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