xref: /openbmc/linux/drivers/xen/evtchn.c (revision f0931824) 
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 	bool unbinding;
89 };
90 
91 static void evtchn_free_ring(evtchn_port_t *ring)
92 {
93 	kvfree(ring);
94 }
95 
96 static unsigned int evtchn_ring_offset(struct per_user_data *u,
97 				       unsigned int idx)
98 {
99 	return idx & (u->ring_size - 1);
100 }
101 
102 static evtchn_port_t *evtchn_ring_entry(struct per_user_data *u,
103 					unsigned int idx)
104 {
105 	return u->ring + evtchn_ring_offset(u, idx);
106 }
107 
108 static int add_evtchn(struct per_user_data *u, struct user_evtchn *evtchn)
109 {
110 	struct rb_node **new = &(u->evtchns.rb_node), *parent = NULL;
111 
112 	u->nr_evtchns++;
113 
114 	while (*new) {
115 		struct user_evtchn *this;
116 
117 		this = rb_entry(*new, struct user_evtchn, node);
118 
119 		parent = *new;
120 		if (this->port < evtchn->port)
121 			new = &((*new)->rb_left);
122 		else if (this->port > evtchn->port)
123 			new = &((*new)->rb_right);
124 		else
125 			return -EEXIST;
126 	}
127 
128 	/* Add new node and rebalance tree. */
129 	rb_link_node(&evtchn->node, parent, new);
130 	rb_insert_color(&evtchn->node, &u->evtchns);
131 
132 	return 0;
133 }
134 
135 static void del_evtchn(struct per_user_data *u, struct user_evtchn *evtchn)
136 {
137 	u->nr_evtchns--;
138 	rb_erase(&evtchn->node, &u->evtchns);
139 	kfree(evtchn);
140 }
141 
142 static struct user_evtchn *find_evtchn(struct per_user_data *u,
143 				       evtchn_port_t port)
144 {
145 	struct rb_node *node = u->evtchns.rb_node;
146 
147 	while (node) {
148 		struct user_evtchn *evtchn;
149 
150 		evtchn = rb_entry(node, struct user_evtchn, node);
151 
152 		if (evtchn->port < port)
153 			node = node->rb_left;
154 		else if (evtchn->port > port)
155 			node = node->rb_right;
156 		else
157 			return evtchn;
158 	}
159 	return NULL;
160 }
161 
162 static irqreturn_t evtchn_interrupt(int irq, void *data)
163 {
164 	struct user_evtchn *evtchn = data;
165 	struct per_user_data *u = evtchn->user;
166 	unsigned int prod, cons;
167 
168 	/* Handler might be called when tearing down the IRQ. */
169 	if (evtchn->unbinding)
170 		return IRQ_HANDLED;
171 
172 	WARN(!evtchn->enabled,
173 	     "Interrupt for port %u, but apparently not enabled; per-user %p\n",
174 	     evtchn->port, u);
175 
176 	evtchn->enabled = false;
177 
178 	spin_lock(&u->ring_prod_lock);
179 
180 	prod = READ_ONCE(u->ring_prod);
181 	cons = READ_ONCE(u->ring_cons);
182 
183 	if ((prod - cons) < u->ring_size) {
184 		*evtchn_ring_entry(u, prod) = evtchn->port;
185 		smp_wmb(); /* Ensure ring contents visible */
186 		WRITE_ONCE(u->ring_prod, prod + 1);
187 		if (cons == prod) {
188 			wake_up_interruptible(&u->evtchn_wait);
189 			kill_fasync(&u->evtchn_async_queue,
190 				    SIGIO, POLL_IN);
191 		}
192 	} else
193 		u->ring_overflow = 1;
194 
195 	spin_unlock(&u->ring_prod_lock);
196 
197 	return IRQ_HANDLED;
198 }
199 
200 static ssize_t evtchn_read(struct file *file, char __user *buf,
201 			   size_t count, loff_t *ppos)
202 {
203 	int rc;
204 	unsigned int c, p, bytes1 = 0, bytes2 = 0;
205 	struct per_user_data *u = file->private_data;
206 
207 	/* Whole number of ports. */
208 	count &= ~(sizeof(evtchn_port_t)-1);
209 
210 	if (count == 0)
211 		return 0;
212 
213 	if (count > PAGE_SIZE)
214 		count = PAGE_SIZE;
215 
216 	for (;;) {
217 		mutex_lock(&u->ring_cons_mutex);
218 
219 		rc = -EFBIG;
220 		if (u->ring_overflow)
221 			goto unlock_out;
222 
223 		c = READ_ONCE(u->ring_cons);
224 		p = READ_ONCE(u->ring_prod);
225 		if (c != p)
226 			break;
227 
228 		mutex_unlock(&u->ring_cons_mutex);
229 
230 		if (file->f_flags & O_NONBLOCK)
231 			return -EAGAIN;
232 
233 		rc = wait_event_interruptible(u->evtchn_wait,
234 			READ_ONCE(u->ring_cons) != READ_ONCE(u->ring_prod));
235 		if (rc)
236 			return rc;
237 	}
238 
239 	/* Byte lengths of two chunks. Chunk split (if any) is at ring wrap. */
240 	if (((c ^ p) & u->ring_size) != 0) {
241 		bytes1 = (u->ring_size - evtchn_ring_offset(u, c)) *
242 			sizeof(evtchn_port_t);
243 		bytes2 = evtchn_ring_offset(u, p) * sizeof(evtchn_port_t);
244 	} else {
245 		bytes1 = (p - c) * sizeof(evtchn_port_t);
246 		bytes2 = 0;
247 	}
248 
249 	/* Truncate chunks according to caller's maximum byte count. */
250 	if (bytes1 > count) {
251 		bytes1 = count;
252 		bytes2 = 0;
253 	} else if ((bytes1 + bytes2) > count) {
254 		bytes2 = count - bytes1;
255 	}
256 
257 	rc = -EFAULT;
258 	smp_rmb(); /* Ensure that we see the port before we copy it. */
259 	if (copy_to_user(buf, evtchn_ring_entry(u, c), bytes1) ||
260 	    ((bytes2 != 0) &&
261 	     copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
262 		goto unlock_out;
263 
264 	WRITE_ONCE(u->ring_cons, c + (bytes1 + bytes2) / sizeof(evtchn_port_t));
265 	rc = bytes1 + bytes2;
266 
267  unlock_out:
268 	mutex_unlock(&u->ring_cons_mutex);
269 	return rc;
270 }
271 
272 static ssize_t evtchn_write(struct file *file, const char __user *buf,
273 			    size_t count, loff_t *ppos)
274 {
275 	int rc, i;
276 	evtchn_port_t *kbuf = (evtchn_port_t *)__get_free_page(GFP_KERNEL);
277 	struct per_user_data *u = file->private_data;
278 
279 	if (kbuf == NULL)
280 		return -ENOMEM;
281 
282 	/* Whole number of ports. */
283 	count &= ~(sizeof(evtchn_port_t)-1);
284 
285 	rc = 0;
286 	if (count == 0)
287 		goto out;
288 
289 	if (count > PAGE_SIZE)
290 		count = PAGE_SIZE;
291 
292 	rc = -EFAULT;
293 	if (copy_from_user(kbuf, buf, count) != 0)
294 		goto out;
295 
296 	mutex_lock(&u->bind_mutex);
297 
298 	for (i = 0; i < (count/sizeof(evtchn_port_t)); i++) {
299 		evtchn_port_t port = kbuf[i];
300 		struct user_evtchn *evtchn;
301 
302 		evtchn = find_evtchn(u, port);
303 		if (evtchn && !evtchn->enabled) {
304 			evtchn->enabled = true;
305 			xen_irq_lateeoi(irq_from_evtchn(port), 0);
306 		}
307 	}
308 
309 	mutex_unlock(&u->bind_mutex);
310 
311 	rc = count;
312 
313  out:
314 	free_page((unsigned long)kbuf);
315 	return rc;
316 }
317 
318 static int evtchn_resize_ring(struct per_user_data *u)
319 {
320 	unsigned int new_size;
321 	evtchn_port_t *new_ring, *old_ring;
322 
323 	/*
324 	 * Ensure the ring is large enough to capture all possible
325 	 * events. i.e., one free slot for each bound event.
326 	 */
327 	if (u->nr_evtchns <= u->ring_size)
328 		return 0;
329 
330 	if (u->ring_size == 0)
331 		new_size = 64;
332 	else
333 		new_size = 2 * u->ring_size;
334 
335 	new_ring = kvmalloc_array(new_size, sizeof(*new_ring), GFP_KERNEL);
336 	if (!new_ring)
337 		return -ENOMEM;
338 
339 	old_ring = u->ring;
340 
341 	/*
342 	 * Access to the ring contents is serialized by either the
343 	 * prod /or/ cons lock so take both when resizing.
344 	 */
345 	mutex_lock(&u->ring_cons_mutex);
346 	spin_lock_irq(&u->ring_prod_lock);
347 
348 	/*
349 	 * Copy the old ring contents to the new ring.
350 	 *
351 	 * To take care of wrapping, a full ring, and the new index
352 	 * pointing into the second half, simply copy the old contents
353 	 * twice.
354 	 *
355 	 * +---------+    +------------------+
356 	 * |34567  12| -> |34567  1234567  12|
357 	 * +-----p-c-+    +-------c------p---+
358 	 */
359 	memcpy(new_ring, old_ring, u->ring_size * sizeof(*u->ring));
360 	memcpy(new_ring + u->ring_size, old_ring,
361 	       u->ring_size * sizeof(*u->ring));
362 
363 	u->ring = new_ring;
364 	u->ring_size = new_size;
365 
366 	spin_unlock_irq(&u->ring_prod_lock);
367 	mutex_unlock(&u->ring_cons_mutex);
368 
369 	evtchn_free_ring(old_ring);
370 
371 	return 0;
372 }
373 
374 static int evtchn_bind_to_user(struct per_user_data *u, evtchn_port_t port,
375 			       bool is_static)
376 {
377 	struct user_evtchn *evtchn;
378 	int rc = 0;
379 
380 	/*
381 	 * Ports are never reused, so every caller should pass in a
382 	 * unique port.
383 	 *
384 	 * (Locking not necessary because we haven't registered the
385 	 * interrupt handler yet, and our caller has already
386 	 * serialized bind operations.)
387 	 */
388 
389 	evtchn = kzalloc(sizeof(*evtchn), GFP_KERNEL);
390 	if (!evtchn)
391 		return -ENOMEM;
392 
393 	evtchn->user = u;
394 	evtchn->port = port;
395 	evtchn->enabled = true; /* start enabled */
396 
397 	rc = add_evtchn(u, evtchn);
398 	if (rc < 0)
399 		goto err;
400 
401 	rc = evtchn_resize_ring(u);
402 	if (rc < 0)
403 		goto err;
404 
405 	rc = bind_evtchn_to_irqhandler_lateeoi(port, evtchn_interrupt, IRQF_SHARED,
406 					       u->name, evtchn);
407 	if (rc < 0)
408 		goto err;
409 
410 	rc = evtchn_make_refcounted(port, is_static);
411 	return rc;
412 
413 err:
414 	/* bind failed, should close the port now */
415 	if (!is_static)
416 		xen_evtchn_close(port);
417 
418 	del_evtchn(u, evtchn);
419 	return rc;
420 }
421 
422 static void evtchn_unbind_from_user(struct per_user_data *u,
423 				    struct user_evtchn *evtchn)
424 {
425 	int irq = irq_from_evtchn(evtchn->port);
426 
427 	BUG_ON(irq < 0);
428 
429 	evtchn->unbinding = true;
430 	unbind_from_irqhandler(irq, evtchn);
431 
432 	del_evtchn(u, evtchn);
433 }
434 
435 static long evtchn_ioctl(struct file *file,
436 			 unsigned int cmd, unsigned long arg)
437 {
438 	int rc;
439 	struct per_user_data *u = file->private_data;
440 	void __user *uarg = (void __user *) arg;
441 
442 	/* Prevent bind from racing with unbind */
443 	mutex_lock(&u->bind_mutex);
444 
445 	switch (cmd) {
446 	case IOCTL_EVTCHN_BIND_VIRQ: {
447 		struct ioctl_evtchn_bind_virq bind;
448 		struct evtchn_bind_virq bind_virq;
449 
450 		rc = -EACCES;
451 		if (u->restrict_domid != UNRESTRICTED_DOMID)
452 			break;
453 
454 		rc = -EFAULT;
455 		if (copy_from_user(&bind, uarg, sizeof(bind)))
456 			break;
457 
458 		bind_virq.virq = bind.virq;
459 		bind_virq.vcpu = xen_vcpu_nr(0);
460 		rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_virq,
461 						 &bind_virq);
462 		if (rc != 0)
463 			break;
464 
465 		rc = evtchn_bind_to_user(u, bind_virq.port, false);
466 		if (rc == 0)
467 			rc = bind_virq.port;
468 		break;
469 	}
470 
471 	case IOCTL_EVTCHN_BIND_INTERDOMAIN: {
472 		struct ioctl_evtchn_bind_interdomain bind;
473 		struct evtchn_bind_interdomain bind_interdomain;
474 
475 		rc = -EFAULT;
476 		if (copy_from_user(&bind, uarg, sizeof(bind)))
477 			break;
478 
479 		rc = -EACCES;
480 		if (u->restrict_domid != UNRESTRICTED_DOMID &&
481 		    u->restrict_domid != bind.remote_domain)
482 			break;
483 
484 		bind_interdomain.remote_dom  = bind.remote_domain;
485 		bind_interdomain.remote_port = bind.remote_port;
486 		rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_interdomain,
487 						 &bind_interdomain);
488 		if (rc != 0)
489 			break;
490 
491 		rc = evtchn_bind_to_user(u, bind_interdomain.local_port, false);
492 		if (rc == 0)
493 			rc = bind_interdomain.local_port;
494 		break;
495 	}
496 
497 	case IOCTL_EVTCHN_BIND_UNBOUND_PORT: {
498 		struct ioctl_evtchn_bind_unbound_port bind;
499 		struct evtchn_alloc_unbound alloc_unbound;
500 
501 		rc = -EACCES;
502 		if (u->restrict_domid != UNRESTRICTED_DOMID)
503 			break;
504 
505 		rc = -EFAULT;
506 		if (copy_from_user(&bind, uarg, sizeof(bind)))
507 			break;
508 
509 		alloc_unbound.dom        = DOMID_SELF;
510 		alloc_unbound.remote_dom = bind.remote_domain;
511 		rc = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound,
512 						 &alloc_unbound);
513 		if (rc != 0)
514 			break;
515 
516 		rc = evtchn_bind_to_user(u, alloc_unbound.port, false);
517 		if (rc == 0)
518 			rc = alloc_unbound.port;
519 		break;
520 	}
521 
522 	case IOCTL_EVTCHN_UNBIND: {
523 		struct ioctl_evtchn_unbind unbind;
524 		struct user_evtchn *evtchn;
525 
526 		rc = -EFAULT;
527 		if (copy_from_user(&unbind, uarg, sizeof(unbind)))
528 			break;
529 
530 		rc = -EINVAL;
531 		if (unbind.port >= xen_evtchn_nr_channels())
532 			break;
533 
534 		rc = -ENOTCONN;
535 		evtchn = find_evtchn(u, unbind.port);
536 		if (!evtchn)
537 			break;
538 
539 		disable_irq(irq_from_evtchn(unbind.port));
540 		evtchn_unbind_from_user(u, evtchn);
541 		rc = 0;
542 		break;
543 	}
544 
545 	case IOCTL_EVTCHN_BIND_STATIC: {
546 		struct ioctl_evtchn_bind bind;
547 		struct user_evtchn *evtchn;
548 
549 		rc = -EFAULT;
550 		if (copy_from_user(&bind, uarg, sizeof(bind)))
551 			break;
552 
553 		rc = -EISCONN;
554 		evtchn = find_evtchn(u, bind.port);
555 		if (evtchn)
556 			break;
557 
558 		rc = evtchn_bind_to_user(u, bind.port, true);
559 		break;
560 	}
561 
562 	case IOCTL_EVTCHN_NOTIFY: {
563 		struct ioctl_evtchn_notify notify;
564 		struct user_evtchn *evtchn;
565 
566 		rc = -EFAULT;
567 		if (copy_from_user(&notify, uarg, sizeof(notify)))
568 			break;
569 
570 		rc = -ENOTCONN;
571 		evtchn = find_evtchn(u, notify.port);
572 		if (evtchn) {
573 			notify_remote_via_evtchn(notify.port);
574 			rc = 0;
575 		}
576 		break;
577 	}
578 
579 	case IOCTL_EVTCHN_RESET: {
580 		/* Initialise the ring to empty. Clear errors. */
581 		mutex_lock(&u->ring_cons_mutex);
582 		spin_lock_irq(&u->ring_prod_lock);
583 		WRITE_ONCE(u->ring_cons, 0);
584 		WRITE_ONCE(u->ring_prod, 0);
585 		u->ring_overflow = 0;
586 		spin_unlock_irq(&u->ring_prod_lock);
587 		mutex_unlock(&u->ring_cons_mutex);
588 		rc = 0;
589 		break;
590 	}
591 
592 	case IOCTL_EVTCHN_RESTRICT_DOMID: {
593 		struct ioctl_evtchn_restrict_domid ierd;
594 
595 		rc = -EACCES;
596 		if (u->restrict_domid != UNRESTRICTED_DOMID)
597 			break;
598 
599 		rc = -EFAULT;
600 		if (copy_from_user(&ierd, uarg, sizeof(ierd)))
601 		    break;
602 
603 		rc = -EINVAL;
604 		if (ierd.domid == 0 || ierd.domid >= DOMID_FIRST_RESERVED)
605 			break;
606 
607 		u->restrict_domid = ierd.domid;
608 		rc = 0;
609 
610 		break;
611 	}
612 
613 	default:
614 		rc = -ENOSYS;
615 		break;
616 	}
617 	mutex_unlock(&u->bind_mutex);
618 
619 	return rc;
620 }
621 
622 static __poll_t evtchn_poll(struct file *file, poll_table *wait)
623 {
624 	__poll_t mask = EPOLLOUT | EPOLLWRNORM;
625 	struct per_user_data *u = file->private_data;
626 
627 	poll_wait(file, &u->evtchn_wait, wait);
628 	if (READ_ONCE(u->ring_cons) != READ_ONCE(u->ring_prod))
629 		mask |= EPOLLIN | EPOLLRDNORM;
630 	if (u->ring_overflow)
631 		mask = EPOLLERR;
632 	return mask;
633 }
634 
635 static int evtchn_fasync(int fd, struct file *filp, int on)
636 {
637 	struct per_user_data *u = filp->private_data;
638 	return fasync_helper(fd, filp, on, &u->evtchn_async_queue);
639 }
640 
641 static int evtchn_open(struct inode *inode, struct file *filp)
642 {
643 	struct per_user_data *u;
644 
645 	u = kzalloc(sizeof(*u), GFP_KERNEL);
646 	if (u == NULL)
647 		return -ENOMEM;
648 
649 	u->name = kasprintf(GFP_KERNEL, "evtchn:%s", current->comm);
650 	if (u->name == NULL) {
651 		kfree(u);
652 		return -ENOMEM;
653 	}
654 
655 	init_waitqueue_head(&u->evtchn_wait);
656 
657 	mutex_init(&u->bind_mutex);
658 	mutex_init(&u->ring_cons_mutex);
659 	spin_lock_init(&u->ring_prod_lock);
660 
661 	u->restrict_domid = UNRESTRICTED_DOMID;
662 
663 	filp->private_data = u;
664 
665 	return stream_open(inode, filp);
666 }
667 
668 static int evtchn_release(struct inode *inode, struct file *filp)
669 {
670 	struct per_user_data *u = filp->private_data;
671 	struct rb_node *node;
672 
673 	while ((node = u->evtchns.rb_node)) {
674 		struct user_evtchn *evtchn;
675 
676 		evtchn = rb_entry(node, struct user_evtchn, node);
677 		disable_irq(irq_from_evtchn(evtchn->port));
678 		evtchn_unbind_from_user(u, evtchn);
679 	}
680 
681 	evtchn_free_ring(u->ring);
682 	kfree(u->name);
683 	kfree(u);
684 
685 	return 0;
686 }
687 
688 static const struct file_operations evtchn_fops = {
689 	.owner   = THIS_MODULE,
690 	.read    = evtchn_read,
691 	.write   = evtchn_write,
692 	.unlocked_ioctl = evtchn_ioctl,
693 	.poll    = evtchn_poll,
694 	.fasync  = evtchn_fasync,
695 	.open    = evtchn_open,
696 	.release = evtchn_release,
697 	.llseek	 = no_llseek,
698 };
699 
700 static struct miscdevice evtchn_miscdev = {
701 	.minor        = MISC_DYNAMIC_MINOR,
702 	.name         = "xen/evtchn",
703 	.fops         = &evtchn_fops,
704 };
705 static int __init evtchn_init(void)
706 {
707 	int err;
708 
709 	if (!xen_domain())
710 		return -ENODEV;
711 
712 	/* Create '/dev/xen/evtchn'. */
713 	err = misc_register(&evtchn_miscdev);
714 	if (err != 0) {
715 		pr_err("Could not register /dev/xen/evtchn\n");
716 		return err;
717 	}
718 
719 	pr_info("Event-channel device installed\n");
720 
721 	return 0;
722 }
723 
724 static void __exit evtchn_cleanup(void)
725 {
726 	misc_deregister(&evtchn_miscdev);
727 }
728 
729 module_init(evtchn_init);
730 module_exit(evtchn_cleanup);
731 
732 MODULE_LICENSE("GPL");
733