1 /* 2 * CUSE: Character device in Userspace 3 * 4 * Copyright (C) 2008-2009 SUSE Linux Products GmbH 5 * Copyright (C) 2008-2009 Tejun Heo <tj@kernel.org> 6 * 7 * This file is released under the GPLv2. 8 * 9 * CUSE enables character devices to be implemented from userland much 10 * like FUSE allows filesystems. On initialization /dev/cuse is 11 * created. By opening the file and replying to the CUSE_INIT request 12 * userland CUSE server can create a character device. After that the 13 * operation is very similar to FUSE. 14 * 15 * A CUSE instance involves the following objects. 16 * 17 * cuse_conn : contains fuse_conn and serves as bonding structure 18 * channel : file handle connected to the userland CUSE server 19 * cdev : the implemented character device 20 * dev : generic device for cdev 21 * 22 * Note that 'channel' is what 'dev' is in FUSE. As CUSE deals with 23 * devices, it's called 'channel' to reduce confusion. 24 * 25 * channel determines when the character device dies. When channel is 26 * closed, everything begins to destruct. The cuse_conn is taken off 27 * the lookup table preventing further access from cdev, cdev and 28 * generic device are removed and the base reference of cuse_conn is 29 * put. 30 * 31 * On each open, the matching cuse_conn is looked up and if found an 32 * additional reference is taken which is released when the file is 33 * closed. 34 */ 35 36 #include <linux/fuse.h> 37 #include <linux/cdev.h> 38 #include <linux/device.h> 39 #include <linux/file.h> 40 #include <linux/fs.h> 41 #include <linux/kdev_t.h> 42 #include <linux/kthread.h> 43 #include <linux/list.h> 44 #include <linux/magic.h> 45 #include <linux/miscdevice.h> 46 #include <linux/mutex.h> 47 #include <linux/slab.h> 48 #include <linux/stat.h> 49 #include <linux/module.h> 50 51 #include "fuse_i.h" 52 53 #define CUSE_CONNTBL_LEN 64 54 55 struct cuse_conn { 56 struct list_head list; /* linked on cuse_conntbl */ 57 struct fuse_conn fc; /* fuse connection */ 58 struct cdev *cdev; /* associated character device */ 59 struct device *dev; /* device representing @cdev */ 60 61 /* init parameters, set once during initialization */ 62 bool unrestricted_ioctl; 63 }; 64 65 static DEFINE_MUTEX(cuse_lock); /* protects registration */ 66 static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN]; 67 static struct class *cuse_class; 68 69 static struct cuse_conn *fc_to_cc(struct fuse_conn *fc) 70 { 71 return container_of(fc, struct cuse_conn, fc); 72 } 73 74 static struct list_head *cuse_conntbl_head(dev_t devt) 75 { 76 return &cuse_conntbl[(MAJOR(devt) + MINOR(devt)) % CUSE_CONNTBL_LEN]; 77 } 78 79 80 /************************************************************************** 81 * CUSE frontend operations 82 * 83 * These are file operations for the character device. 84 * 85 * On open, CUSE opens a file from the FUSE mnt and stores it to 86 * private_data of the open file. All other ops call FUSE ops on the 87 * FUSE file. 88 */ 89 90 static ssize_t cuse_read(struct file *file, char __user *buf, size_t count, 91 loff_t *ppos) 92 { 93 loff_t pos = 0; 94 95 return fuse_direct_io(file, buf, count, &pos, 0); 96 } 97 98 static ssize_t cuse_write(struct file *file, const char __user *buf, 99 size_t count, loff_t *ppos) 100 { 101 loff_t pos = 0; 102 /* 103 * No locking or generic_write_checks(), the server is 104 * responsible for locking and sanity checks. 105 */ 106 return fuse_direct_io(file, buf, count, &pos, 1); 107 } 108 109 static int cuse_open(struct inode *inode, struct file *file) 110 { 111 dev_t devt = inode->i_cdev->dev; 112 struct cuse_conn *cc = NULL, *pos; 113 int rc; 114 115 /* look up and get the connection */ 116 mutex_lock(&cuse_lock); 117 list_for_each_entry(pos, cuse_conntbl_head(devt), list) 118 if (pos->dev->devt == devt) { 119 fuse_conn_get(&pos->fc); 120 cc = pos; 121 break; 122 } 123 mutex_unlock(&cuse_lock); 124 125 /* dead? */ 126 if (!cc) 127 return -ENODEV; 128 129 /* 130 * Generic permission check is already done against the chrdev 131 * file, proceed to open. 132 */ 133 rc = fuse_do_open(&cc->fc, 0, file, 0); 134 if (rc) 135 fuse_conn_put(&cc->fc); 136 return rc; 137 } 138 139 static int cuse_release(struct inode *inode, struct file *file) 140 { 141 struct fuse_file *ff = file->private_data; 142 struct fuse_conn *fc = ff->fc; 143 144 fuse_sync_release(ff, file->f_flags); 145 fuse_conn_put(fc); 146 147 return 0; 148 } 149 150 static long cuse_file_ioctl(struct file *file, unsigned int cmd, 151 unsigned long arg) 152 { 153 struct fuse_file *ff = file->private_data; 154 struct cuse_conn *cc = fc_to_cc(ff->fc); 155 unsigned int flags = 0; 156 157 if (cc->unrestricted_ioctl) 158 flags |= FUSE_IOCTL_UNRESTRICTED; 159 160 return fuse_do_ioctl(file, cmd, arg, flags); 161 } 162 163 static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd, 164 unsigned long arg) 165 { 166 struct fuse_file *ff = file->private_data; 167 struct cuse_conn *cc = fc_to_cc(ff->fc); 168 unsigned int flags = FUSE_IOCTL_COMPAT; 169 170 if (cc->unrestricted_ioctl) 171 flags |= FUSE_IOCTL_UNRESTRICTED; 172 173 return fuse_do_ioctl(file, cmd, arg, flags); 174 } 175 176 static const struct file_operations cuse_frontend_fops = { 177 .owner = THIS_MODULE, 178 .read = cuse_read, 179 .write = cuse_write, 180 .open = cuse_open, 181 .release = cuse_release, 182 .unlocked_ioctl = cuse_file_ioctl, 183 .compat_ioctl = cuse_file_compat_ioctl, 184 .poll = fuse_file_poll, 185 .llseek = noop_llseek, 186 }; 187 188 189 /************************************************************************** 190 * CUSE channel initialization and destruction 191 */ 192 193 struct cuse_devinfo { 194 const char *name; 195 }; 196 197 /** 198 * cuse_parse_one - parse one key=value pair 199 * @pp: i/o parameter for the current position 200 * @end: points to one past the end of the packed string 201 * @keyp: out parameter for key 202 * @valp: out parameter for value 203 * 204 * *@pp points to packed strings - "key0=val0\0key1=val1\0" which ends 205 * at @end - 1. This function parses one pair and set *@keyp to the 206 * start of the key and *@valp to the start of the value. Note that 207 * the original string is modified such that the key string is 208 * terminated with '\0'. *@pp is updated to point to the next string. 209 * 210 * RETURNS: 211 * 1 on successful parse, 0 on EOF, -errno on failure. 212 */ 213 static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp) 214 { 215 char *p = *pp; 216 char *key, *val; 217 218 while (p < end && *p == '\0') 219 p++; 220 if (p == end) 221 return 0; 222 223 if (end[-1] != '\0') { 224 printk(KERN_ERR "CUSE: info not properly terminated\n"); 225 return -EINVAL; 226 } 227 228 key = val = p; 229 p += strlen(p); 230 231 if (valp) { 232 strsep(&val, "="); 233 if (!val) 234 val = key + strlen(key); 235 key = strstrip(key); 236 val = strstrip(val); 237 } else 238 key = strstrip(key); 239 240 if (!strlen(key)) { 241 printk(KERN_ERR "CUSE: zero length info key specified\n"); 242 return -EINVAL; 243 } 244 245 *pp = p; 246 *keyp = key; 247 if (valp) 248 *valp = val; 249 250 return 1; 251 } 252 253 /** 254 * cuse_parse_dev_info - parse device info 255 * @p: device info string 256 * @len: length of device info string 257 * @devinfo: out parameter for parsed device info 258 * 259 * Parse @p to extract device info and store it into @devinfo. String 260 * pointed to by @p is modified by parsing and @devinfo points into 261 * them, so @p shouldn't be freed while @devinfo is in use. 262 * 263 * RETURNS: 264 * 0 on success, -errno on failure. 265 */ 266 static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo) 267 { 268 char *end = p + len; 269 char *uninitialized_var(key), *uninitialized_var(val); 270 int rc; 271 272 while (true) { 273 rc = cuse_parse_one(&p, end, &key, &val); 274 if (rc < 0) 275 return rc; 276 if (!rc) 277 break; 278 if (strcmp(key, "DEVNAME") == 0) 279 devinfo->name = val; 280 else 281 printk(KERN_WARNING "CUSE: unknown device info \"%s\"\n", 282 key); 283 } 284 285 if (!devinfo->name || !strlen(devinfo->name)) { 286 printk(KERN_ERR "CUSE: DEVNAME unspecified\n"); 287 return -EINVAL; 288 } 289 290 return 0; 291 } 292 293 static void cuse_gendev_release(struct device *dev) 294 { 295 kfree(dev); 296 } 297 298 /** 299 * cuse_process_init_reply - finish initializing CUSE channel 300 * 301 * This function creates the character device and sets up all the 302 * required data structures for it. Please read the comment at the 303 * top of this file for high level overview. 304 */ 305 static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req) 306 { 307 struct cuse_conn *cc = fc_to_cc(fc), *pos; 308 struct cuse_init_out *arg = req->out.args[0].value; 309 struct page *page = req->pages[0]; 310 struct cuse_devinfo devinfo = { }; 311 struct device *dev; 312 struct cdev *cdev; 313 dev_t devt; 314 int rc, i; 315 316 if (req->out.h.error || 317 arg->major != FUSE_KERNEL_VERSION || arg->minor < 11) { 318 goto err; 319 } 320 321 fc->minor = arg->minor; 322 fc->max_read = max_t(unsigned, arg->max_read, 4096); 323 fc->max_write = max_t(unsigned, arg->max_write, 4096); 324 325 /* parse init reply */ 326 cc->unrestricted_ioctl = arg->flags & CUSE_UNRESTRICTED_IOCTL; 327 328 rc = cuse_parse_devinfo(page_address(page), req->out.args[1].size, 329 &devinfo); 330 if (rc) 331 goto err; 332 333 /* determine and reserve devt */ 334 devt = MKDEV(arg->dev_major, arg->dev_minor); 335 if (!MAJOR(devt)) 336 rc = alloc_chrdev_region(&devt, MINOR(devt), 1, devinfo.name); 337 else 338 rc = register_chrdev_region(devt, 1, devinfo.name); 339 if (rc) { 340 printk(KERN_ERR "CUSE: failed to register chrdev region\n"); 341 goto err; 342 } 343 344 /* devt determined, create device */ 345 rc = -ENOMEM; 346 dev = kzalloc(sizeof(*dev), GFP_KERNEL); 347 if (!dev) 348 goto err_region; 349 350 device_initialize(dev); 351 dev_set_uevent_suppress(dev, 1); 352 dev->class = cuse_class; 353 dev->devt = devt; 354 dev->release = cuse_gendev_release; 355 dev_set_drvdata(dev, cc); 356 dev_set_name(dev, "%s", devinfo.name); 357 358 mutex_lock(&cuse_lock); 359 360 /* make sure the device-name is unique */ 361 for (i = 0; i < CUSE_CONNTBL_LEN; ++i) { 362 list_for_each_entry(pos, &cuse_conntbl[i], list) 363 if (!strcmp(dev_name(pos->dev), dev_name(dev))) 364 goto err_unlock; 365 } 366 367 rc = device_add(dev); 368 if (rc) 369 goto err_unlock; 370 371 /* register cdev */ 372 rc = -ENOMEM; 373 cdev = cdev_alloc(); 374 if (!cdev) 375 goto err_unlock; 376 377 cdev->owner = THIS_MODULE; 378 cdev->ops = &cuse_frontend_fops; 379 380 rc = cdev_add(cdev, devt, 1); 381 if (rc) 382 goto err_cdev; 383 384 cc->dev = dev; 385 cc->cdev = cdev; 386 387 /* make the device available */ 388 list_add(&cc->list, cuse_conntbl_head(devt)); 389 mutex_unlock(&cuse_lock); 390 391 /* announce device availability */ 392 dev_set_uevent_suppress(dev, 0); 393 kobject_uevent(&dev->kobj, KOBJ_ADD); 394 out: 395 kfree(arg); 396 __free_page(page); 397 return; 398 399 err_cdev: 400 cdev_del(cdev); 401 err_unlock: 402 mutex_unlock(&cuse_lock); 403 put_device(dev); 404 err_region: 405 unregister_chrdev_region(devt, 1); 406 err: 407 fuse_conn_kill(fc); 408 goto out; 409 } 410 411 static int cuse_send_init(struct cuse_conn *cc) 412 { 413 int rc; 414 struct fuse_req *req; 415 struct page *page; 416 struct fuse_conn *fc = &cc->fc; 417 struct cuse_init_in *arg; 418 void *outarg; 419 420 BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE); 421 422 req = fuse_get_req(fc); 423 if (IS_ERR(req)) { 424 rc = PTR_ERR(req); 425 goto err; 426 } 427 428 rc = -ENOMEM; 429 page = alloc_page(GFP_KERNEL | __GFP_ZERO); 430 if (!page) 431 goto err_put_req; 432 433 outarg = kzalloc(sizeof(struct cuse_init_out), GFP_KERNEL); 434 if (!outarg) 435 goto err_free_page; 436 437 arg = &req->misc.cuse_init_in; 438 arg->major = FUSE_KERNEL_VERSION; 439 arg->minor = FUSE_KERNEL_MINOR_VERSION; 440 arg->flags |= CUSE_UNRESTRICTED_IOCTL; 441 req->in.h.opcode = CUSE_INIT; 442 req->in.numargs = 1; 443 req->in.args[0].size = sizeof(struct cuse_init_in); 444 req->in.args[0].value = arg; 445 req->out.numargs = 2; 446 req->out.args[0].size = sizeof(struct cuse_init_out); 447 req->out.args[0].value = outarg; 448 req->out.args[1].size = CUSE_INIT_INFO_MAX; 449 req->out.argvar = 1; 450 req->out.argpages = 1; 451 req->pages[0] = page; 452 req->num_pages = 1; 453 req->end = cuse_process_init_reply; 454 fuse_request_send_background(fc, req); 455 456 return 0; 457 458 err_free_page: 459 __free_page(page); 460 err_put_req: 461 fuse_put_request(fc, req); 462 err: 463 return rc; 464 } 465 466 static void cuse_fc_release(struct fuse_conn *fc) 467 { 468 struct cuse_conn *cc = fc_to_cc(fc); 469 kfree(cc); 470 } 471 472 /** 473 * cuse_channel_open - open method for /dev/cuse 474 * @inode: inode for /dev/cuse 475 * @file: file struct being opened 476 * 477 * Userland CUSE server can create a CUSE device by opening /dev/cuse 478 * and replying to the initialization request kernel sends. This 479 * function is responsible for handling CUSE device initialization. 480 * Because the fd opened by this function is used during 481 * initialization, this function only creates cuse_conn and sends 482 * init. The rest is delegated to a kthread. 483 * 484 * RETURNS: 485 * 0 on success, -errno on failure. 486 */ 487 static int cuse_channel_open(struct inode *inode, struct file *file) 488 { 489 struct cuse_conn *cc; 490 int rc; 491 492 /* set up cuse_conn */ 493 cc = kzalloc(sizeof(*cc), GFP_KERNEL); 494 if (!cc) 495 return -ENOMEM; 496 497 fuse_conn_init(&cc->fc); 498 499 INIT_LIST_HEAD(&cc->list); 500 cc->fc.release = cuse_fc_release; 501 502 cc->fc.connected = 1; 503 cc->fc.blocked = 0; 504 rc = cuse_send_init(cc); 505 if (rc) { 506 fuse_conn_put(&cc->fc); 507 return rc; 508 } 509 file->private_data = &cc->fc; /* channel owns base reference to cc */ 510 511 return 0; 512 } 513 514 /** 515 * cuse_channel_release - release method for /dev/cuse 516 * @inode: inode for /dev/cuse 517 * @file: file struct being closed 518 * 519 * Disconnect the channel, deregister CUSE device and initiate 520 * destruction by putting the default reference. 521 * 522 * RETURNS: 523 * 0 on success, -errno on failure. 524 */ 525 static int cuse_channel_release(struct inode *inode, struct file *file) 526 { 527 struct cuse_conn *cc = fc_to_cc(file->private_data); 528 int rc; 529 530 /* remove from the conntbl, no more access from this point on */ 531 mutex_lock(&cuse_lock); 532 list_del_init(&cc->list); 533 mutex_unlock(&cuse_lock); 534 535 /* remove device */ 536 if (cc->dev) 537 device_unregister(cc->dev); 538 if (cc->cdev) { 539 unregister_chrdev_region(cc->cdev->dev, 1); 540 cdev_del(cc->cdev); 541 } 542 543 rc = fuse_dev_release(inode, file); /* puts the base reference */ 544 545 return rc; 546 } 547 548 static struct file_operations cuse_channel_fops; /* initialized during init */ 549 550 551 /************************************************************************** 552 * Misc stuff and module initializatiion 553 * 554 * CUSE exports the same set of attributes to sysfs as fusectl. 555 */ 556 557 static ssize_t cuse_class_waiting_show(struct device *dev, 558 struct device_attribute *attr, char *buf) 559 { 560 struct cuse_conn *cc = dev_get_drvdata(dev); 561 562 return sprintf(buf, "%d\n", atomic_read(&cc->fc.num_waiting)); 563 } 564 565 static ssize_t cuse_class_abort_store(struct device *dev, 566 struct device_attribute *attr, 567 const char *buf, size_t count) 568 { 569 struct cuse_conn *cc = dev_get_drvdata(dev); 570 571 fuse_abort_conn(&cc->fc); 572 return count; 573 } 574 575 static struct device_attribute cuse_class_dev_attrs[] = { 576 __ATTR(waiting, S_IFREG | 0400, cuse_class_waiting_show, NULL), 577 __ATTR(abort, S_IFREG | 0200, NULL, cuse_class_abort_store), 578 { } 579 }; 580 581 static struct miscdevice cuse_miscdev = { 582 .minor = MISC_DYNAMIC_MINOR, 583 .name = "cuse", 584 .fops = &cuse_channel_fops, 585 }; 586 587 static int __init cuse_init(void) 588 { 589 int i, rc; 590 591 /* init conntbl */ 592 for (i = 0; i < CUSE_CONNTBL_LEN; i++) 593 INIT_LIST_HEAD(&cuse_conntbl[i]); 594 595 /* inherit and extend fuse_dev_operations */ 596 cuse_channel_fops = fuse_dev_operations; 597 cuse_channel_fops.owner = THIS_MODULE; 598 cuse_channel_fops.open = cuse_channel_open; 599 cuse_channel_fops.release = cuse_channel_release; 600 601 cuse_class = class_create(THIS_MODULE, "cuse"); 602 if (IS_ERR(cuse_class)) 603 return PTR_ERR(cuse_class); 604 605 cuse_class->dev_attrs = cuse_class_dev_attrs; 606 607 rc = misc_register(&cuse_miscdev); 608 if (rc) { 609 class_destroy(cuse_class); 610 return rc; 611 } 612 613 return 0; 614 } 615 616 static void __exit cuse_exit(void) 617 { 618 misc_deregister(&cuse_miscdev); 619 class_destroy(cuse_class); 620 } 621 622 module_init(cuse_init); 623 module_exit(cuse_exit); 624 625 MODULE_AUTHOR("Tejun Heo <tj@kernel.org>"); 626 MODULE_DESCRIPTION("Character device in Userspace"); 627 MODULE_LICENSE("GPL"); 628