fs/char_dev.c

   1 /*
   2  *  linux/fs/char_dev.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6
   7 #include <linux/init.h>
   8 #include <linux/fs.h>
   9 #include <linux/kdev_t.h>
  10 #include <linux/slab.h>
  11 #include <linux/string.h>
  12
  13 #include <linux/major.h>
  14 #include <linux/errno.h>
  15 #include <linux/module.h>
  16 #include <linux/seq_file.h>
  17
  18 #include <linux/kobject.h>
  19 #include <linux/kobj_map.h>
  20 #include <linux/cdev.h>
  21 #include <linux/mutex.h>
  22 #include <linux/backing-dev.h>
  23 #include <linux/tty.h>
  24
  25 #include "internal.h"
  26
  27 static struct kobj_map *cdev_map;
  28
  29 static DEFINE_MUTEX(chrdevs_lock);
  30
  31 static struct char_device_struct {
  32         struct char_device_struct *next;
  33         unsigned int major;
  34         unsigned int baseminor;
  35         int minorct;
  36         char name[64];
  37         struct cdev *cdev;              /* will die */
  38 } *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
  39
  40 /* index in the above */
  41 static inline int major_to_index(unsigned major)
  42 {
  43         return major % CHRDEV_MAJOR_HASH_SIZE;
  44 }
  45
  46 #ifdef CONFIG_PROC_FS
  47
  48 void chrdev_show(struct seq_file *f, off_t offset)
  49 {
  50         struct char_device_struct *cd;
  51
  52         if (offset < CHRDEV_MAJOR_HASH_SIZE) {
  53                 mutex_lock(&chrdevs_lock);
  54                 for (cd = chrdevs[offset]; cd; cd = cd->next)
  55                         seq_printf(f, "%3d %s\n", cd->major, cd->name);
  56                 mutex_unlock(&chrdevs_lock);
  57         }
  58 }
  59
  60 #endif /* CONFIG_PROC_FS */
  61
  62 /*
  63  * Register a single major with a specified minor range.
  64  *
  65  * If major == 0 this functions will dynamically allocate a major and return
  66  * its number.
  67  *
  68  * If major > 0 this function will attempt to reserve the passed range of
  69  * minors and will return zero on success.
  70  *
  71  * Returns a -ve errno on failure.
  72  */
  73 static struct char_device_struct *
  74 __register_chrdev_region(unsigned int major, unsigned int baseminor,
  75                            int minorct, const char *name)
  76 {
  77         struct char_device_struct *cd, **cp;
  78         int ret = 0;
  79         int i;
  80
  81         cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
  82         if (cd == NULL)
  83                 return ERR_PTR(-ENOMEM);
  84
  85         mutex_lock(&chrdevs_lock);
  86
  87         /* temporary */
  88         if (major == 0) {
  89                 for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
  90                         if (chrdevs[i] == NULL)
  91                                 break;
  92                 }
  93
  94                 if (i < CHRDEV_MAJOR_DYN_END)
  95                         pr_warn("CHRDEV \"%s\" major number %d goes below the dynamic allocation range\n",
  96                                 name, i);
  97
  98                 if (i == 0) {
  99                         ret = -EBUSY;
 100                         goto out;
 101                 }
 102                 major = i;
 103         }
 104
 105         cd->major = major;
 106         cd->baseminor = baseminor;
 107         cd->minorct = minorct;
 108         strlcpy(cd->name, name, sizeof(cd->name));
 109
 110         i = major_to_index(major);
 111
 112         for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 113                 if ((*cp)->major > major ||
 114                     ((*cp)->major == major &&
 115                      (((*cp)->baseminor >= baseminor) ||
 116                       ((*cp)->baseminor + (*cp)->minorct > baseminor))))
 117                         break;
 118
 119         /* Check for overlapping minor ranges.  */
 120         if (*cp && (*cp)->major == major) {
 121                 int old_min = (*cp)->baseminor;
 122                 int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
 123                 int new_min = baseminor;
 124                 int new_max = baseminor + minorct - 1;
 125
 126                 /* New driver overlaps from the left.  */
 127                 if (new_max >= old_min && new_max <= old_max) {
 128                         ret = -EBUSY;
 129                         goto out;
 130                 }
 131
 132                 /* New driver overlaps from the right.  */
 133                 if (new_min <= old_max && new_min >= old_min) {
 134                         ret = -EBUSY;
 135                         goto out;
 136                 }
 137         }
 138
 139         cd->next = *cp;
 140         *cp = cd;
 141         mutex_unlock(&chrdevs_lock);
 142         return cd;
 143 out:
 144         mutex_unlock(&chrdevs_lock);
 145         kfree(cd);
 146         return ERR_PTR(ret);
 147 }
 148
 149 static struct char_device_struct *
 150 __unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
 151 {
 152         struct char_device_struct *cd = NULL, **cp;
 153         int i = major_to_index(major);
 154
 155         mutex_lock(&chrdevs_lock);
 156         for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 157                 if ((*cp)->major == major &&
 158                     (*cp)->baseminor == baseminor &&
 159                     (*cp)->minorct == minorct)
 160                         break;
 161         if (*cp) {
 162                 cd = *cp;
 163                 *cp = cd->next;
 164         }
 165         mutex_unlock(&chrdevs_lock);
 166         return cd;
 167 }
 168
 169 /**
 170  * register_chrdev_region() - register a range of device numbers
 171  * @from: the first in the desired range of device numbers; must include
 172  *        the major number.
 173  * @count: the number of consecutive device numbers required
 174  * @name: the name of the device or driver.
 175  *
 176  * Return value is zero on success, a negative error code on failure.
 177  */
 178 int register_chrdev_region(dev_t from, unsigned count, const char *name)
 179 {
 180         struct char_device_struct *cd;
 181         dev_t to = from + count;
 182         dev_t n, next;
 183
 184         for (n = from; n < to; n = next) {
 185                 next = MKDEV(MAJOR(n)+1, 0);
 186                 if (next > to)
 187                         next = to;
 188                 cd = __register_chrdev_region(MAJOR(n), MINOR(n),
 189                                next - n, name);
 190                 if (IS_ERR(cd))
 191                         goto fail;
 192         }
 193         return 0;
 194 fail:
 195         to = n;
 196         for (n = from; n < to; n = next) {
 197                 next = MKDEV(MAJOR(n)+1, 0);
 198                 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 199         }
 200         return PTR_ERR(cd);
 201 }
 202
 203 /**
 204  * alloc_chrdev_region() - register a range of char device numbers
 205  * @dev: output parameter for first assigned number
 206  * @baseminor: first of the requested range of minor numbers
 207  * @count: the number of minor numbers required
 208  * @name: the name of the associated device or driver
 209  *
 210  * Allocates a range of char device numbers.  The major number will be
 211  * chosen dynamically, and returned (along with the first minor number)
 212  * in @dev.  Returns zero or a negative error code.
 213  */
 214 int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
 215                         const char *name)
 216 {
 217         struct char_device_struct *cd;
 218         cd = __register_chrdev_region(0, baseminor, count, name);
 219         if (IS_ERR(cd))
 220                 return PTR_ERR(cd);
 221         *dev = MKDEV(cd->major, cd->baseminor);
 222         return 0;
 223 }
 224
 225 /**
 226  * __register_chrdev() - create and register a cdev occupying a range of minors
 227  * @major: major device number or 0 for dynamic allocation
 228  * @baseminor: first of the requested range of minor numbers
 229  * @count: the number of minor numbers required
 230  * @name: name of this range of devices
 231  * @fops: file operations associated with this devices
 232  *
 233  * If @major == 0 this functions will dynamically allocate a major and return
 234  * its number.
 235  *
 236  * If @major > 0 this function will attempt to reserve a device with the given
 237  * major number and will return zero on success.
 238  *
 239  * Returns a -ve errno on failure.
 240  *
 241  * The name of this device has nothing to do with the name of the device in
 242  * /dev. It only helps to keep track of the different owners of devices. If
 243  * your module name has only one type of devices it's ok to use e.g. the name
 244  * of the module here.
 245  */
 246 int __register_chrdev(unsigned int major, unsigned int baseminor,
 247                       unsigned int count, const char *name,
 248                       const struct file_operations *fops)
 249 {
 250         struct char_device_struct *cd;
 251         struct cdev *cdev;
 252         int err = -ENOMEM;
 253
 254         cd = __register_chrdev_region(major, baseminor, count, name);
 255         if (IS_ERR(cd))
 256                 return PTR_ERR(cd);
 257
 258         cdev = cdev_alloc();
 259         if (!cdev)
 260                 goto out2;
 261
 262         cdev->owner = fops->owner;
 263         cdev->ops = fops;
 264         kobject_set_name(&cdev->kobj, "%s", name);
 265
 266         err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
 267         if (err)
 268                 goto out;
 269
 270         cd->cdev = cdev;
 271
 272         return major ? 0 : cd->major;
 273 out:
 274         kobject_put(&cdev->kobj);
 275 out2:
 276         kfree(__unregister_chrdev_region(cd->major, baseminor, count));
 277         return err;
 278 }
 279
 280 /**
 281  * unregister_chrdev_region() - unregister a range of device numbers
 282  * @from: the first in the range of numbers to unregister
 283  * @count: the number of device numbers to unregister
 284  *
 285  * This function will unregister a range of @count device numbers,
 286  * starting with @from.  The caller should normally be the one who
 287  * allocated those numbers in the first place...
 288  */
 289 void unregister_chrdev_region(dev_t from, unsigned count)
 290 {
 291         dev_t to = from + count;
 292         dev_t n, next;
 293
 294         for (n = from; n < to; n = next) {
 295                 next = MKDEV(MAJOR(n)+1, 0);
 296                 if (next > to)
 297                         next = to;
 298                 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 299         }
 300 }
 301
 302 /**
 303  * __unregister_chrdev - unregister and destroy a cdev
 304  * @major: major device number
 305  * @baseminor: first of the range of minor numbers
 306  * @count: the number of minor numbers this cdev is occupying
 307  * @name: name of this range of devices
 308  *
 309  * Unregister and destroy the cdev occupying the region described by
 310  * @major, @baseminor and @count.  This function undoes what
 311  * __register_chrdev() did.
 312  */
 313 void __unregister_chrdev(unsigned int major, unsigned int baseminor,
 314                          unsigned int count, const char *name)
 315 {
 316         struct char_device_struct *cd;
 317
 318         cd = __unregister_chrdev_region(major, baseminor, count);
 319         if (cd && cd->cdev)
 320                 cdev_del(cd->cdev);
 321         kfree(cd);
 322 }
 323
 324 static DEFINE_SPINLOCK(cdev_lock);
 325
 326 static struct kobject *cdev_get(struct cdev *p)
 327 {
 328         struct module *owner = p->owner;
 329         struct kobject *kobj;
 330
 331         if (owner && !try_module_get(owner))
 332                 return NULL;
 333         kobj = kobject_get(&p->kobj);
 334         if (!kobj)
 335                 module_put(owner);
 336         return kobj;
 337 }
 338
 339 void cdev_put(struct cdev *p)
 340 {
 341         if (p) {
 342                 struct module *owner = p->owner;
 343                 kobject_put(&p->kobj);
 344                 module_put(owner);
 345         }
 346 }
 347
 348 /*
 349  * Called every time a character special file is opened
 350  */
 351 static int chrdev_open(struct inode *inode, struct file *filp)
 352 {
 353         const struct file_operations *fops;
 354         struct cdev *p;
 355         struct cdev *new = NULL;
 356         int ret = 0;
 357
 358         spin_lock(&cdev_lock);
 359         p = inode->i_cdev;
 360         if (!p) {
 361                 struct kobject *kobj;
 362                 int idx;
 363                 spin_unlock(&cdev_lock);
 364                 kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
 365                 if (!kobj)
 366                         return -ENXIO;
 367                 new = container_of(kobj, struct cdev, kobj);
 368                 spin_lock(&cdev_lock);
 369                 /* Check i_cdev again in case somebody beat us to it while
 370                    we dropped the lock. */
 371                 p = inode->i_cdev;
 372                 if (!p) {
 373                         inode->i_cdev = p = new;
 374                         list_add(&inode->i_devices, &p->list);
 375                         new = NULL;
 376                 } else if (!cdev_get(p))
 377                         ret = -ENXIO;
 378         } else if (!cdev_get(p))
 379                 ret = -ENXIO;
 380         spin_unlock(&cdev_lock);
 381         cdev_put(new);
 382         if (ret)
 383                 return ret;
 384
 385         ret = -ENXIO;
 386         fops = fops_get(p->ops);
 387         if (!fops)
 388                 goto out_cdev_put;
 389
 390         replace_fops(filp, fops);
 391         if (filp->f_op->open) {
 392                 ret = filp->f_op->open(inode, filp);
 393                 if (ret)
 394                         goto out_cdev_put;
 395         }
 396
 397         return 0;
 398
 399  out_cdev_put:
 400         cdev_put(p);
 401         return ret;
 402 }
 403
 404 void cd_forget(struct inode *inode)
 405 {
 406         spin_lock(&cdev_lock);
 407         list_del_init(&inode->i_devices);
 408         inode->i_cdev = NULL;
 409         inode->i_mapping = &inode->i_data;
 410         spin_unlock(&cdev_lock);
 411 }
 412
 413 static void cdev_purge(struct cdev *cdev)
 414 {
 415         spin_lock(&cdev_lock);
 416         while (!list_empty(&cdev->list)) {
 417                 struct inode *inode;
 418                 inode = container_of(cdev->list.next, struct inode, i_devices);
 419                 list_del_init(&inode->i_devices);
 420                 inode->i_cdev = NULL;
 421         }
 422         spin_unlock(&cdev_lock);
 423 }
 424
 425 /*
 426  * Dummy default file-operations: the only thing this does
 427  * is contain the open that then fills in the correct operations
 428  * depending on the special file...
 429  */
 430 const struct file_operations def_chr_fops = {
 431         .open = chrdev_open,
 432         .llseek = noop_llseek,
 433 };
 434
 435 static struct kobject *exact_match(dev_t dev, int *part, void *data)
 436 {
 437         struct cdev *p = data;
 438         return &p->kobj;
 439 }
 440
 441 static int exact_lock(dev_t dev, void *data)
 442 {
 443         struct cdev *p = data;
 444         return cdev_get(p) ? 0 : -1;
 445 }
 446
 447 /**
 448  * cdev_add() - add a char device to the system
 449  * @p: the cdev structure for the device
 450  * @dev: the first device number for which this device is responsible
 451  * @count: the number of consecutive minor numbers corresponding to this
 452  *         device
 453  *
 454  * cdev_add() adds the device represented by @p to the system, making it
 455  * live immediately.  A negative error code is returned on failure.
 456  */
 457 int cdev_add(struct cdev *p, dev_t dev, unsigned count)
 458 {
 459         int error;
 460
 461         p->dev = dev;
 462         p->count = count;
 463
 464         error = kobj_map(cdev_map, dev, count, NULL,
 465                          exact_match, exact_lock, p);
 466         if (error)
 467                 return error;
 468
 469         kobject_get(p->kobj.parent);
 470
 471         return 0;
 472 }
 473
 474 /**
 475  * cdev_set_parent() - set the parent kobject for a char device
 476  * @p: the cdev structure
 477  * @kobj: the kobject to take a reference to
 478  *
 479  * cdev_set_parent() sets a parent kobject which will be referenced
 480  * appropriately so the parent is not freed before the cdev. This
 481  * should be called before cdev_add.
 482  */
 483 void cdev_set_parent(struct cdev *p, struct kobject *kobj)
 484 {
 485         WARN_ON(!kobj->state_initialized);
 486         p->kobj.parent = kobj;
 487 }
 488
 489 /**
 490  * cdev_device_add() - add a char device and it's corresponding
 491  *      struct device, linkink
 492  * @dev: the device structure
 493  * @cdev: the cdev structure
 494  *
 495  * cdev_device_add() adds the char device represented by @cdev to the system,
 496  * just as cdev_add does. It then adds @dev to the system using device_add
 497  * The dev_t for the char device will be taken from the struct device which
 498  * needs to be initialized first. This helper function correctly takes a
 499  * reference to the parent device so the parent will not get released until
 500  * all references to the cdev are released.
 501  *
 502  * This helper uses dev->devt for the device number. If it is not set
 503  * it will not add the cdev and it will be equivalent to device_add.
 504  *
 505  * This function should be used whenever the struct cdev and the
 506  * struct device are members of the same structure whose lifetime is
 507  * managed by the struct device.
 508  *
 509  * NOTE: Callers must assume that userspace was able to open the cdev and
 510  * can call cdev fops callbacks at any time, even if this function fails.
 511  */
 512 int cdev_device_add(struct cdev *cdev, struct device *dev)
 513 {
 514         int rc = 0;
 515
 516         if (dev->devt) {
 517                 cdev_set_parent(cdev, &dev->kobj);
 518
 519                 rc = cdev_add(cdev, dev->devt, 1);
 520                 if (rc)
 521                         return rc;
 522         }
 523
 524         rc = device_add(dev);
 525         if (rc)
 526                 cdev_del(cdev);
 527
 528         return rc;
 529 }
 530
 531 /**
 532  * cdev_device_del() - inverse of cdev_device_add
 533  * @dev: the device structure
 534  * @cdev: the cdev structure
 535  *
 536  * cdev_device_del() is a helper function to call cdev_del and device_del.
 537  * It should be used whenever cdev_device_add is used.
 538  *
 539  * If dev->devt is not set it will not remove the cdev and will be equivalent
 540  * to device_del.
 541  *
 542  * NOTE: This guarantees that associated sysfs callbacks are not running
 543  * or runnable, however any cdevs already open will remain and their fops
 544  * will still be callable even after this function returns.
 545  */
 546 void cdev_device_del(struct cdev *cdev, struct device *dev)
 547 {
 548         device_del(dev);
 549         if (dev->devt)
 550                 cdev_del(cdev);
 551 }
 552
 553 static void cdev_unmap(dev_t dev, unsigned count)
 554 {
 555         kobj_unmap(cdev_map, dev, count);
 556 }
 557
 558 /**
 559  * cdev_del() - remove a cdev from the system
 560  * @p: the cdev structure to be removed
 561  *
 562  * cdev_del() removes @p from the system, possibly freeing the structure
 563  * itself.
 564  *
 565  * NOTE: This guarantees that cdev device will no longer be able to be
 566  * opened, however any cdevs already open will remain and their fops will
 567  * still be callable even after cdev_del returns.
 568  */
 569 void cdev_del(struct cdev *p)
 570 {
 571         cdev_unmap(p->dev, p->count);
 572         kobject_put(&p->kobj);
 573 }
 574
 575
 576 static void cdev_default_release(struct kobject *kobj)
 577 {
 578         struct cdev *p = container_of(kobj, struct cdev, kobj);
 579         struct kobject *parent = kobj->parent;
 580
 581         cdev_purge(p);
 582         kobject_put(parent);
 583 }
 584
 585 static void cdev_dynamic_release(struct kobject *kobj)
 586 {
 587         struct cdev *p = container_of(kobj, struct cdev, kobj);
 588         struct kobject *parent = kobj->parent;
 589
 590         cdev_purge(p);
 591         kfree(p);
 592         kobject_put(parent);
 593 }
 594
 595 static struct kobj_type ktype_cdev_default = {
 596         .release        = cdev_default_release,
 597 };
 598
 599 static struct kobj_type ktype_cdev_dynamic = {
 600         .release        = cdev_dynamic_release,
 601 };
 602
 603 /**
 604  * cdev_alloc() - allocate a cdev structure
 605  *
 606  * Allocates and returns a cdev structure, or NULL on failure.
 607  */
 608 struct cdev *cdev_alloc(void)
 609 {
 610         struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
 611         if (p) {
 612                 INIT_LIST_HEAD(&p->list);
 613                 kobject_init(&p->kobj, &ktype_cdev_dynamic);
 614         }
 615         return p;
 616 }
 617
 618 /**
 619  * cdev_init() - initialize a cdev structure
 620  * @cdev: the structure to initialize
 621  * @fops: the file_operations for this device
 622  *
 623  * Initializes @cdev, remembering @fops, making it ready to add to the
 624  * system with cdev_add().
 625  */
 626 void cdev_init(struct cdev *cdev, const struct file_operations *fops)
 627 {
 628         memset(cdev, 0, sizeof *cdev);
 629         INIT_LIST_HEAD(&cdev->list);
 630         kobject_init(&cdev->kobj, &ktype_cdev_default);
 631         cdev->ops = fops;
 632 }
 633
 634 static struct kobject *base_probe(dev_t dev, int *part, void *data)
 635 {
 636         if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
 637                 /* Make old-style 2.4 aliases work */
 638                 request_module("char-major-%d", MAJOR(dev));
 639         return NULL;
 640 }
 641
 642 void __init chrdev_init(void)
 643 {
 644         cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
 645 }
 646
 647
 648 /* Let modules do char dev stuff */
 649 EXPORT_SYMBOL(register_chrdev_region);
 650 EXPORT_SYMBOL(unregister_chrdev_region);
 651 EXPORT_SYMBOL(alloc_chrdev_region);
 652 EXPORT_SYMBOL(cdev_init);
 653 EXPORT_SYMBOL(cdev_alloc);
 654 EXPORT_SYMBOL(cdev_del);
 655 EXPORT_SYMBOL(cdev_add);
 656 EXPORT_SYMBOL(cdev_set_parent);
 657 EXPORT_SYMBOL(cdev_device_add);
 658 EXPORT_SYMBOL(cdev_device_del);
 659 EXPORT_SYMBOL(__register_chrdev);
 660 EXPORT_SYMBOL(__unregister_chrdev);