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 cdev *cdev;              /* will die */
  59 } *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
  60
  61 /* index in the above */
  62 static inline int major_to_index(int major)
  63 {
  64         return major % CHRDEV_MAJOR_HASH_SIZE;
  65 }
  66
  67 #ifdef CONFIG_PROC_FS
  68
  69 void 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  */
  94 static 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         strncpy(cd->name,name, 64);
 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;
 161 out:
 162         mutex_unlock(&chrdevs_lock);
 163         kfree(cd);
 164         return ERR_PTR(ret);
 165 }
 166
 167 static 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  */
 196 int 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;
 212 fail:
 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  */
 232 int 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() - Register a major number for character devices.
 245  * @major: major device number or 0 for dynamic allocation
 246  * @name: name of this range of devices
 247  * @fops: file operations associated with this devices
 248  *
 249  * If @major == 0 this functions will dynamically allocate a major and return
 250  * its number.
 251  *
 252  * If @major > 0 this function will attempt to reserve a device with the given
 253  * major number and will return zero on success.
 254  *
 255  * Returns a -ve errno on failure.
 256  *
 257  * The name of this device has nothing to do with the name of the device in
 258  * /dev. It only helps to keep track of the different owners of devices. If
 259  * your module name has only one type of devices it's ok to use e.g. the name
 260  * of the module here.
 261  *
 262  * This function registers a range of 256 minor numbers. The first minor number
 263  * is 0.
 264  */
 265 int register_chrdev(unsigned int major, const char *name,
 266                     const struct file_operations *fops)
 267 {
 268         struct char_device_struct *cd;
 269         struct cdev *cdev;
 270         char *s;
 271         int err = -ENOMEM;
 272
 273         cd = __register_chrdev_region(major, 0, 256, name);
 274         if (IS_ERR(cd))
 275                 return PTR_ERR(cd);
 276
 277         cdev = cdev_alloc();
 278         if (!cdev)
 279                 goto out2;
 280
 281         cdev->owner = fops->owner;
 282         cdev->ops = fops;
 283         kobject_set_name(&cdev->kobj, "%s", name);
 284         for (s = strchr(kobject_name(&cdev->kobj),'/'); s; s = strchr(s, '/'))
 285                 *s = '!';
 286
 287         err = cdev_add(cdev, MKDEV(cd->major, 0), 256);
 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, 0, 256));
 298         return err;
 299 }
 300
 301 /**
 302  * unregister_chrdev_region() - return 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 void unregister_chrdev(unsigned int major, const char *name)
 324 {
 325         struct char_device_struct *cd;
 326         cd = __unregister_chrdev_region(major, 0, 256);
 327         if (cd && cd->cdev)
 328                 cdev_del(cd->cdev);
 329         kfree(cd);
 330 }
 331
 332 static DEFINE_SPINLOCK(cdev_lock);
 333
 334 static struct kobject *cdev_get(struct cdev *p)
 335 {
 336         struct module *owner = p->owner;
 337         struct kobject *kobj;
 338
 339         if (owner && !try_module_get(owner))
 340                 return NULL;
 341         kobj = kobject_get(&p->kobj);
 342         if (!kobj)
 343                 module_put(owner);
 344         return kobj;
 345 }
 346
 347 void cdev_put(struct cdev *p)
 348 {
 349         if (p) {
 350                 struct module *owner = p->owner;
 351                 kobject_put(&p->kobj);
 352                 module_put(owner);
 353         }
 354 }
 355
 356 /*
 357  * Called every time a character special file is opened
 358  */
 359 static int chrdev_open(struct inode *inode, struct file *filp)
 360 {
 361         struct cdev *p;
 362         struct cdev *new = NULL;
 363         int ret = 0;
 364
 365         spin_lock(&cdev_lock);
 366         p = inode->i_cdev;
 367         if (!p) {
 368                 struct kobject *kobj;
 369                 int idx;
 370                 spin_unlock(&cdev_lock);
 371                 kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
 372                 if (!kobj)
 373                         return -ENXIO;
 374                 new = container_of(kobj, struct cdev, kobj);
 375                 spin_lock(&cdev_lock);
 376                 p = inode->i_cdev;
 377                 if (!p) {
 378                         inode->i_cdev = p = new;
 379                         inode->i_cindex = idx;
 380                         list_add(&inode->i_devices, &p->list);
 381                         new = NULL;
 382                 } else if (!cdev_get(p))
 383                         ret = -ENXIO;
 384         } else if (!cdev_get(p))
 385                 ret = -ENXIO;
 386         spin_unlock(&cdev_lock);
 387         cdev_put(new);
 388         if (ret)
 389                 return ret;
 390         filp->f_op = fops_get(p->ops);
 391         if (!filp->f_op) {
 392                 cdev_put(p);
 393                 return -ENXIO;
 394         }
 395         if (filp->f_op->open) {
 396                 lock_kernel();
 397                 ret = filp->f_op->open(inode,filp);
 398                 unlock_kernel();
 399         }
 400         if (ret)
 401                 cdev_put(p);
 402         return ret;
 403 }
 404
 405 void cd_forget(struct inode *inode)
 406 {
 407         spin_lock(&cdev_lock);
 408         list_del_init(&inode->i_devices);
 409         inode->i_cdev = NULL;
 410         spin_unlock(&cdev_lock);
 411 }
 412
 413 static void cdev_purge(struct cdev *cdev)
 414 {
 415         spin_lock(&cdev_lock);
 416         while (!list_empty(&cdev->list)) {
 417                 struct inode *inode;
 418                 inode = container_of(cdev->list.next, struct inode, i_devices);
 419                 list_del_init(&inode->i_devices);
 420                 inode->i_cdev = NULL;
 421         }
 422         spin_unlock(&cdev_lock);
 423 }
 424
 425 /*
 426  * Dummy default file-operations: the only thing this does
 427  * is contain the open that then fills in the correct operations
 428  * depending on the special file...
 429  */
 430 const struct file_operations def_chr_fops = {
 431         .open = chrdev_open,
 432 };
 433
 434 static struct kobject *exact_match(dev_t dev, int *part, void *data)
 435 {
 436         struct cdev *p = data;
 437         return &p->kobj;
 438 }
 439
 440 static int exact_lock(dev_t dev, void *data)
 441 {
 442         struct cdev *p = data;
 443         return cdev_get(p) ? 0 : -1;
 444 }
 445
 446 /**
 447  * cdev_add() - add a char device to the system
 448  * @p: the cdev structure for the device
 449  * @dev: the first device number for which this device is responsible
 450  * @count: the number of consecutive minor numbers corresponding to this
 451  *         device
 452  *
 453  * cdev_add() adds the device represented by @p to the system, making it
 454  * live immediately.  A negative error code is returned on failure.
 455  */
 456 int cdev_add(struct cdev *p, dev_t dev, unsigned count)
 457 {
 458         p->dev = dev;
 459         p->count = count;
 460         return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
 461 }
 462
 463 static void cdev_unmap(dev_t dev, unsigned count)
 464 {
 465         kobj_unmap(cdev_map, dev, count);
 466 }
 467
 468 /**
 469  * cdev_del() - remove a cdev from the system
 470  * @p: the cdev structure to be removed
 471  *
 472  * cdev_del() removes @p from the system, possibly freeing the structure
 473  * itself.
 474  */
 475 void cdev_del(struct cdev *p)
 476 {
 477         cdev_unmap(p->dev, p->count);
 478         kobject_put(&p->kobj);
 479 }
 480
 481
 482 static void cdev_default_release(struct kobject *kobj)
 483 {
 484         struct cdev *p = container_of(kobj, struct cdev, kobj);
 485         cdev_purge(p);
 486 }
 487
 488 static void cdev_dynamic_release(struct kobject *kobj)
 489 {
 490         struct cdev *p = container_of(kobj, struct cdev, kobj);
 491         cdev_purge(p);
 492         kfree(p);
 493 }
 494
 495 static struct kobj_type ktype_cdev_default = {
 496         .release        = cdev_default_release,
 497 };
 498
 499 static struct kobj_type ktype_cdev_dynamic = {
 500         .release        = cdev_dynamic_release,
 501 };
 502
 503 /**
 504  * cdev_alloc() - allocate a cdev structure
 505  *
 506  * Allocates and returns a cdev structure, or NULL on failure.
 507  */
 508 struct cdev *cdev_alloc(void)
 509 {
 510         struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
 511         if (p) {
 512                 INIT_LIST_HEAD(&p->list);
 513                 kobject_init(&p->kobj, &ktype_cdev_dynamic);
 514         }
 515         return p;
 516 }
 517
 518 /**
 519  * cdev_init() - initialize a cdev structure
 520  * @cdev: the structure to initialize
 521  * @fops: the file_operations for this device
 522  *
 523  * Initializes @cdev, remembering @fops, making it ready to add to the
 524  * system with cdev_add().
 525  */
 526 void cdev_init(struct cdev *cdev, const struct file_operations *fops)
 527 {
 528         memset(cdev, 0, sizeof *cdev);
 529         INIT_LIST_HEAD(&cdev->list);
 530         kobject_init(&cdev->kobj, &ktype_cdev_default);
 531         cdev->ops = fops;
 532 }
 533
 534 static struct kobject *base_probe(dev_t dev, int *part, void *data)
 535 {
 536         if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
 537                 /* Make old-style 2.4 aliases work */
 538                 request_module("char-major-%d", MAJOR(dev));
 539         return NULL;
 540 }
 541
 542 void __init chrdev_init(void)
 543 {
 544         cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
 545         bdi_init(&directly_mappable_cdev_bdi);
 546 }
 547
 548
 549 /* Let modules do char dev stuff */
 550 EXPORT_SYMBOL(register_chrdev_region);
 551 EXPORT_SYMBOL(unregister_chrdev_region);
 552 EXPORT_SYMBOL(alloc_chrdev_region);
 553 EXPORT_SYMBOL(cdev_init);
 554 EXPORT_SYMBOL(cdev_alloc);
 555 EXPORT_SYMBOL(cdev_del);
 556 EXPORT_SYMBOL(cdev_add);
 557 EXPORT_SYMBOL(register_chrdev);
 558 EXPORT_SYMBOL(unregister_chrdev);
 559 EXPORT_SYMBOL(directly_mappable_cdev_bdi);