xref: /openbmc/linux/drivers/xen/evtchn.c (revision adb19164) 
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 	evtchn_port_t port;
87 	bool enabled;
88 };
89 
90 static void evtchn_free_ring(evtchn_port_t *ring)
91 {
92 	kvfree(ring);
93 }
94 
95 static unsigned int evtchn_ring_offset(struct per_user_data *u,
96 				       unsigned int idx)
97 {
98 	return idx & (u->ring_size - 1);
99 }
100 
101 static evtchn_port_t *evtchn_ring_entry(struct per_user_data *u,
102 					unsigned int idx)
103 {
104 	return u->ring + evtchn_ring_offset(u, idx);
105 }
106 
107 static int add_evtchn(struct per_user_data *u, struct user_evtchn *evtchn)
108 {
109 	struct rb_node **new = &(u->evtchns.rb_node), *parent = NULL;
110 
111 	u->nr_evtchns++;
112 
113 	while (*new) {
114 		struct user_evtchn *this;
115 
116 		this = rb_entry(*new, struct user_evtchn, node);
117 
118 		parent = *new;
119 		if (this->port < evtchn->port)
120 			new = &((*new)->rb_left);
121 		else if (this->port > evtchn->port)
122 			new = &((*new)->rb_right);
123 		else
124 			return -EEXIST;
125 	}
126 
127 	/* Add new node and rebalance tree. */
128 	rb_link_node(&evtchn->node, parent, new);
129 	rb_insert_color(&evtchn->node, &u->evtchns);
130 
131 	return 0;
132 }
133 
134 static void del_evtchn(struct per_user_data *u, struct user_evtchn *evtchn)
135 {
136 	u->nr_evtchns--;
137 	rb_erase(&evtchn->node, &u->evtchns);
138 	kfree(evtchn);
139 }
140 
141 static struct user_evtchn *find_evtchn(struct per_user_data *u,
142 				       evtchn_port_t port)
143 {
144 	struct rb_node *node = u->evtchns.rb_node;
145 
146 	while (node) {
147 		struct user_evtchn *evtchn;
148 
149 		evtchn = rb_entry(node, struct user_evtchn, node);
150 
151 		if (evtchn->port < port)
152 			node = node->rb_left;
153 		else if (evtchn->port > port)
154 			node = node->rb_right;
155 		else
156 			return evtchn;
157 	}
158 	return NULL;
159 }
160 
161 static irqreturn_t evtchn_interrupt(int irq, void *data)
162 {
163 	struct user_evtchn *evtchn = data;
164 	struct per_user_data *u = evtchn->user;
165 	unsigned int prod, cons;
166 
167 	WARN(!evtchn->enabled,
168 	     "Interrupt for port %u, but apparently not enabled; per-user %p\n",
169 	     evtchn->port, u);
170 
171 	evtchn->enabled = false;
172 
173 	spin_lock(&u->ring_prod_lock);
174 
175 	prod = READ_ONCE(u->ring_prod);
176 	cons = READ_ONCE(u->ring_cons);
177 
178 	if ((prod - cons) < u->ring_size) {
179 		*evtchn_ring_entry(u, prod) = evtchn->port;
180 		smp_wmb(); /* Ensure ring contents visible */
181 		WRITE_ONCE(u->ring_prod, prod + 1);
182 		if (cons == prod) {
183 			wake_up_interruptible(&u->evtchn_wait);
184 			kill_fasync(&u->evtchn_async_queue,
185 				    SIGIO, POLL_IN);
186 		}
187 	} else
188 		u->ring_overflow = 1;
189 
190 	spin_unlock(&u->ring_prod_lock);
191 
192 	return IRQ_HANDLED;
193 }
194 
195 static ssize_t evtchn_read(struct file *file, char __user *buf,
196 			   size_t count, loff_t *ppos)
197 {
198 	int rc;
199 	unsigned int c, p, bytes1 = 0, bytes2 = 0;
200 	struct per_user_data *u = file->private_data;
201 
202 	/* Whole number of ports. */
203 	count &= ~(sizeof(evtchn_port_t)-1);
204 
205 	if (count == 0)
206 		return 0;
207 
208 	if (count > PAGE_SIZE)
209 		count = PAGE_SIZE;
210 
211 	for (;;) {
212 		mutex_lock(&u->ring_cons_mutex);
213 
214 		rc = -EFBIG;
215 		if (u->ring_overflow)
216 			goto unlock_out;
217 
218 		c = READ_ONCE(u->ring_cons);
219 		p = READ_ONCE(u->ring_prod);
220 		if (c != p)
221 			break;
222 
223 		mutex_unlock(&u->ring_cons_mutex);
224 
225 		if (file->f_flags & O_NONBLOCK)
226 			return -EAGAIN;
227 
228 		rc = wait_event_interruptible(u->evtchn_wait,
229 			READ_ONCE(u->ring_cons) != READ_ONCE(u->ring_prod));
230 		if (rc)
231 			return rc;
232 	}
233 
234 	/* Byte lengths of two chunks. Chunk split (if any) is at ring wrap. */
235 	if (((c ^ p) & u->ring_size) != 0) {
236 		bytes1 = (u->ring_size - evtchn_ring_offset(u, c)) *
237 			sizeof(evtchn_port_t);
238 		bytes2 = evtchn_ring_offset(u, p) * sizeof(evtchn_port_t);
239 	} else {
240 		bytes1 = (p - c) * sizeof(evtchn_port_t);
241 		bytes2 = 0;
242 	}
243 
244 	/* Truncate chunks according to caller's maximum byte count. */
245 	if (bytes1 > count) {
246 		bytes1 = count;
247 		bytes2 = 0;
248 	} else if ((bytes1 + bytes2) > count) {
249 		bytes2 = count - bytes1;
250 	}
251 
252 	rc = -EFAULT;
253 	smp_rmb(); /* Ensure that we see the port before we copy it. */
254 	if (copy_to_user(buf, evtchn_ring_entry(u, c), bytes1) ||
255 	    ((bytes2 != 0) &&
256 	     copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
257 		goto unlock_out;
258 
259 	WRITE_ONCE(u->ring_cons, c + (bytes1 + bytes2) / sizeof(evtchn_port_t));
260 	rc = bytes1 + bytes2;
261 
262  unlock_out:
263 	mutex_unlock(&u->ring_cons_mutex);
264 	return rc;
265 }
266 
267 static ssize_t evtchn_write(struct file *file, const char __user *buf,
268 			    size_t count, loff_t *ppos)
269 {
270 	int rc, i;
271 	evtchn_port_t *kbuf = (evtchn_port_t *)__get_free_page(GFP_KERNEL);
272 	struct per_user_data *u = file->private_data;
273 
274 	if (kbuf == NULL)
275 		return -ENOMEM;
276 
277 	/* Whole number of ports. */
278 	count &= ~(sizeof(evtchn_port_t)-1);
279 
280 	rc = 0;
281 	if (count == 0)
282 		goto out;
283 
284 	if (count > PAGE_SIZE)
285 		count = PAGE_SIZE;
286 
287 	rc = -EFAULT;
288 	if (copy_from_user(kbuf, buf, count) != 0)
289 		goto out;
290 
291 	mutex_lock(&u->bind_mutex);
292 
293 	for (i = 0; i < (count/sizeof(evtchn_port_t)); i++) {
294 		evtchn_port_t port = kbuf[i];
295 		struct user_evtchn *evtchn;
296 
297 		evtchn = find_evtchn(u, port);
298 		if (evtchn && !evtchn->enabled) {
299 			evtchn->enabled = true;
300 			xen_irq_lateeoi(irq_from_evtchn(port), 0);
301 		}
302 	}
303 
304 	mutex_unlock(&u->bind_mutex);
305 
306 	rc = count;
307 
308  out:
309 	free_page((unsigned long)kbuf);
310 	return rc;
311 }
312 
313 static int evtchn_resize_ring(struct per_user_data *u)
314 {
315 	unsigned int new_size;
316 	evtchn_port_t *new_ring, *old_ring;
317 
318 	/*
319 	 * Ensure the ring is large enough to capture all possible
320 	 * events. i.e., one free slot for each bound event.
321 	 */
322 	if (u->nr_evtchns <= u->ring_size)
323 		return 0;
324 
325 	if (u->ring_size == 0)
326 		new_size = 64;
327 	else
328 		new_size = 2 * u->ring_size;
329 
330 	new_ring = kvmalloc_array(new_size, sizeof(*new_ring), GFP_KERNEL);
331 	if (!new_ring)
332 		return -ENOMEM;
333 
334 	old_ring = u->ring;
335 
336 	/*
337 	 * Access to the ring contents is serialized by either the
338 	 * prod /or/ cons lock so take both when resizing.
339 	 */
340 	mutex_lock(&u->ring_cons_mutex);
341 	spin_lock_irq(&u->ring_prod_lock);
342 
343 	/*
344 	 * Copy the old ring contents to the new ring.
345 	 *
346 	 * To take care of wrapping, a full ring, and the new index
347 	 * pointing into the second half, simply copy the old contents
348 	 * twice.
349 	 *
350 	 * +---------+    +------------------+
351 	 * |34567  12| -> |34567  1234567  12|
352 	 * +-----p-c-+    +-------c------p---+
353 	 */
354 	memcpy(new_ring, old_ring, u->ring_size * sizeof(*u->ring));
355 	memcpy(new_ring + u->ring_size, old_ring,
356 	       u->ring_size * sizeof(*u->ring));
357 
358 	u->ring = new_ring;
359 	u->ring_size = new_size;
360 
361 	spin_unlock_irq(&u->ring_prod_lock);
362 	mutex_unlock(&u->ring_cons_mutex);
363 
364 	evtchn_free_ring(old_ring);
365 
366 	return 0;
367 }
368 
369 static int evtchn_bind_to_user(struct per_user_data *u, evtchn_port_t port,
370 			       bool is_static)
371 {
372 	struct user_evtchn *evtchn;
373 	int rc = 0;
374 
375 	/*
376 	 * Ports are never reused, so every caller should pass in a
377 	 * unique port.
378 	 *
379 	 * (Locking not necessary because we haven't registered the
380 	 * interrupt handler yet, and our caller has already
381 	 * serialized bind operations.)
382 	 */
383 
384 	evtchn = kzalloc(sizeof(*evtchn), GFP_KERNEL);
385 	if (!evtchn)
386 		return -ENOMEM;
387 
388 	evtchn->user = u;
389 	evtchn->port = port;
390 	evtchn->enabled = true; /* start enabled */
391 
392 	rc = add_evtchn(u, evtchn);
393 	if (rc < 0)
394 		goto err;
395 
396 	rc = evtchn_resize_ring(u);
397 	if (rc < 0)
398 		goto err;
399 
400 	rc = bind_evtchn_to_irqhandler_lateeoi(port, evtchn_interrupt, IRQF_SHARED,
401 					       u->name, evtchn);
402 	if (rc < 0)
403 		goto err;
404 
405 	rc = evtchn_make_refcounted(port, is_static);
406 	return rc;
407 
408 err:
409 	/* bind failed, should close the port now */
410 	if (!is_static)
411 		xen_evtchn_close(port);
412 
413 	del_evtchn(u, evtchn);
414 	return rc;
415 }
416 
417 static void evtchn_unbind_from_user(struct per_user_data *u,
418 				    struct user_evtchn *evtchn)
419 {
420 	int irq = irq_from_evtchn(evtchn->port);
421 
422 	BUG_ON(irq < 0);
423 
424 	unbind_from_irqhandler(irq, evtchn);
425 
426 	del_evtchn(u, evtchn);
427 }
428 
429 static long evtchn_ioctl(struct file *file,
430 			 unsigned int cmd, unsigned long arg)
431 {
432 	int rc;
433 	struct per_user_data *u = file->private_data;
434 	void __user *uarg = (void __user *) arg;
435 
436 	/* Prevent bind from racing with unbind */
437 	mutex_lock(&u->bind_mutex);
438 
439 	switch (cmd) {
440 	case IOCTL_EVTCHN_BIND_VIRQ: {
441 		struct ioctl_evtchn_bind_virq bind;
442 		struct evtchn_bind_virq bind_virq;
443 
444 		rc = -EACCES;
445 		if (u->restrict_domid != UNRESTRICTED_DOMID)
446 			break;
447 
448 		rc = -EFAULT;
449 		if (copy_from_user(&bind, uarg, sizeof(bind)))
450 			break;
451 
452 		bind_virq.virq = bind.virq;
453 		bind_virq.vcpu = xen_vcpu_nr(0);
454 		rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_virq,
455 						 &bind_virq);
456 		if (rc != 0)
457 			break;
458 
459 		rc = evtchn_bind_to_user(u, bind_virq.port, false);
460 		if (rc == 0)
461 			rc = bind_virq.port;
462 		break;
463 	}
464 
465 	case IOCTL_EVTCHN_BIND_INTERDOMAIN: {
466 		struct ioctl_evtchn_bind_interdomain bind;
467 		struct evtchn_bind_interdomain bind_interdomain;
468 
469 		rc = -EFAULT;
470 		if (copy_from_user(&bind, uarg, sizeof(bind)))
471 			break;
472 
473 		rc = -EACCES;
474 		if (u->restrict_domid != UNRESTRICTED_DOMID &&
475 		    u->restrict_domid != bind.remote_domain)
476 			break;
477 
478 		bind_interdomain.remote_dom  = bind.remote_domain;
479 		bind_interdomain.remote_port = bind.remote_port;
480 		rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_interdomain,
481 						 &bind_interdomain);
482 		if (rc != 0)
483 			break;
484 
485 		rc = evtchn_bind_to_user(u, bind_interdomain.local_port, false);
486 		if (rc == 0)
487 			rc = bind_interdomain.local_port;
488 		break;
489 	}
490 
491 	case IOCTL_EVTCHN_BIND_UNBOUND_PORT: {
492 		struct ioctl_evtchn_bind_unbound_port bind;
493 		struct evtchn_alloc_unbound alloc_unbound;
494 
495 		rc = -EACCES;
496 		if (u->restrict_domid != UNRESTRICTED_DOMID)
497 			break;
498 
499 		rc = -EFAULT;
500 		if (copy_from_user(&bind, uarg, sizeof(bind)))
501 			break;
502 
503 		alloc_unbound.dom        = DOMID_SELF;
504 		alloc_unbound.remote_dom = bind.remote_domain;
505 		rc = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound,
506 						 &alloc_unbound);
507 		if (rc != 0)
508 			break;
509 
510 		rc = evtchn_bind_to_user(u, alloc_unbound.port, false);
511 		if (rc == 0)
512 			rc = alloc_unbound.port;
513 		break;
514 	}
515 
516 	case IOCTL_EVTCHN_UNBIND: {
517 		struct ioctl_evtchn_unbind unbind;
518 		struct user_evtchn *evtchn;
519 
520 		rc = -EFAULT;
521 		if (copy_from_user(&unbind, uarg, sizeof(unbind)))
522 			break;
523 
524 		rc = -EINVAL;
525 		if (unbind.port >= xen_evtchn_nr_channels())
526 			break;
527 
528 		rc = -ENOTCONN;
529 		evtchn = find_evtchn(u, unbind.port);
530 		if (!evtchn)
531 			break;
532 
533 		disable_irq(irq_from_evtchn(unbind.port));
534 		evtchn_unbind_from_user(u, evtchn);
535 		rc = 0;
536 		break;
537 	}
538 
539 	case IOCTL_EVTCHN_BIND_STATIC: {
540 		struct ioctl_evtchn_bind bind;
541 		struct user_evtchn *evtchn;
542 
543 		rc = -EFAULT;
544 		if (copy_from_user(&bind, uarg, sizeof(bind)))
545 			break;
546 
547 		rc = -EISCONN;
548 		evtchn = find_evtchn(u, bind.port);
549 		if (evtchn)
550 			break;
551 
552 		rc = evtchn_bind_to_user(u, bind.port, true);
553 		break;
554 	}
555 
556 	case IOCTL_EVTCHN_NOTIFY: {
557 		struct ioctl_evtchn_notify notify;
558 		struct user_evtchn *evtchn;
559 
560 		rc = -EFAULT;
561 		if (copy_from_user(&notify, uarg, sizeof(notify)))
562 			break;
563 
564 		rc = -ENOTCONN;
565 		evtchn = find_evtchn(u, notify.port);
566 		if (evtchn) {
567 			notify_remote_via_evtchn(notify.port);
568 			rc = 0;
569 		}
570 		break;
571 	}
572 
573 	case IOCTL_EVTCHN_RESET: {
574 		/* Initialise the ring to empty. Clear errors. */
575 		mutex_lock(&u->ring_cons_mutex);
576 		spin_lock_irq(&u->ring_prod_lock);
577 		WRITE_ONCE(u->ring_cons, 0);
578 		WRITE_ONCE(u->ring_prod, 0);
579 		u->ring_overflow = 0;
580 		spin_unlock_irq(&u->ring_prod_lock);
581 		mutex_unlock(&u->ring_cons_mutex);
582 		rc = 0;
583 		break;
584 	}
585 
586 	case IOCTL_EVTCHN_RESTRICT_DOMID: {
587 		struct ioctl_evtchn_restrict_domid ierd;
588 
589 		rc = -EACCES;
590 		if (u->restrict_domid != UNRESTRICTED_DOMID)
591 			break;
592 
593 		rc = -EFAULT;
594 		if (copy_from_user(&ierd, uarg, sizeof(ierd)))
595 		    break;
596 
597 		rc = -EINVAL;
598 		if (ierd.domid == 0 || ierd.domid >= DOMID_FIRST_RESERVED)
599 			break;
600 
601 		u->restrict_domid = ierd.domid;
602 		rc = 0;
603 
604 		break;
605 	}
606 
607 	default:
608 		rc = -ENOSYS;
609 		break;
610 	}
611 	mutex_unlock(&u->bind_mutex);
612 
613 	return rc;
614 }
615 
616 static __poll_t evtchn_poll(struct file *file, poll_table *wait)
617 {
618 	__poll_t mask = EPOLLOUT | EPOLLWRNORM;
619 	struct per_user_data *u = file->private_data;
620 
621 	poll_wait(file, &u->evtchn_wait, wait);
622 	if (READ_ONCE(u->ring_cons) != READ_ONCE(u->ring_prod))
623 		mask |= EPOLLIN | EPOLLRDNORM;
624 	if (u->ring_overflow)
625 		mask = EPOLLERR;
626 	return mask;
627 }
628 
629 static int evtchn_fasync(int fd, struct file *filp, int on)
630 {
631 	struct per_user_data *u = filp->private_data;
632 	return fasync_helper(fd, filp, on, &u->evtchn_async_queue);
633 }
634 
635 static int evtchn_open(struct inode *inode, struct file *filp)
636 {
637 	struct per_user_data *u;
638 
639 	u = kzalloc(sizeof(*u), GFP_KERNEL);
640 	if (u == NULL)
641 		return -ENOMEM;
642 
643 	u->name = kasprintf(GFP_KERNEL, "evtchn:%s", current->comm);
644 	if (u->name == NULL) {
645 		kfree(u);
646 		return -ENOMEM;
647 	}
648 
649 	init_waitqueue_head(&u->evtchn_wait);
650 
651 	mutex_init(&u->bind_mutex);
652 	mutex_init(&u->ring_cons_mutex);
653 	spin_lock_init(&u->ring_prod_lock);
654 
655 	u->restrict_domid = UNRESTRICTED_DOMID;
656 
657 	filp->private_data = u;
658 
659 	return stream_open(inode, filp);
660 }
661 
662 static int evtchn_release(struct inode *inode, struct file *filp)
663 {
664 	struct per_user_data *u = filp->private_data;
665 	struct rb_node *node;
666 
667 	while ((node = u->evtchns.rb_node)) {
668 		struct user_evtchn *evtchn;
669 
670 		evtchn = rb_entry(node, struct user_evtchn, node);
671 		disable_irq(irq_from_evtchn(evtchn->port));
672 		evtchn_unbind_from_user(u, evtchn);
673 	}
674 
675 	evtchn_free_ring(u->ring);
676 	kfree(u->name);
677 	kfree(u);
678 
679 	return 0;
680 }
681 
682 static const struct file_operations evtchn_fops = {
683 	.owner   = THIS_MODULE,
684 	.read    = evtchn_read,
685 	.write   = evtchn_write,
686 	.unlocked_ioctl = evtchn_ioctl,
687 	.poll    = evtchn_poll,
688 	.fasync  = evtchn_fasync,
689 	.open    = evtchn_open,
690 	.release = evtchn_release,
691 	.llseek	 = no_llseek,
692 };
693 
694 static struct miscdevice evtchn_miscdev = {
695 	.minor        = MISC_DYNAMIC_MINOR,
696 	.name         = "xen/evtchn",
697 	.fops         = &evtchn_fops,
698 };
699 static int __init evtchn_init(void)
700 {
701 	int err;
702 
703 	if (!xen_domain())
704 		return -ENODEV;
705 
706 	/* Create '/dev/xen/evtchn'. */
707 	err = misc_register(&evtchn_miscdev);
708 	if (err != 0) {
709 		pr_err("Could not register /dev/xen/evtchn\n");
710 		return err;
711 	}
712 
713 	pr_info("Event-channel device installed\n");
714 
715 	return 0;
716 }
717 
718 static void __exit evtchn_cleanup(void)
719 {
720 	misc_deregister(&evtchn_miscdev);
721 }
722 
723 module_init(evtchn_init);
724 module_exit(evtchn_cleanup);
725 
726 MODULE_LICENSE("GPL");
727