linux/fs/char_dev.c
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   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/*
  28 * capabilities for /dev/mem, /dev/kmem and similar directly mappable character
  29 * devices
  30 * - permits shared-mmap for read, write and/or exec
  31 * - does not permit private mmap in NOMMU mode (can't do COW)
  32 * - no readahead or I/O queue unplugging required
  33 */
  34struct backing_dev_info directly_mappable_cdev_bdi = {
  35        .name = "char",
  36        .capabilities   = (
  37#ifdef CONFIG_MMU
  38                /* permit private copies of the data to be taken */
  39                BDI_CAP_MAP_COPY |
  40#endif
  41                /* permit direct mmap, for read, write or exec */
  42                BDI_CAP_MAP_DIRECT |
  43                BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP |
  44                /* no writeback happens */
  45                BDI_CAP_NO_ACCT_AND_WRITEBACK),
  46};
  47
  48static struct kobj_map *cdev_map;
  49
  50static DEFINE_MUTEX(chrdevs_lock);
  51
  52static struct char_device_struct {
  53        struct char_device_struct *next;
  54        unsigned int major;
  55        unsigned int baseminor;
  56        int minorct;
  57        char name[64];
  58        struct cdev *cdev;              /* will die */
  59} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
  60
  61/* index in the above */
  62static inline int major_to_index(unsigned major)
  63{
  64        return major % CHRDEV_MAJOR_HASH_SIZE;
  65}
  66
  67#ifdef CONFIG_PROC_FS
  68
  69void chrdev_show(struct seq_file *f, off_t offset)
  70{
  71        struct char_device_struct *cd;
  72
  73        if (offset < CHRDEV_MAJOR_HASH_SIZE) {
  74                mutex_lock(&chrdevs_lock);
  75                for (cd = chrdevs[offset]; cd; cd = cd->next)
  76                        seq_printf(f, "%3d %s\n", cd->major, cd->name);
  77                mutex_unlock(&chrdevs_lock);
  78        }
  79}
  80
  81#endif /* CONFIG_PROC_FS */
  82
  83/*
  84 * Register a single major with a specified minor range.
  85 *
  86 * If major == 0 this functions will dynamically allocate a major and return
  87 * its number.
  88 *
  89 * If major > 0 this function will attempt to reserve the passed range of
  90 * minors and will return zero on success.
  91 *
  92 * Returns a -ve errno on failure.
  93 */
  94static struct char_device_struct *
  95__register_chrdev_region(unsigned int major, unsigned int baseminor,
  96                           int minorct, const char *name)
  97{
  98        struct char_device_struct *cd, **cp;
  99        int ret = 0;
 100        int i;
 101
 102        cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
 103        if (cd == NULL)
 104                return ERR_PTR(-ENOMEM);
 105
 106        mutex_lock(&chrdevs_lock);
 107
 108        /* temporary */
 109        if (major == 0) {
 110                for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
 111                        if (chrdevs[i] == NULL)
 112                                break;
 113                }
 114
 115                if (i == 0) {
 116                        ret = -EBUSY;
 117                        goto out;
 118                }
 119                major = i;
 120                ret = major;
 121        }
 122
 123        cd->major = major;
 124        cd->baseminor = baseminor;
 125        cd->minorct = minorct;
 126        strlcpy(cd->name, name, sizeof(cd->name));
 127
 128        i = major_to_index(major);
 129
 130        for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 131                if ((*cp)->major > major ||
 132                    ((*cp)->major == major &&
 133                     (((*cp)->baseminor >= baseminor) ||
 134                      ((*cp)->baseminor + (*cp)->minorct > baseminor))))
 135                        break;
 136
 137        /* Check for overlapping minor ranges.  */
 138        if (*cp && (*cp)->major == major) {
 139                int old_min = (*cp)->baseminor;
 140                int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
 141                int new_min = baseminor;
 142                int new_max = baseminor + minorct - 1;
 143
 144                /* New driver overlaps from the left.  */
 145                if (new_max >= old_min && new_max <= old_max) {
 146                        ret = -EBUSY;
 147                        goto out;
 148                }
 149
 150                /* New driver overlaps from the right.  */
 151                if (new_min <= old_max && new_min >= old_min) {
 152                        ret = -EBUSY;
 153                        goto out;
 154                }
 155        }
 156
 157        cd->next = *cp;
 158        *cp = cd;
 159        mutex_unlock(&chrdevs_lock);
 160        return cd;
 161out:
 162        mutex_unlock(&chrdevs_lock);
 163        kfree(cd);
 164        return ERR_PTR(ret);
 165}
 166
 167static struct char_device_struct *
 168__unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
 169{
 170        struct char_device_struct *cd = NULL, **cp;
 171        int i = major_to_index(major);
 172
 173        mutex_lock(&chrdevs_lock);
 174        for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 175                if ((*cp)->major == major &&
 176                    (*cp)->baseminor == baseminor &&
 177                    (*cp)->minorct == minorct)
 178                        break;
 179        if (*cp) {
 180                cd = *cp;
 181                *cp = cd->next;
 182        }
 183        mutex_unlock(&chrdevs_lock);
 184        return cd;
 185}
 186
 187/**
 188 * register_chrdev_region() - register a range of device numbers
 189 * @from: the first in the desired range of device numbers; must include
 190 *        the major number.
 191 * @count: the number of consecutive device numbers required
 192 * @name: the name of the device or driver.
 193 *
 194 * Return value is zero on success, a negative error code on failure.
 195 */
 196int register_chrdev_region(dev_t from, unsigned count, const char *name)
 197{
 198        struct char_device_struct *cd;
 199        dev_t to = from + count;
 200        dev_t n, next;
 201
 202        for (n = from; n < to; n = next) {
 203                next = MKDEV(MAJOR(n)+1, 0);
 204                if (next > to)
 205                        next = to;
 206                cd = __register_chrdev_region(MAJOR(n), MINOR(n),
 207                               next - n, name);
 208                if (IS_ERR(cd))
 209                        goto fail;
 210        }
 211        return 0;
 212fail:
 213        to = n;
 214        for (n = from; n < to; n = next) {
 215                next = MKDEV(MAJOR(n)+1, 0);
 216                kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 217        }
 218        return PTR_ERR(cd);
 219}
 220
 221/**
 222 * alloc_chrdev_region() - register a range of char device numbers
 223 * @dev: output parameter for first assigned number
 224 * @baseminor: first of the requested range of minor numbers
 225 * @count: the number of minor numbers required
 226 * @name: the name of the associated device or driver
 227 *
 228 * Allocates a range of char device numbers.  The major number will be
 229 * chosen dynamically, and returned (along with the first minor number)
 230 * in @dev.  Returns zero or a negative error code.
 231 */
 232int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
 233                        const char *name)
 234{
 235        struct char_device_struct *cd;
 236        cd = __register_chrdev_region(0, baseminor, count, name);
 237        if (IS_ERR(cd))
 238                return PTR_ERR(cd);
 239        *dev = MKDEV(cd->major, cd->baseminor);
 240        return 0;
 241}
 242
 243/**
 244 * __register_chrdev() - create and register a cdev occupying a range of minors
 245 * @major: major device number or 0 for dynamic allocation
 246 * @baseminor: first of the requested range of minor numbers
 247 * @count: the number of minor numbers required
 248 * @name: name of this range of devices
 249 * @fops: file operations associated with this devices
 250 *
 251 * If @major == 0 this functions will dynamically allocate a major and return
 252 * its number.
 253 *
 254 * If @major > 0 this function will attempt to reserve a device with the given
 255 * major number and will return zero on success.
 256 *
 257 * Returns a -ve errno on failure.
 258 *
 259 * The name of this device has nothing to do with the name of the device in
 260 * /dev. It only helps to keep track of the different owners of devices. If
 261 * your module name has only one type of devices it's ok to use e.g. the name
 262 * of the module here.
 263 */
 264int __register_chrdev(unsigned int major, unsigned int baseminor,
 265                      unsigned int count, const char *name,
 266                      const struct file_operations *fops)
 267{
 268        struct char_device_struct *cd;
 269        struct cdev *cdev;
 270        int err = -ENOMEM;
 271
 272        cd = __register_chrdev_region(major, baseminor, count, name);
 273        if (IS_ERR(cd))
 274                return PTR_ERR(cd);
 275
 276        cdev = cdev_alloc();
 277        if (!cdev)
 278                goto out2;
 279
 280        cdev->owner = fops->owner;
 281        cdev->ops = fops;
 282        kobject_set_name(&cdev->kobj, "%s", name);
 283
 284        err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
 285        if (err)
 286                goto out;
 287
 288        cd->cdev = cdev;
 289
 290        return major ? 0 : cd->major;
 291out:
 292        kobject_put(&cdev->kobj);
 293out2:
 294        kfree(__unregister_chrdev_region(cd->major, baseminor, count));
 295        return err;
 296}
 297
 298/**
 299 * unregister_chrdev_region() - return a range of device numbers
 300 * @from: the first in the range of numbers to unregister
 301 * @count: the number of device numbers to unregister
 302 *
 303 * This function will unregister a range of @count device numbers,
 304 * starting with @from.  The caller should normally be the one who
 305 * allocated those numbers in the first place...
 306 */
 307void unregister_chrdev_region(dev_t from, unsigned count)
 308{
 309        dev_t to = from + count;
 310        dev_t n, next;
 311
 312        for (n = from; n < to; n = next) {
 313                next = MKDEV(MAJOR(n)+1, 0);
 314                if (next > to)
 315                        next = to;
 316                kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 317        }
 318}
 319
 320/**
 321 * __unregister_chrdev - unregister and destroy a cdev
 322 * @major: major device number
 323 * @baseminor: first of the range of minor numbers
 324 * @count: the number of minor numbers this cdev is occupying
 325 * @name: name of this range of devices
 326 *
 327 * Unregister and destroy the cdev occupying the region described by
 328 * @major, @baseminor and @count.  This function undoes what
 329 * __register_chrdev() did.
 330 */
 331void __unregister_chrdev(unsigned int major, unsigned int baseminor,
 332                         unsigned int count, const char *name)
 333{
 334        struct char_device_struct *cd;
 335
 336        cd = __unregister_chrdev_region(major, baseminor, count);
 337        if (cd && cd->cdev)
 338                cdev_del(cd->cdev);
 339        kfree(cd);
 340}
 341
 342static DEFINE_SPINLOCK(cdev_lock);
 343
 344static struct kobject *cdev_get(struct cdev *p)
 345{
 346        struct module *owner = p->owner;
 347        struct kobject *kobj;
 348
 349        if (owner && !try_module_get(owner))
 350                return NULL;
 351        kobj = kobject_get(&p->kobj);
 352        if (!kobj)
 353                module_put(owner);
 354        return kobj;
 355}
 356
 357void cdev_put(struct cdev *p)
 358{
 359        if (p) {
 360                struct module *owner = p->owner;
 361                kobject_put(&p->kobj);
 362                module_put(owner);
 363        }
 364}
 365
 366/*
 367 * Called every time a character special file is opened
 368 */
 369static int chrdev_open(struct inode *inode, struct file *filp)
 370{
 371        const struct file_operations *fops;
 372        struct cdev *p;
 373        struct cdev *new = NULL;
 374        int ret = 0;
 375
 376        spin_lock(&cdev_lock);
 377        p = inode->i_cdev;
 378        if (!p) {
 379                struct kobject *kobj;
 380                int idx;
 381                spin_unlock(&cdev_lock);
 382                kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
 383                if (!kobj)
 384                        return -ENXIO;
 385                new = container_of(kobj, struct cdev, kobj);
 386                spin_lock(&cdev_lock);
 387                /* Check i_cdev again in case somebody beat us to it while
 388                   we dropped the lock. */
 389                p = inode->i_cdev;
 390                if (!p) {
 391                        inode->i_cdev = p = new;
 392                        list_add(&inode->i_devices, &p->list);
 393                        new = NULL;
 394                } else if (!cdev_get(p))
 395                        ret = -ENXIO;
 396        } else if (!cdev_get(p))
 397                ret = -ENXIO;
 398        spin_unlock(&cdev_lock);
 399        cdev_put(new);
 400        if (ret)
 401                return ret;
 402
 403        ret = -ENXIO;
 404        fops = fops_get(p->ops);
 405        if (!fops)
 406                goto out_cdev_put;
 407
 408        replace_fops(filp, fops);
 409        if (filp->f_op->open) {
 410                ret = filp->f_op->open(inode, filp);
 411                if (ret)
 412                        goto out_cdev_put;
 413        }
 414
 415        return 0;
 416
 417 out_cdev_put:
 418        cdev_put(p);
 419        return ret;
 420}
 421
 422void cd_forget(struct inode *inode)
 423{
 424        spin_lock(&cdev_lock);
 425        list_del_init(&inode->i_devices);
 426        inode->i_cdev = NULL;
 427        spin_unlock(&cdev_lock);
 428}
 429
 430static void cdev_purge(struct cdev *cdev)
 431{
 432        spin_lock(&cdev_lock);
 433        while (!list_empty(&cdev->list)) {
 434                struct inode *inode;
 435                inode = container_of(cdev->list.next, struct inode, i_devices);
 436                list_del_init(&inode->i_devices);
 437                inode->i_cdev = NULL;
 438        }
 439        spin_unlock(&cdev_lock);
 440}
 441
 442/*
 443 * Dummy default file-operations: the only thing this does
 444 * is contain the open that then fills in the correct operations
 445 * depending on the special file...
 446 */
 447const struct file_operations def_chr_fops = {
 448        .open = chrdev_open,
 449        .llseek = noop_llseek,
 450};
 451
 452static struct kobject *exact_match(dev_t dev, int *part, void *data)
 453{
 454        struct cdev *p = data;
 455        return &p->kobj;
 456}
 457
 458static int exact_lock(dev_t dev, void *data)
 459{
 460        struct cdev *p = data;
 461        return cdev_get(p) ? 0 : -1;
 462}
 463
 464/**
 465 * cdev_add() - add a char device to the system
 466 * @p: the cdev structure for the device
 467 * @dev: the first device number for which this device is responsible
 468 * @count: the number of consecutive minor numbers corresponding to this
 469 *         device
 470 *
 471 * cdev_add() adds the device represented by @p to the system, making it
 472 * live immediately.  A negative error code is returned on failure.
 473 */
 474int cdev_add(struct cdev *p, dev_t dev, unsigned count)
 475{
 476        int error;
 477
 478        p->dev = dev;
 479        p->count = count;
 480
 481        error = kobj_map(cdev_map, dev, count, NULL,
 482                         exact_match, exact_lock, p);
 483        if (error)
 484                return error;
 485
 486        kobject_get(p->kobj.parent);
 487
 488        return 0;
 489}
 490
 491static void cdev_unmap(dev_t dev, unsigned count)
 492{
 493        kobj_unmap(cdev_map, dev, count);
 494}
 495
 496/**
 497 * cdev_del() - remove a cdev from the system
 498 * @p: the cdev structure to be removed
 499 *
 500 * cdev_del() removes @p from the system, possibly freeing the structure
 501 * itself.
 502 */
 503void cdev_del(struct cdev *p)
 504{
 505        cdev_unmap(p->dev, p->count);
 506        kobject_put(&p->kobj);
 507}
 508
 509
 510static void cdev_default_release(struct kobject *kobj)
 511{
 512        struct cdev *p = container_of(kobj, struct cdev, kobj);
 513        struct kobject *parent = kobj->parent;
 514
 515        cdev_purge(p);
 516        kobject_put(parent);
 517}
 518
 519static void cdev_dynamic_release(struct kobject *kobj)
 520{
 521        struct cdev *p = container_of(kobj, struct cdev, kobj);
 522        struct kobject *parent = kobj->parent;
 523
 524        cdev_purge(p);
 525        kfree(p);
 526        kobject_put(parent);
 527}
 528
 529static struct kobj_type ktype_cdev_default = {
 530        .release        = cdev_default_release,
 531};
 532
 533static struct kobj_type ktype_cdev_dynamic = {
 534        .release        = cdev_dynamic_release,
 535};
 536
 537/**
 538 * cdev_alloc() - allocate a cdev structure
 539 *
 540 * Allocates and returns a cdev structure, or NULL on failure.
 541 */
 542struct cdev *cdev_alloc(void)
 543{
 544        struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
 545        if (p) {
 546                INIT_LIST_HEAD(&p->list);
 547                kobject_init(&p->kobj, &ktype_cdev_dynamic);
 548        }
 549        return p;
 550}
 551
 552/**
 553 * cdev_init() - initialize a cdev structure
 554 * @cdev: the structure to initialize
 555 * @fops: the file_operations for this device
 556 *
 557 * Initializes @cdev, remembering @fops, making it ready to add to the
 558 * system with cdev_add().
 559 */
 560void cdev_init(struct cdev *cdev, const struct file_operations *fops)
 561{
 562        memset(cdev, 0, sizeof *cdev);
 563        INIT_LIST_HEAD(&cdev->list);
 564        kobject_init(&cdev->kobj, &ktype_cdev_default);
 565        cdev->ops = fops;
 566}
 567
 568static struct kobject *base_probe(dev_t dev, int *part, void *data)
 569{
 570        if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
 571                /* Make old-style 2.4 aliases work */
 572                request_module("char-major-%d", MAJOR(dev));
 573        return NULL;
 574}
 575
 576void __init chrdev_init(void)
 577{
 578        cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
 579        if (bdi_init(&directly_mappable_cdev_bdi))
 580                panic("Failed to init directly mappable cdev bdi");
 581}
 582
 583
 584/* Let modules do char dev stuff */
 585EXPORT_SYMBOL(register_chrdev_region);
 586EXPORT_SYMBOL(unregister_chrdev_region);
 587EXPORT_SYMBOL(alloc_chrdev_region);
 588EXPORT_SYMBOL(cdev_init);
 589EXPORT_SYMBOL(cdev_alloc);
 590EXPORT_SYMBOL(cdev_del);
 591EXPORT_SYMBOL(cdev_add);
 592EXPORT_SYMBOL(__register_chrdev);
 593EXPORT_SYMBOL(__unregister_chrdev);
 594EXPORT_SYMBOL(directly_mappable_cdev_bdi);
 595