device *_dev, struct device_driver *_drv)
+{
+        struct xenbus_driver *drv = to_xenbus_driver(_drv);
+
+        if (!drv->ids)
+                return 0;
+
+        return match_device(drv->ids, to_xenbus_device(_dev)) != NULL;
+}
+
+/* device/<type>/<id> => <type>-<id> */
+static int frontend_bus_id(char bus_id[BUS_ID_SIZE], const char *nodename)
+{
+        nodename = strchr(nodename, '/');
+        if (!nodename || strlen(nodename + 1) >= BUS_ID_SIZE) {
+                printk(KERN_WARNING "XENBUS: bad frontend %s\n", nodename);
+                return -EINVAL;
+        }
+
+        strlcpy(bus_id, nodename + 1, 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;
+}
+
+
+static void free_otherend_details(struct xenbus_device *dev)
+{
+        kfree(dev->otherend);
+        dev->otherend = NULL;
+}
+
+
+static void free_otherend_watch(struct xenbus_device *dev)
+{
+        if (dev->otherend_watch.node) {
+                unregister_xenbus_watch(&dev->otherend_watch);
+                kfree(dev->otherend_watch.node);
+                dev->otherend_watch.node = NULL;
+        }
+}
+
+
+int read_otherend_details(struct xenbus_device *xendev,
+                                 char *id_node, char *path_node)
+{
+        int err = xenbus_gather(XBT_NIL, xendev->nodename,
+                                id_node, "%i", &xendev->otherend_id,
+                                path_node, NULL, &xendev->otherend,
+                                NULL);
+        if (err) {
+                xenbus_dev_fatal(xendev, err,
+                                 "reading other end details from %s",
+                                 xendev->nodename);
+                return err;
+        }
+        if (strlen(xendev->otherend) == 0 ||
+            !xenbus_exists(XBT_NIL, xendev->otherend, "")) {
+                xenbus_dev_fatal(xendev, -ENOENT,
+                                 "unable to read other end from %s.  "
+                                 "missing or inaccessible.",
+                                 xendev->nodename);
+                free_otherend_details(xendev);
+                return -ENOENT;
+        }
+
+        return 0;
+}
+
+
+static int read_backend_details(struct xenbus_device *xendev)
+{
+        return read_otherend_details(xendev, "backend-id", "backend");
+}
+
+
+/* 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,
+                .probe    = xenbus_dev_probe,
+                .remove   = xenbus_dev_remove,
+                .shutdown = xenbus_dev_shutdown,
+        },
+};
+
+static void otherend_changed(struct xenbus_watch *watch,
+                             const char **vec, unsigned int len)
+{
+        struct xenbus_device *dev =
+                container_of(watch, struct xenbus_device, otherend_watch);
+        struct xenbus_driver *drv = to_xenbus_driver(dev->dev.driver);
+        enum xenbus_state state;
+
+        /* Protect us against watches firing on old details when the otherend
+           details change, say immediately after a resume. */
+        if (!dev->otherend ||
+            strncmp(dev->otherend, vec[XS_WATCH_PATH],
+                    strlen(dev->otherend))) {
+                dev_dbg(&dev->dev, "Ignoring watch at %s", vec[XS_WATCH_PATH]);
+                return;
+        }
+
+        state = xenbus_read_driver_state(dev->otherend);
+
+        dev_dbg(&dev->dev, "state is %d, (%s), %s, %s",
+                state, xenbus_strstate(state), dev->otherend_watch.node,
+                vec[XS_WATCH_PATH]);
+
+        /*
+         * Ignore xenbus transitions during shutdown. This prevents us doing
+         * 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))
+                        xenbus_frontend_closed(dev);
+                return;
+        }
+
+        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");
+}
+
+
+int xenbus_dev_probe(struct device *_dev)
+{
+        struct xenbus_device *dev = to_xenbus_device(_dev);
+        struct xenbus_driver *drv = to_xenbus_driver(_dev->driver);
+        const struct xenbus_device_id *id;
+        int err;
+
+        DPRINTK("%s", dev->nodename);
+
+        if (!drv->probe) {
+                err = -ENODEV;
+                goto fail;
+        }
+
+        id = match_device(drv->ids, dev);
+        if (!id) {
+                err = -ENODEV;
+                goto fail;
+        }
+
+        err = talk_to_otherend(dev);
+        if (err) {
+                dev_warn(&dev->dev, "talk_to_otherend on %s failed.\n",
+                         dev->nodename);
+                return err;
+        }
+
+        err = drv->probe(dev, id);
+        if (err)
+                goto fail;
+
+        err = watch_otherend(dev);
+        if (err) {
+                dev_warn(&dev->dev, "watch_otherend on %s failed.\n",
+                       dev->nodename);
+                return err;
+        }
+
+        return 0;
+fail:
+        xenbus_dev_error(dev, err, "xenbus_dev_probe on %s", dev->nodename);
+        xenbus_switch_state(dev, XenbusStateClosed);
+        return -ENODEV;
+}
+
+int xenbus_dev_remove(struct device *_dev)
+{
+        struct xenbus_device *dev = to_xenbus_device(_dev);
+        struct xenbus_driver *drv = to_xenbus_driver(_dev->driver);
+
+        DPRINTK("%s", dev->nodename);
+
+        free_otherend_watch(dev);
+        free_otherend_details(dev);
+
+        if (drv->remove)
+                drv->remove(dev);
+
+        xenbus_switch_state(dev, XenbusStateClosed);
+        return 0;
+}
+
+static void xenbus_dev_shutdown(struct device *_dev)
+{
+        struct xenbus_device *dev = to_xenbus_device(_dev);
+        unsigned long timeout = 5*HZ;
+
+        DPRINTK("%s", dev->nodename);
+
+        get_device(&dev->dev);
+        if (dev->state != XenbusStateConnected) {
+                printk(KERN_INFO "%s: %s: %s != Connected, skipping\n", __func__,
+                       dev->nodename, xenbus_strstate(dev->state));
+                goto out;
+        }
+        xenbus_switch_state(dev, XenbusStateClosing);
+        timeout = wait_for_completion_timeout(&dev->down, timeout);
+        if (!timeout)
+                printk(KERN_INFO "%s: %s timeout closing device\n",
+                       __func__, dev->nodename);
+ out:
+        put_device(&dev->dev);
+}
+
+int xenbus_register_driver_common(struct xenbus_driver *drv,
+                                  struct xen_bus_type *bus,
+                                  struct module *owner,
+                                  const char *mod_name)
+{
+        drv->driver.name = drv->name;
+        drv->driver.bus = &bus->bus;
+        drv->driver.owner = owner;
+        drv->driver.mod_name = mod_name;
+
+        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);
+
+void xenbus_unregister_driver(struct xenbus_driver *drv)
+{
+        driver_unregister(&drv->driver);
+}
+EXPORT_SYMBOL_GPL(xenbus_unregister_driver);
+
+struct xb_find_info
+{
+        struct xenbus_device *dev;
+        const char *nodename;
+};
+
+static int cmp_dev(struct device *dev, void *data)
+{
+        struct xenbus_device *xendev = to_xenbus_device(dev);
+        struct xb_find_info *info = data;
+
+        if (!strcmp(xendev->nodename, info->nodename)) {
+                info->dev = xendev;
+                get_device(dev);
+                return 1;
+        }
+        return 0;
+}
+
+struct xenbus_device *xenbus_device_find(const char *nodename,
+                                         struct bus_type *bus)
+{
+        struct xb_find_info info = { .dev = NULL, .nodename = nodename };
+
+        bus_for_each_dev(bus, NULL, &info, cmp_dev);
+        return info.dev;
+}
+
+static int cleanup_dev(struct device *dev, void *data)
+{
+        struct xenbus_device *xendev = to_xenbus_device(dev);
+        struct xb_find_info *info = data;
+        int len = strlen(info->nodename);
+
+        DPRINTK("%s", info->nodename);
+
+        /* Match the info->nodename path, or any subdirectory of that path. */
+        if (strncmp(xendev->nodename, info->nodename, len))
+                return 0;
+
+        /* If the node name is longer, ensure it really is a subdirectory. */
+        if ((strlen(xendev->nodename) > len) && (xendev->nodename[len] != '/'))
+                return 0;
+
+        info->dev = xendev;
+        get_device(dev);
+        return 1;
+}
+
+static void xenbus_cleanup_devices(const char *path, struct bus_type *bus)
+{
+        struct xb_find_info info = { .nodename = path };
+
+        do {
+                info.dev = NULL;
+                bus_for_each_dev(bus, NULL, &info, cleanup_dev);
+                if (info.dev) {
+                        device_unregister(&info.dev->dev);
+                        put_device(&info.dev->dev);
+                }
+        } while (info.dev);
+}
+
+static void xenbus_dev_release(struct device *dev)
+{
+        if (dev)
+                kfree(to_xenbus_device(dev));
+}
+
+static ssize_t xendev_show_nodename(struct device *dev,
+                                    struct device_attribute *attr, char *buf)
+{
+        return sprintf(buf, "%s\n", to_xenbus_device(dev)->nodename);
+}
+DEVICE_ATTR(nodename, S_IRUSR | S_IRGRP | S_IROTH, xendev_show_nodename, NULL);
+
+static ssize_t xendev_show_devtype(struct device *dev,
+                                   struct device_attribute *attr, char *buf)
+{
+        return sprintf(buf, "%s\n", to_xenbus_device(dev)->devicetype);
+}
+DEVICE_ATTR(devtype, S_IRUSR | S_IRGRP | S_IROTH, xendev_show_devtype, NULL);
+
+
+int xenbus_probe_node(struct xen_bus_type *bus,
+                      const char *type,
+                      const char *nodename)
+{
+        int err;
+        struct xenbus_device *xendev;
+        size_t stringlen;
+        char *tmpstring;
+
+        enum xenbus_state state = xenbus_read_driver_state(nodename);
+
+        if (state != XenbusStateInitialising) {
+                /* Device is not new, so ignore it.  This can happen if a
+                   device is going away after switching to Closed.  */
+                return 0;
+        }
+
+        stringlen = strlen(nodename) + 1 + strlen(type) + 1;
+        xendev = kzalloc(sizeof(*xendev) + stringlen, GFP_KERNEL);
+        if (!xendev)
+                return -ENOMEM;
+
+        xendev->state = XenbusStateInitialising;
+
+        /* Copy the strings into the extra space. */
+
+        tmpstring = (char *)(xendev + 1);
+        strcpy(tmpstring, nodename);
+        xendev->nodename = tmpstring;
+
+        tmpstring += strlen(tmpstring) + 1;
+        strcpy(tmpstring, type);
+        xendev->devicetype = tmpstring;
+        init_completion(&xendev->down);
+
+        xendev->dev.bus = &bus->bus;
+        xendev->dev.release = xenbus_dev_release;
+
+        err = bus->get_bus_id(xendev->dev.bus_id, xendev->nodename);
+        if (err)
+                goto fail;
+
+        /* Register with generic device framework. */
+        err = device_register(&xendev->dev);
+        if (err)
+                goto fail;
+
+        err = device_create_file(&xendev->dev, &dev_attr_nodename);
+        if (err)
+                goto fail_unregister;
+
+        err = device_create_file(&xendev->dev, &dev_attr_devtype);
+        if (err)
+                goto fail_remove_file;
+
+        return 0;
+fail_remove_file:
+        device_remove_file(&xendev->dev, &dev_attr_nodename);
+fail_unregister:
+        device_unregister(&xendev->dev);
+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;
+}
+
+static int xenbus_probe_device_type(struct xen_bus_type *bus, const char *type)
+{
+        int err = 0;
+        char **dir;
+        unsigned int dir_n = 0;
+        int i;
+
+        dir = xenbus_directory(XBT_NIL, bus->root, type, &dir_n);
+        if (IS_ERR(dir))
+                return PTR_ERR(dir);
+
+        for (i = 0; i < dir_n; i++) {
+                err = bus->probe(type, dir[i]);
+                if (err)
+                        break;
+        }
+        kfree(dir);
+        return err;
+}
+
+int xenbus_probe_devices(struct xen_bus_type *bus)
+{
+        int err = 0;
+        char **dir;
+        unsigned int i, dir_n;
+
+        dir = xenbus_directory(XBT_NIL, bus->root, "", &dir_n);
+        if (IS_ERR(dir))
+                return PTR_ERR(dir);
+
+        for (i = 0; i < dir_n; i++) {
+                err = xenbus_probe_device_type(bus, dir[i]);
+                if (err)
+                        break;
+        }
+        kfree(dir);
+        return err;
+}
+
+static unsigned int char_count(const char *str, char c)
+{
+        unsigned int i, ret = 0;
+
+        for (i = 0; str[i]; i++)
+                if (str[i] == c)
+                        ret++;
+        return ret;
+}
+
+static int strsep_len(const char *str, char c, unsigned int len)
+{
+        unsigned int i;
+
+        for (i = 0; str[i]; i++)
+                if (str[i] == c) {
+                        if (len == 0)
+                                return i;
+                        len--;
+                }
+        return (len == 0) ? i : -ERANGE;
+}
+
+void xenbus_dev_changed(const char *node, struct xen_bus_type *bus)
+{
+        int exists, rootlen;
+        struct xenbus_device *dev;
+        char type[BUS_ID_SIZE];
+        const char *p, *root;
+
+        if (char_count(node, '/') < 2)
+                return;
+
+        exists = xenbus_exists(XBT_NIL, node, "");
+        if (!exists) {
+                xenbus_cleanup_devices(node, &bus->bus);
+                return;
+        }
+
+        /* backend/<type>/... or device/<type>/... */
+        p = strchr(node, '/') + 1;
+        snprintf(type, BUS_ID_SIZE, "%.*s", (int)strcspn(p, "/"), p);
+        type[BUS_ID_SIZE-1] = '\0';
+
+        rootlen = strsep_len(node, '/', bus->levels);
+        if (rootlen < 0)
+                return;
+        root = kasprintf(GFP_KERNEL, "%.*s", rootlen, node);
+        if (!root)
+                return;
+
+        dev = xenbus_device_find(root, &bus->bus);
+        if (!dev)
+                xenbus_probe_node(bus, type, root);
+        else
+                put_device(&dev->dev);
+
+        kfree(root);
+}
+
+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 suspend_dev(struct device *dev, void *data)
+{
+        int err = 0;
+        struct xenbus_driver *drv;
+        struct xenbus_device *xdev;
+
+        DPRINTK("");
+
+        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);
+        if (err)
+                printk(KERN_WARNING
+                       "xenbus: suspend %s failed: %i\n", dev->bus_id, err);
+        return 0;
+}
+
+static int suspend_cancel_dev(struct device *dev, void *data)
+{
+        int err = 0;
+        struct xenbus_driver *drv;
+        struct xenbus_device *xdev;
+
+        DPRINTK("");
+
+        if (dev->driver == NULL)
+                return 0;
+        drv = to_xenbus_driver(dev->driver);
+        xdev = container_of(dev, struct xenbus_device, dev);
+        if (drv->suspend_cancel)
+                err = drv->suspend_cancel(xdev);
+        if (err)
+                printk(KERN_WARNING
+                       "xenbus: suspend_cancel %s failed: %i\n",
+                       dev->bus_id, err);
+        return 0;
+}
+
+static int resume_dev(struct device *dev, void *data)
+{
+        int err;
+        struct xenbus_driver *drv;
+        struct xenbus_device *xdev;
+
+        DPRINTK("");
+
+        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
+                       "xenbus: resume (talk_to_otherend) %s failed: %i\n",
+                       dev->bus_id, err);
+                return err;
+        }
+
+        xdev->state = XenbusStateInitialising;
+
+        if (drv->resume) {
+                err = drv->resume(xdev);
+                if (err) {
+                        printk(KERN_WARNING
+                               "xenbus: resume %s failed: %i\n",
+                               dev->bus_id, err);
+                        return err;
+                }
+        }
+
+        err = watch_otherend(xdev);
+        if (err) {
+                printk(KERN_WARNING
+                       "xenbus_probe: resume (watch_otherend) %s failed: "
+                       "%d.\n", dev->bus_id, err);
+                return err;
+        }
+
+        return 0;
+}
+
+void xenbus_suspend(void)
+{
+        DPRINTK("");
+
+        bus_for_each_dev(&xenbus_frontend.bus, NULL, NULL, suspend_dev);
+        xenbus_backend_suspend(suspend_dev);
+        xs_suspend();
+}
+EXPORT_SYMBOL_GPL(xenbus_suspend);
+
+void xenbus_resume(void)
+{
+        xb_init_comms();
+        xs_resume();
+        bus_for_each_dev(&xenbus_frontend.bus, NULL, NULL, resume_dev);
+        xenbus_backend_resume(resume_dev);
+}
+EXPORT_SYMBOL_GPL(xenbus_resume);
+
+void xenbus_suspend_cancel(void)
+{
+        xs_suspend_cancel();
+        bus_for_each_dev(&xenbus_frontend.bus, NULL, NULL, suspend_cancel_dev);
+        xenbus_backend_resume(suspend_cancel_dev);
+}
+EXPORT_SYMBOL_GPL(xenbus_suspend_cancel);
+
+/* A flag to determine if xenstored is 'ready' (i.e. has started) */
+int xenstored_ready = 0;
+
+
+int register_xenstore_notifier(struct notifier_block *nb)
+{
+        int ret = 0;
+
+        if (xenstored_ready > 0)
+                ret = nb->notifier_call(nb, 0, NULL);
+        else
+                blocking_notifier_chain_register(&xenstore_chain, nb);
+
+        return ret;
+}
+EXPORT_SYMBOL_GPL(register_xenstore_notifier);
+
+void unregister_xenstore_notifier(struct notifier_block *nb)
+{
+        blocking_notifier_chain_unregister(&xenstore_chain, nb);
+}
+EXPORT_SYMBOL_GPL(unregister_xenstore_notifier);
+
+void xenbus_probe(struct work_struct *unused)
+{
+        BUG_ON((xenstored_ready <= 0));
+
+        /* 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);
+}
+
+static int __init xenbus_probe_init(void)
+{
+        int err = 0;
+
+        DPRINTK("");
+
+        err = -ENODEV;
+        if (!is_running_on_xen())
+                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.
+         */
+        if (is_initial_xendomain()) {
+                /* dom0 not yet supported */
+        } else {
+                xenstored_ready = 1;
+                xen_store_evtchn = xen_start_info->store_evtchn;
+                xen_store_mfn = xen_start_info->store_mfn;
+        }
+        xen_store_interface = mfn_to_virt(xen_store_mfn);
+
+        /* Initialize the interface to xenstore. */
+        err = xs_init();
+        if (err) {
+                printk(KERN_WARNING
+                       "XENBUS: Error initializing xenstore comms: %i\n", err);
+                goto out_unreg_back;
+        }
+
+        if (!is_initial_xendomain())
+                xenbus_probe(NULL);
+
+        return 0;
+
+  out_unreg_back:
+        xenbus_backend_bus_unregister();
+
+  out_unreg_front:
+        bus_unregister(&xenbus_frontend.bus);
+
+  out_error:
+        return err;
+}
+
+postcore_initcall(xenbus_probe_init);
+
+MODULE_LICENSE("GPL");
+
+static int is_disconnected_device(struct device *dev, void *data)
+{
+        struct xenbus_device *xendev = to_xenbus_device(dev);
+        struct device_driver *drv = data;
+
+        /*
+         * 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;
+
+        return (xendev->state != XenbusStateConnected);
+}
+
+static int exists_disconnected_device(struct device_driver *drv)
+{
+        return bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
+                                is_disconnected_device);
+}
+
+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) {
+                printk(KERN_WARNING "XENBUS: Timeout connecting "
+                       "to device: %s (state %d)\n",
+                       xendev->nodename, xendev->state);
+        }
+
+        return 0;
+}
+
+/* We only wait for device setup after most initcalls have run. */
+static int ready_to_wait_for_devices;
+
+/*
+ * On a 10 second 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 timeout = jiffies + 10*HZ;
+        struct device_driver *drv = xendrv ? &xendrv->driver : NULL;
+
+        if (!ready_to_wait_for_devices || !is_running_on_xen())
+                return;
+
+        while (exists_disconnected_device(drv)) {
+                if (time_after(jiffies, timeout))
+                        break;
+                schedule_timeout_interruptible(HZ/10);
+        }
+
+        bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
+                         print_device_status);
+}
+
+#ifndef MODULE
+static int __init boot_wait_for_devices(void)
+{
+        ready_to_wait_for_devices = 1;
+        wait_for_devices(NULL);
+        return 0;
+}
+
+late_initcall(boot_wait_for_devices);
+#endif