linux/fs/char_dev.c
<<
>>
Prefs
   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
  28static struct kobj_map *cdev_map;
  29
  30static DEFINE_MUTEX(chrdevs_lock);
  31
  32#define CHRDEV_MAJOR_HASH_SIZE 255
  33
  34static 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 */
  44static inline int major_to_index(unsigned major)
  45{
  46        return major % CHRDEV_MAJOR_HASH_SIZE;
  47}
  48
  49#ifdef CONFIG_PROC_FS
  50
  51void 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
  65static 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 */
  96static 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;
 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        ret = -EBUSY;
 133        i = major_to_index(major);
 134        for (curr = chrdevs[i]; curr; prev = curr, curr = curr->next) {
 135                if (curr->major < major)
 136                        continue;
 137
 138                if (curr->major > major)
 139                        break;
 140
 141                if (curr->baseminor + curr->minorct <= baseminor)
 142                        continue;
 143
 144                if (curr->baseminor >= baseminor + minorct)
 145                        break;
 146
 147                goto out;
 148        }
 149
 150        cd->major = major;
 151        cd->baseminor = baseminor;
 152        cd->minorct = minorct;
 153        strlcpy(cd->name, name, sizeof(cd->name));
 154
 155        if (!prev) {
 156                cd->next = curr;
 157                chrdevs[i] = cd;
 158        } else {
 159                cd->next = prev->next;
 160                prev->next = cd;
 161        }
 162
 163        mutex_unlock(&chrdevs_lock);
 164        return cd;
 165out:
 166        mutex_unlock(&chrdevs_lock);
 167        kfree(cd);
 168        return ERR_PTR(ret);
 169}
 170
 171static struct char_device_struct *
 172__unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
 173{
 174        struct char_device_struct *cd = NULL, **cp;
 175        int i = major_to_index(major);
 176
 177        mutex_lock(&chrdevs_lock);
 178        for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 179                if ((*cp)->major == major &&
 180                    (*cp)->baseminor == baseminor &&
 181                    (*cp)->minorct == minorct)
 182                        break;
 183        if (*cp) {
 184                cd = *cp;
 185                *cp = cd->next;
 186        }
 187        mutex_unlock(&chrdevs_lock);
 188        return cd;
 189}
 190
 191/**
 192 * register_chrdev_region() - register a range of device numbers
 193 * @from: the first in the desired range of device numbers; must include
 194 *        the major number.
 195 * @count: the number of consecutive device numbers required
 196 * @name: the name of the device or driver.
 197 *
 198 * Return value is zero on success, a negative error code on failure.
 199 */
 200int register_chrdev_region(dev_t from, unsigned count, const char *name)
 201{
 202        struct char_device_struct *cd;
 203        dev_t to = from + count;
 204        dev_t n, next;
 205
 206        for (n = from; n < to; n = next) {
 207                next = MKDEV(MAJOR(n)+1, 0);
 208                if (next > to)
 209                        next = to;
 210                cd = __register_chrdev_region(MAJOR(n), MINOR(n),
 211                               next - n, name);
 212                if (IS_ERR(cd))
 213                        goto fail;
 214        }
 215        return 0;
 216fail:
 217        to = n;
 218        for (n = from; n < to; n = next) {
 219                next = MKDEV(MAJOR(n)+1, 0);
 220                kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 221        }
 222        return PTR_ERR(cd);
 223}
 224
 225/**
 226 * alloc_chrdev_region() - register a range of char device numbers
 227 * @dev: output parameter for first assigned number
 228 * @baseminor: first of the requested range of minor numbers
 229 * @count: the number of minor numbers required
 230 * @name: the name of the associated device or driver
 231 *
 232 * Allocates a range of char device numbers.  The major number will be
 233 * chosen dynamically, and returned (along with the first minor number)
 234 * in @dev.  Returns zero or a negative error code.
 235 */
 236int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
 237                        const char *name)
 238{
 239        struct char_device_struct *cd;
 240        cd = __register_chrdev_region(0, baseminor, count, name);
 241        if (IS_ERR(cd))
 242                return PTR_ERR(cd);
 243        *dev = MKDEV(cd->major, cd->baseminor);
 244        return 0;
 245}
 246
 247/**
 248 * __register_chrdev() - create and register a cdev occupying a range of minors
 249 * @major: major device number or 0 for dynamic allocation
 250 * @baseminor: first of the requested range of minor numbers
 251 * @count: the number of minor numbers required
 252 * @name: name of this range of devices
 253 * @fops: file operations associated with this devices
 254 *
 255 * If @major == 0 this functions will dynamically allocate a major and return
 256 * its number.
 257 *
 258 * If @major > 0 this function will attempt to reserve a device with the given
 259 * major number and will return zero on success.
 260 *
 261 * Returns a -ve errno on failure.
 262 *
 263 * The name of this device has nothing to do with the name of the device in
 264 * /dev. It only helps to keep track of the different owners of devices. If
 265 * your module name has only one type of devices it's ok to use e.g. the name
 266 * of the module here.
 267 */
 268int __register_chrdev(unsigned int major, unsigned int baseminor,
 269                      unsigned int count, const char *name,
 270                      const struct file_operations *fops)
 271{
 272        struct char_device_struct *cd;
 273        struct cdev *cdev;
 274        int err = -ENOMEM;
 275
 276        cd = __register_chrdev_region(major, baseminor, count, name);
 277        if (IS_ERR(cd))
 278                return PTR_ERR(cd);
 279
 280        cdev = cdev_alloc();
 281        if (!cdev)
 282                goto out2;
 283
 284        cdev->owner = fops->owner;
 285        cdev->ops = fops;
 286        kobject_set_name(&cdev->kobj, "%s", name);
 287
 288        err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
 289        if (err)
 290                goto out;
 291
 292        cd->cdev = cdev;
 293
 294        return major ? 0 : cd->major;
 295out:
 296        kobject_put(&cdev->kobj);
 297out2:
 298        kfree(__unregister_chrdev_region(cd->major, baseminor, count));
 299        return err;
 300}
 301
 302/**
 303 * unregister_chrdev_region() - unregister a range of device numbers
 304 * @from: the first in the range of numbers to unregister
 305 * @count: the number of device numbers to unregister
 306 *
 307 * This function will unregister a range of @count device numbers,
 308 * starting with @from.  The caller should normally be the one who
 309 * allocated those numbers in the first place...
 310 */
 311void unregister_chrdev_region(dev_t from, unsigned count)
 312{
 313        dev_t to = from + count;
 314        dev_t n, next;
 315
 316        for (n = from; n < to; n = next) {
 317                next = MKDEV(MAJOR(n)+1, 0);
 318                if (next > to)
 319                        next = to;
 320                kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 321        }
 322}
 323
 324/**
 325 * __unregister_chrdev - unregister and destroy a cdev
 326 * @major: major device number
 327 * @baseminor: first of the range of minor numbers
 328 * @count: the number of minor numbers this cdev is occupying
 329 * @name: name of this range of devices
 330 *
 331 * Unregister and destroy the cdev occupying the region described by
 332 * @major, @baseminor and @count.  This function undoes what
 333 * __register_chrdev() did.
 334 */
 335void __unregister_chrdev(unsigned int major, unsigned int baseminor,
 336                         unsigned int count, const char *name)
 337{
 338        struct char_device_struct *cd;
 339
 340        cd = __unregister_chrdev_region(major, baseminor, count);
 341        if (cd && cd->cdev)
 342                cdev_del(cd->cdev);
 343        kfree(cd);
 344}
 345
 346static DEFINE_SPINLOCK(cdev_lock);
 347
 348static struct kobject *cdev_get(struct cdev *p)
 349{
 350        struct module *owner = p->owner;
 351        struct kobject *kobj;
 352
 353        if (owner && !try_module_get(owner))
 354                return NULL;
 355        kobj = kobject_get_unless_zero(&p->kobj);
 356        if (!kobj)
 357                module_put(owner);
 358        return kobj;
 359}
 360
 361void cdev_put(struct cdev *p)
 362{
 363        if (p) {
 364                struct module *owner = p->owner;
 365                kobject_put(&p->kobj);
 366                module_put(owner);
 367        }
 368}
 369
 370/*
 371 * Called every time a character special file is opened
 372 */
 373static int chrdev_open(struct inode *inode, struct file *filp)
 374{
 375        const struct file_operations *fops;
 376        struct cdev *p;
 377        struct cdev *new = NULL;
 378        int ret = 0;
 379
 380        spin_lock(&cdev_lock);
 381        p = inode->i_cdev;
 382        if (!p) {
 383                struct kobject *kobj;
 384                int idx;
 385                spin_unlock(&cdev_lock);
 386                kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
 387                if (!kobj)
 388                        return -ENXIO;
 389                new = container_of(kobj, struct cdev, kobj);
 390                spin_lock(&cdev_lock);
 391                /* Check i_cdev again in case somebody beat us to it while
 392                   we dropped the lock. */
 393                p = inode->i_cdev;
 394                if (!p) {
 395                        inode->i_cdev = p = new;
 396                        list_add(&inode->i_devices, &p->list);
 397                        new = NULL;
 398                } else if (!cdev_get(p))
 399                        ret = -ENXIO;
 400        } else if (!cdev_get(p))
 401                ret = -ENXIO;
 402        spin_unlock(&cdev_lock);
 403        cdev_put(new);
 404        if (ret)
 405                return ret;
 406
 407        ret = -ENXIO;
 408        fops = fops_get(p->ops);
 409        if (!fops)
 410                goto out_cdev_put;
 411
 412        replace_fops(filp, fops);
 413        if (filp->f_op->open) {
 414                ret = filp->f_op->open(inode, filp);
 415                if (ret)
 416                        goto out_cdev_put;
 417        }
 418
 419        return 0;
 420
 421 out_cdev_put:
 422        cdev_put(p);
 423        return ret;
 424}
 425
 426void cd_forget(struct inode *inode)
 427{
 428        spin_lock(&cdev_lock);
 429        list_del_init(&inode->i_devices);
 430        inode->i_cdev = NULL;
 431        inode->i_mapping = &inode->i_data;
 432        spin_unlock(&cdev_lock);
 433}
 434
 435static void cdev_purge(struct cdev *cdev)
 436{
 437        spin_lock(&cdev_lock);
 438        while (!list_empty(&cdev->list)) {
 439                struct inode *inode;
 440                inode = container_of(cdev->list.next, struct inode, i_devices);
 441                list_del_init(&inode->i_devices);
 442                inode->i_cdev = NULL;
 443        }
 444        spin_unlock(&cdev_lock);
 445}
 446
 447/*
 448 * Dummy default file-operations: the only thing this does
 449 * is contain the open that then fills in the correct operations
 450 * depending on the special file...
 451 */
 452const struct file_operations def_chr_fops = {
 453        .open = chrdev_open,
 454        .llseek = noop_llseek,
 455};
 456
 457static struct kobject *exact_match(dev_t dev, int *part, void *data)
 458{
 459        struct cdev *p = data;
 460        return &p->kobj;
 461}
 462
 463static int exact_lock(dev_t dev, void *data)
 464{
 465        struct cdev *p = data;
 466        return cdev_get(p) ? 0 : -1;
 467}
 468
 469/**
 470 * cdev_add() - add a char device to the system
 471 * @p: the cdev structure for the device
 472 * @dev: the first device number for which this device is responsible
 473 * @count: the number of consecutive minor numbers corresponding to this
 474 *         device
 475 *
 476 * cdev_add() adds the device represented by @p to the system, making it
 477 * live immediately.  A negative error code is returned on failure.
 478 */
 479int cdev_add(struct cdev *p, dev_t dev, unsigned count)
 480{
 481        int error;
 482
 483        p->dev = dev;
 484        p->count = count;
 485
 486        if (WARN_ON(dev == WHITEOUT_DEV))
 487                return -EBUSY;
 488
 489        error = kobj_map(cdev_map, dev, count, NULL,
 490                         exact_match, exact_lock, p);
 491        if (error)
 492                return error;
 493
 494        kobject_get(p->kobj.parent);
 495
 496        return 0;
 497}
 498
 499/**
 500 * cdev_set_parent() - set the parent kobject for a char device
 501 * @p: the cdev structure
 502 * @kobj: the kobject to take a reference to
 503 *
 504 * cdev_set_parent() sets a parent kobject which will be referenced
 505 * appropriately so the parent is not freed before the cdev. This
 506 * should be called before cdev_add.
 507 */
 508void cdev_set_parent(struct cdev *p, struct kobject *kobj)
 509{
 510        WARN_ON(!kobj->state_initialized);
 511        p->kobj.parent = kobj;
 512}
 513
 514/**
 515 * cdev_device_add() - add a char device and it's corresponding
 516 *      struct device, linkink
 517 * @dev: the device structure
 518 * @cdev: the cdev structure
 519 *
 520 * cdev_device_add() adds the char device represented by @cdev to the system,
 521 * just as cdev_add does. It then adds @dev to the system using device_add
 522 * The dev_t for the char device will be taken from the struct device which
 523 * needs to be initialized first. This helper function correctly takes a
 524 * reference to the parent device so the parent will not get released until
 525 * all references to the cdev are released.
 526 *
 527 * This helper uses dev->devt for the device number. If it is not set
 528 * it will not add the cdev and it will be equivalent to device_add.
 529 *
 530 * This function should be used whenever the struct cdev and the
 531 * struct device are members of the same structure whose lifetime is
 532 * managed by the struct device.
 533 *
 534 * NOTE: Callers must assume that userspace was able to open the cdev and
 535 * can call cdev fops callbacks at any time, even if this function fails.
 536 */
 537int cdev_device_add(struct cdev *cdev, struct device *dev)
 538{
 539        int rc = 0;
 540
 541        if (dev->devt) {
 542                cdev_set_parent(cdev, &dev->kobj);
 543
 544                rc = cdev_add(cdev, dev->devt, 1);
 545                if (rc)
 546                        return rc;
 547        }
 548
 549        rc = device_add(dev);
 550        if (rc)
 551                cdev_del(cdev);
 552
 553        return rc;
 554}
 555
 556/**
 557 * cdev_device_del() - inverse of cdev_device_add
 558 * @dev: the device structure
 559 * @cdev: the cdev structure
 560 *
 561 * cdev_device_del() is a helper function to call cdev_del and device_del.
 562 * It should be used whenever cdev_device_add is used.
 563 *
 564 * If dev->devt is not set it will not remove the cdev and will be equivalent
 565 * to device_del.
 566 *
 567 * NOTE: This guarantees that associated sysfs callbacks are not running
 568 * or runnable, however any cdevs already open will remain and their fops
 569 * will still be callable even after this function returns.
 570 */
 571void cdev_device_del(struct cdev *cdev, struct device *dev)
 572{
 573        device_del(dev);
 574        if (dev->devt)
 575                cdev_del(cdev);
 576}
 577
 578static void cdev_unmap(dev_t dev, unsigned count)
 579{
 580        kobj_unmap(cdev_map, dev, count);
 581}
 582
 583/**
 584 * cdev_del() - remove a cdev from the system
 585 * @p: the cdev structure to be removed
 586 *
 587 * cdev_del() removes @p from the system, possibly freeing the structure
 588 * itself.
 589 *
 590 * NOTE: This guarantees that cdev device will no longer be able to be
 591 * opened, however any cdevs already open will remain and their fops will
 592 * still be callable even after cdev_del returns.
 593 */
 594void cdev_del(struct cdev *p)
 595{
 596        cdev_unmap(p->dev, p->count);
 597        kobject_put(&p->kobj);
 598}
 599
 600
 601static void cdev_default_release(struct kobject *kobj)
 602{
 603        struct cdev *p = container_of(kobj, struct cdev, kobj);
 604        struct kobject *parent = kobj->parent;
 605
 606        cdev_purge(p);
 607        kobject_put(parent);
 608}
 609
 610static void cdev_dynamic_release(struct kobject *kobj)
 611{
 612        struct cdev *p = container_of(kobj, struct cdev, kobj);
 613        struct kobject *parent = kobj->parent;
 614
 615        cdev_purge(p);
 616        kfree(p);
 617        kobject_put(parent);
 618}
 619
 620static struct kobj_type ktype_cdev_default = {
 621        .release        = cdev_default_release,
 622};
 623
 624static struct kobj_type ktype_cdev_dynamic = {
 625        .release        = cdev_dynamic_release,
 626};
 627
 628/**
 629 * cdev_alloc() - allocate a cdev structure
 630 *
 631 * Allocates and returns a cdev structure, or NULL on failure.
 632 */
 633struct cdev *cdev_alloc(void)
 634{
 635        struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
 636        if (p) {
 637                INIT_LIST_HEAD(&p->list);
 638                kobject_init(&p->kobj, &ktype_cdev_dynamic);
 639        }
 640        return p;
 641}
 642
 643/**
 644 * cdev_init() - initialize a cdev structure
 645 * @cdev: the structure to initialize
 646 * @fops: the file_operations for this device
 647 *
 648 * Initializes @cdev, remembering @fops, making it ready to add to the
 649 * system with cdev_add().
 650 */
 651void cdev_init(struct cdev *cdev, const struct file_operations *fops)
 652{
 653        memset(cdev, 0, sizeof *cdev);
 654        INIT_LIST_HEAD(&cdev->list);
 655        kobject_init(&cdev->kobj, &ktype_cdev_default);
 656        cdev->ops = fops;
 657}
 658
 659static struct kobject *base_probe(dev_t dev, int *part, void *data)
 660{
 661        if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
 662                /* Make old-style 2.4 aliases work */
 663                request_module("char-major-%d", MAJOR(dev));
 664        return NULL;
 665}
 666
 667void __init chrdev_init(void)
 668{
 669        cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
 670}
 671
 672
 673/* Let modules do char dev stuff */
 674EXPORT_SYMBOL(register_chrdev_region);
 675EXPORT_SYMBOL(unregister_chrdev_region);
 676EXPORT_SYMBOL(alloc_chrdev_region);
 677EXPORT_SYMBOL(cdev_init);
 678EXPORT_SYMBOL(cdev_alloc);
 679EXPORT_SYMBOL(cdev_del);
 680EXPORT_SYMBOL(cdev_add);
 681EXPORT_SYMBOL(cdev_set_parent);
 682EXPORT_SYMBOL(cdev_device_add);
 683EXPORT_SYMBOL(cdev_device_del);
 684EXPORT_SYMBOL(__register_chrdev);
 685EXPORT_SYMBOL(__unregister_chrdev);
 686
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.