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/module.h> 59 60 #include "xenbus_comms.h" 61 62 #include <xen/xenbus.h> 63 #include <xen/xen.h> 64 #include <asm/xen/hypervisor.h> 65 66 MODULE_LICENSE("GPL"); 67 68 /* 69 * An element of a list of outstanding transactions, for which we're 70 * still waiting a reply. 71 */ 72 struct xenbus_transaction_holder { 73 struct list_head list; 74 struct xenbus_transaction handle; 75 }; 76 77 /* 78 * A buffer of data on the queue. 79 */ 80 struct read_buffer { 81 struct list_head list; 82 unsigned int cons; 83 unsigned int len; 84 char msg[]; 85 }; 86 87 struct xenbus_file_priv { 88 /* 89 * msgbuffer_mutex is held while partial requests are built up 90 * and complete requests are acted on. It therefore protects 91 * the "transactions" and "watches" lists, and the partial 92 * request length and buffer. 93 * 94 * reply_mutex protects the reply being built up to return to 95 * usermode. It nests inside msgbuffer_mutex but may be held 96 * alone during a watch callback. 97 */ 98 struct mutex msgbuffer_mutex; 99 100 /* In-progress transactions */ 101 struct list_head transactions; 102 103 /* Active watches. */ 104 struct list_head watches; 105 106 /* Partial request. */ 107 unsigned int len; 108 union { 109 struct xsd_sockmsg msg; 110 char buffer[XENSTORE_PAYLOAD_MAX]; 111 } u; 112 113 /* Response queue. */ 114 struct mutex reply_mutex; 115 struct list_head read_buffers; 116 wait_queue_head_t read_waitq; 117 118 }; 119 120 /* Read out any raw xenbus messages queued up. */ 121 static ssize_t xenbus_file_read(struct file *filp, 122 char __user *ubuf, 123 size_t len, loff_t *ppos) 124 { 125 struct xenbus_file_priv *u = filp->private_data; 126 struct read_buffer *rb; 127 unsigned i; 128 int ret; 129 130 mutex_lock(&u->reply_mutex); 131 again: 132 while (list_empty(&u->read_buffers)) { 133 mutex_unlock(&u->reply_mutex); 134 if (filp->f_flags & O_NONBLOCK) 135 return -EAGAIN; 136 137 ret = wait_event_interruptible(u->read_waitq, 138 !list_empty(&u->read_buffers)); 139 if (ret) 140 return ret; 141 mutex_lock(&u->reply_mutex); 142 } 143 144 rb = list_entry(u->read_buffers.next, struct read_buffer, list); 145 i = 0; 146 while (i < len) { 147 unsigned sz = min((unsigned)len - i, rb->len - rb->cons); 148 149 ret = copy_to_user(ubuf + i, &rb->msg[rb->cons], sz); 150 151 i += sz - ret; 152 rb->cons += sz - ret; 153 154 if (ret != 0) { 155 if (i == 0) 156 i = -EFAULT; 157 goto out; 158 } 159 160 /* Clear out buffer if it has been consumed */ 161 if (rb->cons == rb->len) { 162 list_del(&rb->list); 163 kfree(rb); 164 if (list_empty(&u->read_buffers)) 165 break; 166 rb = list_entry(u->read_buffers.next, 167 struct read_buffer, list); 168 } 169 } 170 if (i == 0) 171 goto again; 172 173 out: 174 mutex_unlock(&u->reply_mutex); 175 return i; 176 } 177 178 /* 179 * Add a buffer to the queue. Caller must hold the appropriate lock 180 * if the queue is not local. (Commonly the caller will build up 181 * multiple queued buffers on a temporary local list, and then add it 182 * to the appropriate list under lock once all the buffers have een 183 * successfully allocated.) 184 */ 185 static int queue_reply(struct list_head *queue, const void *data, size_t len) 186 { 187 struct read_buffer *rb; 188 189 if (len == 0) 190 return 0; 191 192 rb = kmalloc(sizeof(*rb) + len, GFP_KERNEL); 193 if (rb == NULL) 194 return -ENOMEM; 195 196 rb->cons = 0; 197 rb->len = len; 198 199 memcpy(rb->msg, data, len); 200 201 list_add_tail(&rb->list, queue); 202 return 0; 203 } 204 205 /* 206 * Free all the read_buffer s on a list. 207 * Caller must have sole reference to list. 208 */ 209 static void queue_cleanup(struct list_head *list) 210 { 211 struct read_buffer *rb; 212 213 while (!list_empty(list)) { 214 rb = list_entry(list->next, struct read_buffer, list); 215 list_del(list->next); 216 kfree(rb); 217 } 218 } 219 220 struct watch_adapter { 221 struct list_head list; 222 struct xenbus_watch watch; 223 struct xenbus_file_priv *dev_data; 224 char *token; 225 }; 226 227 static void free_watch_adapter(struct watch_adapter *watch) 228 { 229 kfree(watch->watch.node); 230 kfree(watch->token); 231 kfree(watch); 232 } 233 234 static struct watch_adapter *alloc_watch_adapter(const char *path, 235 const char *token) 236 { 237 struct watch_adapter *watch; 238 239 watch = kzalloc(sizeof(*watch), GFP_KERNEL); 240 if (watch == NULL) 241 goto out_fail; 242 243 watch->watch.node = kstrdup(path, GFP_KERNEL); 244 if (watch->watch.node == NULL) 245 goto out_free; 246 247 watch->token = kstrdup(token, GFP_KERNEL); 248 if (watch->token == NULL) 249 goto out_free; 250 251 return watch; 252 253 out_free: 254 free_watch_adapter(watch); 255 256 out_fail: 257 return NULL; 258 } 259 260 static void watch_fired(struct xenbus_watch *watch, 261 const char **vec, 262 unsigned int len) 263 { 264 struct watch_adapter *adap; 265 struct xsd_sockmsg hdr; 266 const char *path, *token; 267 int path_len, tok_len, body_len, data_len = 0; 268 int ret; 269 LIST_HEAD(staging_q); 270 271 adap = container_of(watch, struct watch_adapter, watch); 272 273 path = vec[XS_WATCH_PATH]; 274 token = adap->token; 275 276 path_len = strlen(path) + 1; 277 tok_len = strlen(token) + 1; 278 if (len > 2) 279 data_len = vec[len] - vec[2] + 1; 280 body_len = path_len + tok_len + data_len; 281 282 hdr.type = XS_WATCH_EVENT; 283 hdr.len = body_len; 284 285 mutex_lock(&adap->dev_data->reply_mutex); 286 287 ret = queue_reply(&staging_q, &hdr, sizeof(hdr)); 288 if (!ret) 289 ret = queue_reply(&staging_q, path, path_len); 290 if (!ret) 291 ret = queue_reply(&staging_q, token, tok_len); 292 if (!ret && len > 2) 293 ret = queue_reply(&staging_q, vec[2], data_len); 294 295 if (!ret) { 296 /* success: pass reply list onto watcher */ 297 list_splice_tail(&staging_q, &adap->dev_data->read_buffers); 298 wake_up(&adap->dev_data->read_waitq); 299 } else 300 queue_cleanup(&staging_q); 301 302 mutex_unlock(&adap->dev_data->reply_mutex); 303 } 304 305 static int xenbus_write_transaction(unsigned msg_type, 306 struct xenbus_file_priv *u) 307 { 308 int rc; 309 void *reply; 310 struct xenbus_transaction_holder *trans = NULL; 311 LIST_HEAD(staging_q); 312 313 if (msg_type == XS_TRANSACTION_START) { 314 trans = kmalloc(sizeof(*trans), GFP_KERNEL); 315 if (!trans) { 316 rc = -ENOMEM; 317 goto out; 318 } 319 } 320 321 reply = xenbus_dev_request_and_reply(&u->u.msg); 322 if (IS_ERR(reply)) { 323 kfree(trans); 324 rc = PTR_ERR(reply); 325 goto out; 326 } 327 328 if (msg_type == XS_TRANSACTION_START) { 329 trans->handle.id = simple_strtoul(reply, NULL, 0); 330 331 list_add(&trans->list, &u->transactions); 332 } else if (msg_type == XS_TRANSACTION_END) { 333 list_for_each_entry(trans, &u->transactions, list) 334 if (trans->handle.id == u->u.msg.tx_id) 335 break; 336 BUG_ON(&trans->list == &u->transactions); 337 list_del(&trans->list); 338 339 kfree(trans); 340 } 341 342 mutex_lock(&u->reply_mutex); 343 rc = queue_reply(&staging_q, &u->u.msg, sizeof(u->u.msg)); 344 if (!rc) 345 rc = queue_reply(&staging_q, reply, u->u.msg.len); 346 if (!rc) { 347 list_splice_tail(&staging_q, &u->read_buffers); 348 wake_up(&u->read_waitq); 349 } else { 350 queue_cleanup(&staging_q); 351 } 352 mutex_unlock(&u->reply_mutex); 353 354 kfree(reply); 355 356 out: 357 return rc; 358 } 359 360 static int xenbus_write_watch(unsigned msg_type, struct xenbus_file_priv *u) 361 { 362 struct watch_adapter *watch, *tmp_watch; 363 char *path, *token; 364 int err, rc; 365 LIST_HEAD(staging_q); 366 367 path = u->u.buffer + sizeof(u->u.msg); 368 token = memchr(path, 0, u->u.msg.len); 369 if (token == NULL) { 370 rc = -EILSEQ; 371 goto out; 372 } 373 token++; 374 if (memchr(token, 0, u->u.msg.len - (token - path)) == NULL) { 375 rc = -EILSEQ; 376 goto out; 377 } 378 379 if (msg_type == XS_WATCH) { 380 watch = alloc_watch_adapter(path, token); 381 if (watch == NULL) { 382 rc = -ENOMEM; 383 goto out; 384 } 385 386 watch->watch.callback = watch_fired; 387 watch->dev_data = u; 388 389 err = register_xenbus_watch(&watch->watch); 390 if (err) { 391 free_watch_adapter(watch); 392 rc = err; 393 goto out; 394 } 395 list_add(&watch->list, &u->watches); 396 } else { 397 list_for_each_entry_safe(watch, tmp_watch, &u->watches, list) { 398 if (!strcmp(watch->token, token) && 399 !strcmp(watch->watch.node, path)) { 400 unregister_xenbus_watch(&watch->watch); 401 list_del(&watch->list); 402 free_watch_adapter(watch); 403 break; 404 } 405 } 406 } 407 408 /* Success. Synthesize a reply to say all is OK. */ 409 { 410 struct { 411 struct xsd_sockmsg hdr; 412 char body[3]; 413 } __packed reply = { 414 { 415 .type = msg_type, 416 .len = sizeof(reply.body) 417 }, 418 "OK" 419 }; 420 421 mutex_lock(&u->reply_mutex); 422 rc = queue_reply(&u->read_buffers, &reply, sizeof(reply)); 423 wake_up(&u->read_waitq); 424 mutex_unlock(&u->reply_mutex); 425 } 426 427 out: 428 return rc; 429 } 430 431 static ssize_t xenbus_file_write(struct file *filp, 432 const char __user *ubuf, 433 size_t len, loff_t *ppos) 434 { 435 struct xenbus_file_priv *u = filp->private_data; 436 uint32_t msg_type; 437 int rc = len; 438 int ret; 439 LIST_HEAD(staging_q); 440 441 /* 442 * We're expecting usermode to be writing properly formed 443 * xenbus messages. If they write an incomplete message we 444 * buffer it up. Once it is complete, we act on it. 445 */ 446 447 /* 448 * Make sure concurrent writers can't stomp all over each 449 * other's messages and make a mess of our partial message 450 * buffer. We don't make any attemppt to stop multiple 451 * writers from making a mess of each other's incomplete 452 * messages; we're just trying to guarantee our own internal 453 * consistency and make sure that single writes are handled 454 * atomically. 455 */ 456 mutex_lock(&u->msgbuffer_mutex); 457 458 /* Get this out of the way early to avoid confusion */ 459 if (len == 0) 460 goto out; 461 462 /* Can't write a xenbus message larger we can buffer */ 463 if (len > sizeof(u->u.buffer) - u->len) { 464 /* On error, dump existing buffer */ 465 u->len = 0; 466 rc = -EINVAL; 467 goto out; 468 } 469 470 ret = copy_from_user(u->u.buffer + u->len, ubuf, len); 471 472 if (ret != 0) { 473 rc = -EFAULT; 474 goto out; 475 } 476 477 /* Deal with a partial copy. */ 478 len -= ret; 479 rc = len; 480 481 u->len += len; 482 483 /* Return if we haven't got a full message yet */ 484 if (u->len < sizeof(u->u.msg)) 485 goto out; /* not even the header yet */ 486 487 /* If we're expecting a message that's larger than we can 488 possibly send, dump what we have and return an error. */ 489 if ((sizeof(u->u.msg) + u->u.msg.len) > sizeof(u->u.buffer)) { 490 rc = -E2BIG; 491 u->len = 0; 492 goto out; 493 } 494 495 if (u->len < (sizeof(u->u.msg) + u->u.msg.len)) 496 goto out; /* incomplete data portion */ 497 498 /* 499 * OK, now we have a complete message. Do something with it. 500 */ 501 502 msg_type = u->u.msg.type; 503 504 switch (msg_type) { 505 case XS_WATCH: 506 case XS_UNWATCH: 507 /* (Un)Ask for some path to be watched for changes */ 508 ret = xenbus_write_watch(msg_type, u); 509 break; 510 511 default: 512 /* Send out a transaction */ 513 ret = xenbus_write_transaction(msg_type, u); 514 break; 515 } 516 if (ret != 0) 517 rc = ret; 518 519 /* Buffered message consumed */ 520 u->len = 0; 521 522 out: 523 mutex_unlock(&u->msgbuffer_mutex); 524 return rc; 525 } 526 527 static int xenbus_file_open(struct inode *inode, struct file *filp) 528 { 529 struct xenbus_file_priv *u; 530 531 if (xen_store_evtchn == 0) 532 return -ENOENT; 533 534 nonseekable_open(inode, filp); 535 536 u = kzalloc(sizeof(*u), GFP_KERNEL); 537 if (u == NULL) 538 return -ENOMEM; 539 540 INIT_LIST_HEAD(&u->transactions); 541 INIT_LIST_HEAD(&u->watches); 542 INIT_LIST_HEAD(&u->read_buffers); 543 init_waitqueue_head(&u->read_waitq); 544 545 mutex_init(&u->reply_mutex); 546 mutex_init(&u->msgbuffer_mutex); 547 548 filp->private_data = u; 549 550 return 0; 551 } 552 553 static int xenbus_file_release(struct inode *inode, struct file *filp) 554 { 555 struct xenbus_file_priv *u = filp->private_data; 556 struct xenbus_transaction_holder *trans, *tmp; 557 struct watch_adapter *watch, *tmp_watch; 558 struct read_buffer *rb, *tmp_rb; 559 560 /* 561 * No need for locking here because there are no other users, 562 * by definition. 563 */ 564 565 list_for_each_entry_safe(trans, tmp, &u->transactions, list) { 566 xenbus_transaction_end(trans->handle, 1); 567 list_del(&trans->list); 568 kfree(trans); 569 } 570 571 list_for_each_entry_safe(watch, tmp_watch, &u->watches, list) { 572 unregister_xenbus_watch(&watch->watch); 573 list_del(&watch->list); 574 free_watch_adapter(watch); 575 } 576 577 list_for_each_entry_safe(rb, tmp_rb, &u->read_buffers, list) { 578 list_del(&rb->list); 579 kfree(rb); 580 } 581 kfree(u); 582 583 return 0; 584 } 585 586 static unsigned int xenbus_file_poll(struct file *file, poll_table *wait) 587 { 588 struct xenbus_file_priv *u = file->private_data; 589 590 poll_wait(file, &u->read_waitq, wait); 591 if (!list_empty(&u->read_buffers)) 592 return POLLIN | POLLRDNORM; 593 return 0; 594 } 595 596 const struct file_operations xen_xenbus_fops = { 597 .read = xenbus_file_read, 598 .write = xenbus_file_write, 599 .open = xenbus_file_open, 600 .release = xenbus_file_release, 601 .poll = xenbus_file_poll, 602 .llseek = no_llseek, 603 }; 604 EXPORT_SYMBOL_GPL(xen_xenbus_fops); 605 606 static struct miscdevice xenbus_dev = { 607 .minor = MISC_DYNAMIC_MINOR, 608 .name = "xen/xenbus", 609 .fops = &xen_xenbus_fops, 610 }; 611 612 static int __init xenbus_init(void) 613 { 614 int err; 615 616 if (!xen_domain()) 617 return -ENODEV; 618 619 err = misc_register(&xenbus_dev); 620 if (err) 621 pr_err("Could not register xenbus frontend device\n"); 622 return err; 623 } 624 625 static void __exit xenbus_exit(void) 626 { 627 misc_deregister(&xenbus_dev); 628 } 629 630 module_init(xenbus_init); 631 module_exit(xenbus_exit); 632