fs/char_dev.c

   1 /*
   2  *  linux/fs/char_dev.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6
   7 #include <linux/config.h>
   8 #include <linux/init.h>
   9 #include <linux/fs.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/devfs_fs_kernel.h>
  18
  19 #include <linux/kobject.h>
  20 #include <linux/kobj_map.h>
  21 #include <linux/cdev.h>
  22
  23 #ifdef CONFIG_KMOD
  24 #include <linux/kmod.h>
  25 #endif
  26
  27 static struct kobj_map *cdev_map;
  28
  29 #define MAX_PROBE_HASH 255      /* random */
  30
  31 static rwlock_t chrdevs_lock = RW_LOCK_UNLOCKED;
  32
  33 static struct char_device_struct {
  34         struct char_device_struct *next;
  35         unsigned int major;
  36         unsigned int baseminor;
  37         int minorct;
  38         const char *name;
  39         struct file_operations *fops;
  40         struct cdev *cdev;              /* will die */
  41 } *chrdevs[MAX_PROBE_HASH];
  42
  43 /* index in the above */
  44 static inline int major_to_index(int major)
  45 {
  46         return major % MAX_PROBE_HASH;
  47 }
  48
  49 /* get char device names in somewhat random order */
  50 int get_chrdev_list(char *page)
  51 {
  52         struct char_device_struct *cd;
  53         int i, len;
  54
  55         len = sprintf(page, "Character devices:\n");
  56
  57         read_lock(&chrdevs_lock);
  58         for (i = 0; i < ARRAY_SIZE(chrdevs) ; i++) {
  59                 for (cd = chrdevs[i]; cd; cd = cd->next)
  60                         len += sprintf(page+len, "%3d %s\n",
  61                                        cd->major, cd->name);
  62         }
  63         read_unlock(&chrdevs_lock);
  64
  65         return len;
  66 }
  67
  68 /*
  69  * Register a single major with a specified minor range.
  70  *
  71  * If major == 0 this functions will dynamically allocate a major and return
  72  * its number.
  73  *
  74  * If major > 0 this function will attempt to reserve the passed range of
  75  * minors and will return zero on success.
  76  *
  77  * Returns a -ve errno on failure.
  78  */
  79 static struct char_device_struct *
  80 __register_chrdev_region(unsigned int major, unsigned int baseminor,
  81                            int minorct, const char *name)
  82 {
  83         struct char_device_struct *cd, **cp;
  84         int ret = 0;
  85         int i;
  86
  87         cd = kmalloc(sizeof(struct char_device_struct), GFP_KERNEL);
  88         if (cd == NULL)
  89                 return ERR_PTR(-ENOMEM);
  90
  91         memset(cd, 0, sizeof(struct char_device_struct));
  92
  93         write_lock_irq(&chrdevs_lock);
  94
  95         /* temporary */
  96         if (major == 0) {
  97                 for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
  98                         if (chrdevs[i] == NULL)
  99                                 break;
 100                 }
 101
 102                 if (i == 0) {
 103                         ret = -EBUSY;
 104                         goto out;
 105                 }
 106                 major = i;
 107                 ret = major;
 108         }
 109
 110         cd->major = major;
 111         cd->baseminor = baseminor;
 112         cd->minorct = minorct;
 113         cd->name = name;
 114
 115         i = major_to_index(major);
 116
 117         for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 118                 if ((*cp)->major > major ||
 119                     ((*cp)->major == major && (*cp)->baseminor >= baseminor))
 120                         break;
 121         if (*cp && (*cp)->major == major &&
 122             (*cp)->baseminor < baseminor + minorct) {
 123                 ret = -EBUSY;
 124                 goto out;
 125         }
 126         cd->next = *cp;
 127         *cp = cd;
 128         write_unlock_irq(&chrdevs_lock);
 129         return cd;
 130 out:
 131         write_unlock_irq(&chrdevs_lock);
 132         kfree(cd);
 133         return ERR_PTR(ret);
 134 }
 135
 136 static struct char_device_struct *
 137 __unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
 138 {
 139         struct char_device_struct *cd = NULL, **cp;
 140         int i = major_to_index(major);
 141
 142         write_lock_irq(&chrdevs_lock);
 143         for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
 144                 if ((*cp)->major == major &&
 145                     (*cp)->baseminor == baseminor &&
 146                     (*cp)->minorct == minorct)
 147                         break;
 148         if (*cp) {
 149                 cd = *cp;
 150                 *cp = cd->next;
 151         }
 152         write_unlock_irq(&chrdevs_lock);
 153         return cd;
 154 }
 155
 156 int register_chrdev_region(dev_t from, unsigned count, char *name)
 157 {
 158         struct char_device_struct *cd;
 159         dev_t to = from + count;
 160         dev_t n, next;
 161
 162         for (n = from; n < to; n = next) {
 163                 next = MKDEV(MAJOR(n)+1, 0);
 164                 if (next > to)
 165                         next = to;
 166                 cd = __register_chrdev_region(MAJOR(n), MINOR(n),
 167                                next - n, name);
 168                 if (IS_ERR(cd))
 169                         goto fail;
 170         }
 171         return 0;
 172 fail:
 173         to = n;
 174         for (n = from; n < to; n = next) {
 175                 next = MKDEV(MAJOR(n)+1, 0);
 176                 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 177         }
 178         return PTR_ERR(cd);
 179 }
 180
 181 int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count, char *name)
 182 {
 183         struct char_device_struct *cd;
 184         cd = __register_chrdev_region(0, baseminor, count, name);
 185         if (IS_ERR(cd))
 186                 return PTR_ERR(cd);
 187         *dev = MKDEV(cd->major, cd->baseminor);
 188         return 0;
 189 }
 190
 191 int register_chrdev(unsigned int major, const char *name,
 192                     struct file_operations *fops)
 193 {
 194         struct char_device_struct *cd;
 195         struct cdev *cdev;
 196         char *s;
 197         int err = -ENOMEM;
 198
 199         cd = __register_chrdev_region(major, 0, 256, name);
 200         if (IS_ERR(cd))
 201                 return PTR_ERR(cd);
 202
 203         cdev = cdev_alloc();
 204         if (!cdev)
 205                 goto out2;
 206
 207         cdev->owner = fops->owner;
 208         cdev->ops = fops;
 209         strcpy(cdev->kobj.name, name);
 210         for (s = strchr(cdev->kobj.name, '/'); s; s = strchr(s, '/'))
 211                 *s = '!';
 212
 213         err = cdev_add(cdev, MKDEV(cd->major, 0), 256);
 214         if (err)
 215                 goto out;
 216
 217         cd->cdev = cdev;
 218
 219         return major ? 0 : cd->major;
 220 out:
 221         kobject_put(&cdev->kobj);
 222 out2:
 223         kfree(__unregister_chrdev_region(cd->major, 0, 256));
 224         return err;
 225 }
 226
 227 void unregister_chrdev_region(dev_t from, unsigned count)
 228 {
 229         dev_t to = from + count;
 230         dev_t n, next;
 231
 232         for (n = from; n < to; n = next) {
 233                 next = MKDEV(MAJOR(n)+1, 0);
 234                 if (next > to)
 235                         next = to;
 236                 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
 237         }
 238 }
 239
 240 int unregister_chrdev(unsigned int major, const char *name)
 241 {
 242         struct char_device_struct *cd;
 243         cd = __unregister_chrdev_region(major, 0, 256);
 244         if (cd && cd->cdev)
 245                 cdev_del(cd->cdev);
 246         kfree(cd);
 247         return 0;
 248 }
 249
 250 static spinlock_t cdev_lock = SPIN_LOCK_UNLOCKED;
 251 /*
 252  * Called every time a character special file is opened
 253  */
 254 int chrdev_open(struct inode * inode, struct file * filp)
 255 {
 256         struct cdev *p;
 257         struct cdev *new = NULL;
 258         int ret = 0;
 259
 260         spin_lock(&cdev_lock);
 261         p = inode->i_cdev;
 262         if (!p) {
 263                 struct kobject *kobj;
 264                 int idx;
 265                 spin_unlock(&cdev_lock);
 266                 kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
 267                 if (!kobj)
 268                         return -ENXIO;
 269                 new = container_of(kobj, struct cdev, kobj);
 270                 spin_lock(&cdev_lock);
 271                 p = inode->i_cdev;
 272                 if (!p) {
 273                         inode->i_cdev = p = new;
 274                         inode->i_cindex = idx;
 275                         list_add(&inode->i_devices, &p->list);
 276                         new = NULL;
 277                 } else if (!cdev_get(p))
 278                         ret = -ENXIO;
 279         } else if (!cdev_get(p))
 280                 ret = -ENXIO;
 281         spin_unlock(&cdev_lock);
 282         cdev_put(new);
 283         if (ret)
 284                 return ret;
 285         filp->f_op = fops_get(p->ops);
 286         if (!filp->f_op) {
 287                 cdev_put(p);
 288                 return -ENXIO;
 289         }
 290         if (filp->f_op->open) {
 291                 lock_kernel();
 292                 ret = filp->f_op->open(inode,filp);
 293                 unlock_kernel();
 294         }
 295         if (ret)
 296                 cdev_put(p);
 297         return ret;
 298 }
 299
 300 void cd_forget(struct inode *inode)
 301 {
 302         spin_lock(&cdev_lock);
 303         list_del_init(&inode->i_devices);
 304         inode->i_cdev = NULL;
 305         spin_unlock(&cdev_lock);
 306 }
 307
 308 void cdev_purge(struct cdev *cdev)
 309 {
 310         spin_lock(&cdev_lock);
 311         while (!list_empty(&cdev->list)) {
 312                 struct inode *inode;
 313                 inode = container_of(cdev->list.next, struct inode, i_devices);
 314                 list_del_init(&inode->i_devices);
 315                 inode->i_cdev = NULL;
 316         }
 317         spin_unlock(&cdev_lock);
 318 }
 319
 320 /*
 321  * Dummy default file-operations: the only thing this does
 322  * is contain the open that then fills in the correct operations
 323  * depending on the special file...
 324  */
 325 struct file_operations def_chr_fops = {
 326         .open = chrdev_open,
 327 };
 328
 329 static struct kobject *exact_match(dev_t dev, int *part, void *data)
 330 {
 331         struct cdev *p = data;
 332         return &p->kobj;
 333 }
 334
 335 static int exact_lock(dev_t dev, void *data)
 336 {
 337         struct cdev *p = data;
 338         return cdev_get(p) ? 0 : -1;
 339 }
 340
 341 int cdev_add(struct cdev *p, dev_t dev, unsigned count)
 342 {
 343         p->dev = dev;
 344         p->count = count;
 345         return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
 346 }
 347
 348 static void cdev_unmap(dev_t dev, unsigned count)
 349 {
 350         kobj_unmap(cdev_map, dev, count);
 351 }
 352
 353 void cdev_del(struct cdev *p)
 354 {
 355         cdev_unmap(p->dev, p->count);
 356         kobject_put(&p->kobj);
 357 }
 358
 359 struct kobject *cdev_get(struct cdev *p)
 360 {
 361         struct module *owner = p->owner;
 362         struct kobject *kobj;
 363
 364         if (owner && !try_module_get(owner))
 365                 return NULL;
 366         kobj = kobject_get(&p->kobj);
 367         if (!kobj)
 368                 module_put(owner);
 369         return kobj;
 370 }
 371
 372 void cdev_put(struct cdev *p)
 373 {
 374         if (p) {
 375                 kobject_put(&p->kobj);
 376                 module_put(p->owner);
 377         }
 378 }
 379
 380 static decl_subsys(cdev, NULL, NULL);
 381
 382 static void cdev_default_release(struct kobject *kobj)
 383 {
 384         struct cdev *p = container_of(kobj, struct cdev, kobj);
 385         cdev_purge(p);
 386 }
 387
 388 static void cdev_dynamic_release(struct kobject *kobj)
 389 {
 390         struct cdev *p = container_of(kobj, struct cdev, kobj);
 391         cdev_purge(p);
 392         kfree(p);
 393 }
 394
 395 static struct kobj_type ktype_cdev_default = {
 396         .release        = cdev_default_release,
 397 };
 398
 399 static struct kobj_type ktype_cdev_dynamic = {
 400         .release        = cdev_dynamic_release,
 401 };
 402
 403 struct cdev *cdev_alloc(void)
 404 {
 405         struct cdev *p = kmalloc(sizeof(struct cdev), GFP_KERNEL);
 406         if (p) {
 407                 memset(p, 0, sizeof(struct cdev));
 408                 p->kobj.ktype = &ktype_cdev_dynamic;
 409                 INIT_LIST_HEAD(&p->list);
 410                 kobject_init(&p->kobj);
 411         }
 412         return p;
 413 }
 414
 415 void cdev_init(struct cdev *cdev, struct file_operations *fops)
 416 {
 417         INIT_LIST_HEAD(&cdev->list);
 418         cdev->kobj.ktype = &ktype_cdev_default;
 419         kobject_init(&cdev->kobj);
 420         cdev->ops = fops;
 421 }
 422
 423 static struct kobject *base_probe(dev_t dev, int *part, void *data)
 424 {
 425         if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
 426                 /* Make old-style 2.4 aliases work */
 427                 request_module("char-major-%d", MAJOR(dev));
 428         return NULL;
 429 }
 430
 431 void __init chrdev_init(void)
 432 {
 433 /*
 434  * Keep cdev_subsys around because (and only because) the kobj_map code
 435  * depends on the rwsem it contains.  We don't make it public in sysfs,
 436  * however.
 437  */
 438         subsystem_init(&cdev_subsys);
 439         cdev_map = kobj_map_init(base_probe, &cdev_subsys);
 440 }
 441
 442
 443 /* Let modules do char dev stuff */
 444 EXPORT_SYMBOL(register_chrdev_region);
 445 EXPORT_SYMBOL(unregister_chrdev_region);
 446 EXPORT_SYMBOL(alloc_chrdev_region);
 447 EXPORT_SYMBOL(cdev_init);
 448 EXPORT_SYMBOL(cdev_alloc);
 449 EXPORT_SYMBOL(cdev_get);
 450 EXPORT_SYMBOL(cdev_put);
 451 EXPORT_SYMBOL(cdev_del);
 452 EXPORT_SYMBOL(cdev_add);
 453 EXPORT_SYMBOL(register_chrdev);
 454 EXPORT_SYMBOL(unregister_chrdev);