xref: /openbmc/linux/drivers/xen/evtchn.c (revision 165f2d28) 
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 
166 	WARN(!evtchn->enabled,
167 	     "Interrupt for port %u, but apparently not enabled; per-user %p\n",
168 	     evtchn->port, u);
169 
170 	disable_irq_nosync(irq);
171 	evtchn->enabled = false;
172 
173 	spin_lock(&u->ring_prod_lock);
174 
175 	if ((u->ring_prod - u->ring_cons) < u->ring_size) {
176 		*evtchn_ring_entry(u, u->ring_prod) = evtchn->port;
177 		wmb(); /* Ensure ring contents visible */
178 		if (u->ring_cons == u->ring_prod++) {
179 			wake_up_interruptible(&u->evtchn_wait);
180 			kill_fasync(&u->evtchn_async_queue,
181 				    SIGIO, POLL_IN);
182 		}
183 	} else
184 		u->ring_overflow = 1;
185 
186 	spin_unlock(&u->ring_prod_lock);
187 
188 	return IRQ_HANDLED;
189 }
190 
191 static ssize_t evtchn_read(struct file *file, char __user *buf,
192 			   size_t count, loff_t *ppos)
193 {
194 	int rc;
195 	unsigned int c, p, bytes1 = 0, bytes2 = 0;
196 	struct per_user_data *u = file->private_data;
197 
198 	/* Whole number of ports. */
199 	count &= ~(sizeof(evtchn_port_t)-1);
200 
201 	if (count == 0)
202 		return 0;
203 
204 	if (count > PAGE_SIZE)
205 		count = PAGE_SIZE;
206 
207 	for (;;) {
208 		mutex_lock(&u->ring_cons_mutex);
209 
210 		rc = -EFBIG;
211 		if (u->ring_overflow)
212 			goto unlock_out;
213 
214 		c = u->ring_cons;
215 		p = u->ring_prod;
216 		if (c != p)
217 			break;
218 
219 		mutex_unlock(&u->ring_cons_mutex);
220 
221 		if (file->f_flags & O_NONBLOCK)
222 			return -EAGAIN;
223 
224 		rc = wait_event_interruptible(u->evtchn_wait,
225 					      u->ring_cons != u->ring_prod);
226 		if (rc)
227 			return rc;
228 	}
229 
230 	/* Byte lengths of two chunks. Chunk split (if any) is at ring wrap. */
231 	if (((c ^ p) & u->ring_size) != 0) {
232 		bytes1 = (u->ring_size - evtchn_ring_offset(u, c)) *
233 			sizeof(evtchn_port_t);
234 		bytes2 = evtchn_ring_offset(u, p) * sizeof(evtchn_port_t);
235 	} else {
236 		bytes1 = (p - c) * sizeof(evtchn_port_t);
237 		bytes2 = 0;
238 	}
239 
240 	/* Truncate chunks according to caller's maximum byte count. */
241 	if (bytes1 > count) {
242 		bytes1 = count;
243 		bytes2 = 0;
244 	} else if ((bytes1 + bytes2) > count) {
245 		bytes2 = count - bytes1;
246 	}
247 
248 	rc = -EFAULT;
249 	rmb(); /* Ensure that we see the port before we copy it. */
250 	if (copy_to_user(buf, evtchn_ring_entry(u, c), bytes1) ||
251 	    ((bytes2 != 0) &&
252 	     copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
253 		goto unlock_out;
254 
255 	u->ring_cons += (bytes1 + bytes2) / sizeof(evtchn_port_t);
256 	rc = bytes1 + bytes2;
257 
258  unlock_out:
259 	mutex_unlock(&u->ring_cons_mutex);
260 	return rc;
261 }
262 
263 static ssize_t evtchn_write(struct file *file, const char __user *buf,
264 			    size_t count, loff_t *ppos)
265 {
266 	int rc, i;
267 	evtchn_port_t *kbuf = (evtchn_port_t *)__get_free_page(GFP_KERNEL);
268 	struct per_user_data *u = file->private_data;
269 
270 	if (kbuf == NULL)
271 		return -ENOMEM;
272 
273 	/* Whole number of ports. */
274 	count &= ~(sizeof(evtchn_port_t)-1);
275 
276 	rc = 0;
277 	if (count == 0)
278 		goto out;
279 
280 	if (count > PAGE_SIZE)
281 		count = PAGE_SIZE;
282 
283 	rc = -EFAULT;
284 	if (copy_from_user(kbuf, buf, count) != 0)
285 		goto out;
286 
287 	mutex_lock(&u->bind_mutex);
288 
289 	for (i = 0; i < (count/sizeof(evtchn_port_t)); i++) {
290 		evtchn_port_t port = kbuf[i];
291 		struct user_evtchn *evtchn;
292 
293 		evtchn = find_evtchn(u, port);
294 		if (evtchn && !evtchn->enabled) {
295 			evtchn->enabled = true;
296 			enable_irq(irq_from_evtchn(port));
297 		}
298 	}
299 
300 	mutex_unlock(&u->bind_mutex);
301 
302 	rc = count;
303 
304  out:
305 	free_page((unsigned long)kbuf);
306 	return rc;
307 }
308 
309 static int evtchn_resize_ring(struct per_user_data *u)
310 {
311 	unsigned int new_size;
312 	evtchn_port_t *new_ring, *old_ring;
313 
314 	/*
315 	 * Ensure the ring is large enough to capture all possible
316 	 * events. i.e., one free slot for each bound event.
317 	 */
318 	if (u->nr_evtchns <= u->ring_size)
319 		return 0;
320 
321 	if (u->ring_size == 0)
322 		new_size = 64;
323 	else
324 		new_size = 2 * u->ring_size;
325 
326 	new_ring = kvmalloc_array(new_size, sizeof(*new_ring), GFP_KERNEL);
327 	if (!new_ring)
328 		return -ENOMEM;
329 
330 	old_ring = u->ring;
331 
332 	/*
333 	 * Access to the ring contents is serialized by either the
334 	 * prod /or/ cons lock so take both when resizing.
335 	 */
336 	mutex_lock(&u->ring_cons_mutex);
337 	spin_lock_irq(&u->ring_prod_lock);
338 
339 	/*
340 	 * Copy the old ring contents to the new ring.
341 	 *
342 	 * To take care of wrapping, a full ring, and the new index
343 	 * pointing into the second half, simply copy the old contents
344 	 * twice.
345 	 *
346 	 * +---------+    +------------------+
347 	 * |34567  12| -> |34567  1234567  12|
348 	 * +-----p-c-+    +-------c------p---+
349 	 */
350 	memcpy(new_ring, old_ring, u->ring_size * sizeof(*u->ring));
351 	memcpy(new_ring + u->ring_size, old_ring,
352 	       u->ring_size * sizeof(*u->ring));
353 
354 	u->ring = new_ring;
355 	u->ring_size = new_size;
356 
357 	spin_unlock_irq(&u->ring_prod_lock);
358 	mutex_unlock(&u->ring_cons_mutex);
359 
360 	evtchn_free_ring(old_ring);
361 
362 	return 0;
363 }
364 
365 static int evtchn_bind_to_user(struct per_user_data *u, evtchn_port_t port)
366 {
367 	struct user_evtchn *evtchn;
368 	struct evtchn_close close;
369 	int rc = 0;
370 
371 	/*
372 	 * Ports are never reused, so every caller should pass in a
373 	 * unique port.
374 	 *
375 	 * (Locking not necessary because we haven't registered the
376 	 * interrupt handler yet, and our caller has already
377 	 * serialized bind operations.)
378 	 */
379 
380 	evtchn = kzalloc(sizeof(*evtchn), GFP_KERNEL);
381 	if (!evtchn)
382 		return -ENOMEM;
383 
384 	evtchn->user = u;
385 	evtchn->port = port;
386 	evtchn->enabled = true; /* start enabled */
387 
388 	rc = add_evtchn(u, evtchn);
389 	if (rc < 0)
390 		goto err;
391 
392 	rc = evtchn_resize_ring(u);
393 	if (rc < 0)
394 		goto err;
395 
396 	rc = bind_evtchn_to_irqhandler(port, evtchn_interrupt, 0,
397 				       u->name, evtchn);
398 	if (rc < 0)
399 		goto err;
400 
401 	rc = evtchn_make_refcounted(port);
402 	return rc;
403 
404 err:
405 	/* bind failed, should close the port now */
406 	close.port = port;
407 	if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close) != 0)
408 		BUG();
409 	del_evtchn(u, evtchn);
410 	return rc;
411 }
412 
413 static void evtchn_unbind_from_user(struct per_user_data *u,
414 				    struct user_evtchn *evtchn)
415 {
416 	int irq = irq_from_evtchn(evtchn->port);
417 
418 	BUG_ON(irq < 0);
419 
420 	unbind_from_irqhandler(irq, evtchn);
421 
422 	del_evtchn(u, evtchn);
423 }
424 
425 static DEFINE_PER_CPU(int, bind_last_selected_cpu);
426 
427 static void evtchn_bind_interdom_next_vcpu(evtchn_port_t evtchn)
428 {
429 	unsigned int selected_cpu, irq;
430 	struct irq_desc *desc;
431 	unsigned long flags;
432 
433 	irq = irq_from_evtchn(evtchn);
434 	desc = irq_to_desc(irq);
435 
436 	if (!desc)
437 		return;
438 
439 	raw_spin_lock_irqsave(&desc->lock, flags);
440 	selected_cpu = this_cpu_read(bind_last_selected_cpu);
441 	selected_cpu = cpumask_next_and(selected_cpu,
442 			desc->irq_common_data.affinity, cpu_online_mask);
443 
444 	if (unlikely(selected_cpu >= nr_cpu_ids))
445 		selected_cpu = cpumask_first_and(desc->irq_common_data.affinity,
446 				cpu_online_mask);
447 
448 	this_cpu_write(bind_last_selected_cpu, selected_cpu);
449 
450 	/* unmask expects irqs to be disabled */
451 	xen_set_affinity_evtchn(desc, selected_cpu);
452 	raw_spin_unlock_irqrestore(&desc->lock, flags);
453 }
454 
455 static long evtchn_ioctl(struct file *file,
456 			 unsigned int cmd, unsigned long arg)
457 {
458 	int rc;
459 	struct per_user_data *u = file->private_data;
460 	void __user *uarg = (void __user *) arg;
461 
462 	/* Prevent bind from racing with unbind */
463 	mutex_lock(&u->bind_mutex);
464 
465 	switch (cmd) {
466 	case IOCTL_EVTCHN_BIND_VIRQ: {
467 		struct ioctl_evtchn_bind_virq bind;
468 		struct evtchn_bind_virq bind_virq;
469 
470 		rc = -EACCES;
471 		if (u->restrict_domid != UNRESTRICTED_DOMID)
472 			break;
473 
474 		rc = -EFAULT;
475 		if (copy_from_user(&bind, uarg, sizeof(bind)))
476 			break;
477 
478 		bind_virq.virq = bind.virq;
479 		bind_virq.vcpu = xen_vcpu_nr(0);
480 		rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_virq,
481 						 &bind_virq);
482 		if (rc != 0)
483 			break;
484 
485 		rc = evtchn_bind_to_user(u, bind_virq.port);
486 		if (rc == 0)
487 			rc = bind_virq.port;
488 		break;
489 	}
490 
491 	case IOCTL_EVTCHN_BIND_INTERDOMAIN: {
492 		struct ioctl_evtchn_bind_interdomain bind;
493 		struct evtchn_bind_interdomain bind_interdomain;
494 
495 		rc = -EFAULT;
496 		if (copy_from_user(&bind, uarg, sizeof(bind)))
497 			break;
498 
499 		rc = -EACCES;
500 		if (u->restrict_domid != UNRESTRICTED_DOMID &&
501 		    u->restrict_domid != bind.remote_domain)
502 			break;
503 
504 		bind_interdomain.remote_dom  = bind.remote_domain;
505 		bind_interdomain.remote_port = bind.remote_port;
506 		rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_interdomain,
507 						 &bind_interdomain);
508 		if (rc != 0)
509 			break;
510 
511 		rc = evtchn_bind_to_user(u, bind_interdomain.local_port);
512 		if (rc == 0) {
513 			rc = bind_interdomain.local_port;
514 			evtchn_bind_interdom_next_vcpu(rc);
515 		}
516 		break;
517 	}
518 
519 	case IOCTL_EVTCHN_BIND_UNBOUND_PORT: {
520 		struct ioctl_evtchn_bind_unbound_port bind;
521 		struct evtchn_alloc_unbound alloc_unbound;
522 
523 		rc = -EACCES;
524 		if (u->restrict_domid != UNRESTRICTED_DOMID)
525 			break;
526 
527 		rc = -EFAULT;
528 		if (copy_from_user(&bind, uarg, sizeof(bind)))
529 			break;
530 
531 		alloc_unbound.dom        = DOMID_SELF;
532 		alloc_unbound.remote_dom = bind.remote_domain;
533 		rc = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound,
534 						 &alloc_unbound);
535 		if (rc != 0)
536 			break;
537 
538 		rc = evtchn_bind_to_user(u, alloc_unbound.port);
539 		if (rc == 0)
540 			rc = alloc_unbound.port;
541 		break;
542 	}
543 
544 	case IOCTL_EVTCHN_UNBIND: {
545 		struct ioctl_evtchn_unbind unbind;
546 		struct user_evtchn *evtchn;
547 
548 		rc = -EFAULT;
549 		if (copy_from_user(&unbind, uarg, sizeof(unbind)))
550 			break;
551 
552 		rc = -EINVAL;
553 		if (unbind.port >= xen_evtchn_nr_channels())
554 			break;
555 
556 		rc = -ENOTCONN;
557 		evtchn = find_evtchn(u, unbind.port);
558 		if (!evtchn)
559 			break;
560 
561 		disable_irq(irq_from_evtchn(unbind.port));
562 		evtchn_unbind_from_user(u, evtchn);
563 		rc = 0;
564 		break;
565 	}
566 
567 	case IOCTL_EVTCHN_NOTIFY: {
568 		struct ioctl_evtchn_notify notify;
569 		struct user_evtchn *evtchn;
570 
571 		rc = -EFAULT;
572 		if (copy_from_user(&notify, uarg, sizeof(notify)))
573 			break;
574 
575 		rc = -ENOTCONN;
576 		evtchn = find_evtchn(u, notify.port);
577 		if (evtchn) {
578 			notify_remote_via_evtchn(notify.port);
579 			rc = 0;
580 		}
581 		break;
582 	}
583 
584 	case IOCTL_EVTCHN_RESET: {
585 		/* Initialise the ring to empty. Clear errors. */
586 		mutex_lock(&u->ring_cons_mutex);
587 		spin_lock_irq(&u->ring_prod_lock);
588 		u->ring_cons = u->ring_prod = u->ring_overflow = 0;
589 		spin_unlock_irq(&u->ring_prod_lock);
590 		mutex_unlock(&u->ring_cons_mutex);
591 		rc = 0;
592 		break;
593 	}
594 
595 	case IOCTL_EVTCHN_RESTRICT_DOMID: {
596 		struct ioctl_evtchn_restrict_domid ierd;
597 
598 		rc = -EACCES;
599 		if (u->restrict_domid != UNRESTRICTED_DOMID)
600 			break;
601 
602 		rc = -EFAULT;
603 		if (copy_from_user(&ierd, uarg, sizeof(ierd)))
604 		    break;
605 
606 		rc = -EINVAL;
607 		if (ierd.domid == 0 || ierd.domid >= DOMID_FIRST_RESERVED)
608 			break;
609 
610 		u->restrict_domid = ierd.domid;
611 		rc = 0;
612 
613 		break;
614 	}
615 
616 	default:
617 		rc = -ENOSYS;
618 		break;
619 	}
620 	mutex_unlock(&u->bind_mutex);
621 
622 	return rc;
623 }
624 
625 static __poll_t evtchn_poll(struct file *file, poll_table *wait)
626 {
627 	__poll_t mask = EPOLLOUT | EPOLLWRNORM;
628 	struct per_user_data *u = file->private_data;
629 
630 	poll_wait(file, &u->evtchn_wait, wait);
631 	if (u->ring_cons != u->ring_prod)
632 		mask |= EPOLLIN | EPOLLRDNORM;
633 	if (u->ring_overflow)
634 		mask = EPOLLERR;
635 	return mask;
636 }
637 
638 static int evtchn_fasync(int fd, struct file *filp, int on)
639 {
640 	struct per_user_data *u = filp->private_data;
641 	return fasync_helper(fd, filp, on, &u->evtchn_async_queue);
642 }
643 
644 static int evtchn_open(struct inode *inode, struct file *filp)
645 {
646 	struct per_user_data *u;
647 
648 	u = kzalloc(sizeof(*u), GFP_KERNEL);
649 	if (u == NULL)
650 		return -ENOMEM;
651 
652 	u->name = kasprintf(GFP_KERNEL, "evtchn:%s", current->comm);
653 	if (u->name == NULL) {
654 		kfree(u);
655 		return -ENOMEM;
656 	}
657 
658 	init_waitqueue_head(&u->evtchn_wait);
659 
660 	mutex_init(&u->bind_mutex);
661 	mutex_init(&u->ring_cons_mutex);
662 	spin_lock_init(&u->ring_prod_lock);
663 
664 	u->restrict_domid = UNRESTRICTED_DOMID;
665 
666 	filp->private_data = u;
667 
668 	return stream_open(inode, filp);
669 }
670 
671 static int evtchn_release(struct inode *inode, struct file *filp)
672 {
673 	struct per_user_data *u = filp->private_data;
674 	struct rb_node *node;
675 
676 	while ((node = u->evtchns.rb_node)) {
677 		struct user_evtchn *evtchn;
678 
679 		evtchn = rb_entry(node, struct user_evtchn, node);
680 		disable_irq(irq_from_evtchn(evtchn->port));
681 		evtchn_unbind_from_user(u, evtchn);
682 	}
683 
684 	evtchn_free_ring(u->ring);
685 	kfree(u->name);
686 	kfree(u);
687 
688 	return 0;
689 }
690 
691 static const struct file_operations evtchn_fops = {
692 	.owner   = THIS_MODULE,
693 	.read    = evtchn_read,
694 	.write   = evtchn_write,
695 	.unlocked_ioctl = evtchn_ioctl,
696 	.poll    = evtchn_poll,
697 	.fasync  = evtchn_fasync,
698 	.open    = evtchn_open,
699 	.release = evtchn_release,
700 	.llseek	 = no_llseek,
701 };
702 
703 static struct miscdevice evtchn_miscdev = {
704 	.minor        = MISC_DYNAMIC_MINOR,
705 	.name         = "xen/evtchn",
706 	.fops         = &evtchn_fops,
707 };
708 static int __init evtchn_init(void)
709 {
710 	int err;
711 
712 	if (!xen_domain())
713 		return -ENODEV;
714 
715 	/* Create '/dev/xen/evtchn'. */
716 	err = misc_register(&evtchn_miscdev);
717 	if (err != 0) {
718 		pr_err("Could not register /dev/xen/evtchn\n");
719 		return err;
720 	}
721 
722 	pr_info("Event-channel device installed\n");
723 
724 	return 0;
725 }
726 
727 static void __exit evtchn_cleanup(void)
728 {
729 	misc_deregister(&evtchn_miscdev);
730 }
731 
732 module_init(evtchn_init);
733 module_exit(evtchn_cleanup);
734 
735 MODULE_LICENSE("GPL");
736