text: /******************************************************************************
   * 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 <xen/xen.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.
  	 *
  	 * transaction_mutex must be held before incrementing
  	 * transaction_count. The mutex is held when a suspend is in
  	 * progress to prevent new transactions starting.
  	 *
  	 * When decrementing transaction_count to zero the wait queue
  	 * should be woken up, the suspend code waits for count to
  	 * reach zero.
  	 */
  
  	/* 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 mutex transaction_mutex;
  	atomic_t transaction_count;
  	wait_queue_head_t transaction_wq;
  
  	/* 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;
  }
  
  static void transaction_start(void)
  {
  	mutex_lock(&xs_state.transaction_mutex);
  	atomic_inc(&xs_state.transaction_count);
  	mutex_unlock(&xs_state.transaction_mutex);
  }
  
  static void transaction_end(void)
  {
  	if (atomic_dec_and_test(&xs_state.transaction_count))
  		wake_up(&xs_state.transaction_wq);
  }
  
  static void transaction_suspend(void)
  {
  	mutex_lock(&xs_state.transaction_mutex);
  	wait_event(xs_state.transaction_wq,
  		   atomic_read(&xs_state.transaction_count) == 0);
  }
  
  static void transaction_resume(void)
  {
  	mutex_unlock(&xs_state.transaction_mutex);
  }
  
  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)
  		transaction_start();
  
  	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)))
  		transaction_end();
  
  	return ret;
  }
  EXPORT_SYMBOL(xenbus_dev_request_and_reply);
  
  /* 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_NOIO | __GFP_HIGH, "%s", dir);
  	else
  		buffer = kasprintf(GFP_NOIO | __GFP_HIGH, "%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_NOIO | __GFP_HIGH);
  	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;
  
  	transaction_start();
  
  	id_str = xs_single(XBT_NIL, XS_TRANSACTION_START, "", NULL);
  	if (IS_ERR(id_str)) {
  		transaction_end();
  		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));
  
  	transaction_end();
  
  	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;
  	char *buf;
  
  	va_start(ap, fmt);
  	buf = kvasprintf(GFP_NOIO | __GFP_HIGH, fmt, ap);
  	va_end(ap);
  
  	if (!buf)
  		return -ENOMEM;
  
  	ret = xenbus_write(t, dir, node, buf);
  
  	kfree(buf);
  
  	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);
  
  	if (err) {
  		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)
  {
  	transaction_suspend();
  	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];
  
  	xb_init_comms();
  
  	mutex_unlock(&xs_state.response_mutex);
  	mutex_unlock(&xs_state.request_mutex);
  	transaction_resume();
  
  	/* 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);
  	mutex_unlock(&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_NOIO | __GFP_HIGH);
  	if (msg == NULL) {
  		err = -ENOMEM;
  		goto out;
  	}
  
  	err = xb_read(&msg->hdr, sizeof(msg->hdr));
  	if (err) {
  		kfree(msg);
  		goto out;
  	}
  
  	if (msg->hdr.len > XENSTORE_PAYLOAD_MAX) {
  		kfree(msg);
  		err = -EINVAL;
  		goto out;
  	}
  
  	body = kmalloc(msg->hdr.len + 1, GFP_NOIO | __GFP_HIGH);
  	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)) {
  			err = PTR_ERR(msg->u.watch.vec);
  			kfree(msg);
  			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);
  	mutex_init(&xs_state.transaction_mutex);
  	init_rwsem(&xs_state.watch_mutex);
  	atomic_set(&xs_state.transaction_count, 0);
  	init_waitqueue_head(&xs_state.transaction_wq);
  
  	/* 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;
  }
  