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 == 0) {
  95                         ret = -EBUSY;
  96                         goto out;
  97                 }
  98                 major = i;
  99         }
 100
 101         cd->major = major;
 102         cd->baseminor = baseminor;
 103         cd->minorct = minorct;
 104         strlcpy(cd->name, name, sizeof(cd->name));
 105
 106         i = major_to_index(major);
 107
 108         for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 109                 if ((*cp)->major > major ||
 110                     ((*cp)->major == major &&
 111                      (((*cp)->baseminor >= baseminor) ||
 112                       ((*cp)->baseminor + (*cp)->minorct > baseminor))))
 113                         break;
 114
 115         /* Check for overlapping minor ranges.  */
 116         if (*cp && (*cp)->major == major) {
 117                 int old_min = (*cp)->baseminor;
 118                 int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
 119                 int new_min = baseminor;
 120                 int new_max = baseminor + minorct - 1;
 121
 122                 /* New driver overlaps from the left.  */
 123                 if (new_max >= old_min && new_max <= old_max) {
 124                         ret = -EBUSY;
 125                         goto out;
 126                 }
 127
 128                 /* New driver overlaps from the right.  */
 129                 if (new_min <= old_max && new_min >= old_min) {
 130                         ret = -EBUSY;
 131                         goto out;
 132                 }
 133
 134                 if (new_min < old_min && new_max > old_max) {
 135                         ret = -EBUSY;
 136                         goto out;
 137                 }
 138
 139         }
 140
 141         cd->next = *cp;
 142         *cp = cd;
 143         mutex_unlock(&chrdevs_lock);
 144         return cd;
 145 out:
 146         mutex_unlock(&chrdevs_lock);
 147         kfree(cd);
 148         return ERR_PTR(ret);
 149 }
 150
 151 static struct char_device_struct *
 152 __unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
 153 {
 154         struct char_device_struct *cd = NULL, **cp;
 155         int i = major_to_index(major);
 156
 157         mutex_lock(&chrdevs_lock);
 158         for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 159                 if ((*cp)->major == major &&
 160                     (*cp)->baseminor == baseminor &&
 161                     (*cp)->minorct == minorct)
 162                         break;
 163         if (*cp) {
 164                 cd = *cp;
 165                 *cp = cd->next;
 166         }
 167         mutex_unlock(&chrdevs_lock);
 168         return cd;
 169 }
 170
 171 /**
 172  * register_chrdev_region() - register a range of device numbers
 173  * @from: the first in the desired range of device numbers; must include
 174  *        the major number.
 175  * @count: the number of consecutive device numbers required
 176  * @name: the name of the device or driver.
 177  *
 178  * Return value is zero on success, a negative error code on failure.
 179  */
 180 int register_chrdev_region(dev_t from, unsigned count, const char *name)
 181 {
 182         struct char_device_struct *cd;
 183         dev_t to = from + count;
 184         dev_t n, next;
 185
 186         for (n = from; n < to; n = next) {
 187                 next = MKDEV(MAJOR(n)+1, 0);
 188                 if (next > to)
 189                         next = to;
 190                 cd = __register_chrdev_region(MAJOR(n), MINOR(n),
 191                                next - n, name);
 192                 if (IS_ERR(cd))
 193                         goto fail;
 194         }
 195         return 0;
 196 fail:
 197         to = n;
 198         for (n = from; n < to; n = next) {
 199                 next = MKDEV(MAJOR(n)+1, 0);
 200                 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 201         }
 202         return PTR_ERR(cd);
 203 }
 204
 205 /**
 206  * alloc_chrdev_region() - register a range of char device numbers
 207  * @dev: output parameter for first assigned number
 208  * @baseminor: first of the requested range of minor numbers
 209  * @count: the number of minor numbers required
 210  * @name: the name of the associated device or driver
 211  *
 212  * Allocates a range of char device numbers.  The major number will be
 213  * chosen dynamically, and returned (along with the first minor number)
 214  * in @dev.  Returns zero or a negative error code.
 215  */
 216 int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
 217                         const char *name)
 218 {
 219         struct char_device_struct *cd;
 220         cd = __register_chrdev_region(0, baseminor, count, name);
 221         if (IS_ERR(cd))
 222                 return PTR_ERR(cd);
 223         *dev = MKDEV(cd->major, cd->baseminor);
 224         return 0;
 225 }
 226
 227 /**
 228  * __register_chrdev() - create and register a cdev occupying a range of minors
 229  * @major: major device number or 0 for dynamic allocation
 230  * @baseminor: first of the requested range of minor numbers
 231  * @count: the number of minor numbers required
 232  * @name: name of this range of devices
 233  * @fops: file operations associated with this devices
 234  *
 235  * If @major == 0 this functions will dynamically allocate a major and return
 236  * its number.
 237  *
 238  * If @major > 0 this function will attempt to reserve a device with the given
 239  * major number and will return zero on success.
 240  *
 241  * Returns a -ve errno on failure.
 242  *
 243  * The name of this device has nothing to do with the name of the device in
 244  * /dev. It only helps to keep track of the different owners of devices. If
 245  * your module name has only one type of devices it's ok to use e.g. the name
 246  * of the module here.
 247  */
 248 int __register_chrdev(unsigned int major, unsigned int baseminor,
 249                       unsigned int count, const char *name,
 250                       const struct file_operations *fops)
 251 {
 252         struct char_device_struct *cd;
 253         struct cdev *cdev;
 254         int err = -ENOMEM;
 255
 256         cd = __register_chrdev_region(major, baseminor, count, name);
 257         if (IS_ERR(cd))
 258                 return PTR_ERR(cd);
 259
 260         cdev = cdev_alloc();
 261         if (!cdev)
 262                 goto out2;
 263
 264         cdev->owner = fops->owner;
 265         cdev->ops = fops;
 266         kobject_set_name(&cdev->kobj, "%s", name);
 267
 268         err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
 269         if (err)
 270                 goto out;
 271
 272         cd->cdev = cdev;
 273
 274         return major ? 0 : cd->major;
 275 out:
 276         kobject_put(&cdev->kobj);
 277 out2:
 278         kfree(__unregister_chrdev_region(cd->major, baseminor, count));
 279         return err;
 280 }
 281
 282 /**
 283  * unregister_chrdev_region() - unregister a range of device numbers
 284  * @from: the first in the range of numbers to unregister
 285  * @count: the number of device numbers to unregister
 286  *
 287  * This function will unregister a range of @count device numbers,
 288  * starting with @from.  The caller should normally be the one who
 289  * allocated those numbers in the first place...
 290  */
 291 void unregister_chrdev_region(dev_t from, unsigned count)
 292 {
 293         dev_t to = from + count;
 294         dev_t n, next;
 295
 296         for (n = from; n < to; n = next) {
 297                 next = MKDEV(MAJOR(n)+1, 0);
 298                 if (next > to)
 299                         next = to;
 300                 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 301         }
 302 }
 303
 304 /**
 305  * __unregister_chrdev - unregister and destroy a cdev
 306  * @major: major device number
 307  * @baseminor: first of the range of minor numbers
 308  * @count: the number of minor numbers this cdev is occupying
 309  * @name: name of this range of devices
 310  *
 311  * Unregister and destroy the cdev occupying the region described by
 312  * @major, @baseminor and @count.  This function undoes what
 313  * __register_chrdev() did.
 314  */
 315 void __unregister_chrdev(unsigned int major, unsigned int baseminor,
 316                          unsigned int count, const char *name)
 317 {
 318         struct char_device_struct *cd;
 319
 320         cd = __unregister_chrdev_region(major, baseminor, count);
 321         if (cd && cd->cdev)
 322                 cdev_del(cd->cdev);
 323         kfree(cd);
 324 }
 325
 326 static DEFINE_SPINLOCK(cdev_lock);
 327
 328 static struct kobject *cdev_get(struct cdev *p)
 329 {
 330         struct module *owner = p->owner;
 331         struct kobject *kobj;
 332
 333         if (owner && !try_module_get(owner))
 334                 return NULL;
 335         kobj = kobject_get(&p->kobj);
 336         if (!kobj)
 337                 module_put(owner);
 338         return kobj;
 339 }
 340
 341 void cdev_put(struct cdev *p)
 342 {
 343         if (p) {
 344                 struct module *owner = p->owner;
 345                 kobject_put(&p->kobj);
 346                 module_put(owner);
 347         }
 348 }
 349
 350 /*
 351  * Called every time a character special file is opened
 352  */
 353 static int chrdev_open(struct inode *inode, struct file *filp)
 354 {
 355         const struct file_operations *fops;
 356         struct cdev *p;
 357         struct cdev *new = NULL;
 358         int ret = 0;
 359
 360         spin_lock(&cdev_lock);
 361         p = inode->i_cdev;
 362         if (!p) {
 363                 struct kobject *kobj;
 364                 int idx;
 365                 spin_unlock(&cdev_lock);
 366                 kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
 367                 if (!kobj)
 368                         return -ENXIO;
 369                 new = container_of(kobj, struct cdev, kobj);
 370                 spin_lock(&cdev_lock);
 371                 /* Check i_cdev again in case somebody beat us to it while
 372                    we dropped the lock. */
 373                 p = inode->i_cdev;
 374                 if (!p) {
 375                         inode->i_cdev = p = new;
 376                         list_add(&inode->i_devices, &p->list);
 377                         new = NULL;
 378                 } else if (!cdev_get(p))
 379                         ret = -ENXIO;
 380         } else if (!cdev_get(p))
 381                 ret = -ENXIO;
 382         spin_unlock(&cdev_lock);
 383         cdev_put(new);
 384         if (ret)
 385                 return ret;
 386
 387         ret = -ENXIO;
 388         fops = fops_get(p->ops);
 389         if (!fops)
 390                 goto out_cdev_put;
 391
 392         replace_fops(filp, fops);
 393         if (filp->f_op->open) {
 394                 ret = filp->f_op->open(inode, filp);
 395                 if (ret)
 396                         goto out_cdev_put;
 397         }
 398
 399         return 0;
 400
 401  out_cdev_put:
 402         cdev_put(p);
 403         return ret;
 404 }
 405
 406 void cd_forget(struct inode *inode)
 407 {
 408         spin_lock(&cdev_lock);
 409         list_del_init(&inode->i_devices);
 410         inode->i_cdev = NULL;
 411         spin_unlock(&cdev_lock);
 412 }
 413
 414 static void cdev_purge(struct cdev *cdev)
 415 {
 416         spin_lock(&cdev_lock);
 417         while (!list_empty(&cdev->list)) {
 418                 struct inode *inode;
 419                 inode = container_of(cdev->list.next, struct inode, i_devices);
 420                 list_del_init(&inode->i_devices);
 421                 inode->i_cdev = NULL;
 422         }
 423         spin_unlock(&cdev_lock);
 424 }
 425
 426 /*
 427  * Dummy default file-operations: the only thing this does
 428  * is contain the open that then fills in the correct operations
 429  * depending on the special file...
 430  */
 431 const struct file_operations def_chr_fops = {
 432         .open = chrdev_open,
 433         .llseek = noop_llseek,
 434 };
 435
 436 static struct kobject *exact_match(dev_t dev, int *part, void *data)
 437 {
 438         struct cdev *p = data;
 439         return &p->kobj;
 440 }
 441
 442 static int exact_lock(dev_t dev, void *data)
 443 {
 444         struct cdev *p = data;
 445         return cdev_get(p) ? 0 : -1;
 446 }
 447
 448 /**
 449  * cdev_add() - add a char device to the system
 450  * @p: the cdev structure for the device
 451  * @dev: the first device number for which this device is responsible
 452  * @count: the number of consecutive minor numbers corresponding to this
 453  *         device
 454  *
 455  * cdev_add() adds the device represented by @p to the system, making it
 456  * live immediately.  A negative error code is returned on failure.
 457  */
 458 int cdev_add(struct cdev *p, dev_t dev, unsigned count)
 459 {
 460         int error;
 461
 462         p->dev = dev;
 463         p->count = count;
 464
 465         error = kobj_map(cdev_map, dev, count, NULL,
 466                          exact_match, exact_lock, p);
 467         if (error)
 468                 return error;
 469
 470         kobject_get(p->kobj.parent);
 471
 472         return 0;
 473 }
 474
 475 static void cdev_unmap(dev_t dev, unsigned count)
 476 {
 477         kobj_unmap(cdev_map, dev, count);
 478 }
 479
 480 /**
 481  * cdev_del() - remove a cdev from the system
 482  * @p: the cdev structure to be removed
 483  *
 484  * cdev_del() removes @p from the system, possibly freeing the structure
 485  * itself.
 486  */
 487 void cdev_del(struct cdev *p)
 488 {
 489         cdev_unmap(p->dev, p->count);
 490         kobject_put(&p->kobj);
 491 }
 492
 493
 494 static void cdev_default_release(struct kobject *kobj)
 495 {
 496         struct cdev *p = container_of(kobj, struct cdev, kobj);
 497         struct kobject *parent = kobj->parent;
 498
 499         cdev_purge(p);
 500         kobject_put(parent);
 501 }
 502
 503 static void cdev_dynamic_release(struct kobject *kobj)
 504 {
 505         struct cdev *p = container_of(kobj, struct cdev, kobj);
 506         struct kobject *parent = kobj->parent;
 507
 508         cdev_purge(p);
 509         kfree(p);
 510         kobject_put(parent);
 511 }
 512
 513 static struct kobj_type ktype_cdev_default = {
 514         .release        = cdev_default_release,
 515 };
 516
 517 static struct kobj_type ktype_cdev_dynamic = {
 518         .release        = cdev_dynamic_release,
 519 };
 520
 521 /**
 522  * cdev_alloc() - allocate a cdev structure
 523  *
 524  * Allocates and returns a cdev structure, or NULL on failure.
 525  */
 526 struct cdev *cdev_alloc(void)
 527 {
 528         struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
 529         if (p) {
 530                 INIT_LIST_HEAD(&p->list);
 531                 kobject_init(&p->kobj, &ktype_cdev_dynamic);
 532         }
 533         return p;
 534 }
 535
 536 /**
 537  * cdev_init() - initialize a cdev structure
 538  * @cdev: the structure to initialize
 539  * @fops: the file_operations for this device
 540  *
 541  * Initializes @cdev, remembering @fops, making it ready to add to the
 542  * system with cdev_add().
 543  */
 544 void cdev_init(struct cdev *cdev, const struct file_operations *fops)
 545 {
 546         memset(cdev, 0, sizeof *cdev);
 547         INIT_LIST_HEAD(&cdev->list);
 548         kobject_init(&cdev->kobj, &ktype_cdev_default);
 549         cdev->ops = fops;
 550 }
 551
 552 static struct kobject *base_probe(dev_t dev, int *part, void *data)
 553 {
 554         if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
 555                 /* Make old-style 2.4 aliases work */
 556                 request_module("char-major-%d", MAJOR(dev));
 557         return NULL;
 558 }
 559
 560 void __init chrdev_init(void)
 561 {
 562         cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
 563 }
 564
 565
 566 /* Let modules do char dev stuff */
 567 EXPORT_SYMBOL(register_chrdev_region);
 568 EXPORT_SYMBOL(unregister_chrdev_region);
 569 EXPORT_SYMBOL(alloc_chrdev_region);
 570 EXPORT_SYMBOL(cdev_init);
 571 EXPORT_SYMBOL(cdev_alloc);
 572 EXPORT_SYMBOL(cdev_del);
 573 EXPORT_SYMBOL(cdev_add);
 574 EXPORT_SYMBOL(__register_chrdev);
 575 EXPORT_SYMBOL(__unregister_chrdev);