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