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