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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 /******************************************************************************
  * 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.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #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/reboot.h>
 #include <linux/rwsem.h>
 #include <linux/mutex.h>
 #include <asm/xen/hypervisor.h>
 #include <xen/xenbus.h>
 #include <xen/xen.h>
 #include "xenbus.h"
 
 /*
  * Framework to protect suspend/resume handling against normal Xenstore
  * message handling:
  * During suspend/resume there must be no open transaction and no pending
  * Xenstore request.
  * New watch events happening in this time can be ignored by firing all watches
  * after resume.
  */
 
 /* Lock protecting enter/exit critical region. */
 static DEFINE_SPINLOCK(xs_state_lock);
 /* Number of users in critical region (protected by xs_state_lock). */
 static unsigned int xs_state_users;
 /* Suspend handler waiting or already active (protected by xs_state_lock)? */
 static int xs_suspend_active;
 /* Unique Xenstore request id (protected by xs_state_lock). */
 static uint32_t xs_request_id;
 
 /* Wait queue for all callers waiting for critical region to become usable. */
 static DECLARE_WAIT_QUEUE_HEAD(xs_state_enter_wq);
 /* Wait queue for suspend handling waiting for critical region being empty. */
 static DECLARE_WAIT_QUEUE_HEAD(xs_state_exit_wq);
 
 /* 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);
 
 /* Protect watch (de)register against save/restore. */
 static DECLARE_RWSEM(xs_watch_rwsem);
 
 /*
  * 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 void xs_suspend_enter(void)
 {
     spin_lock(&xs_state_lock);
     xs_suspend_active++;
     spin_unlock(&xs_state_lock);
     wait_event(xs_state_exit_wq, xs_state_users == 0);
 }
 
 static void xs_suspend_exit(void)
 {
     xb_dev_generation_id++;
     spin_lock(&xs_state_lock);
     xs_suspend_active--;
     spin_unlock(&xs_state_lock);
     wake_up_all(&xs_state_enter_wq);
 }
 
 static uint32_t xs_request_enter(struct xb_req_data *req)
 {
     uint32_t rq_id;
 
     req->type = req->msg.type;
 
     spin_lock(&xs_state_lock);
 
     while (!xs_state_users && xs_suspend_active) {
         spin_unlock(&xs_state_lock);
         wait_event(xs_state_enter_wq, xs_suspend_active == 0);
         spin_lock(&xs_state_lock);
     }
 
     if (req->type == XS_TRANSACTION_START && !req->user_req)
         xs_state_users++;
     xs_state_users++;
     rq_id = xs_request_id++;
 
     spin_unlock(&xs_state_lock);
 
     return rq_id;
 }
 
 void xs_request_exit(struct xb_req_data *req)
 {
     spin_lock(&xs_state_lock);
     xs_state_users--;
     if ((req->type == XS_TRANSACTION_START && req->msg.type == XS_ERROR) ||
         (req->type == XS_TRANSACTION_END && !req->user_req &&
          !WARN_ON_ONCE(req->msg.type == XS_ERROR &&
                !strcmp(req->body, "ENOENT"))))
         xs_state_users--;
     spin_unlock(&xs_state_lock);
 
     if (xs_suspend_active && !xs_state_users)
         wake_up(&xs_state_exit_wq);
 }
 
 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) {
             pr_warn("xen store gave: unknown error %s\n",
                 errorstring);
             return EINVAL;
         }
     }
     return xsd_errors[i].errnum;
 }
 
 static bool xenbus_ok(void)
 {
     switch (xen_store_domain_type) {
     case XS_LOCAL:
         switch (system_state) {
         case SYSTEM_POWER_OFF:
         case SYSTEM_RESTART:
         case SYSTEM_HALT:
             return false;
         default:
             break;
         }
         return true;
     case XS_PV:
     case XS_HVM:
         /* FIXME: Could check that the remote domain is alive,
          * but it is normally initial domain. */
         return true;
     default:
         break;
     }
     return false;
 }
 
 static bool test_reply(struct xb_req_data *req)
 {
     if (req->state == xb_req_state_got_reply || !xenbus_ok()) {
         /* read req->state before all other fields */
         virt_rmb();
         return true;
     }
 
     /* Make sure to reread req->state each time. */
     barrier();
 
     return false;
 }
 
 static void *read_reply(struct xb_req_data *req)
 {
     do {
         wait_event(req->wq, test_reply(req));
 
         if (!xenbus_ok())
             /*
              * If we are in the process of being shut-down there is
              * no point of trying to contact XenBus - it is either
              * killed (xenstored application) or the other domain
              * has been killed or is unreachable.
              */
             return ERR_PTR(-EIO);
         if (req->err)
             return ERR_PTR(req->err);
 
     } while (req->state != xb_req_state_got_reply);
 
     return req->body;
 }
 
 static void xs_send(struct xb_req_data *req, struct xsd_sockmsg *msg)
 {
     bool notify;
 
     req->msg = *msg;
     req->err = 0;
     req->state = xb_req_state_queued;
     init_waitqueue_head(&req->wq);
 
     /* Save the caller req_id and restore it later in the reply */
     req->caller_req_id = req->msg.req_id;
     req->msg.req_id = xs_request_enter(req);
 
     mutex_lock(&xb_write_mutex);
     list_add_tail(&req->list, &xb_write_list);
     notify = list_is_singular(&xb_write_list);
     mutex_unlock(&xb_write_mutex);
 
     if (notify)
         wake_up(&xb_waitq);
 }
 
 static void *xs_wait_for_reply(struct xb_req_data *req, struct xsd_sockmsg *msg)
 {
     void *ret;
 
     ret = read_reply(req);
 
     xs_request_exit(req);
 
     msg->type = req->msg.type;
     msg->len = req->msg.len;
 
     mutex_lock(&xb_write_mutex);
     if (req->state == xb_req_state_queued ||
         req->state == xb_req_state_wait_reply)
         req->state = xb_req_state_aborted;
     else
         kfree(req);
     mutex_unlock(&xb_write_mutex);
 
     return ret;
 }
 
 static void xs_wake_up(struct xb_req_data *req)
 {
     wake_up(&req->wq);
 }
 
 int xenbus_dev_request_and_reply(struct xsd_sockmsg *msg, void *par)
 {
     struct xb_req_data *req;
     struct kvec *vec;
 
     req = kmalloc(sizeof(*req) + sizeof(*vec), GFP_KERNEL);
     if (!req)
         return -ENOMEM;
 
     vec = (struct kvec *)(req + 1);
     vec->iov_len = msg->len;
     vec->iov_base = msg + 1;
 
     req->vec = vec;
     req->num_vecs = 1;
     req->cb = xenbus_dev_queue_reply;
     req->par = par;
     req->user_req = true;
 
     xs_send(req, msg);
 
     return 0;
 }
 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 xb_req_data *req;
     struct xsd_sockmsg msg;
     void *ret = NULL;
     unsigned int i;
     int err;
 
     req = kmalloc(sizeof(*req), GFP_NOIO | __GFP_HIGH);
     if (!req)
         return ERR_PTR(-ENOMEM);
 
     req->vec = iovec;
     req->num_vecs = num_vecs;
     req->cb = xs_wake_up;
     req->user_req = false;
 
     msg.req_id = 0;
     msg.tx_id = t.id;
     msg.type = type;
     msg.len = 0;
     for (i = 0; i < num_vecs; i++)
         msg.len += iovec[i].iov_len;
 
     xs_send(req, &msg);
 
     ret = xs_wait_for_reply(req, &msg);
     if (len)
         *len = msg.len;
 
     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) {
         pr_warn_ratelimited("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;
 
     id_str = xs_single(XBT_NIL, XS_TRANSACTION_START, "", NULL);
     if (IS_ERR(id_str))
         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];
 
     if (abort)
         strcpy(abortstr, "F");
     else
         strcpy(abortstr, "T");
 
     return xs_error(xs_single(t, XS_TRANSACTION_END, abortstr, NULL));
 }
 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);
 
 /* Read an (optional) unsigned value. */
 unsigned int xenbus_read_unsigned(const char *dir, const char *node,
                   unsigned int default_val)
 {
     unsigned int val;
     int ret;
 
     ret = xenbus_scanf(XBT_NIL, dir, node, "%u", &val);
     if (ret <= 0)
         val = default_val;
 
     return val;
 }
 EXPORT_SYMBOL_GPL(xenbus_read_unsigned);
 
 /* 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;
 }
 
 int xs_watch_msg(struct xs_watch_event *event)
 {
     if (count_strings(event->body, event->len) != 2) {
         kfree(event);
         return -EINVAL;
     }
     event->path = (const char *)event->body;
     event->token = (const char *)strchr(event->body, '\0') + 1;
 
     spin_lock(&watches_lock);
     event->handle = find_watch(event->token);
     if (event->handle != NULL &&
             (!event->handle->will_handle ||
              event->handle->will_handle(event->handle,
                  event->path, event->token))) {
         spin_lock(&watch_events_lock);
         list_add_tail(&event->list, &watch_events);
         event->handle->nr_pending++;
         wake_up(&watch_events_waitq);
         spin_unlock(&watch_events_lock);
     } else
         kfree(event);
     spin_unlock(&watches_lock);
 
     return 0;
 }
 
 /*
  * Certain older XenBus toolstack cannot handle reading values that are
  * not populated. Some Xen 3.4 installation are incapable of doing this
  * so if we are running on anything older than 4 do not attempt to read
  * control/platform-feature-xs_reset_watches.
  */
 static bool xen_strict_xenbus_quirk(void)
 {
 #ifdef CONFIG_X86
     uint32_t eax, ebx, ecx, edx, base;
 
     base = xen_cpuid_base();
     cpuid(base + 1, &eax, &ebx, &ecx, &edx);
 
     if ((eax >> 16) < 4)
         return true;
 #endif
     return false;
 
 }
 static void xs_reset_watches(void)
 {
     int err;
 
     if (!xen_hvm_domain() || xen_initial_domain())
         return;
 
     if (xen_strict_xenbus_quirk())
         return;
 
     if (!xenbus_read_unsigned("control",
                   "platform-feature-xs_reset_watches", 0))
         return;
 
     err = xs_error(xs_single(XBT_NIL, XS_RESET_WATCHES, "", NULL));
     if (err && err != -EEXIST)
         pr_warn("xs_reset_watches failed: %d\n", err);
 }
 
 /* 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);
 
     watch->nr_pending = 0;
 
     down_read(&xs_watch_rwsem);
 
     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_watch_rwsem);
 
     return err;
 }
 EXPORT_SYMBOL_GPL(register_xenbus_watch);
 
 void unregister_xenbus_watch(struct xenbus_watch *watch)
 {
     struct xs_watch_event *event, *tmp;
     char token[sizeof(watch) * 2 + 1];
     int err;
 
     sprintf(token, "%lX", (long)watch);
 
     down_read(&xs_watch_rwsem);
 
     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)
         pr_warn("Failed to release watch %s: %i\n", watch->node, err);
 
     up_read(&xs_watch_rwsem);
 
     /* 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);
     if (watch->nr_pending) {
         list_for_each_entry_safe(event, tmp, &watch_events, list) {
             if (event->handle != watch)
                 continue;
             list_del(&event->list);
             kfree(event);
         }
         watch->nr_pending = 0;
     }
     spin_unlock(&watch_events_lock);
 
     if (current->pid != xenwatch_pid)
         mutex_unlock(&xenwatch_mutex);
 }
 EXPORT_SYMBOL_GPL(unregister_xenbus_watch);
 
 void xs_suspend(void)
 {
     xs_suspend_enter();
 
     down_write(&xs_watch_rwsem);
     mutex_lock(&xs_response_mutex);
 }
 
 void xs_resume(void)
 {
     struct xenbus_watch *watch;
     char token[sizeof(watch) * 2 + 1];
 
     xb_init_comms();
 
     mutex_unlock(&xs_response_mutex);
 
     xs_suspend_exit();
 
     /* No need for watches_lock: the xs_watch_rwsem is sufficient. */
     list_for_each_entry(watch, &watches, list) {
         sprintf(token, "%lX", (long)watch);
         xs_watch(watch->node, token);
     }
 
     up_write(&xs_watch_rwsem);
 }
 
 void xs_suspend_cancel(void)
 {
     mutex_unlock(&xs_response_mutex);
     up_write(&xs_watch_rwsem);
 
     xs_suspend_exit();
 }
 
 static int xenwatch_thread(void *unused)
 {
     struct xs_watch_event *event;
 
     xenwatch_pid = current->pid;
 
     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);
         event = list_first_entry_or_null(&watch_events,
                 struct xs_watch_event, list);
         if (event) {
             list_del(&event->list);
             event->handle->nr_pending--;
         }
         spin_unlock(&watch_events_lock);
 
         if (event) {
             event->handle->callback(event->handle, event->path,
                         event->token);
             kfree(event);
         }
 
         mutex_unlock(&xenwatch_mutex);
     }
 
     return 0;
 }
 
 /*
  * Wake up all threads waiting for a xenstore reply. In case of shutdown all
  * pending replies will be marked as "aborted" in order to let the waiters
  * return in spite of xenstore possibly no longer being able to reply. This
  * will avoid blocking shutdown by a thread waiting for xenstore but being
  * necessary for shutdown processing to proceed.
  */
 static int xs_reboot_notify(struct notifier_block *nb,
                 unsigned long code, void *unused)
 {
     struct xb_req_data *req;
 
     mutex_lock(&xb_write_mutex);
     list_for_each_entry(req, &xs_reply_list, list)
         wake_up(&req->wq);
     list_for_each_entry(req, &xb_write_list, list)
         wake_up(&req->wq);
     mutex_unlock(&xb_write_mutex);
     return NOTIFY_DONE;
 }
 
 static struct notifier_block xs_reboot_nb = {
     .notifier_call = xs_reboot_notify,
 };
 
 int xs_init(void)
 {
     int err;
     struct task_struct *task;
 
     register_reboot_notifier(&xs_reboot_nb);
 
     /* 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);
 
     /* shutdown watches for kexec boot */
     xs_reset_watches();
 
     return 0;
 }

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