fs/char_dev.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/fs/char_dev.c
   4  *
   5  *  Copyright (C) 1991, 1992  Linus Torvalds
   6  */
   7
   8 #include <linux/init.h>
   9 #include <linux/fs.h>
  10 #include <linux/kdev_t.h>
  11 #include <linux/slab.h>
  12 #include <linux/string.h>
  13
  14 #include <linux/major.h>
  15 #include <linux/errno.h>
  16 #include <linux/module.h>
  17 #include <linux/seq_file.h>
  18
  19 #include <linux/kobject.h>
  20 #include <linux/kobj_map.h>
  21 #include <linux/cdev.h>
  22 #include <linux/mutex.h>
  23 #include <linux/backing-dev.h>
  24 #include <linux/tty.h>
  25
  26 #include "internal.h"
  27
  28 static struct kobj_map *cdev_map;
  29
  30 static DEFINE_MUTEX(chrdevs_lock);
  31
  32 #define CHRDEV_MAJOR_HASH_SIZE 255
  33
  34 static struct char_device_struct {
  35         struct char_device_struct *next;
  36         unsigned int major;
  37         unsigned int baseminor;
  38         int minorct;
  39         char name[64];
  40         struct cdev *cdev;              /* will die */
  41 } *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
  42
  43 /* index in the above */
  44 static inline int major_to_index(unsigned major)
  45 {
  46         return major % CHRDEV_MAJOR_HASH_SIZE;
  47 }
  48
  49 #ifdef CONFIG_PROC_FS
  50
  51 void chrdev_show(struct seq_file *f, off_t offset)
  52 {
  53         struct char_device_struct *cd;
  54
  55         mutex_lock(&chrdevs_lock);
  56         for (cd = chrdevs[major_to_index(offset)]; cd; cd = cd->next) {
  57                 if (cd->major == offset)
  58                         seq_printf(f, "%3d %s\n", cd->major, cd->name);
  59         }
  60         mutex_unlock(&chrdevs_lock);
  61 }
  62
  63 #endif /* CONFIG_PROC_FS */
  64
  65 static int find_dynamic_major(void)
  66 {
  67         int i;
  68         struct char_device_struct *cd;
  69
  70         for (i = ARRAY_SIZE(chrdevs)-1; i >= CHRDEV_MAJOR_DYN_END; i--) {
  71                 if (chrdevs[i] == NULL)
  72                         return i;
  73         }
  74
  75         for (i = CHRDEV_MAJOR_DYN_EXT_START;
  76              i >= CHRDEV_MAJOR_DYN_EXT_END; i--) {
  77                 for (cd = chrdevs[major_to_index(i)]; cd; cd = cd->next)
  78                         if (cd->major == i)
  79                                 break;
  80
  81                 if (cd == NULL)
  82                         return i;
  83         }
  84
  85         return -EBUSY;
  86 }
  87
  88 /*
  89  * Register a single major with a specified minor range.
  90  *
  91  * If major == 0 this function will dynamically allocate an unused major.
  92  * If major > 0 this function will attempt to reserve the range of minors
  93  * with given major.
  94  *
  95  */
  96 static struct char_device_struct *
  97 __register_chrdev_region(unsigned int major, unsigned int baseminor,
  98                            int minorct, const char *name)
  99 {
 100         struct char_device_struct *cd, *curr, *prev = NULL;
 101         int ret = -EBUSY;
 102         int i;
 103
 104         if (major >= CHRDEV_MAJOR_MAX) {
 105                 pr_err("CHRDEV \"%s\" major requested (%u) is greater than the maximum (%u)\n",
 106                        name, major, CHRDEV_MAJOR_MAX-1);
 107                 return ERR_PTR(-EINVAL);
 108         }
 109
 110         if (minorct > MINORMASK + 1 - baseminor) {
 111                 pr_err("CHRDEV \"%s\" minor range requested (%u-%u) is out of range of maximum range (%u-%u) for a single major\n",
 112                         name, baseminor, baseminor + minorct - 1, 0, MINORMASK);
 113                 return ERR_PTR(-EINVAL);
 114         }
 115
 116         cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
 117         if (cd == NULL)
 118                 return ERR_PTR(-ENOMEM);
 119
 120         mutex_lock(&chrdevs_lock);
 121
 122         if (major == 0) {
 123                 ret = find_dynamic_major();
 124                 if (ret < 0) {
 125                         pr_err("CHRDEV \"%s\" dynamic allocation region is full\n",
 126                                name);
 127                         goto out;
 128                 }
 129                 major = ret;
 130         }
 131
 132         i = major_to_index(major);
 133         for (curr = chrdevs[i]; curr; prev = curr, curr = curr->next) {
 134                 if (curr->major < major)
 135                         continue;
 136
 137                 if (curr->major > major)
 138                         break;
 139
 140                 if (curr->baseminor + curr->minorct <= baseminor)
 141                         continue;
 142
 143                 if (curr->baseminor >= baseminor + minorct)
 144                         break;
 145
 146                 goto out;
 147         }
 148
 149         cd->major = major;
 150         cd->baseminor = baseminor;
 151         cd->minorct = minorct;
 152         strlcpy(cd->name, name, sizeof(cd->name));
 153
 154         if (!prev) {
 155                 cd->next = curr;
 156                 chrdevs[i] = cd;
 157         } else {
 158                 cd->next = prev->next;
 159                 prev->next = cd;
 160         }
 161
 162         mutex_unlock(&chrdevs_lock);
 163         return cd;
 164 out:
 165         mutex_unlock(&chrdevs_lock);
 166         kfree(cd);
 167         return ERR_PTR(ret);
 168 }
 169
 170 static struct char_device_struct *
 171 __unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
 172 {
 173         struct char_device_struct *cd = NULL, **cp;
 174         int i = major_to_index(major);
 175
 176         mutex_lock(&chrdevs_lock);
 177         for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 178                 if ((*cp)->major == major &&
 179                     (*cp)->baseminor == baseminor &&
 180                     (*cp)->minorct == minorct)
 181                         break;
 182         if (*cp) {
 183                 cd = *cp;
 184                 *cp = cd->next;
 185         }
 186         mutex_unlock(&chrdevs_lock);
 187         return cd;
 188 }
 189
 190 /**
 191  * register_chrdev_region() - register a range of device numbers
 192  * @from: the first in the desired range of device numbers; must include
 193  *        the major number.
 194  * @count: the number of consecutive device numbers required
 195  * @name: the name of the device or driver.
 196  *
 197  * Return value is zero on success, a negative error code on failure.
 198  */
 199 int register_chrdev_region(dev_t from, unsigned count, const char *name)
 200 {
 201         struct char_device_struct *cd;
 202         dev_t to = from + count;
 203         dev_t n, next;
 204
 205         for (n = from; n < to; n = next) {
 206                 next = MKDEV(MAJOR(n)+1, 0);
 207                 if (next > to)
 208                         next = to;
 209                 cd = __register_chrdev_region(MAJOR(n), MINOR(n),
 210                                next - n, name);
 211                 if (IS_ERR(cd))
 212                         goto fail;
 213         }
 214         return 0;
 215 fail:
 216         to = n;
 217         for (n = from; n < to; n = next) {
 218                 next = MKDEV(MAJOR(n)+1, 0);
 219                 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 220         }
 221         return PTR_ERR(cd);
 222 }
 223
 224 /**
 225  * alloc_chrdev_region() - register a range of char device numbers
 226  * @dev: output parameter for first assigned number
 227  * @baseminor: first of the requested range of minor numbers
 228  * @count: the number of minor numbers required
 229  * @name: the name of the associated device or driver
 230  *
 231  * Allocates a range of char device numbers.  The major number will be
 232  * chosen dynamically, and returned (along with the first minor number)
 233  * in @dev.  Returns zero or a negative error code.
 234  */
 235 int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
 236                         const char *name)
 237 {
 238         struct char_device_struct *cd;
 239         cd = __register_chrdev_region(0, baseminor, count, name);
 240         if (IS_ERR(cd))
 241                 return PTR_ERR(cd);
 242         *dev = MKDEV(cd->major, cd->baseminor);
 243         return 0;
 244 }
 245
 246 /**
 247  * __register_chrdev() - create and register a cdev occupying a range of minors
 248  * @major: major device number or 0 for dynamic allocation
 249  * @baseminor: first of the requested range of minor numbers
 250  * @count: the number of minor numbers required
 251  * @name: name of this range of devices
 252  * @fops: file operations associated with this devices
 253  *
 254  * If @major == 0 this functions will dynamically allocate a major and return
 255  * its number.
 256  *
 257  * If @major > 0 this function will attempt to reserve a device with the given
 258  * major number and will return zero on success.
 259  *
 260  * Returns a -ve errno on failure.
 261  *
 262  * The name of this device has nothing to do with the name of the device in
 263  * /dev. It only helps to keep track of the different owners of devices. If
 264  * your module name has only one type of devices it's ok to use e.g. the name
 265  * of the module here.
 266  */
 267 int __register_chrdev(unsigned int major, unsigned int baseminor,
 268                       unsigned int count, const char *name,
 269                       const struct file_operations *fops)
 270 {
 271         struct char_device_struct *cd;
 272         struct cdev *cdev;
 273         int err = -ENOMEM;
 274
 275         cd = __register_chrdev_region(major, baseminor, count, name);
 276         if (IS_ERR(cd))
 277                 return PTR_ERR(cd);
 278
 279         cdev = cdev_alloc();
 280         if (!cdev)
 281                 goto out2;
 282
 283         cdev->owner = fops->owner;
 284         cdev->ops = fops;
 285         kobject_set_name(&cdev->kobj, "%s", name);
 286
 287         err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
 288         if (err)
 289                 goto out;
 290
 291         cd->cdev = cdev;
 292
 293         return major ? 0 : cd->major;
 294 out:
 295         kobject_put(&cdev->kobj);
 296 out2:
 297         kfree(__unregister_chrdev_region(cd->major, baseminor, count));
 298         return err;
 299 }
 300
 301 /**
 302  * unregister_chrdev_region() - unregister a range of device numbers
 303  * @from: the first in the range of numbers to unregister
 304  * @count: the number of device numbers to unregister
 305  *
 306  * This function will unregister a range of @count device numbers,
 307  * starting with @from.  The caller should normally be the one who
 308  * allocated those numbers in the first place...
 309  */
 310 void unregister_chrdev_region(dev_t from, unsigned count)
 311 {
 312         dev_t to = from + count;
 313         dev_t n, next;
 314
 315         for (n = from; n < to; n = next) {
 316                 next = MKDEV(MAJOR(n)+1, 0);
 317                 if (next > to)
 318                         next = to;
 319                 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 320         }
 321 }
 322
 323 /**
 324  * __unregister_chrdev - unregister and destroy a cdev
 325  * @major: major device number
 326  * @baseminor: first of the range of minor numbers
 327  * @count: the number of minor numbers this cdev is occupying
 328  * @name: name of this range of devices
 329  *
 330  * Unregister and destroy the cdev occupying the region described by
 331  * @major, @baseminor and @count.  This function undoes what
 332  * __register_chrdev() did.
 333  */
 334 void __unregister_chrdev(unsigned int major, unsigned int baseminor,
 335                          unsigned int count, const char *name)
 336 {
 337         struct char_device_struct *cd;
 338
 339         cd = __unregister_chrdev_region(major, baseminor, count);
 340         if (cd && cd->cdev)
 341                 cdev_del(cd->cdev);
 342         kfree(cd);
 343 }
 344
 345 static DEFINE_SPINLOCK(cdev_lock);
 346
 347 static struct kobject *cdev_get(struct cdev *p)
 348 {
 349         struct module *owner = p->owner;
 350         struct kobject *kobj;
 351
 352         if (owner && !try_module_get(owner))
 353                 return NULL;
 354         kobj = kobject_get(&p->kobj);
 355         if (!kobj)
 356                 module_put(owner);
 357         return kobj;
 358 }
 359
 360 void cdev_put(struct cdev *p)
 361 {
 362         if (p) {
 363                 struct module *owner = p->owner;
 364                 kobject_put(&p->kobj);
 365                 module_put(owner);
 366         }
 367 }
 368
 369 /*
 370  * Called every time a character special file is opened
 371  */
 372 static int chrdev_open(struct inode *inode, struct file *filp)
 373 {
 374         const struct file_operations *fops;
 375         struct cdev *p;
 376         struct cdev *new = NULL;
 377         int ret = 0;
 378
 379         spin_lock(&cdev_lock);
 380         p = inode->i_cdev;
 381         if (!p) {
 382                 struct kobject *kobj;
 383                 int idx;
 384                 spin_unlock(&cdev_lock);
 385                 kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
 386                 if (!kobj)
 387                         return -ENXIO;
 388                 new = container_of(kobj, struct cdev, kobj);
 389                 spin_lock(&cdev_lock);
 390                 /* Check i_cdev again in case somebody beat us to it while
 391                    we dropped the lock. */
 392                 p = inode->i_cdev;
 393                 if (!p) {
 394                         inode->i_cdev = p = new;
 395                         list_add(&inode->i_devices, &p->list);
 396                         new = NULL;
 397                 } else if (!cdev_get(p))
 398                         ret = -ENXIO;
 399         } else if (!cdev_get(p))
 400                 ret = -ENXIO;
 401         spin_unlock(&cdev_lock);
 402         cdev_put(new);
 403         if (ret)
 404                 return ret;
 405
 406         ret = -ENXIO;
 407         fops = fops_get(p->ops);
 408         if (!fops)
 409                 goto out_cdev_put;
 410
 411         replace_fops(filp, fops);
 412         if (filp->f_op->open) {
 413                 ret = filp->f_op->open(inode, filp);
 414                 if (ret)
 415                         goto out_cdev_put;
 416         }
 417
 418         return 0;
 419
 420  out_cdev_put:
 421         cdev_put(p);
 422         return ret;
 423 }
 424
 425 void cd_forget(struct inode *inode)
 426 {
 427         spin_lock(&cdev_lock);
 428         list_del_init(&inode->i_devices);
 429         inode->i_cdev = NULL;
 430         inode->i_mapping = &inode->i_data;
 431         spin_unlock(&cdev_lock);
 432 }
 433
 434 static void cdev_purge(struct cdev *cdev)
 435 {
 436         spin_lock(&cdev_lock);
 437         while (!list_empty(&cdev->list)) {
 438                 struct inode *inode;
 439                 inode = container_of(cdev->list.next, struct inode, i_devices);
 440                 list_del_init(&inode->i_devices);
 441                 inode->i_cdev = NULL;
 442         }
 443         spin_unlock(&cdev_lock);
 444 }
 445
 446 /*
 447  * Dummy default file-operations: the only thing this does
 448  * is contain the open that then fills in the correct operations
 449  * depending on the special file...
 450  */
 451 const struct file_operations def_chr_fops = {
 452         .open = chrdev_open,
 453         .llseek = noop_llseek,
 454 };
 455
 456 static struct kobject *exact_match(dev_t dev, int *part, void *data)
 457 {
 458         struct cdev *p = data;
 459         return &p->kobj;
 460 }
 461
 462 static int exact_lock(dev_t dev, void *data)
 463 {
 464         struct cdev *p = data;
 465         return cdev_get(p) ? 0 : -1;
 466 }
 467
 468 /**
 469  * cdev_add() - add a char device to the system
 470  * @p: the cdev structure for the device
 471  * @dev: the first device number for which this device is responsible
 472  * @count: the number of consecutive minor numbers corresponding to this
 473  *         device
 474  *
 475  * cdev_add() adds the device represented by @p to the system, making it
 476  * live immediately.  A negative error code is returned on failure.
 477  */
 478 int cdev_add(struct cdev *p, dev_t dev, unsigned count)
 479 {
 480         int error;
 481
 482         p->dev = dev;
 483         p->count = count;
 484
 485         error = kobj_map(cdev_map, dev, count, NULL,
 486                          exact_match, exact_lock, p);
 487         if (error)
 488                 return error;
 489
 490         kobject_get(p->kobj.parent);
 491
 492         return 0;
 493 }
 494
 495 /**
 496  * cdev_set_parent() - set the parent kobject for a char device
 497  * @p: the cdev structure
 498  * @kobj: the kobject to take a reference to
 499  *
 500  * cdev_set_parent() sets a parent kobject which will be referenced
 501  * appropriately so the parent is not freed before the cdev. This
 502  * should be called before cdev_add.
 503  */
 504 void cdev_set_parent(struct cdev *p, struct kobject *kobj)
 505 {
 506         WARN_ON(!kobj->state_initialized);
 507         p->kobj.parent = kobj;
 508 }
 509
 510 /**
 511  * cdev_device_add() - add a char device and it's corresponding
 512  *      struct device, linkink
 513  * @dev: the device structure
 514  * @cdev: the cdev structure
 515  *
 516  * cdev_device_add() adds the char device represented by @cdev to the system,
 517  * just as cdev_add does. It then adds @dev to the system using device_add
 518  * The dev_t for the char device will be taken from the struct device which
 519  * needs to be initialized first. This helper function correctly takes a
 520  * reference to the parent device so the parent will not get released until
 521  * all references to the cdev are released.
 522  *
 523  * This helper uses dev->devt for the device number. If it is not set
 524  * it will not add the cdev and it will be equivalent to device_add.
 525  *
 526  * This function should be used whenever the struct cdev and the
 527  * struct device are members of the same structure whose lifetime is
 528  * managed by the struct device.
 529  *
 530  * NOTE: Callers must assume that userspace was able to open the cdev and
 531  * can call cdev fops callbacks at any time, even if this function fails.
 532  */
 533 int cdev_device_add(struct cdev *cdev, struct device *dev)
 534 {
 535         int rc = 0;
 536
 537         if (dev->devt) {
 538                 cdev_set_parent(cdev, &dev->kobj);
 539
 540                 rc = cdev_add(cdev, dev->devt, 1);
 541                 if (rc)
 542                         return rc;
 543         }
 544
 545         rc = device_add(dev);
 546         if (rc)
 547                 cdev_del(cdev);
 548
 549         return rc;
 550 }
 551
 552 /**
 553  * cdev_device_del() - inverse of cdev_device_add
 554  * @dev: the device structure
 555  * @cdev: the cdev structure
 556  *
 557  * cdev_device_del() is a helper function to call cdev_del and device_del.
 558  * It should be used whenever cdev_device_add is used.
 559  *
 560  * If dev->devt is not set it will not remove the cdev and will be equivalent
 561  * to device_del.
 562  *
 563  * NOTE: This guarantees that associated sysfs callbacks are not running
 564  * or runnable, however any cdevs already open will remain and their fops
 565  * will still be callable even after this function returns.
 566  */
 567 void cdev_device_del(struct cdev *cdev, struct device *dev)
 568 {
 569         device_del(dev);
 570         if (dev->devt)
 571                 cdev_del(cdev);
 572 }
 573
 574 static void cdev_unmap(dev_t dev, unsigned count)
 575 {
 576         kobj_unmap(cdev_map, dev, count);
 577 }
 578
 579 /**
 580  * cdev_del() - remove a cdev from the system
 581  * @p: the cdev structure to be removed
 582  *
 583  * cdev_del() removes @p from the system, possibly freeing the structure
 584  * itself.
 585  *
 586  * NOTE: This guarantees that cdev device will no longer be able to be
 587  * opened, however any cdevs already open will remain and their fops will
 588  * still be callable even after cdev_del returns.
 589  */
 590 void cdev_del(struct cdev *p)
 591 {
 592         cdev_unmap(p->dev, p->count);
 593         kobject_put(&p->kobj);
 594 }
 595
 596
 597 static void cdev_default_release(struct kobject *kobj)
 598 {
 599         struct cdev *p = container_of(kobj, struct cdev, kobj);
 600         struct kobject *parent = kobj->parent;
 601
 602         cdev_purge(p);
 603         kobject_put(parent);
 604 }
 605
 606 static void cdev_dynamic_release(struct kobject *kobj)
 607 {
 608         struct cdev *p = container_of(kobj, struct cdev, kobj);
 609         struct kobject *parent = kobj->parent;
 610
 611         cdev_purge(p);
 612         kfree(p);
 613         kobject_put(parent);
 614 }
 615
 616 static struct kobj_type ktype_cdev_default = {
 617         .release        = cdev_default_release,
 618 };
 619
 620 static struct kobj_type ktype_cdev_dynamic = {
 621         .release        = cdev_dynamic_release,
 622 };
 623
 624 /**
 625  * cdev_alloc() - allocate a cdev structure
 626  *
 627  * Allocates and returns a cdev structure, or NULL on failure.
 628  */
 629 struct cdev *cdev_alloc(void)
 630 {
 631         struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
 632         if (p) {
 633                 INIT_LIST_HEAD(&p->list);
 634                 kobject_init(&p->kobj, &ktype_cdev_dynamic);
 635         }
 636         return p;
 637 }
 638
 639 /**
 640  * cdev_init() - initialize a cdev structure
 641  * @cdev: the structure to initialize
 642  * @fops: the file_operations for this device
 643  *
 644  * Initializes @cdev, remembering @fops, making it ready to add to the
 645  * system with cdev_add().
 646  */
 647 void cdev_init(struct cdev *cdev, const struct file_operations *fops)
 648 {
 649         memset(cdev, 0, sizeof *cdev);
 650         INIT_LIST_HEAD(&cdev->list);
 651         kobject_init(&cdev->kobj, &ktype_cdev_default);
 652         cdev->ops = fops;
 653 }
 654
 655 static struct kobject *base_probe(dev_t dev, int *part, void *data)
 656 {
 657         if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
 658                 /* Make old-style 2.4 aliases work */
 659                 request_module("char-major-%d", MAJOR(dev));
 660         return NULL;
 661 }
 662
 663 void __init chrdev_init(void)
 664 {
 665         cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
 666 }
 667
 668
 669 /* Let modules do char dev stuff */
 670 EXPORT_SYMBOL(register_chrdev_region);
 671 EXPORT_SYMBOL(unregister_chrdev_region);
 672 EXPORT_SYMBOL(alloc_chrdev_region);
 673 EXPORT_SYMBOL(cdev_init);
 674 EXPORT_SYMBOL(cdev_alloc);
 675 EXPORT_SYMBOL(cdev_del);
 676 EXPORT_SYMBOL(cdev_add);
 677 EXPORT_SYMBOL(cdev_set_parent);
 678 EXPORT_SYMBOL(cdev_device_add);
 679 EXPORT_SYMBOL(cdev_device_del);
 680 EXPORT_SYMBOL(__register_chrdev);
 681 EXPORT_SYMBOL(__unregister_chrdev);