drivers/xen/evtchn.c

   1 /******************************************************************************
   2  * evtchn.c
   3  *
   4  * Driver for receiving and demuxing event-channel signals.
   5  *
   6  * Copyright (c) 2004-2005, K A Fraser
   7  * Multi-process extensions Copyright (c) 2004, Steven Smith
   8  *
   9  * This program is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU General Public License version 2
  11  * as published by the Free Software Foundation; or, when distributed
  12  * separately from the Linux kernel or incorporated into other
  13  * software packages, subject to the following license:
  14  *
  15  * Permission is hereby granted, free of charge, to any person obtaining a copy
  16  * of this source file (the "Software"), to deal in the Software without
  17  * restriction, including without limitation the rights to use, copy, modify,
  18  * merge, publish, distribute, sublicense, and/or sell copies of the Software,
  19  * and to permit persons to whom the Software is furnished to do so, subject to
  20  * the following conditions:
  21  *
  22  * The above copyright notice and this permission notice shall be included in
  23  * all copies or substantial portions of the Software.
  24  *
  25  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  26  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  27  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  28  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  29  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  30  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  31  * IN THE SOFTWARE.
  32  */
  33
  34 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
  35
  36 #include <linux/module.h>
  37 #include <linux/kernel.h>
  38 #include <linux/sched.h>
  39 #include <linux/slab.h>
  40 #include <linux/string.h>
  41 #include <linux/errno.h>
  42 #include <linux/fs.h>
  43 #include <linux/miscdevice.h>
  44 #include <linux/major.h>
  45 #include <linux/proc_fs.h>
  46 #include <linux/stat.h>
  47 #include <linux/poll.h>
  48 #include <linux/irq.h>
  49 #include <linux/init.h>
  50 #include <linux/mutex.h>
  51 #include <linux/cpu.h>
  52 #include <linux/mm.h>
  53 #include <linux/vmalloc.h>
  54
  55 #include <xen/xen.h>
  56 #include <xen/events.h>
  57 #include <xen/evtchn.h>
  58 #include <xen/xen-ops.h>
  59 #include <asm/xen/hypervisor.h>
  60
  61 struct per_user_data {
  62         struct mutex bind_mutex; /* serialize bind/unbind operations */
  63         struct rb_root evtchns;
  64         unsigned int nr_evtchns;
  65
  66         /* Notification ring, accessed via /dev/xen/evtchn. */
  67         unsigned int ring_size;
  68         evtchn_port_t *ring;
  69         unsigned int ring_cons, ring_prod, ring_overflow;
  70         struct mutex ring_cons_mutex; /* protect against concurrent readers */
  71         spinlock_t ring_prod_lock; /* product against concurrent interrupts */
  72
  73         /* Processes wait on this queue when ring is empty. */
  74         wait_queue_head_t evtchn_wait;
  75         struct fasync_struct *evtchn_async_queue;
  76         const char *name;
  77
  78         domid_t restrict_domid;
  79 };
  80
  81 #define UNRESTRICTED_DOMID ((domid_t)-1)
  82
  83 struct user_evtchn {
  84         struct rb_node node;
  85         struct per_user_data *user;
  86         unsigned port;
  87         bool enabled;
  88 };
  89
  90 static evtchn_port_t *evtchn_alloc_ring(unsigned int size)
  91 {
  92         evtchn_port_t *ring;
  93         size_t s = size * sizeof(*ring);
  94
  95         ring = kmalloc(s, GFP_KERNEL);
  96         if (!ring)
  97                 ring = vmalloc(s);
  98
  99         return ring;
 100 }
 101
 102 static void evtchn_free_ring(evtchn_port_t *ring)
 103 {
 104         kvfree(ring);
 105 }
 106
 107 static unsigned int evtchn_ring_offset(struct per_user_data *u,
 108                                        unsigned int idx)
 109 {
 110         return idx & (u->ring_size - 1);
 111 }
 112
 113 static evtchn_port_t *evtchn_ring_entry(struct per_user_data *u,
 114                                         unsigned int idx)
 115 {
 116         return u->ring + evtchn_ring_offset(u, idx);
 117 }
 118
 119 static int add_evtchn(struct per_user_data *u, struct user_evtchn *evtchn)
 120 {
 121         struct rb_node **new = &(u->evtchns.rb_node), *parent = NULL;
 122
 123         u->nr_evtchns++;
 124
 125         while (*new) {
 126                 struct user_evtchn *this;
 127
 128                 this = container_of(*new, struct user_evtchn, node);
 129
 130                 parent = *new;
 131                 if (this->port < evtchn->port)
 132                         new = &((*new)->rb_left);
 133                 else if (this->port > evtchn->port)
 134                         new = &((*new)->rb_right);
 135                 else
 136                         return -EEXIST;
 137         }
 138
 139         /* Add new node and rebalance tree. */
 140         rb_link_node(&evtchn->node, parent, new);
 141         rb_insert_color(&evtchn->node, &u->evtchns);
 142
 143         return 0;
 144 }
 145
 146 static void del_evtchn(struct per_user_data *u, struct user_evtchn *evtchn)
 147 {
 148         u->nr_evtchns--;
 149         rb_erase(&evtchn->node, &u->evtchns);
 150         kfree(evtchn);
 151 }
 152
 153 static struct user_evtchn *find_evtchn(struct per_user_data *u, unsigned port)
 154 {
 155         struct rb_node *node = u->evtchns.rb_node;
 156
 157         while (node) {
 158                 struct user_evtchn *evtchn;
 159
 160                 evtchn = container_of(node, struct user_evtchn, node);
 161
 162                 if (evtchn->port < port)
 163                         node = node->rb_left;
 164                 else if (evtchn->port > port)
 165                         node = node->rb_right;
 166                 else
 167                         return evtchn;
 168         }
 169         return NULL;
 170 }
 171
 172 static irqreturn_t evtchn_interrupt(int irq, void *data)
 173 {
 174         struct user_evtchn *evtchn = data;
 175         struct per_user_data *u = evtchn->user;
 176
 177         WARN(!evtchn->enabled,
 178              "Interrupt for port %d, but apparently not enabled; per-user %p\n",
 179              evtchn->port, u);
 180
 181         disable_irq_nosync(irq);
 182         evtchn->enabled = false;
 183
 184         spin_lock(&u->ring_prod_lock);
 185
 186         if ((u->ring_prod - u->ring_cons) < u->ring_size) {
 187                 *evtchn_ring_entry(u, u->ring_prod) = evtchn->port;
 188                 wmb(); /* Ensure ring contents visible */
 189                 if (u->ring_cons == u->ring_prod++) {
 190                         wake_up_interruptible(&u->evtchn_wait);
 191                         kill_fasync(&u->evtchn_async_queue,
 192                                     SIGIO, POLL_IN);
 193                 }
 194         } else
 195                 u->ring_overflow = 1;
 196
 197         spin_unlock(&u->ring_prod_lock);
 198
 199         return IRQ_HANDLED;
 200 }
 201
 202 static ssize_t evtchn_read(struct file *file, char __user *buf,
 203                            size_t count, loff_t *ppos)
 204 {
 205         int rc;
 206         unsigned int c, p, bytes1 = 0, bytes2 = 0;
 207         struct per_user_data *u = file->private_data;
 208
 209         /* Whole number of ports. */
 210         count &= ~(sizeof(evtchn_port_t)-1);
 211
 212         if (count == 0)
 213                 return 0;
 214
 215         if (count > PAGE_SIZE)
 216                 count = PAGE_SIZE;
 217
 218         for (;;) {
 219                 mutex_lock(&u->ring_cons_mutex);
 220
 221                 rc = -EFBIG;
 222                 if (u->ring_overflow)
 223                         goto unlock_out;
 224
 225                 c = u->ring_cons;
 226                 p = u->ring_prod;
 227                 if (c != p)
 228                         break;
 229
 230                 mutex_unlock(&u->ring_cons_mutex);
 231
 232                 if (file->f_flags & O_NONBLOCK)
 233                         return -EAGAIN;
 234
 235                 rc = wait_event_interruptible(u->evtchn_wait,
 236                                               u->ring_cons != u->ring_prod);
 237                 if (rc)
 238                         return rc;
 239         }
 240
 241         /* Byte lengths of two chunks. Chunk split (if any) is at ring wrap. */
 242         if (((c ^ p) & u->ring_size) != 0) {
 243                 bytes1 = (u->ring_size - evtchn_ring_offset(u, c)) *
 244                         sizeof(evtchn_port_t);
 245                 bytes2 = evtchn_ring_offset(u, p) * sizeof(evtchn_port_t);
 246         } else {
 247                 bytes1 = (p - c) * sizeof(evtchn_port_t);
 248                 bytes2 = 0;
 249         }
 250
 251         /* Truncate chunks according to caller's maximum byte count. */
 252         if (bytes1 > count) {
 253                 bytes1 = count;
 254                 bytes2 = 0;
 255         } else if ((bytes1 + bytes2) > count) {
 256                 bytes2 = count - bytes1;
 257         }
 258
 259         rc = -EFAULT;
 260         rmb(); /* Ensure that we see the port before we copy it. */
 261         if (copy_to_user(buf, evtchn_ring_entry(u, c), bytes1) ||
 262             ((bytes2 != 0) &&
 263              copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
 264                 goto unlock_out;
 265
 266         u->ring_cons += (bytes1 + bytes2) / sizeof(evtchn_port_t);
 267         rc = bytes1 + bytes2;
 268
 269  unlock_out:
 270         mutex_unlock(&u->ring_cons_mutex);
 271         return rc;
 272 }
 273
 274 static ssize_t evtchn_write(struct file *file, const char __user *buf,
 275                             size_t count, loff_t *ppos)
 276 {
 277         int rc, i;
 278         evtchn_port_t *kbuf = (evtchn_port_t *)__get_free_page(GFP_KERNEL);
 279         struct per_user_data *u = file->private_data;
 280
 281         if (kbuf == NULL)
 282                 return -ENOMEM;
 283
 284         /* Whole number of ports. */
 285         count &= ~(sizeof(evtchn_port_t)-1);
 286
 287         rc = 0;
 288         if (count == 0)
 289                 goto out;
 290
 291         if (count > PAGE_SIZE)
 292                 count = PAGE_SIZE;
 293
 294         rc = -EFAULT;
 295         if (copy_from_user(kbuf, buf, count) != 0)
 296                 goto out;
 297
 298         mutex_lock(&u->bind_mutex);
 299
 300         for (i = 0; i < (count/sizeof(evtchn_port_t)); i++) {
 301                 unsigned port = kbuf[i];
 302                 struct user_evtchn *evtchn;
 303
 304                 evtchn = find_evtchn(u, port);
 305                 if (evtchn && !evtchn->enabled) {
 306                         evtchn->enabled = true;
 307                         enable_irq(irq_from_evtchn(port));
 308                 }
 309         }
 310
 311         mutex_unlock(&u->bind_mutex);
 312
 313         rc = count;
 314
 315  out:
 316         free_page((unsigned long)kbuf);
 317         return rc;
 318 }
 319
 320 static int evtchn_resize_ring(struct per_user_data *u)
 321 {
 322         unsigned int new_size;
 323         evtchn_port_t *new_ring, *old_ring;
 324
 325         /*
 326          * Ensure the ring is large enough to capture all possible
 327          * events. i.e., one free slot for each bound event.
 328          */
 329         if (u->nr_evtchns <= u->ring_size)
 330                 return 0;
 331
 332         if (u->ring_size == 0)
 333                 new_size = 64;
 334         else
 335                 new_size = 2 * u->ring_size;
 336
 337         new_ring = evtchn_alloc_ring(new_size);
 338         if (!new_ring)
 339                 return -ENOMEM;
 340
 341         old_ring = u->ring;
 342
 343         /*
 344          * Access to the ring contents is serialized by either the
 345          * prod /or/ cons lock so take both when resizing.
 346          */
 347         mutex_lock(&u->ring_cons_mutex);
 348         spin_lock_irq(&u->ring_prod_lock);
 349
 350         /*
 351          * Copy the old ring contents to the new ring.
 352          *
 353          * To take care of wrapping, a full ring, and the new index
 354          * pointing into the second half, simply copy the old contents
 355          * twice.
 356          *
 357          * +---------+    +------------------+
 358          * |34567  12| -> |34567  1234567  12|
 359          * +-----p-c-+    +-------c------p---+
 360          */
 361         memcpy(new_ring, old_ring, u->ring_size * sizeof(*u->ring));
 362         memcpy(new_ring + u->ring_size, old_ring,
 363                u->ring_size * sizeof(*u->ring));
 364
 365         u->ring = new_ring;
 366         u->ring_size = new_size;
 367
 368         spin_unlock_irq(&u->ring_prod_lock);
 369         mutex_unlock(&u->ring_cons_mutex);
 370
 371         evtchn_free_ring(old_ring);
 372
 373         return 0;
 374 }
 375
 376 static int evtchn_bind_to_user(struct per_user_data *u, int port)
 377 {
 378         struct user_evtchn *evtchn;
 379         struct evtchn_close close;
 380         int rc = 0;
 381
 382         /*
 383          * Ports are never reused, so every caller should pass in a
 384          * unique port.
 385          *
 386          * (Locking not necessary because we haven't registered the
 387          * interrupt handler yet, and our caller has already
 388          * serialized bind operations.)
 389          */
 390
 391         evtchn = kzalloc(sizeof(*evtchn), GFP_KERNEL);
 392         if (!evtchn)
 393                 return -ENOMEM;
 394
 395         evtchn->user = u;
 396         evtchn->port = port;
 397         evtchn->enabled = true; /* start enabled */
 398
 399         rc = add_evtchn(u, evtchn);
 400         if (rc < 0)
 401                 goto err;
 402
 403         rc = evtchn_resize_ring(u);
 404         if (rc < 0)
 405                 goto err;
 406
 407         rc = bind_evtchn_to_irqhandler(port, evtchn_interrupt, 0,
 408                                        u->name, evtchn);
 409         if (rc < 0)
 410                 goto err;
 411
 412         rc = evtchn_make_refcounted(port);
 413         return rc;
 414
 415 err:
 416         /* bind failed, should close the port now */
 417         close.port = port;
 418         if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close) != 0)
 419                 BUG();
 420         del_evtchn(u, evtchn);
 421         return rc;
 422 }
 423
 424 static void evtchn_unbind_from_user(struct per_user_data *u,
 425                                     struct user_evtchn *evtchn)
 426 {
 427         int irq = irq_from_evtchn(evtchn->port);
 428
 429         BUG_ON(irq < 0);
 430
 431         unbind_from_irqhandler(irq, evtchn);
 432
 433         del_evtchn(u, evtchn);
 434 }
 435
 436 static long evtchn_ioctl(struct file *file,
 437                          unsigned int cmd, unsigned long arg)
 438 {
 439         int rc;
 440         struct per_user_data *u = file->private_data;
 441         void __user *uarg = (void __user *) arg;
 442
 443         /* Prevent bind from racing with unbind */
 444         mutex_lock(&u->bind_mutex);
 445
 446         switch (cmd) {
 447         case IOCTL_EVTCHN_BIND_VIRQ: {
 448                 struct ioctl_evtchn_bind_virq bind;
 449                 struct evtchn_bind_virq bind_virq;
 450
 451                 rc = -EACCES;
 452                 if (u->restrict_domid != UNRESTRICTED_DOMID)
 453                         break;
 454
 455                 rc = -EFAULT;
 456                 if (copy_from_user(&bind, uarg, sizeof(bind)))
 457                         break;
 458
 459                 bind_virq.virq = bind.virq;
 460                 bind_virq.vcpu = xen_vcpu_nr(0);
 461                 rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_virq,
 462                                                  &bind_virq);
 463                 if (rc != 0)
 464                         break;
 465
 466                 rc = evtchn_bind_to_user(u, bind_virq.port);
 467                 if (rc == 0)
 468                         rc = bind_virq.port;
 469                 break;
 470         }
 471
 472         case IOCTL_EVTCHN_BIND_INTERDOMAIN: {
 473                 struct ioctl_evtchn_bind_interdomain bind;
 474                 struct evtchn_bind_interdomain bind_interdomain;
 475
 476                 rc = -EFAULT;
 477                 if (copy_from_user(&bind, uarg, sizeof(bind)))
 478                         break;
 479
 480                 rc = -EACCES;
 481                 if (u->restrict_domid != UNRESTRICTED_DOMID &&
 482                     u->restrict_domid != bind.remote_domain)
 483                         break;
 484
 485                 bind_interdomain.remote_dom  = bind.remote_domain;
 486                 bind_interdomain.remote_port = bind.remote_port;
 487                 rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_interdomain,
 488                                                  &bind_interdomain);
 489                 if (rc != 0)
 490                         break;
 491
 492                 rc = evtchn_bind_to_user(u, bind_interdomain.local_port);
 493                 if (rc == 0)
 494                         rc = bind_interdomain.local_port;
 495                 break;
 496         }
 497
 498         case IOCTL_EVTCHN_BIND_UNBOUND_PORT: {
 499                 struct ioctl_evtchn_bind_unbound_port bind;
 500                 struct evtchn_alloc_unbound alloc_unbound;
 501
 502                 rc = -EACCES;
 503                 if (u->restrict_domid != UNRESTRICTED_DOMID)
 504                         break;
 505
 506                 rc = -EFAULT;
 507                 if (copy_from_user(&bind, uarg, sizeof(bind)))
 508                         break;
 509
 510                 alloc_unbound.dom        = DOMID_SELF;
 511                 alloc_unbound.remote_dom = bind.remote_domain;
 512                 rc = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound,
 513                                                  &alloc_unbound);
 514                 if (rc != 0)
 515                         break;
 516
 517                 rc = evtchn_bind_to_user(u, alloc_unbound.port);
 518                 if (rc == 0)
 519                         rc = alloc_unbound.port;
 520                 break;
 521         }
 522
 523         case IOCTL_EVTCHN_UNBIND: {
 524                 struct ioctl_evtchn_unbind unbind;
 525                 struct user_evtchn *evtchn;
 526
 527                 rc = -EFAULT;
 528                 if (copy_from_user(&unbind, uarg, sizeof(unbind)))
 529                         break;
 530
 531                 rc = -EINVAL;
 532                 if (unbind.port >= xen_evtchn_nr_channels())
 533                         break;
 534
 535                 rc = -ENOTCONN;
 536                 evtchn = find_evtchn(u, unbind.port);
 537                 if (!evtchn)
 538                         break;
 539
 540                 disable_irq(irq_from_evtchn(unbind.port));
 541                 evtchn_unbind_from_user(u, evtchn);
 542                 rc = 0;
 543                 break;
 544         }
 545
 546         case IOCTL_EVTCHN_NOTIFY: {
 547                 struct ioctl_evtchn_notify notify;
 548                 struct user_evtchn *evtchn;
 549
 550                 rc = -EFAULT;
 551                 if (copy_from_user(&notify, uarg, sizeof(notify)))
 552                         break;
 553
 554                 rc = -ENOTCONN;
 555                 evtchn = find_evtchn(u, notify.port);
 556                 if (evtchn) {
 557                         notify_remote_via_evtchn(notify.port);
 558                         rc = 0;
 559                 }
 560                 break;
 561         }
 562
 563         case IOCTL_EVTCHN_RESET: {
 564                 /* Initialise the ring to empty. Clear errors. */
 565                 mutex_lock(&u->ring_cons_mutex);
 566                 spin_lock_irq(&u->ring_prod_lock);
 567                 u->ring_cons = u->ring_prod = u->ring_overflow = 0;
 568                 spin_unlock_irq(&u->ring_prod_lock);
 569                 mutex_unlock(&u->ring_cons_mutex);
 570                 rc = 0;
 571                 break;
 572         }
 573
 574         case IOCTL_EVTCHN_RESTRICT_DOMID: {
 575                 struct ioctl_evtchn_restrict_domid ierd;
 576
 577                 rc = -EACCES;
 578                 if (u->restrict_domid != UNRESTRICTED_DOMID)
 579                         break;
 580
 581                 rc = -EFAULT;
 582                 if (copy_from_user(&ierd, uarg, sizeof(ierd)))
 583                     break;
 584
 585                 rc = -EINVAL;
 586                 if (ierd.domid == 0 || ierd.domid >= DOMID_FIRST_RESERVED)
 587                         break;
 588
 589                 u->restrict_domid = ierd.domid;
 590                 rc = 0;
 591
 592                 break;
 593         }
 594
 595         default:
 596                 rc = -ENOSYS;
 597                 break;
 598         }
 599         mutex_unlock(&u->bind_mutex);
 600
 601         return rc;
 602 }
 603
 604 static unsigned int evtchn_poll(struct file *file, poll_table *wait)
 605 {
 606         unsigned int mask = POLLOUT | POLLWRNORM;
 607         struct per_user_data *u = file->private_data;
 608
 609         poll_wait(file, &u->evtchn_wait, wait);
 610         if (u->ring_cons != u->ring_prod)
 611                 mask |= POLLIN | POLLRDNORM;
 612         if (u->ring_overflow)
 613                 mask = POLLERR;
 614         return mask;
 615 }
 616
 617 static int evtchn_fasync(int fd, struct file *filp, int on)
 618 {
 619         struct per_user_data *u = filp->private_data;
 620         return fasync_helper(fd, filp, on, &u->evtchn_async_queue);
 621 }
 622
 623 static int evtchn_open(struct inode *inode, struct file *filp)
 624 {
 625         struct per_user_data *u;
 626
 627         u = kzalloc(sizeof(*u), GFP_KERNEL);
 628         if (u == NULL)
 629                 return -ENOMEM;
 630
 631         u->name = kasprintf(GFP_KERNEL, "evtchn:%s", current->comm);
 632         if (u->name == NULL) {
 633                 kfree(u);
 634                 return -ENOMEM;
 635         }
 636
 637         init_waitqueue_head(&u->evtchn_wait);
 638
 639         mutex_init(&u->bind_mutex);
 640         mutex_init(&u->ring_cons_mutex);
 641         spin_lock_init(&u->ring_prod_lock);
 642
 643         u->restrict_domid = UNRESTRICTED_DOMID;
 644
 645         filp->private_data = u;
 646
 647         return nonseekable_open(inode, filp);
 648 }
 649
 650 static int evtchn_release(struct inode *inode, struct file *filp)
 651 {
 652         struct per_user_data *u = filp->private_data;
 653         struct rb_node *node;
 654
 655         while ((node = u->evtchns.rb_node)) {
 656                 struct user_evtchn *evtchn;
 657
 658                 evtchn = rb_entry(node, struct user_evtchn, node);
 659                 disable_irq(irq_from_evtchn(evtchn->port));
 660                 evtchn_unbind_from_user(u, evtchn);
 661         }
 662
 663         evtchn_free_ring(u->ring);
 664         kfree(u->name);
 665         kfree(u);
 666
 667         return 0;
 668 }
 669
 670 static const struct file_operations evtchn_fops = {
 671         .owner   = THIS_MODULE,
 672         .read    = evtchn_read,
 673         .write   = evtchn_write,
 674         .unlocked_ioctl = evtchn_ioctl,
 675         .poll    = evtchn_poll,
 676         .fasync  = evtchn_fasync,
 677         .open    = evtchn_open,
 678         .release = evtchn_release,
 679         .llseek  = no_llseek,
 680 };
 681
 682 static struct miscdevice evtchn_miscdev = {
 683         .minor        = MISC_DYNAMIC_MINOR,
 684         .name         = "xen/evtchn",
 685         .fops         = &evtchn_fops,
 686 };
 687 static int __init evtchn_init(void)
 688 {
 689         int err;
 690
 691         if (!xen_domain())
 692                 return -ENODEV;
 693
 694         /* Create '/dev/xen/evtchn'. */
 695         err = misc_register(&evtchn_miscdev);
 696         if (err != 0) {
 697                 pr_err("Could not register /dev/xen/evtchn\n");
 698                 return err;
 699         }
 700
 701         pr_info("Event-channel device installed\n");
 702
 703         return 0;
 704 }
 705
 706 static void __exit evtchn_cleanup(void)
 707 {
 708         misc_deregister(&evtchn_miscdev);
 709 }
 710
 711 module_init(evtchn_init);
 712 module_exit(evtchn_cleanup);
 713
 714 MODULE_LICENSE("GPL");