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

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