1 // SPDX-License-Identifier: GPL-2.0
5 * Copyright (C) 1991, 1992 Linus Torvalds
8 #include <linux/init.h>
10 #include <linux/kdev_t.h>
11 #include <linux/slab.h>
12 #include <linux/string.h>
14 #include <linux/major.h>
15 #include <linux/errno.h>
16 #include <linux/module.h>
17 #include <linux/seq_file.h>
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 #include <linux/tty.h>
28 static struct kobj_map *cdev_map;
30 static DEFINE_MUTEX(chrdevs_lock);
32 #define CHRDEV_MAJOR_HASH_SIZE 255
34 static struct char_device_struct {
35 struct char_device_struct *next;
37 unsigned int baseminor;
40 struct cdev *cdev; /* will die */
41 } *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
43 /* index in the above */
44 static inline int major_to_index(unsigned major)
46 return major % CHRDEV_MAJOR_HASH_SIZE;
51 void chrdev_show(struct seq_file *f, off_t offset)
53 struct char_device_struct *cd;
55 mutex_lock(&chrdevs_lock);
56 for (cd = chrdevs[major_to_index(offset)]; cd; cd = cd->next) {
57 if (cd->major == offset)
58 seq_printf(f, "%3d %s\n", cd->major, cd->name);
60 mutex_unlock(&chrdevs_lock);
63 #endif /* CONFIG_PROC_FS */
65 static int find_dynamic_major(void)
68 struct char_device_struct *cd;
70 for (i = ARRAY_SIZE(chrdevs)-1; i >= CHRDEV_MAJOR_DYN_END; i--) {
71 if (chrdevs[i] == NULL)
75 for (i = CHRDEV_MAJOR_DYN_EXT_START;
76 i >= CHRDEV_MAJOR_DYN_EXT_END; i--) {
77 for (cd = chrdevs[major_to_index(i)]; cd; cd = cd->next)
89 * Register a single major with a specified minor range.
91 * If major == 0 this function will dynamically allocate an unused major.
92 * If major > 0 this function will attempt to reserve the range of minors
96 static struct char_device_struct *
97 __register_chrdev_region(unsigned int major, unsigned int baseminor,
98 int minorct, const char *name)
100 struct char_device_struct *cd, *curr, *prev = NULL;
104 if (major >= CHRDEV_MAJOR_MAX) {
105 pr_err("CHRDEV \"%s\" major requested (%u) is greater than the maximum (%u)\n",
106 name, major, CHRDEV_MAJOR_MAX-1);
107 return ERR_PTR(-EINVAL);
110 if (minorct > MINORMASK + 1 - baseminor) {
111 pr_err("CHRDEV \"%s\" minor range requested (%u-%u) is out of range of maximum range (%u-%u) for a single major\n",
112 name, baseminor, baseminor + minorct - 1, 0, MINORMASK);
113 return ERR_PTR(-EINVAL);
116 cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
118 return ERR_PTR(-ENOMEM);
120 mutex_lock(&chrdevs_lock);
123 ret = find_dynamic_major();
125 pr_err("CHRDEV \"%s\" dynamic allocation region is full\n",
132 i = major_to_index(major);
133 for (curr = chrdevs[i]; curr; prev = curr, curr = curr->next) {
134 if (curr->major < major)
137 if (curr->major > major)
140 if (curr->baseminor + curr->minorct <= baseminor)
143 if (curr->baseminor >= baseminor + minorct)
150 cd->baseminor = baseminor;
151 cd->minorct = minorct;
152 strlcpy(cd->name, name, sizeof(cd->name));
158 cd->next = prev->next;
162 mutex_unlock(&chrdevs_lock);
165 mutex_unlock(&chrdevs_lock);
170 static struct char_device_struct *
171 __unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
173 struct char_device_struct *cd = NULL, **cp;
174 int i = major_to_index(major);
176 mutex_lock(&chrdevs_lock);
177 for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
178 if ((*cp)->major == major &&
179 (*cp)->baseminor == baseminor &&
180 (*cp)->minorct == minorct)
186 mutex_unlock(&chrdevs_lock);
191 * register_chrdev_region() - register a range of device numbers
192 * @from: the first in the desired range of device numbers; must include
194 * @count: the number of consecutive device numbers required
195 * @name: the name of the device or driver.
197 * Return value is zero on success, a negative error code on failure.
199 int register_chrdev_region(dev_t from, unsigned count, const char *name)
201 struct char_device_struct *cd;
202 dev_t to = from + count;
205 for (n = from; n < to; n = next) {
206 next = MKDEV(MAJOR(n)+1, 0);
209 cd = __register_chrdev_region(MAJOR(n), MINOR(n),
217 for (n = from; n < to; n = next) {
218 next = MKDEV(MAJOR(n)+1, 0);
219 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
225 * alloc_chrdev_region() - register a range of char device numbers
226 * @dev: output parameter for first assigned number
227 * @baseminor: first of the requested range of minor numbers
228 * @count: the number of minor numbers required
229 * @name: the name of the associated device or driver
231 * Allocates a range of char device numbers. The major number will be
232 * chosen dynamically, and returned (along with the first minor number)
233 * in @dev. Returns zero or a negative error code.
235 int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
238 struct char_device_struct *cd;
239 cd = __register_chrdev_region(0, baseminor, count, name);
242 *dev = MKDEV(cd->major, cd->baseminor);
247 * __register_chrdev() - create and register a cdev occupying a range of minors
248 * @major: major device number or 0 for dynamic allocation
249 * @baseminor: first of the requested range of minor numbers
250 * @count: the number of minor numbers required
251 * @name: name of this range of devices
252 * @fops: file operations associated with this devices
254 * If @major == 0 this functions will dynamically allocate a major and return
257 * If @major > 0 this function will attempt to reserve a device with the given
258 * major number and will return zero on success.
260 * Returns a -ve errno on failure.
262 * The name of this device has nothing to do with the name of the device in
263 * /dev. It only helps to keep track of the different owners of devices. If
264 * your module name has only one type of devices it's ok to use e.g. the name
265 * of the module here.
267 int __register_chrdev(unsigned int major, unsigned int baseminor,
268 unsigned int count, const char *name,
269 const struct file_operations *fops)
271 struct char_device_struct *cd;
275 cd = __register_chrdev_region(major, baseminor, count, name);
283 cdev->owner = fops->owner;
285 kobject_set_name(&cdev->kobj, "%s", name);
287 err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
293 return major ? 0 : cd->major;
295 kobject_put(&cdev->kobj);
297 kfree(__unregister_chrdev_region(cd->major, baseminor, count));
302 * unregister_chrdev_region() - unregister 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
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...
310 void unregister_chrdev_region(dev_t from, unsigned count)
312 dev_t to = from + count;
315 for (n = from; n < to; n = next) {
316 next = MKDEV(MAJOR(n)+1, 0);
319 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
324 * __unregister_chrdev - unregister and destroy a cdev
325 * @major: major device number
326 * @baseminor: first of the range of minor numbers
327 * @count: the number of minor numbers this cdev is occupying
328 * @name: name of this range of devices
330 * Unregister and destroy the cdev occupying the region described by
331 * @major, @baseminor and @count. This function undoes what
332 * __register_chrdev() did.
334 void __unregister_chrdev(unsigned int major, unsigned int baseminor,
335 unsigned int count, const char *name)
337 struct char_device_struct *cd;
339 cd = __unregister_chrdev_region(major, baseminor, count);
345 static DEFINE_SPINLOCK(cdev_lock);
347 static struct kobject *cdev_get(struct cdev *p)
349 struct module *owner = p->owner;
350 struct kobject *kobj;
352 if (owner && !try_module_get(owner))
354 kobj = kobject_get(&p->kobj);
360 void cdev_put(struct cdev *p)
363 struct module *owner = p->owner;
364 kobject_put(&p->kobj);
370 * Called every time a character special file is opened
372 static int chrdev_open(struct inode *inode, struct file *filp)
374 const struct file_operations *fops;
376 struct cdev *new = NULL;
379 spin_lock(&cdev_lock);
382 struct kobject *kobj;
384 spin_unlock(&cdev_lock);
385 kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
388 new = container_of(kobj, struct cdev, kobj);
389 spin_lock(&cdev_lock);
390 /* Check i_cdev again in case somebody beat us to it while
391 we dropped the lock. */
394 inode->i_cdev = p = new;
395 list_add(&inode->i_devices, &p->list);
397 } else if (!cdev_get(p))
399 } else if (!cdev_get(p))
401 spin_unlock(&cdev_lock);
407 fops = fops_get(p->ops);
411 replace_fops(filp, fops);
412 if (filp->f_op->open) {
413 ret = filp->f_op->open(inode, filp);
425 void cd_forget(struct inode *inode)
427 spin_lock(&cdev_lock);
428 list_del_init(&inode->i_devices);
429 inode->i_cdev = NULL;
430 inode->i_mapping = &inode->i_data;
431 spin_unlock(&cdev_lock);
434 static void cdev_purge(struct cdev *cdev)
436 spin_lock(&cdev_lock);
437 while (!list_empty(&cdev->list)) {
439 inode = container_of(cdev->list.next, struct inode, i_devices);
440 list_del_init(&inode->i_devices);
441 inode->i_cdev = NULL;
443 spin_unlock(&cdev_lock);
447 * Dummy default file-operations: the only thing this does
448 * is contain the open that then fills in the correct operations
449 * depending on the special file...
451 const struct file_operations def_chr_fops = {
453 .llseek = noop_llseek,
456 static struct kobject *exact_match(dev_t dev, int *part, void *data)
458 struct cdev *p = data;
462 static int exact_lock(dev_t dev, void *data)
464 struct cdev *p = data;
465 return cdev_get(p) ? 0 : -1;
469 * cdev_add() - add a char device to the system
470 * @p: the cdev structure for the device
471 * @dev: the first device number for which this device is responsible
472 * @count: the number of consecutive minor numbers corresponding to this
475 * cdev_add() adds the device represented by @p to the system, making it
476 * live immediately. A negative error code is returned on failure.
478 int cdev_add(struct cdev *p, dev_t dev, unsigned count)
485 error = kobj_map(cdev_map, dev, count, NULL,
486 exact_match, exact_lock, p);
490 kobject_get(p->kobj.parent);
496 * cdev_set_parent() - set the parent kobject for a char device
497 * @p: the cdev structure
498 * @kobj: the kobject to take a reference to
500 * cdev_set_parent() sets a parent kobject which will be referenced
501 * appropriately so the parent is not freed before the cdev. This
502 * should be called before cdev_add.
504 void cdev_set_parent(struct cdev *p, struct kobject *kobj)
506 WARN_ON(!kobj->state_initialized);
507 p->kobj.parent = kobj;
511 * cdev_device_add() - add a char device and it's corresponding
512 * struct device, linkink
513 * @dev: the device structure
514 * @cdev: the cdev structure
516 * cdev_device_add() adds the char device represented by @cdev to the system,
517 * just as cdev_add does. It then adds @dev to the system using device_add
518 * The dev_t for the char device will be taken from the struct device which
519 * needs to be initialized first. This helper function correctly takes a
520 * reference to the parent device so the parent will not get released until
521 * all references to the cdev are released.
523 * This helper uses dev->devt for the device number. If it is not set
524 * it will not add the cdev and it will be equivalent to device_add.
526 * This function should be used whenever the struct cdev and the
527 * struct device are members of the same structure whose lifetime is
528 * managed by the struct device.
530 * NOTE: Callers must assume that userspace was able to open the cdev and
531 * can call cdev fops callbacks at any time, even if this function fails.
533 int cdev_device_add(struct cdev *cdev, struct device *dev)
538 cdev_set_parent(cdev, &dev->kobj);
540 rc = cdev_add(cdev, dev->devt, 1);
545 rc = device_add(dev);
553 * cdev_device_del() - inverse of cdev_device_add
554 * @dev: the device structure
555 * @cdev: the cdev structure
557 * cdev_device_del() is a helper function to call cdev_del and device_del.
558 * It should be used whenever cdev_device_add is used.
560 * If dev->devt is not set it will not remove the cdev and will be equivalent
563 * NOTE: This guarantees that associated sysfs callbacks are not running
564 * or runnable, however any cdevs already open will remain and their fops
565 * will still be callable even after this function returns.
567 void cdev_device_del(struct cdev *cdev, struct device *dev)
574 static void cdev_unmap(dev_t dev, unsigned count)
576 kobj_unmap(cdev_map, dev, count);
580 * cdev_del() - remove a cdev from the system
581 * @p: the cdev structure to be removed
583 * cdev_del() removes @p from the system, possibly freeing the structure
586 * NOTE: This guarantees that cdev device will no longer be able to be
587 * opened, however any cdevs already open will remain and their fops will
588 * still be callable even after cdev_del returns.
590 void cdev_del(struct cdev *p)
592 cdev_unmap(p->dev, p->count);
593 kobject_put(&p->kobj);
597 static void cdev_default_release(struct kobject *kobj)
599 struct cdev *p = container_of(kobj, struct cdev, kobj);
600 struct kobject *parent = kobj->parent;
606 static void cdev_dynamic_release(struct kobject *kobj)
608 struct cdev *p = container_of(kobj, struct cdev, kobj);
609 struct kobject *parent = kobj->parent;
616 static struct kobj_type ktype_cdev_default = {
617 .release = cdev_default_release,
620 static struct kobj_type ktype_cdev_dynamic = {
621 .release = cdev_dynamic_release,
625 * cdev_alloc() - allocate a cdev structure
627 * Allocates and returns a cdev structure, or NULL on failure.
629 struct cdev *cdev_alloc(void)
631 struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
633 INIT_LIST_HEAD(&p->list);
634 kobject_init(&p->kobj, &ktype_cdev_dynamic);
640 * cdev_init() - initialize a cdev structure
641 * @cdev: the structure to initialize
642 * @fops: the file_operations for this device
644 * Initializes @cdev, remembering @fops, making it ready to add to the
645 * system with cdev_add().
647 void cdev_init(struct cdev *cdev, const struct file_operations *fops)
649 memset(cdev, 0, sizeof *cdev);
650 INIT_LIST_HEAD(&cdev->list);
651 kobject_init(&cdev->kobj, &ktype_cdev_default);
655 static struct kobject *base_probe(dev_t dev, int *part, void *data)
657 if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
658 /* Make old-style 2.4 aliases work */
659 request_module("char-major-%d", MAJOR(dev));
663 void __init chrdev_init(void)
665 cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
669 /* Let modules do char dev stuff */
670 EXPORT_SYMBOL(register_chrdev_region);
671 EXPORT_SYMBOL(unregister_chrdev_region);
672 EXPORT_SYMBOL(alloc_chrdev_region);
673 EXPORT_SYMBOL(cdev_init);
674 EXPORT_SYMBOL(cdev_alloc);
675 EXPORT_SYMBOL(cdev_del);
676 EXPORT_SYMBOL(cdev_add);
677 EXPORT_SYMBOL(cdev_set_parent);
678 EXPORT_SYMBOL(cdev_device_add);
679 EXPORT_SYMBOL(cdev_device_del);
680 EXPORT_SYMBOL(__register_chrdev);
681 EXPORT_SYMBOL(__unregister_chrdev);