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>

8 files changed, 2726 insertions, 0 deletions

diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index eb42b521eef9..56592f0d6cef 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -1 +1,2 @@
 obj-y   += grant-table.o
+obj-y   += xenbus/
diff --git a/drivers/xen/xenbus/Makefile b/drivers/xen/xenbus/Makefile
new file mode 100644
index 000000000000..5571f5b84223
--- /dev/null
+++ b/drivers/xen/xenbus/Makefile
@@ -0,0 +1,7 @@
+obj-y   += xenbus.o
+
+xenbus-objs =
+xenbus-objs += xenbus_client.o
+xenbus-objs += xenbus_comms.o
+xenbus-objs += xenbus_xs.o
+xenbus-objs += xenbus_probe.o
diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
new file mode 100644
index 000000000000..9fd2f70ab46d
--- /dev/null
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -0,0 +1,569 @@
+/******************************************************************************
+ * Client-facing interface for the Xenbus driver.  In other words, the
+ * interface between the Xenbus and the device-specific code, be it the
+ * frontend or the backend of that driver.
+ *
+ * Copyright (C) 2005 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.
+ */
+
+#include <linux/types.h>
+#include <linux/vmalloc.h>
+#include <asm/xen/hypervisor.h>
+#include <xen/interface/xen.h>
+#include <xen/interface/event_channel.h>
+#include <xen/events.h>
+#include <xen/grant_table.h>
+#include <xen/xenbus.h>
+
+const char *xenbus_strstate(enum xenbus_state state)
+{
+        static const char *const name[] = {
+                [ XenbusStateUnknown      ] = "Unknown",
+                [ XenbusStateInitialising ] = "Initialising",
+                [ XenbusStateInitWait     ] = "InitWait",
+                [ XenbusStateInitialised  ] = "Initialised",
+                [ XenbusStateConnected    ] = "Connected",
+                [ XenbusStateClosing      ] = "Closing",
+                [ XenbusStateClosed       ] = "Closed",
+        };
+        return (state < ARRAY_SIZE(name)) ? name[state] : "INVALID";
+}
+EXPORT_SYMBOL_GPL(xenbus_strstate);
+
+/**
+ * xenbus_watch_path - register a watch
+ * @dev: xenbus device
+ * @path: path to watch
+ * @watch: watch to register
+ * @callback: callback to register
+ *
+ * Register a @watch on the given path, using the given xenbus_watch structure
+ * for storage, and the given @callback function as the callback.  Return 0 on
+ * success, or -errno on error.  On success, the given @path will be saved as
+ * @watch->node, and remains the caller's to free.  On error, @watch->node will
+ * be NULL, the device will switch to %XenbusStateClosing, and the error will
+ * be saved in the store.
+ */
+int xenbus_watch_path(struct xenbus_device *dev, const char *path,
+                      struct xenbus_watch *watch,
+                      void (*callback)(struct xenbus_watch *,
+                                       const char **, unsigned int))
+{
+        int err;
+
+        watch->node = path;
+        watch->callback = callback;
+
+        err = register_xenbus_watch(watch);
+
+        if (err) {
+                watch->node = NULL;
+                watch->callback = NULL;
+                xenbus_dev_fatal(dev, err, "adding watch on %s", path);
+        }
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(xenbus_watch_path);
+
+
+/**
+ * xenbus_watch_pathfmt - register a watch on a sprintf-formatted path
+ * @dev: xenbus device
+ * @watch: watch to register
+ * @callback: callback to register
+ * @pathfmt: format of path to watch
+ *
+ * Register a watch on the given @path, using the given xenbus_watch
+ * structure for storage, and the given @callback function as the callback.
+ * Return 0 on success, or -errno on error.  On success, the watched path
+ * (@path/@path2) will be saved as @watch->node, and becomes the caller's to
+ * kfree().  On error, watch->node will be NULL, so the caller has nothing to
+ * free, the device will switch to %XenbusStateClosing, and the error will be
+ * saved in the store.
+ */
+int xenbus_watch_pathfmt(struct xenbus_device *dev,
+                         struct xenbus_watch *watch,
+                         void (*callback)(struct xenbus_watch *,
+                                        const char **, unsigned int),
+                         const char *pathfmt, ...)
+{
+        int err;
+        va_list ap;
+        char *path;
+
+        va_start(ap, pathfmt);
+        path = kvasprintf(GFP_KERNEL, pathfmt, ap);
+        va_end(ap);
+
+        if (!path) {
+                xenbus_dev_fatal(dev, -ENOMEM, "allocating path for watch");
+                return -ENOMEM;
+        }
+        err = xenbus_watch_path(dev, path, watch, callback);
+
+        if (err)
+                kfree(path);
+        return err;
+}
+EXPORT_SYMBOL_GPL(xenbus_watch_pathfmt);
+
+
+/**
+ * xenbus_switch_state
+ * @dev: xenbus device
+ * @xbt: transaction handle
+ * @state: new state
+ *
+ * Advertise in the store a change of the given driver to the given new_state.
+ * Return 0 on success, or -errno on error.  On error, the device will switch
+ * to XenbusStateClosing, and the error will be saved in the store.
+ */
+int xenbus_switch_state(struct xenbus_device *dev, enum xenbus_state state)
+{
+        /* We check whether the state is currently set to the given value, and
+           if not, then the state is set.  We don't want to unconditionally
+           write the given state, because we don't want to fire watches
+           unnecessarily.  Furthermore, if the node has gone, we don't write
+           to it, as the device will be tearing down, and we don't want to
+           resurrect that directory.
+
+           Note that, because of this cached value of our state, this function
+           will not work inside a Xenstore transaction (something it was
+           trying to in the past) because dev->state would not get reset if
+           the transaction was aborted.
+
+         */
+
+        int current_state;
+        int err;
+
+        if (state == dev->state)
+                return 0;
+
+        err = xenbus_scanf(XBT_NIL, dev->nodename, "state", "%d",
+                           &current_state);
+        if (err != 1)
+                return 0;
+
+        err = xenbus_printf(XBT_NIL, dev->nodename, "state", "%d", state);
+        if (err) {
+                if (state != XenbusStateClosing) /* Avoid looping */
+                        xenbus_dev_fatal(dev, err, "writing new state");
+                return err;
+        }
+
+        dev->state = state;
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(xenbus_switch_state);
+
+int xenbus_frontend_closed(struct xenbus_device *dev)
+{
+        xenbus_switch_state(dev, XenbusStateClosed);
+        complete(&dev->down);
+        return 0;
+}
+EXPORT_SYMBOL_GPL(xenbus_frontend_closed);
+
+/**
+ * Return the path to the error node for the given device, or NULL on failure.
+ * If the value returned is non-NULL, then it is the caller's to kfree.
+ */
+static char *error_path(struct xenbus_device *dev)
+{
+        return kasprintf(GFP_KERNEL, "error/%s", dev->nodename);
+}
+
+
+static void xenbus_va_dev_error(struct xenbus_device *dev, int err,
+                                const char *fmt, va_list ap)
+{
+        int ret;
+        unsigned int len;
+        char *printf_buffer = NULL;
+        char *path_buffer = NULL;
+
+#define PRINTF_BUFFER_SIZE 4096
+        printf_buffer = kmalloc(PRINTF_BUFFER_SIZE, GFP_KERNEL);
+        if (printf_buffer == NULL)
+                goto fail;
+
+        len = sprintf(printf_buffer, "%i ", -err);
+        ret = vsnprintf(printf_buffer+len, PRINTF_BUFFER_SIZE-len, fmt, ap);
+
+        BUG_ON(len + ret > PRINTF_BUFFER_SIZE-1);
+
+        dev_err(&dev->dev, "%s\n", printf_buffer);
+
+        path_buffer = error_path(dev);
+
+        if (path_buffer == NULL) {
+                dev_err(&dev->dev, "failed to write error node for %s (%s)\n",
+                       dev->nodename, printf_buffer);
+                goto fail;
+        }
+
+        if (xenbus_write(XBT_NIL, path_buffer, "error", printf_buffer) != 0) {
+                dev_err(&dev->dev, "failed to write error node for %s (%s)\n",
+                       dev->nodename, printf_buffer);
+                goto fail;
+        }
+
+fail:
+        kfree(printf_buffer);
+        kfree(path_buffer);
+}
+
+
+/**
+ * xenbus_dev_error
+ * @dev: xenbus device
+ * @err: error to report
+ * @fmt: error message format
+ *
+ * Report the given negative errno into the store, along with the given
+ * formatted message.
+ */
+void xenbus_dev_error(struct xenbus_device *dev, int err, const char *fmt, ...)
+{
+        va_list ap;
+
+        va_start(ap, fmt);
+        xenbus_va_dev_error(dev, err, fmt, ap);
+        va_end(ap);
+}
+EXPORT_SYMBOL_GPL(xenbus_dev_error);
+
+/**
+ * xenbus_dev_fatal
+ * @dev: xenbus device
+ * @err: error to report
+ * @fmt: error message format
+ *
+ * Equivalent to xenbus_dev_error(dev, err, fmt, args), followed by
+ * xenbus_switch_state(dev, NULL, XenbusStateClosing) to schedule an orderly
+ * closedown of this driver and its peer.
+ */
+
+void xenbus_dev_fatal(struct xenbus_device *dev, int err, const char *fmt, ...)
+{
+        va_list ap;
+
+        va_start(ap, fmt);
+        xenbus_va_dev_error(dev, err, fmt, ap);
+        va_end(ap);
+
+        xenbus_switch_state(dev, XenbusStateClosing);
+}
+EXPORT_SYMBOL_GPL(xenbus_dev_fatal);
+
+/**
+ * xenbus_grant_ring
+ * @dev: xenbus device
+ * @ring_mfn: mfn of ring to grant
+
+ * Grant access to the given @ring_mfn to the peer of the given device.  Return
+ * 0 on success, or -errno on error.  On error, the device will switch to
+ * XenbusStateClosing, and the error will be saved in the store.
+ */
+int xenbus_grant_ring(struct xenbus_device *dev, unsigned long ring_mfn)
+{
+        int err = gnttab_grant_foreign_access(dev->otherend_id, ring_mfn, 0);
+        if (err < 0)
+                xenbus_dev_fatal(dev, err, "granting access to ring page");
+        return err;
+}
+EXPORT_SYMBOL_GPL(xenbus_grant_ring);
+
+
+/**
+ * Allocate an event channel for the given xenbus_device, assigning the newly
+ * created local port to *port.  Return 0 on success, or -errno on error.  On
+ * error, the device will switch to XenbusStateClosing, and the error will be
+ * saved in the store.
+ */
+int xenbus_alloc_evtchn(struct xenbus_device *dev, int *port)
+{
+        struct evtchn_alloc_unbound alloc_unbound;
+        int err;
+
+        alloc_unbound.dom = DOMID_SELF;
+        alloc_unbound.remote_dom = dev->otherend_id;
+
+        err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound,
+                                          &alloc_unbound);
+        if (err)
+                xenbus_dev_fatal(dev, err, "allocating event channel");
+        else
+                *port = alloc_unbound.port;
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(xenbus_alloc_evtchn);
+
+
+/**
+ * Bind to an existing interdomain event channel in another domain. Returns 0
+ * on success and stores the local port in *port. On error, returns -errno,
+ * switches the device to XenbusStateClosing, and saves the error in XenStore.
+ */
+int xenbus_bind_evtchn(struct xenbus_device *dev, int remote_port, int *port)
+{
+        struct evtchn_bind_interdomain bind_interdomain;
+        int err;
+
+        bind_interdomain.remote_dom = dev->otherend_id;
+        bind_interdomain.remote_port = remote_port;
+
+        err = HYPERVISOR_event_channel_op(EVTCHNOP_bind_interdomain,
+                                          &bind_interdomain);
+        if (err)
+                xenbus_dev_fatal(dev, err,
+                                 "binding to event channel %d from domain %d",
+                                 remote_port, dev->otherend_id);
+        else
+                *port = bind_interdomain.local_port;
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(xenbus_bind_evtchn);
+
+
+/**
+ * Free an existing event channel. Returns 0 on success or -errno on error.
+ */
+int xenbus_free_evtchn(struct xenbus_device *dev, int port)
+{
+        struct evtchn_close close;
+        int err;
+
+        close.port = port;
+
+        err = HYPERVISOR_event_channel_op(EVTCHNOP_close, &close);
+        if (err)
+                xenbus_dev_error(dev, err, "freeing event channel %d", port);
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(xenbus_free_evtchn);
+
+
+/**
+ * xenbus_map_ring_valloc
+ * @dev: xenbus device
+ * @gnt_ref: grant reference
+ * @vaddr: pointer to address to be filled out by mapping
+ *
+ * Based on Rusty Russell's skeleton driver's map_page.
+ * Map a page of memory into this domain from another domain's grant table.
+ * xenbus_map_ring_valloc allocates a page of virtual address space, maps the
+ * page to that address, and sets *vaddr to that address.
+ * Returns 0 on success, and GNTST_* (see xen/include/interface/grant_table.h)
+ * or -ENOMEM on error. If an error is returned, device will switch to
+ * XenbusStateClosing and the error message will be saved in XenStore.
+ */
+int xenbus_map_ring_valloc(struct xenbus_device *dev, int gnt_ref, void **vaddr)
+{
+        struct gnttab_map_grant_ref op = {
+                .flags = GNTMAP_host_map,
+                .ref   = gnt_ref,
+                .dom   = dev->otherend_id,
+        };
+        struct vm_struct *area;
+
+        *vaddr = NULL;
+
+        area = alloc_vm_area(PAGE_SIZE);
+        if (!area)
+                return -ENOMEM;
+
+        op.host_addr = (unsigned long)area->addr;
+
+        if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
+                BUG();
+
+        if (op.status != GNTST_okay) {
+                free_vm_area(area);
+                xenbus_dev_fatal(dev, op.status,
+                                 "mapping in shared page %d from domain %d",
+                                 gnt_ref, dev->otherend_id);
+                return op.status;
+        }
+
+        /* Stuff the handle in an unused field */
+        area->phys_addr = (unsigned long)op.handle;
+
+        *vaddr = area->addr;
+        return 0;
+}
+EXPORT_SYMBOL_GPL(xenbus_map_ring_valloc);
+
+
+/**
+ * xenbus_map_ring
+ * @dev: xenbus device
+ * @gnt_ref: grant reference
+ * @handle: pointer to grant handle to be filled
+ * @vaddr: address to be mapped to
+ *
+ * Map a page of memory into this domain from another domain's grant table.
+ * xenbus_map_ring does not allocate the virtual address space (you must do
+ * this yourself!). It only maps in the page to the specified address.
+ * Returns 0 on success, and GNTST_* (see xen/include/interface/grant_table.h)
+ * or -ENOMEM on error. If an error is returned, device will switch to
+ * XenbusStateClosing and the error message will be saved in XenStore.
+ */
+int xenbus_map_ring(struct xenbus_device *dev, int gnt_ref,
+                    grant_handle_t *handle, void *vaddr)
+{
+        struct gnttab_map_grant_ref op = {
+                .host_addr = (unsigned long)vaddr,
+                .flags     = GNTMAP_host_map,
+                .ref       = gnt_ref,
+                .dom       = dev->otherend_id,
+        };
+
+        if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
+                BUG();
+
+        if (op.status != GNTST_okay) {
+                xenbus_dev_fatal(dev, op.status,
+                                 "mapping in shared page %d from domain %d",
+                                 gnt_ref, dev->otherend_id);
+        } else
+                *handle = op.handle;
+
+        return op.status;
+}
+EXPORT_SYMBOL_GPL(xenbus_map_ring);
+
+
+/**
+ * xenbus_unmap_ring_vfree
+ * @dev: xenbus device
+ * @vaddr: addr to unmap
+ *
+ * Based on Rusty Russell's skeleton driver's unmap_page.
+ * Unmap a page of memory in this domain that was imported from another domain.
+ * Use xenbus_unmap_ring_vfree if you mapped in your memory with
+ * xenbus_map_ring_valloc (it will free the virtual address space).
+ * Returns 0 on success and returns GNTST_* on error
+ * (see xen/include/interface/grant_table.h).
+ */
+int xenbus_unmap_ring_vfree(struct xenbus_device *dev, void *vaddr)
+{
+        struct vm_struct *area;
+        struct gnttab_unmap_grant_ref op = {
+                .host_addr = (unsigned long)vaddr,
+        };
+
+        /* It'd be nice if linux/vmalloc.h provided a find_vm_area(void *addr)
+         * method so that we don't have to muck with vmalloc internals here.
+         * We could force the user to hang on to their struct vm_struct from
+         * xenbus_map_ring_valloc, but these 6 lines considerably simplify
+         * this API.
+         */
+        read_lock(&vmlist_lock);
+        for (area = vmlist; area != NULL; area = area->next) {
+                if (area->addr == vaddr)
+                        break;
+        }
+        read_unlock(&vmlist_lock);
+
+        if (!area) {
+                xenbus_dev_error(dev, -ENOENT,
+                                 "can't find mapped virtual address %p", vaddr);
+                return GNTST_bad_virt_addr;
+        }
+
+        op.handle = (grant_handle_t)area->phys_addr;
+
+        if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, &op, 1))
+                BUG();
+
+        if (op.status == GNTST_okay)
+                free_vm_area(area);
+        else
+                xenbus_dev_error(dev, op.status,
+                                 "unmapping page at handle %d error %d",
+                                 (int16_t)area->phys_addr, op.status);
+
+        return op.status;
+}
+EXPORT_SYMBOL_GPL(xenbus_unmap_ring_vfree);
+
+
+/**
+ * xenbus_unmap_ring
+ * @dev: xenbus device
+ * @handle: grant handle
+ * @vaddr: addr to unmap
+ *
+ * Unmap a page of memory in this domain that was imported from another domain.
+ * Returns 0 on success and returns GNTST_* on error
+ * (see xen/include/interface/grant_table.h).
+ */
+int xenbus_unmap_ring(struct xenbus_device *dev,
+                      grant_handle_t handle, void *vaddr)
+{
+        struct gnttab_unmap_grant_ref op = {
+                .host_addr = (unsigned long)vaddr,
+                .handle    = handle,
+        };
+
+        if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, &op, 1))
+                BUG();
+
+        if (op.status != GNTST_okay)
+                xenbus_dev_error(dev, op.status,
+                                 "unmapping page at handle %d error %d",
+                                 handle, op.status);
+
+        return op.status;
+}
+EXPORT_SYMBOL_GPL(xenbus_unmap_ring);
+
+
+/**
+ * xenbus_read_driver_state
+ * @path: path for driver
+ *
+ * Return the state of the driver rooted at the given store path, or
+ * XenbusStateUnknown if no state can be read.
+ */
+enum xenbus_state xenbus_read_driver_state(const char *path)
+{
+        enum xenbus_state result;
+        int err = xenbus_gather(XBT_NIL, path, "state", "%d", &result, NULL);
+        if (err)
+                result = XenbusStateUnknown;
+
+        return result;
+}
+EXPORT_SYMBOL_GPL(xenbus_read_driver_state);
diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
new file mode 100644
index 000000000000..6efbe3f29ca5
--- /dev/null
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -0,0 +1,233 @@
+/******************************************************************************
+ * xenbus_comms.c
+ *
+ * Low level code to talks to Xen Store: ringbuffer and event channel.
+ *
+ * Copyright (C) 2005 Rusty Russell, IBM Corporation
+ *
+ * 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.
+ */
+
+#include <linux/wait.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <linux/err.h>
+#include <xen/xenbus.h>
+#include <asm/xen/hypervisor.h>
+#include <xen/events.h>
+#include <xen/page.h>
+#include "xenbus_comms.h"
+
+static int xenbus_irq;
+
+static DECLARE_WORK(probe_work, xenbus_probe);
+
+static DECLARE_WAIT_QUEUE_HEAD(xb_waitq);
+
+static irqreturn_t wake_waiting(int irq, void *unused)
+{
+        if (unlikely(xenstored_ready == 0)) {
+                xenstored_ready = 1;
+                schedule_work(&probe_work);
+        }
+
+        wake_up(&xb_waitq);
+        return IRQ_HANDLED;
+}
+
+static int check_indexes(XENSTORE_RING_IDX cons, XENSTORE_RING_IDX prod)
+{
+        return ((prod - cons) <= XENSTORE_RING_SIZE);
+}
+
+static void *get_output_chunk(XENSTORE_RING_IDX cons,
+                              XENSTORE_RING_IDX prod,
+                              char *buf, uint32_t *len)
+{
+        *len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(prod);
+        if ((XENSTORE_RING_SIZE - (prod - cons)) < *len)
+                *len = XENSTORE_RING_SIZE - (prod - cons);
+        return buf + MASK_XENSTORE_IDX(prod);
+}
+
+static const void *get_input_chunk(XENSTORE_RING_IDX cons,
+                                   XENSTORE_RING_IDX prod,
+                                   const char *buf, uint32_t *len)
+{
+        *len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(cons);
+        if ((prod - cons) < *len)
+                *len = prod - cons;
+        return buf + MASK_XENSTORE_IDX(cons);
+}
+
+/**
+ * xb_write - low level write
+ * @data: buffer to send
+ * @len: length of buffer
+ *
+ * Returns 0 on success, error otherwise.
+ */
+int xb_write(const void *data, unsigned len)
+{
+        struct xenstore_domain_interface *intf = xen_store_interface;
+        XENSTORE_RING_IDX cons, prod;
+        int rc;
+
+        while (len != 0) {
+                void *dst;
+                unsigned int avail;
+
+                rc = wait_event_interruptible(
+                        xb_waitq,
+                        (intf->req_prod - intf->req_cons) !=
+                        XENSTORE_RING_SIZE);
+                if (rc < 0)
+                        return rc;
+
+                /* Read indexes, then verify. */
+                cons = intf->req_cons;
+                prod = intf->req_prod;
+                if (!check_indexes(cons, prod)) {
+                        intf->req_cons = intf->req_prod = 0;
+                        return -EIO;
+                }
+
+                dst = get_output_chunk(cons, prod, intf->req, &avail);
+                if (avail == 0)
+                        continue;
+                if (avail > len)
+                        avail = len;
+
+                /* Must write data /after/ reading the consumer index. */
+                mb();
+
+                memcpy(dst, data, avail);
+                data += avail;
+                len -= avail;
+
+                /* Other side must not see new producer until data is there. */
+                wmb();
+                intf->req_prod += avail;
+
+                /* Implies mb(): other side will see the updated producer. */
+                notify_remote_via_evtchn(xen_store_evtchn);
+        }
+
+        return 0;
+}
+
+int xb_data_to_read(void)
+{
+        struct xenstore_domain_interface *intf = xen_store_interface;
+        return (intf->rsp_cons != intf->rsp_prod);
+}
+
+int xb_wait_for_data_to_read(void)
+{
+        return wait_event_interruptible(xb_waitq, xb_data_to_read());
+}
+
+int xb_read(void *data, unsigned len)
+{
+        struct xenstore_domain_interface *intf = xen_store_interface;
+        XENSTORE_RING_IDX cons, prod;
+        int rc;
+
+        while (len != 0) {
+                unsigned int avail;
+                const char *src;
+
+                rc = xb_wait_for_data_to_read();
+                if (rc < 0)
+                        return rc;
+
+                /* Read indexes, then verify. */
+                cons = intf->rsp_cons;
+                prod = intf->rsp_prod;
+                if (!check_indexes(cons, prod)) {
+                        intf->rsp_cons = intf->rsp_prod = 0;
+                        return -EIO;
+                }
+
+                src = get_input_chunk(cons, prod, intf->rsp, &avail);
+                if (avail == 0)
+                        continue;
+                if (avail > len)
+                        avail = len;
+
+                /* Must read data /after/ reading the producer index. */
+                rmb();
+
+                memcpy(data, src, avail);
+                data += avail;
+                len -= avail;
+
+                /* Other side must not see free space until we've copied out */
+                mb();
+                intf->rsp_cons += avail;
+
+                pr_debug("Finished read of %i bytes (%i to go)\n", avail, len);
+
+                /* Implies mb(): other side will see the updated consumer. */
+                notify_remote_via_evtchn(xen_store_evtchn);
+        }
+
+        return 0;
+}
+
+/**
+ * xb_init_comms - Set up interrupt handler off store event channel.
+ */
+int xb_init_comms(void)
+{
+        struct xenstore_domain_interface *intf = xen_store_interface;
+        int err;
+
+        if (intf->req_prod != intf->req_cons)
+                printk(KERN_ERR "XENBUS request ring is not quiescent "
+                       "(%08x:%08x)!\n", intf->req_cons, intf->req_prod);
+
+        if (intf->rsp_prod != intf->rsp_cons) {
+                printk(KERN_WARNING "XENBUS response ring is not quiescent "
+                       "(%08x:%08x): fixing up\n",
+                       intf->rsp_cons, intf->rsp_prod);
+                intf->rsp_cons = intf->rsp_prod;
+        }
+
+        if (xenbus_irq)
+                unbind_from_irqhandler(xenbus_irq, &xb_waitq);
+
+        err = bind_evtchn_to_irqhandler(
+                xen_store_evtchn, wake_waiting,
+                0, "xenbus", &xb_waitq);
+        if (err <= 0) {
+                printk(KERN_ERR "XENBUS request irq failed %i\n", err);
+                return err;
+        }
+
+        xenbus_irq = err;
+
+        return 0;
+}
diff --git a/drivers/xen/xenbus/xenbus_comms.h b/drivers/xen/xenbus/xenbus_comms.h
new file mode 100644
index 000000000000..c21db7513736
--- /dev/null
+++ b/drivers/xen/xenbus/xenbus_comms.h
@@ -0,0 +1,46 @@
+/*
+ * Private include for xenbus communications.
+ *
+ * Copyright (C) 2005 Rusty Russell, IBM Corporation
+ *
+ * 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.
+ */
+
+#ifndef _XENBUS_COMMS_H
+#define _XENBUS_COMMS_H
+
+int xs_init(void);
+int xb_init_comms(void);
+
+/* Low level routines. */
+int xb_write(const void *data, unsigned len);
+int xb_read(void *data, unsigned len);
+int xb_data_to_read(void);
+int xb_wait_for_data_to_read(void);
+int xs_input_avail(void);
+extern struct xenstore_domain_interface *xen_store_interface;
+extern int xen_store_evtchn;
+
+#endif /* _XENBUS_COMMS_H */
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
diff --git a/drivers/xen/xenbus/xenbus_probe.h b/drivers/xen/xenbus/xenbus_probe.h
new file mode 100644
index 000000000000..e09b19415a40
--- /dev/null
+++ b/drivers/xen/xenbus/xenbus_probe.h
@@ -0,0 +1,74 @@
+/******************************************************************************
+ * xenbus_probe.h
+ *
+ * Talks to Xen Store to figure out what devices we have.
+ *
+ * Copyright (C) 2005 Rusty Russell, IBM Corporation
+ * Copyright (C) 2005 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.
+ */
+
+#ifndef _XENBUS_PROBE_H
+#define _XENBUS_PROBE_H
+
+#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[BUS_ID_SIZE], const char *nodename);
+        int (*probe)(const char *type, const char *dir);
+        struct bus_type bus;
+};
+
+extern int xenbus_match(struct device *_dev, struct device_driver *_drv);
+extern int xenbus_dev_probe(struct device *_dev);
+extern int xenbus_dev_remove(struct device *_dev);
+extern int xenbus_register_driver_common(struct xenbus_driver *drv,
+                                         struct xen_bus_type *bus,
+                                         struct module *owner,
+                                         const char *mod_name);
+extern int xenbus_probe_node(struct xen_bus_type *bus,
+                             const char *type,
+                             const char *nodename);
+extern int xenbus_probe_devices(struct xen_bus_type *bus);
+
+extern void xenbus_dev_changed(const char *node, struct xen_bus_type *bus);
+
+#endif
diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
new file mode 100644
index 000000000000..9e943fbce81b
--- /dev/null
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -0,0 +1,861 @@
+/******************************************************************************
+ * xenbus_xs.c
+ *
+ * This is the kernel equivalent of the "xs" library.  We don't need everything
+ * and we use xenbus_comms for communication.
+ *
+ * Copyright (C) 2005 Rusty Russell, IBM Corporation
+ *
+ * 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.
+ */
+
+#include <linux/unistd.h>
+#include <linux/errno.h>
+#include <linux/types.h>
+#include <linux/uio.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/fcntl.h>
+#include <linux/kthread.h>
+#include <linux/rwsem.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <xen/xenbus.h>
+#include "xenbus_comms.h"
+
+struct xs_stored_msg {
+        struct list_head list;
+
+        struct xsd_sockmsg hdr;
+
+        union {
+                /* Queued replies. */
+                struct {
+                        char *body;
+                } reply;
+
+                /* Queued watch events. */
+                struct {
+                        struct xenbus_watch *handle;
+                        char **vec;
+                        unsigned int vec_size;
+                } watch;
+        } u;
+};
+
+struct xs_handle {
+        /* A list of replies. Currently only one will ever be outstanding. */
+        struct list_head reply_list;
+        spinlock_t reply_lock;
+        wait_queue_head_t reply_waitq;
+
+        /*
+         * Mutex ordering: transaction_mutex -> watch_mutex -> request_mutex.
+         * response_mutex is never taken simultaneously with the other three.
+         */
+
+        /* One request at a time. */
+        struct mutex request_mutex;
+
+        /* Protect xenbus reader thread against save/restore. */
+        struct mutex response_mutex;
+
+        /* Protect transactions against save/restore. */
+        struct rw_semaphore transaction_mutex;
+
+        /* Protect watch (de)register against save/restore. */
+        struct rw_semaphore watch_mutex;
+};
+
+static struct xs_handle xs_state;
+
+/* List of registered watches, and a lock to protect it. */
+static LIST_HEAD(watches);
+static DEFINE_SPINLOCK(watches_lock);
+
+/* List of pending watch callback events, and a lock to protect it. */
+static LIST_HEAD(watch_events);
+static DEFINE_SPINLOCK(watch_events_lock);
+
+/*
+ * Details of the xenwatch callback kernel thread. The thread waits on the
+ * watch_events_waitq for work to do (queued on watch_events list). When it
+ * wakes up it acquires the xenwatch_mutex before reading the list and
+ * carrying out work.
+ */
+static pid_t xenwatch_pid;
+static DEFINE_MUTEX(xenwatch_mutex);
+static DECLARE_WAIT_QUEUE_HEAD(watch_events_waitq);
+
+static int get_error(const char *errorstring)
+{
+        unsigned int i;
+
+        for (i = 0; strcmp(errorstring, xsd_errors[i].errstring) != 0; i++) {
+                if (i == ARRAY_SIZE(xsd_errors) - 1) {
+                        printk(KERN_WARNING
+                               "XENBUS xen store gave: unknown error %s",
+                               errorstring);
+                        return EINVAL;
+                }
+        }
+        return xsd_errors[i].errnum;
+}
+
+static void *read_reply(enum xsd_sockmsg_type *type, unsigned int *len)
+{
+        struct xs_stored_msg *msg;
+        char *body;
+
+        spin_lock(&xs_state.reply_lock);
+
+        while (list_empty(&xs_state.reply_list)) {
+                spin_unlock(&xs_state.reply_lock);
+                /* XXX FIXME: Avoid synchronous wait for response here. */
+                wait_event(xs_state.reply_waitq,
+                           !list_empty(&xs_state.reply_list));
+                spin_lock(&xs_state.reply_lock);
+        }
+
+        msg = list_entry(xs_state.reply_list.next,
+                         struct xs_stored_msg, list);
+        list_del(&msg->list);
+
+        spin_unlock(&xs_state.reply_lock);
+
+        *type = msg->hdr.type;
+        if (len)
+                *len = msg->hdr.len;
+        body = msg->u.reply.body;
+
+        kfree(msg);
+
+        return body;
+}
+
+void *xenbus_dev_request_and_reply(struct xsd_sockmsg *msg)
+{
+        void *ret;
+        struct xsd_sockmsg req_msg = *msg;
+        int err;
+
+        if (req_msg.type == XS_TRANSACTION_START)
+                down_read(&xs_state.transaction_mutex);
+
+        mutex_lock(&xs_state.request_mutex);
+
+        err = xb_write(msg, sizeof(*msg) + msg->len);
+        if (err) {
+                msg->type = XS_ERROR;
+                ret = ERR_PTR(err);
+        } else
+                ret = read_reply(&msg->type, &msg->len);
+
+        mutex_unlock(&xs_state.request_mutex);
+
+        if ((msg->type == XS_TRANSACTION_END) ||
+            ((req_msg.type == XS_TRANSACTION_START) &&
+             (msg->type == XS_ERROR)))
+                up_read(&xs_state.transaction_mutex);
+
+        return ret;
+}
+
+/* Send message to xs, get kmalloc'ed reply.  ERR_PTR() on error. */
+static void *xs_talkv(struct xenbus_transaction t,
+                      enum xsd_sockmsg_type type,
+                      const struct kvec *iovec,
+                      unsigned int num_vecs,
+                      unsigned int *len)
+{
+        struct xsd_sockmsg msg;
+        void *ret = NULL;
+        unsigned int i;
+        int err;
+
+        msg.tx_id = t.id;
+        msg.req_id = 0;
+        msg.type = type;
+        msg.len = 0;
+        for (i = 0; i < num_vecs; i++)
+                msg.len += iovec[i].iov_len;
+
+        mutex_lock(&xs_state.request_mutex);
+
+        err = xb_write(&msg, sizeof(msg));
+        if (err) {
+                mutex_unlock(&xs_state.request_mutex);
+                return ERR_PTR(err);
+        }
+
+        for (i = 0; i < num_vecs; i++) {
+                err = xb_write(iovec[i].iov_base, iovec[i].iov_len);
+                if (err) {
+                        mutex_unlock(&xs_state.request_mutex);
+                        return ERR_PTR(err);
+                }
+        }
+
+        ret = read_reply(&msg.type, len);
+
+        mutex_unlock(&xs_state.request_mutex);
+
+        if (IS_ERR(ret))
+                return ret;
+
+        if (msg.type == XS_ERROR) {
+                err = get_error(ret);
+                kfree(ret);
+                return ERR_PTR(-err);
+        }
+
+        if (msg.type != type) {
+                if (printk_ratelimit())
+                        printk(KERN_WARNING
+                               "XENBUS unexpected type [%d], expected [%d]\n",
+                               msg.type, type);
+                kfree(ret);
+                return ERR_PTR(-EINVAL);
+        }
+        return ret;
+}
+
+/* Simplified version of xs_talkv: single message. */
+static void *xs_single(struct xenbus_transaction t,
+                       enum xsd_sockmsg_type type,
+                       const char *string,
+                       unsigned int *len)
+{
+        struct kvec iovec;
+
+        iovec.iov_base = (void *)string;
+        iovec.iov_len = strlen(string) + 1;
+        return xs_talkv(t, type, &iovec, 1, len);
+}
+
+/* Many commands only need an ack, don't care what it says. */
+static int xs_error(char *reply)
+{
+        if (IS_ERR(reply))
+                return PTR_ERR(reply);
+        kfree(reply);
+        return 0;
+}
+
+static unsigned int count_strings(const char *strings, unsigned int len)
+{
+        unsigned int num;
+        const char *p;
+
+        for (p = strings, num = 0; p < strings + len; p += strlen(p) + 1)
+                num++;
+
+        return num;
+}
+
+/* Return the path to dir with /name appended. Buffer must be kfree()'ed. */
+static char *join(const char *dir, const char *name)
+{
+        char *buffer;
+
+        if (strlen(name) == 0)
+                buffer = kasprintf(GFP_KERNEL, "%s", dir);
+        else
+                buffer = kasprintf(GFP_KERNEL, "%s/%s", dir, name);
+        return (!buffer) ? ERR_PTR(-ENOMEM) : buffer;
+}
+
+static char **split(char *strings, unsigned int len, unsigned int *num)
+{
+        char *p, **ret;
+
+        /* Count the strings. */
+        *num = count_strings(strings, len);
+
+        /* Transfer to one big alloc for easy freeing. */
+        ret = kmalloc(*num * sizeof(char *) + len, GFP_KERNEL);
+        if (!ret) {
+                kfree(strings);
+                return ERR_PTR(-ENOMEM);
+        }
+        memcpy(&ret[*num], strings, len);
+        kfree(strings);
+
+        strings = (char *)&ret[*num];
+        for (p = strings, *num = 0; p < strings + len; p += strlen(p) + 1)
+                ret[(*num)++] = p;
+
+        return ret;
+}
+
+char **xenbus_directory(struct xenbus_transaction t,
+                        const char *dir, const char *node, unsigned int *num)
+{
+        char *strings, *path;
+        unsigned int len;
+
+        path = join(dir, node);
+        if (IS_ERR(path))
+                return (char **)path;
+
+        strings = xs_single(t, XS_DIRECTORY, path, &len);
+        kfree(path);
+        if (IS_ERR(strings))
+                return (char **)strings;
+
+        return split(strings, len, num);
+}
+EXPORT_SYMBOL_GPL(xenbus_directory);
+
+/* Check if a path exists. Return 1 if it does. */
+int xenbus_exists(struct xenbus_transaction t,
+                  const char *dir, const char *node)
+{
+        char **d;
+        int dir_n;
+
+        d = xenbus_directory(t, dir, node, &dir_n);
+        if (IS_ERR(d))
+                return 0;
+        kfree(d);
+        return 1;
+}
+EXPORT_SYMBOL_GPL(xenbus_exists);
+
+/* Get the value of a single file.
+ * Returns a kmalloced value: call free() on it after use.
+ * len indicates length in bytes.
+ */
+void *xenbus_read(struct xenbus_transaction t,
+                  const char *dir, const char *node, unsigned int *len)
+{
+        char *path;
+        void *ret;
+
+        path = join(dir, node);
+        if (IS_ERR(path))
+                return (void *)path;
+
+        ret = xs_single(t, XS_READ, path, len);
+        kfree(path);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(xenbus_read);
+
+/* Write the value of a single file.
+ * Returns -err on failure.
+ */
+int xenbus_write(struct xenbus_transaction t,
+                 const char *dir, const char *node, const char *string)
+{
+        const char *path;
+        struct kvec iovec[2];
+        int ret;
+
+        path = join(dir, node);
+        if (IS_ERR(path))
+                return PTR_ERR(path);
+
+        iovec[0].iov_base = (void *)path;
+        iovec[0].iov_len = strlen(path) + 1;
+        iovec[1].iov_base = (void *)string;
+        iovec[1].iov_len = strlen(string);
+
+        ret = xs_error(xs_talkv(t, XS_WRITE, iovec, ARRAY_SIZE(iovec), NULL));
+        kfree(path);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(xenbus_write);
+
+/* Create a new directory. */
+int xenbus_mkdir(struct xenbus_transaction t,
+                 const char *dir, const char *node)
+{
+        char *path;
+        int ret;
+
+        path = join(dir, node);
+        if (IS_ERR(path))
+                return PTR_ERR(path);
+
+        ret = xs_error(xs_single(t, XS_MKDIR, path, NULL));
+        kfree(path);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(xenbus_mkdir);
+
+/* Destroy a file or directory (directories must be empty). */
+int xenbus_rm(struct xenbus_transaction t, const char *dir, const char *node)
+{
+        char *path;
+        int ret;
+
+        path = join(dir, node);
+        if (IS_ERR(path))
+                return PTR_ERR(path);
+
+        ret = xs_error(xs_single(t, XS_RM, path, NULL));
+        kfree(path);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(xenbus_rm);
+
+/* Start a transaction: changes by others will not be seen during this
+ * transaction, and changes will not be visible to others until end.
+ */
+int xenbus_transaction_start(struct xenbus_transaction *t)
+{
+        char *id_str;
+
+        down_read(&xs_state.transaction_mutex);
+
+        id_str = xs_single(XBT_NIL, XS_TRANSACTION_START, "", NULL);
+        if (IS_ERR(id_str)) {
+                up_read(&xs_state.transaction_mutex);
+                return PTR_ERR(id_str);
+        }
+
+        t->id = simple_strtoul(id_str, NULL, 0);
+        kfree(id_str);
+        return 0;
+}
+EXPORT_SYMBOL_GPL(xenbus_transaction_start);
+
+/* End a transaction.
+ * If abandon is true, transaction is discarded instead of committed.
+ */
+int xenbus_transaction_end(struct xenbus_transaction t, int abort)
+{
+        char abortstr[2];
+        int err;
+
+        if (abort)
+                strcpy(abortstr, "F");
+        else
+                strcpy(abortstr, "T");
+
+        err = xs_error(xs_single(t, XS_TRANSACTION_END, abortstr, NULL));
+
+        up_read(&xs_state.transaction_mutex);
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(xenbus_transaction_end);
+
+/* Single read and scanf: returns -errno or num scanned. */
+int xenbus_scanf(struct xenbus_transaction t,
+                 const char *dir, const char *node, const char *fmt, ...)
+{
+        va_list ap;
+        int ret;
+        char *val;
+
+        val = xenbus_read(t, dir, node, NULL);
+        if (IS_ERR(val))
+                return PTR_ERR(val);
+
+        va_start(ap, fmt);
+        ret = vsscanf(val, fmt, ap);
+        va_end(ap);
+        kfree(val);
+        /* Distinctive errno. */
+        if (ret == 0)
+                return -ERANGE;
+        return ret;
+}
+EXPORT_SYMBOL_GPL(xenbus_scanf);
+
+/* Single printf and write: returns -errno or 0. */
+int xenbus_printf(struct xenbus_transaction t,
+                  const char *dir, const char *node, const char *fmt, ...)
+{
+        va_list ap;
+        int ret;
+#define PRINTF_BUFFER_SIZE 4096
+        char *printf_buffer;
+
+        printf_buffer = kmalloc(PRINTF_BUFFER_SIZE, GFP_KERNEL);
+        if (printf_buffer == NULL)
+                return -ENOMEM;
+
+        va_start(ap, fmt);
+        ret = vsnprintf(printf_buffer, PRINTF_BUFFER_SIZE, fmt, ap);
+        va_end(ap);
+
+        BUG_ON(ret > PRINTF_BUFFER_SIZE-1);
+        ret = xenbus_write(t, dir, node, printf_buffer);
+
+        kfree(printf_buffer);
+
+        return ret;
+}
+EXPORT_SYMBOL_GPL(xenbus_printf);
+
+/* Takes tuples of names, scanf-style args, and void **, NULL terminated. */
+int xenbus_gather(struct xenbus_transaction t, const char *dir, ...)
+{
+        va_list ap;
+        const char *name;
+        int ret = 0;
+
+        va_start(ap, dir);
+        while (ret == 0 && (name = va_arg(ap, char *)) != NULL) {
+                const char *fmt = va_arg(ap, char *);
+                void *result = va_arg(ap, void *);
+                char *p;
+
+                p = xenbus_read(t, dir, name, NULL);
+                if (IS_ERR(p)) {
+                        ret = PTR_ERR(p);
+                        break;
+                }
+                if (fmt) {
+                        if (sscanf(p, fmt, result) == 0)
+                                ret = -EINVAL;
+                        kfree(p);
+                } else
+                        *(char **)result = p;
+        }
+        va_end(ap);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(xenbus_gather);
+
+static int xs_watch(const char *path, const char *token)
+{
+        struct kvec iov[2];
+
+        iov[0].iov_base = (void *)path;
+        iov[0].iov_len = strlen(path) + 1;
+        iov[1].iov_base = (void *)token;
+        iov[1].iov_len = strlen(token) + 1;
+
+        return xs_error(xs_talkv(XBT_NIL, XS_WATCH, iov,
+                                 ARRAY_SIZE(iov), NULL));
+}
+
+static int xs_unwatch(const char *path, const char *token)
+{
+        struct kvec iov[2];
+
+        iov[0].iov_base = (char *)path;
+        iov[0].iov_len = strlen(path) + 1;
+        iov[1].iov_base = (char *)token;
+        iov[1].iov_len = strlen(token) + 1;
+
+        return xs_error(xs_talkv(XBT_NIL, XS_UNWATCH, iov,
+                                 ARRAY_SIZE(iov), NULL));
+}
+
+static struct xenbus_watch *find_watch(const char *token)
+{
+        struct xenbus_watch *i, *cmp;
+
+        cmp = (void *)simple_strtoul(token, NULL, 16);
+
+        list_for_each_entry(i, &watches, list)
+                if (i == cmp)
+                        return i;
+
+        return NULL;
+}
+
+/* Register callback to watch this node. */
+int register_xenbus_watch(struct xenbus_watch *watch)
+{
+        /* Pointer in ascii is the token. */
+        char token[sizeof(watch) * 2 + 1];
+        int err;
+
+        sprintf(token, "%lX", (long)watch);
+
+        down_read(&xs_state.watch_mutex);
+
+        spin_lock(&watches_lock);
+        BUG_ON(find_watch(token));
+        list_add(&watch->list, &watches);
+        spin_unlock(&watches_lock);
+
+        err = xs_watch(watch->node, token);
+
+        /* Ignore errors due to multiple registration. */
+        if ((err != 0) && (err != -EEXIST)) {
+                spin_lock(&watches_lock);
+                list_del(&watch->list);
+                spin_unlock(&watches_lock);
+        }
+
+        up_read(&xs_state.watch_mutex);
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(register_xenbus_watch);
+
+void unregister_xenbus_watch(struct xenbus_watch *watch)
+{
+        struct xs_stored_msg *msg, *tmp;
+        char token[sizeof(watch) * 2 + 1];
+        int err;
+
+        sprintf(token, "%lX", (long)watch);
+
+        down_read(&xs_state.watch_mutex);
+
+        spin_lock(&watches_lock);
+        BUG_ON(!find_watch(token));
+        list_del(&watch->list);
+        spin_unlock(&watches_lock);
+
+        err = xs_unwatch(watch->node, token);
+        if (err)
+                printk(KERN_WARNING
+                       "XENBUS Failed to release watch %s: %i\n",
+                       watch->node, err);
+
+        up_read(&xs_state.watch_mutex);
+
+        /* Make sure there are no callbacks running currently (unless
+           its us) */
+        if (current->pid != xenwatch_pid)
+                mutex_lock(&xenwatch_mutex);
+
+        /* Cancel pending watch events. */
+        spin_lock(&watch_events_lock);
+        list_for_each_entry_safe(msg, tmp, &watch_events, list) {
+                if (msg->u.watch.handle != watch)
+                        continue;
+                list_del(&msg->list);
+                kfree(msg->u.watch.vec);
+                kfree(msg);
+        }
+        spin_unlock(&watch_events_lock);
+
+        if (current->pid != xenwatch_pid)
+                mutex_unlock(&xenwatch_mutex);
+}
+EXPORT_SYMBOL_GPL(unregister_xenbus_watch);
+
+void xs_suspend(void)
+{
+        down_write(&xs_state.transaction_mutex);
+        down_write(&xs_state.watch_mutex);
+        mutex_lock(&xs_state.request_mutex);
+        mutex_lock(&xs_state.response_mutex);
+}
+
+void xs_resume(void)
+{
+        struct xenbus_watch *watch;
+        char token[sizeof(watch) * 2 + 1];
+
+        mutex_unlock(&xs_state.response_mutex);
+        mutex_unlock(&xs_state.request_mutex);
+        up_write(&xs_state.transaction_mutex);
+
+        /* No need for watches_lock: the watch_mutex is sufficient. */
+        list_for_each_entry(watch, &watches, list) {
+                sprintf(token, "%lX", (long)watch);
+                xs_watch(watch->node, token);
+        }
+
+        up_write(&xs_state.watch_mutex);
+}
+
+void xs_suspend_cancel(void)
+{
+        mutex_unlock(&xs_state.response_mutex);
+        mutex_unlock(&xs_state.request_mutex);
+        up_write(&xs_state.watch_mutex);
+        up_write(&xs_state.transaction_mutex);
+}
+
+static int xenwatch_thread(void *unused)
+{
+        struct list_head *ent;
+        struct xs_stored_msg *msg;
+
+        for (;;) {
+                wait_event_interruptible(watch_events_waitq,
+                                         !list_empty(&watch_events));
+
+                if (kthread_should_stop())
+                        break;
+
+                mutex_lock(&xenwatch_mutex);
+
+                spin_lock(&watch_events_lock);
+                ent = watch_events.next;
+                if (ent != &watch_events)
+                        list_del(ent);
+                spin_unlock(&watch_events_lock);
+
+                if (ent != &watch_events) {
+                        msg = list_entry(ent, struct xs_stored_msg, list);
+                        msg->u.watch.handle->callback(
+                                msg->u.watch.handle,
+                                (const char **)msg->u.watch.vec,
+                                msg->u.watch.vec_size);
+                        kfree(msg->u.watch.vec);
+                        kfree(msg);
+                }
+
+                mutex_unlock(&xenwatch_mutex);
+        }
+
+        return 0;
+}
+
+static int process_msg(void)
+{
+        struct xs_stored_msg *msg;
+        char *body;
+        int err;
+
+        /*
+         * We must disallow save/restore while reading a xenstore message.
+         * A partial read across s/r leaves us out of sync with xenstored.
+         */
+        for (;;) {
+                err = xb_wait_for_data_to_read();
+                if (err)
+                        return err;
+                mutex_lock(&xs_state.response_mutex);
+                if (xb_data_to_read())
+                        break;
+                /* We raced with save/restore: pending data 'disappeared'. */
+                mutex_unlock(&xs_state.response_mutex);
+        }
+
+
+        msg = kmalloc(sizeof(*msg), GFP_KERNEL);
+        if (msg == NULL) {
+                err = -ENOMEM;
+                goto out;
+        }
+
+        err = xb_read(&msg->hdr, sizeof(msg->hdr));
+        if (err) {
+                kfree(msg);
+                goto out;
+        }
+
+        body = kmalloc(msg->hdr.len + 1, GFP_KERNEL);
+        if (body == NULL) {
+                kfree(msg);
+                err = -ENOMEM;
+                goto out;
+        }
+
+        err = xb_read(body, msg->hdr.len);
+        if (err) {
+                kfree(body);
+                kfree(msg);
+                goto out;
+        }
+        body[msg->hdr.len] = '\0';
+
+        if (msg->hdr.type == XS_WATCH_EVENT) {
+                msg->u.watch.vec = split(body, msg->hdr.len,
+                                         &msg->u.watch.vec_size);
+                if (IS_ERR(msg->u.watch.vec)) {
+                        kfree(msg);
+                        err = PTR_ERR(msg->u.watch.vec);
+                        goto out;
+                }
+
+                spin_lock(&watches_lock);
+                msg->u.watch.handle = find_watch(
+                        msg->u.watch.vec[XS_WATCH_TOKEN]);
+                if (msg->u.watch.handle != NULL) {
+                        spin_lock(&watch_events_lock);
+                        list_add_tail(&msg->list, &watch_events);
+                        wake_up(&watch_events_waitq);
+                        spin_unlock(&watch_events_lock);
+                } else {
+                        kfree(msg->u.watch.vec);
+                        kfree(msg);
+                }
+                spin_unlock(&watches_lock);
+        } else {
+                msg->u.reply.body = body;
+                spin_lock(&xs_state.reply_lock);
+                list_add_tail(&msg->list, &xs_state.reply_list);
+                spin_unlock(&xs_state.reply_lock);
+                wake_up(&xs_state.reply_waitq);
+        }
+
+ out:
+        mutex_unlock(&xs_state.response_mutex);
+        return err;
+}
+
+static int xenbus_thread(void *unused)
+{
+        int err;
+
+        for (;;) {
+                err = process_msg();
+                if (err)
+                        printk(KERN_WARNING "XENBUS error %d while reading "
+                               "message\n", err);
+                if (kthread_should_stop())
+                        break;
+        }
+
+        return 0;
+}
+
+int xs_init(void)
+{
+        int err;
+        struct task_struct *task;
+
+        INIT_LIST_HEAD(&xs_state.reply_list);
+        spin_lock_init(&xs_state.reply_lock);
+        init_waitqueue_head(&xs_state.reply_waitq);
+
+        mutex_init(&xs_state.request_mutex);
+        mutex_init(&xs_state.response_mutex);
+        init_rwsem(&xs_state.transaction_mutex);
+        init_rwsem(&xs_state.watch_mutex);
+
+        /* Initialize the shared memory rings to talk to xenstored */
+        err = xb_init_comms();
+        if (err)
+                return err;
+
+        task = kthread_run(xenwatch_thread, NULL, "xenwatch");
+        if (IS_ERR(task))
+                return PTR_ERR(task);
+        xenwatch_pid = task->pid;
+
+        task = kthread_run(xenbus_thread, NULL, "xenbus");
+        if (IS_ERR(task))
+                return PTR_ERR(task);
+
+        return 0;
+}