1 /******************************************************************************
2 * xenbus_comms.c
3 *
4 * Low level code to talks to Xen Store: ringbuffer and event channel.
5 *
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
33 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
34
35 #include <linux/wait.h>
36 #include <linux/interrupt.h>
37 #include <linux/kthread.h>
38 #include <linux/sched.h>
39 #include <linux/err.h>
40 #include <xen/xenbus.h>
41 #include <asm/xen/hypervisor.h>
42 #include <xen/events.h>
43 #include <xen/page.h>
44 #include "xenbus.h"
45
46 /* A list of replies. Currently only one will ever be outstanding. */
47 LIST_HEAD(xs_reply_list);
48
49 /* A list of write requests. */
50 LIST_HEAD(xb_write_list);
51 DECLARE_WAIT_QUEUE_HEAD(xb_waitq);
52 DEFINE_MUTEX(xb_write_mutex);
53
54 /* Protect xenbus reader thread against save/restore. */
55 DEFINE_MUTEX(xs_response_mutex);
56
57 static int xenbus_irq;
58 static struct task_struct *xenbus_task;
59
60 static DECLARE_WORK(probe_work, xenbus_probe);
61
62
wake_waiting(int irq,void * unused)63 static irqreturn_t wake_waiting(int irq, void *unused)
64 {
65 if (unlikely(xenstored_ready == 0)) {
66 xenstored_ready = 1;
67 schedule_work(&probe_work);
68 }
69
70 wake_up(&xb_waitq);
71 return IRQ_HANDLED;
72 }
73
check_indexes(XENSTORE_RING_IDX cons,XENSTORE_RING_IDX prod)74 static int check_indexes(XENSTORE_RING_IDX cons, XENSTORE_RING_IDX prod)
75 {
76 return ((prod - cons) <= XENSTORE_RING_SIZE);
77 }
78
get_output_chunk(XENSTORE_RING_IDX cons,XENSTORE_RING_IDX prod,char * buf,uint32_t * len)79 static void *get_output_chunk(XENSTORE_RING_IDX cons,
80 XENSTORE_RING_IDX prod,
81 char *buf, uint32_t *len)
82 {
83 *len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(prod);
84 if ((XENSTORE_RING_SIZE - (prod - cons)) < *len)
85 *len = XENSTORE_RING_SIZE - (prod - cons);
86 return buf + MASK_XENSTORE_IDX(prod);
87 }
88
get_input_chunk(XENSTORE_RING_IDX cons,XENSTORE_RING_IDX prod,const char * buf,uint32_t * len)89 static const void *get_input_chunk(XENSTORE_RING_IDX cons,
90 XENSTORE_RING_IDX prod,
91 const char *buf, uint32_t *len)
92 {
93 *len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(cons);
94 if ((prod - cons) < *len)
95 *len = prod - cons;
96 return buf + MASK_XENSTORE_IDX(cons);
97 }
98
xb_data_to_write(void)99 static int xb_data_to_write(void)
100 {
101 struct xenstore_domain_interface *intf = xen_store_interface;
102
103 return (intf->req_prod - intf->req_cons) != XENSTORE_RING_SIZE &&
104 !list_empty(&xb_write_list);
105 }
106
107 /**
108 * xb_write - low level write
109 * @data: buffer to send
110 * @len: length of buffer
111 *
112 * Returns number of bytes written or -err.
113 */
xb_write(const void * data,unsigned int len)114 static int xb_write(const void *data, unsigned int len)
115 {
116 struct xenstore_domain_interface *intf = xen_store_interface;
117 XENSTORE_RING_IDX cons, prod;
118 unsigned int bytes = 0;
119
120 while (len != 0) {
121 void *dst;
122 unsigned int avail;
123
124 /* Read indexes, then verify. */
125 cons = intf->req_cons;
126 prod = intf->req_prod;
127 if (!check_indexes(cons, prod)) {
128 intf->req_cons = intf->req_prod = 0;
129 return -EIO;
130 }
131 if (!xb_data_to_write())
132 return bytes;
133
134 /* Must write data /after/ reading the consumer index. */
135 virt_mb();
136
137 dst = get_output_chunk(cons, prod, intf->req, &avail);
138 if (avail == 0)
139 continue;
140 if (avail > len)
141 avail = len;
142
143 memcpy(dst, data, avail);
144 data += avail;
145 len -= avail;
146 bytes += avail;
147
148 /* Other side must not see new producer until data is there. */
149 virt_wmb();
150 intf->req_prod += avail;
151
152 /* Implies mb(): other side will see the updated producer. */
153 if (prod <= intf->req_cons)
154 notify_remote_via_evtchn(xen_store_evtchn);
155 }
156
157 return bytes;
158 }
159
xb_data_to_read(void)160 static int xb_data_to_read(void)
161 {
162 struct xenstore_domain_interface *intf = xen_store_interface;
163 return (intf->rsp_cons != intf->rsp_prod);
164 }
165
xb_read(void * data,unsigned int len)166 static int xb_read(void *data, unsigned int len)
167 {
168 struct xenstore_domain_interface *intf = xen_store_interface;
169 XENSTORE_RING_IDX cons, prod;
170 unsigned int bytes = 0;
171
172 while (len != 0) {
173 unsigned int avail;
174 const char *src;
175
176 /* Read indexes, then verify. */
177 cons = intf->rsp_cons;
178 prod = intf->rsp_prod;
179 if (cons == prod)
180 return bytes;
181
182 if (!check_indexes(cons, prod)) {
183 intf->rsp_cons = intf->rsp_prod = 0;
184 return -EIO;
185 }
186
187 src = get_input_chunk(cons, prod, intf->rsp, &avail);
188 if (avail == 0)
189 continue;
190 if (avail > len)
191 avail = len;
192
193 /* Must read data /after/ reading the producer index. */
194 virt_rmb();
195
196 memcpy(data, src, avail);
197 data += avail;
198 len -= avail;
199 bytes += avail;
200
201 /* Other side must not see free space until we've copied out */
202 virt_mb();
203 intf->rsp_cons += avail;
204
205 /* Implies mb(): other side will see the updated consumer. */
206 if (intf->rsp_prod - cons >= XENSTORE_RING_SIZE)
207 notify_remote_via_evtchn(xen_store_evtchn);
208 }
209
210 return bytes;
211 }
212
process_msg(void)213 static int process_msg(void)
214 {
215 static struct {
216 struct xsd_sockmsg msg;
217 char *body;
218 union {
219 void *alloc;
220 struct xs_watch_event *watch;
221 };
222 bool in_msg;
223 bool in_hdr;
224 unsigned int read;
225 } state;
226 struct xb_req_data *req;
227 int err;
228 unsigned int len;
229
230 if (!state.in_msg) {
231 state.in_msg = true;
232 state.in_hdr = true;
233 state.read = 0;
234
235 /*
236 * We must disallow save/restore while reading a message.
237 * A partial read across s/r leaves us out of sync with
238 * xenstored.
239 * xs_response_mutex is locked as long as we are processing one
240 * message. state.in_msg will be true as long as we are holding
241 * the lock here.
242 */
243 mutex_lock(&xs_response_mutex);
244
245 if (!xb_data_to_read()) {
246 /* We raced with save/restore: pending data 'gone'. */
247 mutex_unlock(&xs_response_mutex);
248 state.in_msg = false;
249 return 0;
250 }
251 }
252
253 if (state.in_hdr) {
254 if (state.read != sizeof(state.msg)) {
255 err = xb_read((void *)&state.msg + state.read,
256 sizeof(state.msg) - state.read);
257 if (err < 0)
258 goto out;
259 state.read += err;
260 if (state.read != sizeof(state.msg))
261 return 0;
262 if (state.msg.len > XENSTORE_PAYLOAD_MAX) {
263 err = -EINVAL;
264 goto out;
265 }
266 }
267
268 len = state.msg.len + 1;
269 if (state.msg.type == XS_WATCH_EVENT)
270 len += sizeof(*state.watch);
271
272 state.alloc = kmalloc(len, GFP_NOIO | __GFP_HIGH);
273 if (!state.alloc)
274 return -ENOMEM;
275
276 if (state.msg.type == XS_WATCH_EVENT)
277 state.body = state.watch->body;
278 else
279 state.body = state.alloc;
280 state.in_hdr = false;
281 state.read = 0;
282 }
283
284 err = xb_read(state.body + state.read, state.msg.len - state.read);
285 if (err < 0)
286 goto out;
287
288 state.read += err;
289 if (state.read != state.msg.len)
290 return 0;
291
292 state.body[state.msg.len] = '\0';
293
294 if (state.msg.type == XS_WATCH_EVENT) {
295 state.watch->len = state.msg.len;
296 err = xs_watch_msg(state.watch);
297 } else {
298 err = -ENOENT;
299 mutex_lock(&xb_write_mutex);
300 list_for_each_entry(req, &xs_reply_list, list) {
301 if (req->msg.req_id == state.msg.req_id) {
302 list_del(&req->list);
303 err = 0;
304 break;
305 }
306 }
307 mutex_unlock(&xb_write_mutex);
308 if (err)
309 goto out;
310
311 if (req->state == xb_req_state_wait_reply) {
312 req->msg.req_id = req->caller_req_id;
313 req->msg.type = state.msg.type;
314 req->msg.len = state.msg.len;
315 req->body = state.body;
316 req->state = xb_req_state_got_reply;
317 req->cb(req);
318 } else
319 kfree(req);
320 }
321
322 mutex_unlock(&xs_response_mutex);
323
324 state.in_msg = false;
325 state.alloc = NULL;
326 return err;
327
328 out:
329 mutex_unlock(&xs_response_mutex);
330 state.in_msg = false;
331 kfree(state.alloc);
332 state.alloc = NULL;
333 return err;
334 }
335
process_writes(void)336 static int process_writes(void)
337 {
338 static struct {
339 struct xb_req_data *req;
340 int idx;
341 unsigned int written;
342 } state;
343 void *base;
344 unsigned int len;
345 int err = 0;
346
347 if (!xb_data_to_write())
348 return 0;
349
350 mutex_lock(&xb_write_mutex);
351
352 if (!state.req) {
353 state.req = list_first_entry(&xb_write_list,
354 struct xb_req_data, list);
355 state.idx = -1;
356 state.written = 0;
357 }
358
359 if (state.req->state == xb_req_state_aborted)
360 goto out_err;
361
362 while (state.idx < state.req->num_vecs) {
363 if (state.idx < 0) {
364 base = &state.req->msg;
365 len = sizeof(state.req->msg);
366 } else {
367 base = state.req->vec[state.idx].iov_base;
368 len = state.req->vec[state.idx].iov_len;
369 }
370 err = xb_write(base + state.written, len - state.written);
371 if (err < 0)
372 goto out_err;
373 state.written += err;
374 if (state.written != len)
375 goto out;
376
377 state.idx++;
378 state.written = 0;
379 }
380
381 list_del(&state.req->list);
382 state.req->state = xb_req_state_wait_reply;
383 list_add_tail(&state.req->list, &xs_reply_list);
384 state.req = NULL;
385
386 out:
387 mutex_unlock(&xb_write_mutex);
388
389 return 0;
390
391 out_err:
392 state.req->msg.type = XS_ERROR;
393 state.req->err = err;
394 list_del(&state.req->list);
395 if (state.req->state == xb_req_state_aborted)
396 kfree(state.req);
397 else {
398 state.req->state = xb_req_state_got_reply;
399 wake_up(&state.req->wq);
400 }
401
402 mutex_unlock(&xb_write_mutex);
403
404 state.req = NULL;
405
406 return err;
407 }
408
xb_thread_work(void)409 static int xb_thread_work(void)
410 {
411 return xb_data_to_read() || xb_data_to_write();
412 }
413
xenbus_thread(void * unused)414 static int xenbus_thread(void *unused)
415 {
416 int err;
417
418 while (!kthread_should_stop()) {
419 if (wait_event_interruptible(xb_waitq, xb_thread_work()))
420 continue;
421
422 err = process_msg();
423 if (err == -ENOMEM)
424 schedule();
425 else if (err)
426 pr_warn_ratelimited("error %d while reading message\n",
427 err);
428
429 err = process_writes();
430 if (err)
431 pr_warn_ratelimited("error %d while writing message\n",
432 err);
433 }
434
435 xenbus_task = NULL;
436 return 0;
437 }
438
439 /**
440 * xb_init_comms - Set up interrupt handler off store event channel.
441 */
xb_init_comms(void)442 int xb_init_comms(void)
443 {
444 struct xenstore_domain_interface *intf = xen_store_interface;
445
446 if (intf->req_prod != intf->req_cons)
447 pr_err("request ring is not quiescent (%08x:%08x)!\n",
448 intf->req_cons, intf->req_prod);
449
450 if (intf->rsp_prod != intf->rsp_cons) {
451 pr_warn("response ring is not quiescent (%08x:%08x): fixing up\n",
452 intf->rsp_cons, intf->rsp_prod);
453 /* breaks kdump */
454 if (!reset_devices)
455 intf->rsp_cons = intf->rsp_prod;
456 }
457
458 if (xenbus_irq) {
459 /* Already have an irq; assume we're resuming */
460 rebind_evtchn_irq(xen_store_evtchn, xenbus_irq);
461 } else {
462 int err;
463
464 err = bind_evtchn_to_irqhandler(xen_store_evtchn, wake_waiting,
465 0, "xenbus", &xb_waitq);
466 if (err < 0) {
467 pr_err("request irq failed %i\n", err);
468 return err;
469 }
470
471 xenbus_irq = err;
472
473 if (!xenbus_task) {
474 xenbus_task = kthread_run(xenbus_thread, NULL,
475 "xenbus");
476 if (IS_ERR(xenbus_task))
477 return PTR_ERR(xenbus_task);
478 }
479 }
480
481 return 0;
482 }
483
xb_deinit_comms(void)484 void xb_deinit_comms(void)
485 {
486 unbind_from_irqhandler(xenbus_irq, &xb_waitq);
487 xenbus_irq = 0;
488 }
489