1/*
2 * Driver giving user-space access to the kernel's xenbus connection
3 * to xenstore.
4 *
5 * Copyright (c) 2005, Christian Limpach
6 * Copyright (c) 2005, Rusty Russell, IBM Corporation
7 *
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License version 2
10 * as published by the Free Software Foundation; or, when distributed
11 * separately from the Linux kernel or incorporated into other
12 * software packages, subject to the following license:
13 *
14 * Permission is hereby granted, free of charge, to any person obtaining a copy
15 * of this source file (the "Software"), to deal in the Software without
16 * restriction, including without limitation the rights to use, copy, modify,
17 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
18 * and to permit persons to whom the Software is furnished to do so, subject to
19 * the following conditions:
20 *
21 * The above copyright notice and this permission notice shall be included in
22 * all copies or substantial portions of the Software.
23 *
24 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
25 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
26 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
27 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
28 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
29 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
30 * IN THE SOFTWARE.
31 *
32 * Changes:
33 * 2008-10-07  Alex Zeffertt    Replaced /proc/xen/xenbus with xenfs filesystem
34 *                              and /proc/xen compatibility mount point.
35 *                              Turned xenfs into a loadable module.
36 */
37
38#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
39
40#include <linux/kernel.h>
41#include <linux/errno.h>
42#include <linux/uio.h>
43#include <linux/notifier.h>
44#include <linux/wait.h>
45#include <linux/fs.h>
46#include <linux/poll.h>
47#include <linux/mutex.h>
48#include <linux/sched.h>
49#include <linux/spinlock.h>
50#include <linux/mount.h>
51#include <linux/pagemap.h>
52#include <linux/uaccess.h>
53#include <linux/init.h>
54#include <linux/namei.h>
55#include <linux/string.h>
56#include <linux/slab.h>
57#include <linux/miscdevice.h>
58#include <linux/workqueue.h>
59
60#include <xen/xenbus.h>
61#include <xen/xen.h>
62#include <asm/xen/hypervisor.h>
63
64#include "xenbus.h"
65
66unsigned int xb_dev_generation_id;
67
68/*
69 * An element of a list of outstanding transactions, for which we're
70 * still waiting a reply.
71 */
72struct xenbus_transaction_holder {
73	struct list_head list;
74	struct xenbus_transaction handle;
75	unsigned int generation_id;
76};
77
78/*
79 * A buffer of data on the queue.
80 */
81struct read_buffer {
82	struct list_head list;
83	unsigned int cons;
84	unsigned int len;
85	char msg[] __counted_by(len);
86};
87
88struct xenbus_file_priv {
89	/*
90	 * msgbuffer_mutex is held while partial requests are built up
91	 * and complete requests are acted on.  It therefore protects
92	 * the "transactions" and "watches" lists, and the partial
93	 * request length and buffer.
94	 *
95	 * reply_mutex protects the reply being built up to return to
96	 * usermode.  It nests inside msgbuffer_mutex but may be held
97	 * alone during a watch callback.
98	 */
99	struct mutex msgbuffer_mutex;
100
101	/* In-progress transactions */
102	struct list_head transactions;
103
104	/* Active watches. */
105	struct list_head watches;
106
107	/* Partial request. */
108	unsigned int len;
109	union {
110		struct xsd_sockmsg msg;
111		char buffer[XENSTORE_PAYLOAD_MAX];
112	} u;
113
114	/* Response queue. */
115	struct mutex reply_mutex;
116	struct list_head read_buffers;
117	wait_queue_head_t read_waitq;
118
119	struct kref kref;
120
121	struct work_struct wq;
122};
123
124/* Read out any raw xenbus messages queued up. */
125static ssize_t xenbus_file_read(struct file *filp,
126			       char __user *ubuf,
127			       size_t len, loff_t *ppos)
128{
129	struct xenbus_file_priv *u = filp->private_data;
130	struct read_buffer *rb;
131	ssize_t i;
132	int ret;
133
134	mutex_lock(&u->reply_mutex);
135again:
136	while (list_empty(&u->read_buffers)) {
137		mutex_unlock(&u->reply_mutex);
138		if (filp->f_flags & O_NONBLOCK)
139			return -EAGAIN;
140
141		ret = wait_event_interruptible(u->read_waitq,
142					       !list_empty(&u->read_buffers));
143		if (ret)
144			return ret;
145		mutex_lock(&u->reply_mutex);
146	}
147
148	rb = list_entry(u->read_buffers.next, struct read_buffer, list);
149	i = 0;
150	while (i < len) {
151		size_t sz = min_t(size_t, len - i, rb->len - rb->cons);
152
153		ret = copy_to_user(ubuf + i, &rb->msg[rb->cons], sz);
154
155		i += sz - ret;
156		rb->cons += sz - ret;
157
158		if (ret != 0) {
159			if (i == 0)
160				i = -EFAULT;
161			goto out;
162		}
163
164		/* Clear out buffer if it has been consumed */
165		if (rb->cons == rb->len) {
166			list_del(&rb->list);
167			kfree(rb);
168			if (list_empty(&u->read_buffers))
169				break;
170			rb = list_entry(u->read_buffers.next,
171					struct read_buffer, list);
172		}
173	}
174	if (i == 0)
175		goto again;
176
177out:
178	mutex_unlock(&u->reply_mutex);
179	return i;
180}
181
182/*
183 * Add a buffer to the queue.  Caller must hold the appropriate lock
184 * if the queue is not local.  (Commonly the caller will build up
185 * multiple queued buffers on a temporary local list, and then add it
186 * to the appropriate list under lock once all the buffers have een
187 * successfully allocated.)
188 */
189static int queue_reply(struct list_head *queue, const void *data, size_t len)
190{
191	struct read_buffer *rb;
192
193	if (len == 0)
194		return 0;
195	if (len > XENSTORE_PAYLOAD_MAX)
196		return -EINVAL;
197
198	rb = kmalloc(struct_size(rb, msg, len), GFP_KERNEL);
199	if (rb == NULL)
200		return -ENOMEM;
201
202	rb->cons = 0;
203	rb->len = len;
204
205	memcpy(rb->msg, data, len);
206
207	list_add_tail(&rb->list, queue);
208	return 0;
209}
210
211/*
212 * Free all the read_buffer s on a list.
213 * Caller must have sole reference to list.
214 */
215static void queue_cleanup(struct list_head *list)
216{
217	struct read_buffer *rb;
218
219	while (!list_empty(list)) {
220		rb = list_entry(list->next, struct read_buffer, list);
221		list_del(list->next);
222		kfree(rb);
223	}
224}
225
226struct watch_adapter {
227	struct list_head list;
228	struct xenbus_watch watch;
229	struct xenbus_file_priv *dev_data;
230	char *token;
231};
232
233static void free_watch_adapter(struct watch_adapter *watch)
234{
235	kfree(watch->watch.node);
236	kfree(watch->token);
237	kfree(watch);
238}
239
240static struct watch_adapter *alloc_watch_adapter(const char *path,
241						 const char *token)
242{
243	struct watch_adapter *watch;
244
245	watch = kzalloc(sizeof(*watch), GFP_KERNEL);
246	if (watch == NULL)
247		goto out_fail;
248
249	watch->watch.node = kstrdup(path, GFP_KERNEL);
250	if (watch->watch.node == NULL)
251		goto out_free;
252
253	watch->token = kstrdup(token, GFP_KERNEL);
254	if (watch->token == NULL)
255		goto out_free;
256
257	return watch;
258
259out_free:
260	free_watch_adapter(watch);
261
262out_fail:
263	return NULL;
264}
265
266static void watch_fired(struct xenbus_watch *watch,
267			const char *path,
268			const char *token)
269{
270	struct watch_adapter *adap;
271	struct xsd_sockmsg hdr;
272	const char *token_caller;
273	int path_len, tok_len, body_len;
274	int ret;
275	LIST_HEAD(staging_q);
276
277	adap = container_of(watch, struct watch_adapter, watch);
278
279	token_caller = adap->token;
280
281	path_len = strlen(path) + 1;
282	tok_len = strlen(token_caller) + 1;
283	body_len = path_len + tok_len;
284
285	hdr.type = XS_WATCH_EVENT;
286	hdr.len = body_len;
287
288	mutex_lock(&adap->dev_data->reply_mutex);
289
290	ret = queue_reply(&staging_q, &hdr, sizeof(hdr));
291	if (!ret)
292		ret = queue_reply(&staging_q, path, path_len);
293	if (!ret)
294		ret = queue_reply(&staging_q, token_caller, tok_len);
295
296	if (!ret) {
297		/* success: pass reply list onto watcher */
298		list_splice_tail(&staging_q, &adap->dev_data->read_buffers);
299		wake_up(&adap->dev_data->read_waitq);
300	} else
301		queue_cleanup(&staging_q);
302
303	mutex_unlock(&adap->dev_data->reply_mutex);
304}
305
306static void xenbus_worker(struct work_struct *wq)
307{
308	struct xenbus_file_priv *u;
309	struct xenbus_transaction_holder *trans, *tmp;
310	struct watch_adapter *watch, *tmp_watch;
311	struct read_buffer *rb, *tmp_rb;
312
313	u = container_of(wq, struct xenbus_file_priv, wq);
314
315	/*
316	 * No need for locking here because there are no other users,
317	 * by definition.
318	 */
319
320	list_for_each_entry_safe(trans, tmp, &u->transactions, list) {
321		xenbus_transaction_end(trans->handle, 1);
322		list_del(&trans->list);
323		kfree(trans);
324	}
325
326	list_for_each_entry_safe(watch, tmp_watch, &u->watches, list) {
327		unregister_xenbus_watch(&watch->watch);
328		list_del(&watch->list);
329		free_watch_adapter(watch);
330	}
331
332	list_for_each_entry_safe(rb, tmp_rb, &u->read_buffers, list) {
333		list_del(&rb->list);
334		kfree(rb);
335	}
336	kfree(u);
337}
338
339static void xenbus_file_free(struct kref *kref)
340{
341	struct xenbus_file_priv *u;
342
343	/*
344	 * We might be called in xenbus_thread().
345	 * Use workqueue to avoid deadlock.
346	 */
347	u = container_of(kref, struct xenbus_file_priv, kref);
348	schedule_work(&u->wq);
349}
350
351static struct xenbus_transaction_holder *xenbus_get_transaction(
352	struct xenbus_file_priv *u, uint32_t tx_id)
353{
354	struct xenbus_transaction_holder *trans;
355
356	list_for_each_entry(trans, &u->transactions, list)
357		if (trans->handle.id == tx_id)
358			return trans;
359
360	return NULL;
361}
362
363void xenbus_dev_queue_reply(struct xb_req_data *req)
364{
365	struct xenbus_file_priv *u = req->par;
366	struct xenbus_transaction_holder *trans = NULL;
367	int rc;
368	LIST_HEAD(staging_q);
369
370	xs_request_exit(req);
371
372	mutex_lock(&u->msgbuffer_mutex);
373
374	if (req->type == XS_TRANSACTION_START) {
375		trans = xenbus_get_transaction(u, 0);
376		if (WARN_ON(!trans))
377			goto out;
378		if (req->msg.type == XS_ERROR) {
379			list_del(&trans->list);
380			kfree(trans);
381		} else {
382			rc = kstrtou32(req->body, 10, &trans->handle.id);
383			if (WARN_ON(rc))
384				goto out;
385		}
386	} else if (req->type == XS_TRANSACTION_END) {
387		trans = xenbus_get_transaction(u, req->msg.tx_id);
388		if (WARN_ON(!trans))
389			goto out;
390		list_del(&trans->list);
391		kfree(trans);
392	}
393
394	mutex_unlock(&u->msgbuffer_mutex);
395
396	mutex_lock(&u->reply_mutex);
397	rc = queue_reply(&staging_q, &req->msg, sizeof(req->msg));
398	if (!rc)
399		rc = queue_reply(&staging_q, req->body, req->msg.len);
400	if (!rc) {
401		list_splice_tail(&staging_q, &u->read_buffers);
402		wake_up(&u->read_waitq);
403	} else {
404		queue_cleanup(&staging_q);
405	}
406	mutex_unlock(&u->reply_mutex);
407
408	kfree(req->body);
409	kfree(req);
410
411	kref_put(&u->kref, xenbus_file_free);
412
413	return;
414
415 out:
416	mutex_unlock(&u->msgbuffer_mutex);
417}
418
419static int xenbus_command_reply(struct xenbus_file_priv *u,
420				unsigned int msg_type, const char *reply)
421{
422	struct {
423		struct xsd_sockmsg hdr;
424		char body[16];
425	} msg;
426	int rc;
427
428	msg.hdr = u->u.msg;
429	msg.hdr.type = msg_type;
430	msg.hdr.len = strlen(reply) + 1;
431	if (msg.hdr.len > sizeof(msg.body))
432		return -E2BIG;
433	memcpy(&msg.body, reply, msg.hdr.len);
434
435	mutex_lock(&u->reply_mutex);
436	rc = queue_reply(&u->read_buffers, &msg, sizeof(msg.hdr) + msg.hdr.len);
437	wake_up(&u->read_waitq);
438	mutex_unlock(&u->reply_mutex);
439
440	if (!rc)
441		kref_put(&u->kref, xenbus_file_free);
442
443	return rc;
444}
445
446static int xenbus_write_transaction(unsigned msg_type,
447				    struct xenbus_file_priv *u)
448{
449	int rc;
450	struct xenbus_transaction_holder *trans = NULL;
451	struct {
452		struct xsd_sockmsg hdr;
453		char body[];
454	} *msg = (void *)u->u.buffer;
455
456	if (msg_type == XS_TRANSACTION_START) {
457		trans = kzalloc(sizeof(*trans), GFP_KERNEL);
458		if (!trans) {
459			rc = -ENOMEM;
460			goto out;
461		}
462		trans->generation_id = xb_dev_generation_id;
463		list_add(&trans->list, &u->transactions);
464	} else if (msg->hdr.tx_id != 0 &&
465		   !xenbus_get_transaction(u, msg->hdr.tx_id))
466		return xenbus_command_reply(u, XS_ERROR, "ENOENT");
467	else if (msg_type == XS_TRANSACTION_END &&
468		 !(msg->hdr.len == 2 &&
469		   (!strcmp(msg->body, "T") || !strcmp(msg->body, "F"))))
470		return xenbus_command_reply(u, XS_ERROR, "EINVAL");
471	else if (msg_type == XS_TRANSACTION_END) {
472		trans = xenbus_get_transaction(u, msg->hdr.tx_id);
473		if (trans && trans->generation_id != xb_dev_generation_id) {
474			list_del(&trans->list);
475			kfree(trans);
476			if (!strcmp(msg->body, "T"))
477				return xenbus_command_reply(u, XS_ERROR,
478							    "EAGAIN");
479			else
480				return xenbus_command_reply(u,
481							    XS_TRANSACTION_END,
482							    "OK");
483		}
484	}
485
486	rc = xenbus_dev_request_and_reply(&msg->hdr, u);
487	if (rc && trans) {
488		list_del(&trans->list);
489		kfree(trans);
490	}
491
492out:
493	return rc;
494}
495
496static int xenbus_write_watch(unsigned msg_type, struct xenbus_file_priv *u)
497{
498	struct watch_adapter *watch;
499	char *path, *token;
500	int err, rc;
501
502	path = u->u.buffer + sizeof(u->u.msg);
503	token = memchr(path, 0, u->u.msg.len);
504	if (token == NULL) {
505		rc = xenbus_command_reply(u, XS_ERROR, "EINVAL");
506		goto out;
507	}
508	token++;
509	if (memchr(token, 0, u->u.msg.len - (token - path)) == NULL) {
510		rc = xenbus_command_reply(u, XS_ERROR, "EINVAL");
511		goto out;
512	}
513
514	if (msg_type == XS_WATCH) {
515		watch = alloc_watch_adapter(path, token);
516		if (watch == NULL) {
517			rc = -ENOMEM;
518			goto out;
519		}
520
521		watch->watch.callback = watch_fired;
522		watch->dev_data = u;
523
524		err = register_xenbus_watch(&watch->watch);
525		if (err) {
526			free_watch_adapter(watch);
527			rc = err;
528			goto out;
529		}
530		list_add(&watch->list, &u->watches);
531	} else {
532		list_for_each_entry(watch, &u->watches, list) {
533			if (!strcmp(watch->token, token) &&
534			    !strcmp(watch->watch.node, path)) {
535				unregister_xenbus_watch(&watch->watch);
536				list_del(&watch->list);
537				free_watch_adapter(watch);
538				break;
539			}
540		}
541	}
542
543	/* Success.  Synthesize a reply to say all is OK. */
544	rc = xenbus_command_reply(u, msg_type, "OK");
545
546out:
547	return rc;
548}
549
550static ssize_t xenbus_file_write(struct file *filp,
551				const char __user *ubuf,
552				size_t len, loff_t *ppos)
553{
554	struct xenbus_file_priv *u = filp->private_data;
555	uint32_t msg_type;
556	int rc = len;
557	int ret;
558
559	/*
560	 * We're expecting usermode to be writing properly formed
561	 * xenbus messages.  If they write an incomplete message we
562	 * buffer it up.  Once it is complete, we act on it.
563	 */
564
565	/*
566	 * Make sure concurrent writers can't stomp all over each
567	 * other's messages and make a mess of our partial message
568	 * buffer.  We don't make any attemppt to stop multiple
569	 * writers from making a mess of each other's incomplete
570	 * messages; we're just trying to guarantee our own internal
571	 * consistency and make sure that single writes are handled
572	 * atomically.
573	 */
574	mutex_lock(&u->msgbuffer_mutex);
575
576	/* Get this out of the way early to avoid confusion */
577	if (len == 0)
578		goto out;
579
580	/* Can't write a xenbus message larger we can buffer */
581	if (len > sizeof(u->u.buffer) - u->len) {
582		/* On error, dump existing buffer */
583		u->len = 0;
584		rc = -EINVAL;
585		goto out;
586	}
587
588	ret = copy_from_user(u->u.buffer + u->len, ubuf, len);
589
590	if (ret != 0) {
591		rc = -EFAULT;
592		goto out;
593	}
594
595	/* Deal with a partial copy. */
596	len -= ret;
597	rc = len;
598
599	u->len += len;
600
601	/* Return if we haven't got a full message yet */
602	if (u->len < sizeof(u->u.msg))
603		goto out;	/* not even the header yet */
604
605	/* If we're expecting a message that's larger than we can
606	   possibly send, dump what we have and return an error. */
607	if ((sizeof(u->u.msg) + u->u.msg.len) > sizeof(u->u.buffer)) {
608		rc = -E2BIG;
609		u->len = 0;
610		goto out;
611	}
612
613	if (u->len < (sizeof(u->u.msg) + u->u.msg.len))
614		goto out;	/* incomplete data portion */
615
616	/*
617	 * OK, now we have a complete message.  Do something with it.
618	 */
619
620	kref_get(&u->kref);
621
622	msg_type = u->u.msg.type;
623
624	switch (msg_type) {
625	case XS_WATCH:
626	case XS_UNWATCH:
627		/* (Un)Ask for some path to be watched for changes */
628		ret = xenbus_write_watch(msg_type, u);
629		break;
630
631	default:
632		/* Send out a transaction */
633		ret = xenbus_write_transaction(msg_type, u);
634		break;
635	}
636	if (ret != 0) {
637		rc = ret;
638		kref_put(&u->kref, xenbus_file_free);
639	}
640
641	/* Buffered message consumed */
642	u->len = 0;
643
644 out:
645	mutex_unlock(&u->msgbuffer_mutex);
646	return rc;
647}
648
649static int xenbus_file_open(struct inode *inode, struct file *filp)
650{
651	struct xenbus_file_priv *u;
652
653	if (xen_store_evtchn == 0)
654		return -ENOENT;
655
656	stream_open(inode, filp);
657
658	u = kzalloc(sizeof(*u), GFP_KERNEL);
659	if (u == NULL)
660		return -ENOMEM;
661
662	kref_init(&u->kref);
663
664	INIT_LIST_HEAD(&u->transactions);
665	INIT_LIST_HEAD(&u->watches);
666	INIT_LIST_HEAD(&u->read_buffers);
667	init_waitqueue_head(&u->read_waitq);
668	INIT_WORK(&u->wq, xenbus_worker);
669
670	mutex_init(&u->reply_mutex);
671	mutex_init(&u->msgbuffer_mutex);
672
673	filp->private_data = u;
674
675	return 0;
676}
677
678static int xenbus_file_release(struct inode *inode, struct file *filp)
679{
680	struct xenbus_file_priv *u = filp->private_data;
681
682	kref_put(&u->kref, xenbus_file_free);
683
684	return 0;
685}
686
687static __poll_t xenbus_file_poll(struct file *file, poll_table *wait)
688{
689	struct xenbus_file_priv *u = file->private_data;
690
691	poll_wait(file, &u->read_waitq, wait);
692	if (!list_empty(&u->read_buffers))
693		return EPOLLIN | EPOLLRDNORM;
694	return 0;
695}
696
697const struct file_operations xen_xenbus_fops = {
698	.read = xenbus_file_read,
699	.write = xenbus_file_write,
700	.open = xenbus_file_open,
701	.release = xenbus_file_release,
702	.poll = xenbus_file_poll,
703	.llseek = no_llseek,
704};
705EXPORT_SYMBOL_GPL(xen_xenbus_fops);
706
707static struct miscdevice xenbus_dev = {
708	.minor = MISC_DYNAMIC_MINOR,
709	.name = "xen/xenbus",
710	.fops = &xen_xenbus_fops,
711};
712
713static int __init xenbus_init(void)
714{
715	int err;
716
717	if (!xen_domain())
718		return -ENODEV;
719
720	err = misc_register(&xenbus_dev);
721	if (err)
722		pr_err("Could not register xenbus frontend device\n");
723	return err;
724}
725device_initcall(xenbus_init);
726