1/******************************************************************************
2 * xenbus_xs.c
3 *
4 * This is the kernel equivalent of the "xs" library. We don't need everything
5 * and we use xenbus_comms for communication.
6 *
7 * Copyright (C) 2005 Rusty Russell, IBM Corporation
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) KBUILD_MODNAME ": " fmt
35
36#include <linux/unistd.h>
37#include <linux/errno.h>
38#include <linux/types.h>
39#include <linux/uio.h>
40#include <linux/kernel.h>
41#include <linux/string.h>
42#include <linux/err.h>
43#include <linux/slab.h>
44#include <linux/fcntl.h>
45#include <linux/kthread.h>
46#include <linux/reboot.h>
47#include <linux/rwsem.h>
48#include <linux/mutex.h>
49#include <asm/xen/hypervisor.h>
50#include <xen/xenbus.h>
51#include <xen/xen.h>
52#include "xenbus.h"
53
54/*
55 * Framework to protect suspend/resume handling against normal Xenstore
56 * message handling:
57 * During suspend/resume there must be no open transaction and no pending
58 * Xenstore request.
59 * New watch events happening in this time can be ignored by firing all watches
60 * after resume.
61 */
62
63/* Lock protecting enter/exit critical region. */
64static DEFINE_SPINLOCK(xs_state_lock);
65/* Number of users in critical region (protected by xs_state_lock). */
66static unsigned int xs_state_users;
67/* Suspend handler waiting or already active (protected by xs_state_lock)? */
68static int xs_suspend_active;
69/* Unique Xenstore request id (protected by xs_state_lock). */
70static uint32_t xs_request_id;
71
72/* Wait queue for all callers waiting for critical region to become usable. */
73static DECLARE_WAIT_QUEUE_HEAD(xs_state_enter_wq);
74/* Wait queue for suspend handling waiting for critical region being empty. */
75static DECLARE_WAIT_QUEUE_HEAD(xs_state_exit_wq);
76
77/* List of registered watches, and a lock to protect it. */
78static LIST_HEAD(watches);
79static DEFINE_SPINLOCK(watches_lock);
80
81/* List of pending watch callback events, and a lock to protect it. */
82static LIST_HEAD(watch_events);
83static DEFINE_SPINLOCK(watch_events_lock);
84
85/* Protect watch (de)register against save/restore. */
86static DECLARE_RWSEM(xs_watch_rwsem);
87
88/*
89 * Details of the xenwatch callback kernel thread. The thread waits on the
90 * watch_events_waitq for work to do (queued on watch_events list). When it
91 * wakes up it acquires the xenwatch_mutex before reading the list and
92 * carrying out work.
93 */
94static pid_t xenwatch_pid;
95static DEFINE_MUTEX(xenwatch_mutex);
96static DECLARE_WAIT_QUEUE_HEAD(watch_events_waitq);
97
98static void xs_suspend_enter(void)
99{
100 spin_lock(lock: &xs_state_lock);
101 xs_suspend_active++;
102 spin_unlock(lock: &xs_state_lock);
103 wait_event(xs_state_exit_wq, xs_state_users == 0);
104}
105
106static void xs_suspend_exit(void)
107{
108 xb_dev_generation_id++;
109 spin_lock(lock: &xs_state_lock);
110 xs_suspend_active--;
111 spin_unlock(lock: &xs_state_lock);
112 wake_up_all(&xs_state_enter_wq);
113}
114
115static uint32_t xs_request_enter(struct xb_req_data *req)
116{
117 uint32_t rq_id;
118
119 req->type = req->msg.type;
120
121 spin_lock(lock: &xs_state_lock);
122
123 while (!xs_state_users && xs_suspend_active) {
124 spin_unlock(lock: &xs_state_lock);
125 wait_event(xs_state_enter_wq, xs_suspend_active == 0);
126 spin_lock(lock: &xs_state_lock);
127 }
128
129 if (req->type == XS_TRANSACTION_START && !req->user_req)
130 xs_state_users++;
131 xs_state_users++;
132 rq_id = xs_request_id++;
133
134 spin_unlock(lock: &xs_state_lock);
135
136 return rq_id;
137}
138
139void xs_request_exit(struct xb_req_data *req)
140{
141 spin_lock(lock: &xs_state_lock);
142 xs_state_users--;
143 if ((req->type == XS_TRANSACTION_START && req->msg.type == XS_ERROR) ||
144 (req->type == XS_TRANSACTION_END && !req->user_req &&
145 !WARN_ON_ONCE(req->msg.type == XS_ERROR &&
146 !strcmp(req->body, "ENOENT"))))
147 xs_state_users--;
148 spin_unlock(lock: &xs_state_lock);
149
150 if (xs_suspend_active && !xs_state_users)
151 wake_up(&xs_state_exit_wq);
152}
153
154static int get_error(const char *errorstring)
155{
156 unsigned int i;
157
158 for (i = 0; strcmp(errorstring, xsd_errors[i].errstring) != 0; i++) {
159 if (i == ARRAY_SIZE(xsd_errors) - 1) {
160 pr_warn("xen store gave: unknown error %s\n",
161 errorstring);
162 return EINVAL;
163 }
164 }
165 return xsd_errors[i].errnum;
166}
167
168static bool xenbus_ok(void)
169{
170 switch (xen_store_domain_type) {
171 case XS_LOCAL:
172 switch (system_state) {
173 case SYSTEM_POWER_OFF:
174 case SYSTEM_RESTART:
175 case SYSTEM_HALT:
176 return false;
177 default:
178 break;
179 }
180 return true;
181 case XS_PV:
182 case XS_HVM:
183 /* FIXME: Could check that the remote domain is alive,
184 * but it is normally initial domain. */
185 return true;
186 default:
187 break;
188 }
189 return false;
190}
191
192static bool test_reply(struct xb_req_data *req)
193{
194 if (req->state == xb_req_state_got_reply || !xenbus_ok()) {
195 /* read req->state before all other fields */
196 virt_rmb();
197 return true;
198 }
199
200 /* Make sure to reread req->state each time. */
201 barrier();
202
203 return false;
204}
205
206static void *read_reply(struct xb_req_data *req)
207{
208 do {
209 wait_event(req->wq, test_reply(req));
210
211 if (!xenbus_ok())
212 /*
213 * If we are in the process of being shut-down there is
214 * no point of trying to contact XenBus - it is either
215 * killed (xenstored application) or the other domain
216 * has been killed or is unreachable.
217 */
218 return ERR_PTR(error: -EIO);
219 if (req->err)
220 return ERR_PTR(error: req->err);
221
222 } while (req->state != xb_req_state_got_reply);
223
224 return req->body;
225}
226
227static void xs_send(struct xb_req_data *req, struct xsd_sockmsg *msg)
228{
229 bool notify;
230
231 req->msg = *msg;
232 req->err = 0;
233 req->state = xb_req_state_queued;
234 init_waitqueue_head(&req->wq);
235
236 /* Save the caller req_id and restore it later in the reply */
237 req->caller_req_id = req->msg.req_id;
238 req->msg.req_id = xs_request_enter(req);
239
240 mutex_lock(&xb_write_mutex);
241 list_add_tail(new: &req->list, head: &xb_write_list);
242 notify = list_is_singular(head: &xb_write_list);
243 mutex_unlock(lock: &xb_write_mutex);
244
245 if (notify)
246 wake_up(&xb_waitq);
247}
248
249static void *xs_wait_for_reply(struct xb_req_data *req, struct xsd_sockmsg *msg)
250{
251 void *ret;
252
253 ret = read_reply(req);
254
255 xs_request_exit(req);
256
257 msg->type = req->msg.type;
258 msg->len = req->msg.len;
259
260 mutex_lock(&xb_write_mutex);
261 if (req->state == xb_req_state_queued ||
262 req->state == xb_req_state_wait_reply)
263 req->state = xb_req_state_aborted;
264 else
265 kfree(objp: req);
266 mutex_unlock(lock: &xb_write_mutex);
267
268 return ret;
269}
270
271static void xs_wake_up(struct xb_req_data *req)
272{
273 wake_up(&req->wq);
274}
275
276int xenbus_dev_request_and_reply(struct xsd_sockmsg *msg, void *par)
277{
278 struct xb_req_data *req;
279 struct kvec *vec;
280
281 req = kmalloc(size: sizeof(*req) + sizeof(*vec), GFP_KERNEL);
282 if (!req)
283 return -ENOMEM;
284
285 vec = (struct kvec *)(req + 1);
286 vec->iov_len = msg->len;
287 vec->iov_base = msg + 1;
288
289 req->vec = vec;
290 req->num_vecs = 1;
291 req->cb = xenbus_dev_queue_reply;
292 req->par = par;
293 req->user_req = true;
294
295 xs_send(req, msg);
296
297 return 0;
298}
299EXPORT_SYMBOL(xenbus_dev_request_and_reply);
300
301/* Send message to xs, get kmalloc'ed reply. ERR_PTR() on error. */
302static void *xs_talkv(struct xenbus_transaction t,
303 enum xsd_sockmsg_type type,
304 const struct kvec *iovec,
305 unsigned int num_vecs,
306 unsigned int *len)
307{
308 struct xb_req_data *req;
309 struct xsd_sockmsg msg;
310 void *ret = NULL;
311 unsigned int i;
312 int err;
313
314 req = kmalloc(size: sizeof(*req), GFP_NOIO | __GFP_HIGH);
315 if (!req)
316 return ERR_PTR(error: -ENOMEM);
317
318 req->vec = iovec;
319 req->num_vecs = num_vecs;
320 req->cb = xs_wake_up;
321 req->user_req = false;
322
323 msg.req_id = 0;
324 msg.tx_id = t.id;
325 msg.type = type;
326 msg.len = 0;
327 for (i = 0; i < num_vecs; i++)
328 msg.len += iovec[i].iov_len;
329
330 xs_send(req, msg: &msg);
331
332 ret = xs_wait_for_reply(req, msg: &msg);
333 if (len)
334 *len = msg.len;
335
336 if (IS_ERR(ptr: ret))
337 return ret;
338
339 if (msg.type == XS_ERROR) {
340 err = get_error(errorstring: ret);
341 kfree(objp: ret);
342 return ERR_PTR(error: -err);
343 }
344
345 if (msg.type != type) {
346 pr_warn_ratelimited("unexpected type [%d], expected [%d]\n",
347 msg.type, type);
348 kfree(objp: ret);
349 return ERR_PTR(error: -EINVAL);
350 }
351 return ret;
352}
353
354/* Simplified version of xs_talkv: single message. */
355static void *xs_single(struct xenbus_transaction t,
356 enum xsd_sockmsg_type type,
357 const char *string,
358 unsigned int *len)
359{
360 struct kvec iovec;
361
362 iovec.iov_base = (void *)string;
363 iovec.iov_len = strlen(string) + 1;
364 return xs_talkv(t, type, iovec: &iovec, num_vecs: 1, len);
365}
366
367/* Many commands only need an ack, don't care what it says. */
368static int xs_error(char *reply)
369{
370 if (IS_ERR(ptr: reply))
371 return PTR_ERR(ptr: reply);
372 kfree(objp: reply);
373 return 0;
374}
375
376static unsigned int count_strings(const char *strings, unsigned int len)
377{
378 unsigned int num;
379 const char *p;
380
381 for (p = strings, num = 0; p < strings + len; p += strlen(p) + 1)
382 num++;
383
384 return num;
385}
386
387/* Return the path to dir with /name appended. Buffer must be kfree()'ed. */
388static char *join(const char *dir, const char *name)
389{
390 char *buffer;
391
392 if (strlen(name) == 0)
393 buffer = kasprintf(GFP_NOIO | __GFP_HIGH, fmt: "%s", dir);
394 else
395 buffer = kasprintf(GFP_NOIO | __GFP_HIGH, fmt: "%s/%s", dir, name);
396 return (!buffer) ? ERR_PTR(error: -ENOMEM) : buffer;
397}
398
399static char **split(char *strings, unsigned int len, unsigned int *num)
400{
401 char *p, **ret;
402
403 /* Count the strings. */
404 *num = count_strings(strings, len);
405
406 /* Transfer to one big alloc for easy freeing. */
407 ret = kmalloc(size: *num * sizeof(char *) + len, GFP_NOIO | __GFP_HIGH);
408 if (!ret) {
409 kfree(objp: strings);
410 return ERR_PTR(error: -ENOMEM);
411 }
412 memcpy(&ret[*num], strings, len);
413 kfree(objp: strings);
414
415 strings = (char *)&ret[*num];
416 for (p = strings, *num = 0; p < strings + len; p += strlen(p) + 1)
417 ret[(*num)++] = p;
418
419 return ret;
420}
421
422char **xenbus_directory(struct xenbus_transaction t,
423 const char *dir, const char *node, unsigned int *num)
424{
425 char *strings, *path;
426 unsigned int len;
427
428 path = join(dir, name: node);
429 if (IS_ERR(ptr: path))
430 return (char **)path;
431
432 strings = xs_single(t, type: XS_DIRECTORY, string: path, len: &len);
433 kfree(objp: path);
434 if (IS_ERR(ptr: strings))
435 return (char **)strings;
436
437 return split(strings, len, num);
438}
439EXPORT_SYMBOL_GPL(xenbus_directory);
440
441/* Check if a path exists. Return 1 if it does. */
442int xenbus_exists(struct xenbus_transaction t,
443 const char *dir, const char *node)
444{
445 char **d;
446 int dir_n;
447
448 d = xenbus_directory(t, dir, node, &dir_n);
449 if (IS_ERR(ptr: d))
450 return 0;
451 kfree(objp: d);
452 return 1;
453}
454EXPORT_SYMBOL_GPL(xenbus_exists);
455
456/* Get the value of a single file.
457 * Returns a kmalloced value: call free() on it after use.
458 * len indicates length in bytes.
459 */
460void *xenbus_read(struct xenbus_transaction t,
461 const char *dir, const char *node, unsigned int *len)
462{
463 char *path;
464 void *ret;
465
466 path = join(dir, name: node);
467 if (IS_ERR(ptr: path))
468 return (void *)path;
469
470 ret = xs_single(t, type: XS_READ, string: path, len);
471 kfree(objp: path);
472 return ret;
473}
474EXPORT_SYMBOL_GPL(xenbus_read);
475
476/* Write the value of a single file.
477 * Returns -err on failure.
478 */
479int xenbus_write(struct xenbus_transaction t,
480 const char *dir, const char *node, const char *string)
481{
482 const char *path;
483 struct kvec iovec[2];
484 int ret;
485
486 path = join(dir, name: node);
487 if (IS_ERR(ptr: path))
488 return PTR_ERR(ptr: path);
489
490 iovec[0].iov_base = (void *)path;
491 iovec[0].iov_len = strlen(path) + 1;
492 iovec[1].iov_base = (void *)string;
493 iovec[1].iov_len = strlen(string);
494
495 ret = xs_error(reply: xs_talkv(t, type: XS_WRITE, iovec, ARRAY_SIZE(iovec), NULL));
496 kfree(objp: path);
497 return ret;
498}
499EXPORT_SYMBOL_GPL(xenbus_write);
500
501/* Create a new directory. */
502int xenbus_mkdir(struct xenbus_transaction t,
503 const char *dir, const char *node)
504{
505 char *path;
506 int ret;
507
508 path = join(dir, name: node);
509 if (IS_ERR(ptr: path))
510 return PTR_ERR(ptr: path);
511
512 ret = xs_error(reply: xs_single(t, type: XS_MKDIR, string: path, NULL));
513 kfree(objp: path);
514 return ret;
515}
516EXPORT_SYMBOL_GPL(xenbus_mkdir);
517
518/* Destroy a file or directory (directories must be empty). */
519int xenbus_rm(struct xenbus_transaction t, const char *dir, const char *node)
520{
521 char *path;
522 int ret;
523
524 path = join(dir, name: node);
525 if (IS_ERR(ptr: path))
526 return PTR_ERR(ptr: path);
527
528 ret = xs_error(reply: xs_single(t, type: XS_RM, string: path, NULL));
529 kfree(objp: path);
530 return ret;
531}
532EXPORT_SYMBOL_GPL(xenbus_rm);
533
534/* Start a transaction: changes by others will not be seen during this
535 * transaction, and changes will not be visible to others until end.
536 */
537int xenbus_transaction_start(struct xenbus_transaction *t)
538{
539 char *id_str;
540
541 id_str = xs_single(XBT_NIL, type: XS_TRANSACTION_START, string: "", NULL);
542 if (IS_ERR(id_str))
543 return PTR_ERR(id_str);
544
545 t->id = simple_strtoul(id_str, NULL, 0);
546 kfree(id_str);
547 return 0;
548}
549EXPORT_SYMBOL_GPL(xenbus_transaction_start);
550
551/* End a transaction.
552 * If abandon is true, transaction is discarded instead of committed.
553 */
554int xenbus_transaction_end(struct xenbus_transaction t, int abort)
555{
556 char abortstr[2];
557
558 if (abort)
559 strcpy(p: abortstr, q: "F");
560 else
561 strcpy(p: abortstr, q: "T");
562
563 return xs_error(reply: xs_single(t, type: XS_TRANSACTION_END, string: abortstr, NULL));
564}
565EXPORT_SYMBOL_GPL(xenbus_transaction_end);
566
567/* Single read and scanf: returns -errno or num scanned. */
568int xenbus_scanf(struct xenbus_transaction t,
569 const char *dir, const char *node, const char *fmt, ...)
570{
571 va_list ap;
572 int ret;
573 char *val;
574
575 val = xenbus_read(t, dir, node, NULL);
576 if (IS_ERR(ptr: val))
577 return PTR_ERR(ptr: val);
578
579 va_start(ap, fmt);
580 ret = vsscanf(val, fmt, ap);
581 va_end(ap);
582 kfree(objp: val);
583 /* Distinctive errno. */
584 if (ret == 0)
585 return -ERANGE;
586 return ret;
587}
588EXPORT_SYMBOL_GPL(xenbus_scanf);
589
590/* Read an (optional) unsigned value. */
591unsigned int xenbus_read_unsigned(const char *dir, const char *node,
592 unsigned int default_val)
593{
594 unsigned int val;
595 int ret;
596
597 ret = xenbus_scanf(XBT_NIL, dir, node, "%u", &val);
598 if (ret <= 0)
599 val = default_val;
600
601 return val;
602}
603EXPORT_SYMBOL_GPL(xenbus_read_unsigned);
604
605/* Single printf and write: returns -errno or 0. */
606int xenbus_printf(struct xenbus_transaction t,
607 const char *dir, const char *node, const char *fmt, ...)
608{
609 va_list ap;
610 int ret;
611 char *buf;
612
613 va_start(ap, fmt);
614 buf = kvasprintf(GFP_NOIO | __GFP_HIGH, fmt, args: ap);
615 va_end(ap);
616
617 if (!buf)
618 return -ENOMEM;
619
620 ret = xenbus_write(t, dir, node, buf);
621
622 kfree(objp: buf);
623
624 return ret;
625}
626EXPORT_SYMBOL_GPL(xenbus_printf);
627
628/* Takes tuples of names, scanf-style args, and void **, NULL terminated. */
629int xenbus_gather(struct xenbus_transaction t, const char *dir, ...)
630{
631 va_list ap;
632 const char *name;
633 int ret = 0;
634
635 va_start(ap, dir);
636 while (ret == 0 && (name = va_arg(ap, char *)) != NULL) {
637 const char *fmt = va_arg(ap, char *);
638 void *result = va_arg(ap, void *);
639 char *p;
640
641 p = xenbus_read(t, dir, name, NULL);
642 if (IS_ERR(ptr: p)) {
643 ret = PTR_ERR(ptr: p);
644 break;
645 }
646 if (fmt) {
647 if (sscanf(p, fmt, result) == 0)
648 ret = -EINVAL;
649 kfree(objp: p);
650 } else
651 *(char **)result = p;
652 }
653 va_end(ap);
654 return ret;
655}
656EXPORT_SYMBOL_GPL(xenbus_gather);
657
658static int xs_watch(const char *path, const char *token)
659{
660 struct kvec iov[2];
661
662 iov[0].iov_base = (void *)path;
663 iov[0].iov_len = strlen(path) + 1;
664 iov[1].iov_base = (void *)token;
665 iov[1].iov_len = strlen(token) + 1;
666
667 return xs_error(reply: xs_talkv(XBT_NIL, type: XS_WATCH, iovec: iov,
668 ARRAY_SIZE(iov), NULL));
669}
670
671static int xs_unwatch(const char *path, const char *token)
672{
673 struct kvec iov[2];
674
675 iov[0].iov_base = (char *)path;
676 iov[0].iov_len = strlen(path) + 1;
677 iov[1].iov_base = (char *)token;
678 iov[1].iov_len = strlen(token) + 1;
679
680 return xs_error(reply: xs_talkv(XBT_NIL, type: XS_UNWATCH, iovec: iov,
681 ARRAY_SIZE(iov), NULL));
682}
683
684static struct xenbus_watch *find_watch(const char *token)
685{
686 struct xenbus_watch *i, *cmp;
687
688 cmp = (void *)simple_strtoul(token, NULL, 16);
689
690 list_for_each_entry(i, &watches, list)
691 if (i == cmp)
692 return i;
693
694 return NULL;
695}
696
697int xs_watch_msg(struct xs_watch_event *event)
698{
699 if (count_strings(strings: event->body, len: event->len) != 2) {
700 kfree(objp: event);
701 return -EINVAL;
702 }
703 event->path = (const char *)event->body;
704 event->token = (const char *)strchr(event->body, '\0') + 1;
705
706 spin_lock(lock: &watches_lock);
707 event->handle = find_watch(token: event->token);
708 if (event->handle != NULL &&
709 (!event->handle->will_handle ||
710 event->handle->will_handle(event->handle,
711 event->path, event->token))) {
712 spin_lock(lock: &watch_events_lock);
713 list_add_tail(new: &event->list, head: &watch_events);
714 event->handle->nr_pending++;
715 wake_up(&watch_events_waitq);
716 spin_unlock(lock: &watch_events_lock);
717 } else
718 kfree(objp: event);
719 spin_unlock(lock: &watches_lock);
720
721 return 0;
722}
723
724/*
725 * Certain older XenBus toolstack cannot handle reading values that are
726 * not populated. Some Xen 3.4 installation are incapable of doing this
727 * so if we are running on anything older than 4 do not attempt to read
728 * control/platform-feature-xs_reset_watches.
729 */
730static bool xen_strict_xenbus_quirk(void)
731{
732#ifdef CONFIG_X86
733 uint32_t eax, ebx, ecx, edx, base;
734
735 base = xen_cpuid_base();
736 cpuid(op: base + 1, eax: &eax, ebx: &ebx, ecx: &ecx, edx: &edx);
737
738 if ((eax >> 16) < 4)
739 return true;
740#endif
741 return false;
742
743}
744static void xs_reset_watches(void)
745{
746 int err;
747
748 if (!xen_hvm_domain() || xen_initial_domain())
749 return;
750
751 if (xen_strict_xenbus_quirk())
752 return;
753
754 if (!xenbus_read_unsigned("control",
755 "platform-feature-xs_reset_watches", 0))
756 return;
757
758 err = xs_error(reply: xs_single(XBT_NIL, type: XS_RESET_WATCHES, string: "", NULL));
759 if (err && err != -EEXIST)
760 pr_warn("xs_reset_watches failed: %d\n", err);
761}
762
763/* Register callback to watch this node. */
764int register_xenbus_watch(struct xenbus_watch *watch)
765{
766 /* Pointer in ascii is the token. */
767 char token[sizeof(watch) * 2 + 1];
768 int err;
769
770 sprintf(buf: token, fmt: "%lX", (long)watch);
771
772 watch->nr_pending = 0;
773
774 down_read(sem: &xs_watch_rwsem);
775
776 spin_lock(lock: &watches_lock);
777 BUG_ON(find_watch(token));
778 list_add(new: &watch->list, head: &watches);
779 spin_unlock(lock: &watches_lock);
780
781 err = xs_watch(path: watch->node, token);
782
783 if (err) {
784 spin_lock(lock: &watches_lock);
785 list_del(entry: &watch->list);
786 spin_unlock(lock: &watches_lock);
787 }
788
789 up_read(sem: &xs_watch_rwsem);
790
791 return err;
792}
793EXPORT_SYMBOL_GPL(register_xenbus_watch);
794
795void unregister_xenbus_watch(struct xenbus_watch *watch)
796{
797 struct xs_watch_event *event, *tmp;
798 char token[sizeof(watch) * 2 + 1];
799 int err;
800
801 sprintf(buf: token, fmt: "%lX", (long)watch);
802
803 down_read(sem: &xs_watch_rwsem);
804
805 spin_lock(lock: &watches_lock);
806 BUG_ON(!find_watch(token));
807 list_del(entry: &watch->list);
808 spin_unlock(lock: &watches_lock);
809
810 err = xs_unwatch(path: watch->node, token);
811 if (err)
812 pr_warn("Failed to release watch %s: %i\n", watch->node, err);
813
814 up_read(sem: &xs_watch_rwsem);
815
816 /* Make sure there are no callbacks running currently (unless
817 its us) */
818 if (current->pid != xenwatch_pid)
819 mutex_lock(&xenwatch_mutex);
820
821 /* Cancel pending watch events. */
822 spin_lock(lock: &watch_events_lock);
823 if (watch->nr_pending) {
824 list_for_each_entry_safe(event, tmp, &watch_events, list) {
825 if (event->handle != watch)
826 continue;
827 list_del(entry: &event->list);
828 kfree(objp: event);
829 }
830 watch->nr_pending = 0;
831 }
832 spin_unlock(lock: &watch_events_lock);
833
834 if (current->pid != xenwatch_pid)
835 mutex_unlock(lock: &xenwatch_mutex);
836}
837EXPORT_SYMBOL_GPL(unregister_xenbus_watch);
838
839void xs_suspend(void)
840{
841 xs_suspend_enter();
842
843 mutex_lock(&xs_response_mutex);
844 down_write(sem: &xs_watch_rwsem);
845}
846
847void xs_resume(void)
848{
849 struct xenbus_watch *watch;
850 char token[sizeof(watch) * 2 + 1];
851
852 xb_init_comms();
853
854 mutex_unlock(lock: &xs_response_mutex);
855
856 xs_suspend_exit();
857
858 /* No need for watches_lock: the xs_watch_rwsem is sufficient. */
859 list_for_each_entry(watch, &watches, list) {
860 sprintf(buf: token, fmt: "%lX", (long)watch);
861 xs_watch(path: watch->node, token);
862 }
863
864 up_write(sem: &xs_watch_rwsem);
865}
866
867void xs_suspend_cancel(void)
868{
869 up_write(sem: &xs_watch_rwsem);
870 mutex_unlock(lock: &xs_response_mutex);
871
872 xs_suspend_exit();
873}
874
875static int xenwatch_thread(void *unused)
876{
877 struct xs_watch_event *event;
878
879 xenwatch_pid = current->pid;
880
881 for (;;) {
882 wait_event_interruptible(watch_events_waitq,
883 !list_empty(&watch_events));
884
885 if (kthread_should_stop())
886 break;
887
888 mutex_lock(&xenwatch_mutex);
889
890 spin_lock(lock: &watch_events_lock);
891 event = list_first_entry_or_null(&watch_events,
892 struct xs_watch_event, list);
893 if (event) {
894 list_del(entry: &event->list);
895 event->handle->nr_pending--;
896 }
897 spin_unlock(lock: &watch_events_lock);
898
899 if (event) {
900 event->handle->callback(event->handle, event->path,
901 event->token);
902 kfree(objp: event);
903 }
904
905 mutex_unlock(lock: &xenwatch_mutex);
906 }
907
908 return 0;
909}
910
911/*
912 * Wake up all threads waiting for a xenstore reply. In case of shutdown all
913 * pending replies will be marked as "aborted" in order to let the waiters
914 * return in spite of xenstore possibly no longer being able to reply. This
915 * will avoid blocking shutdown by a thread waiting for xenstore but being
916 * necessary for shutdown processing to proceed.
917 */
918static int xs_reboot_notify(struct notifier_block *nb,
919 unsigned long code, void *unused)
920{
921 struct xb_req_data *req;
922
923 mutex_lock(&xb_write_mutex);
924 list_for_each_entry(req, &xs_reply_list, list)
925 wake_up(&req->wq);
926 list_for_each_entry(req, &xb_write_list, list)
927 wake_up(&req->wq);
928 mutex_unlock(lock: &xb_write_mutex);
929 return NOTIFY_DONE;
930}
931
932static struct notifier_block xs_reboot_nb = {
933 .notifier_call = xs_reboot_notify,
934};
935
936int xs_init(void)
937{
938 int err;
939 struct task_struct *task;
940
941 register_reboot_notifier(&xs_reboot_nb);
942
943 /* Initialize the shared memory rings to talk to xenstored */
944 err = xb_init_comms();
945 if (err)
946 return err;
947
948 task = kthread_run(xenwatch_thread, NULL, "xenwatch");
949 if (IS_ERR(ptr: task))
950 return PTR_ERR(ptr: task);
951
952 /* shutdown watches for kexec boot */
953 xs_reset_watches();
954
955 return 0;
956}
957

source code of linux/drivers/xen/xenbus/xenbus_xs.c