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