Root/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/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
24#include "internal.h"
25
26/*
27 * capabilities for /dev/mem, /dev/kmem and similar directly mappable character
28 * devices
29 * - permits shared-mmap for read, write and/or exec
30 * - does not permit private mmap in NOMMU mode (can't do COW)
31 * - no readahead or I/O queue unplugging required
32 */
33struct backing_dev_info directly_mappable_cdev_bdi = {
34    .name = "char",
35    .capabilities = (
36#ifdef CONFIG_MMU
37        /* permit private copies of the data to be taken */
38        BDI_CAP_MAP_COPY |
39#endif
40        /* permit direct mmap, for read, write or exec */
41        BDI_CAP_MAP_DIRECT |
42        BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP),
43};
44
45static struct kobj_map *cdev_map;
46
47static DEFINE_MUTEX(chrdevs_lock);
48
49static struct char_device_struct {
50    struct char_device_struct *next;
51    unsigned int major;
52    unsigned int baseminor;
53    int minorct;
54    char name[64];
55    struct cdev *cdev; /* will die */
56} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
57
58/* index in the above */
59static inline int major_to_index(int major)
60{
61    return major % CHRDEV_MAJOR_HASH_SIZE;
62}
63
64#ifdef CONFIG_PROC_FS
65
66void chrdev_show(struct seq_file *f, off_t offset)
67{
68    struct char_device_struct *cd;
69
70    if (offset < CHRDEV_MAJOR_HASH_SIZE) {
71        mutex_lock(&chrdevs_lock);
72        for (cd = chrdevs[offset]; cd; cd = cd->next)
73            seq_printf(f, "%3d %s\n", cd->major, cd->name);
74        mutex_unlock(&chrdevs_lock);
75    }
76}
77
78#endif /* CONFIG_PROC_FS */
79
80/*
81 * Register a single major with a specified minor range.
82 *
83 * If major == 0 this functions will dynamically allocate a major and return
84 * its number.
85 *
86 * If major > 0 this function will attempt to reserve the passed range of
87 * minors and will return zero on success.
88 *
89 * Returns a -ve errno on failure.
90 */
91static struct char_device_struct *
92__register_chrdev_region(unsigned int major, unsigned int baseminor,
93               int minorct, const char *name)
94{
95    struct char_device_struct *cd, **cp;
96    int ret = 0;
97    int i;
98
99    cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
100    if (cd == NULL)
101        return ERR_PTR(-ENOMEM);
102
103    mutex_lock(&chrdevs_lock);
104
105    /* temporary */
106    if (major == 0) {
107        for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
108            if (chrdevs[i] == NULL)
109                break;
110        }
111
112        if (i == 0) {
113            ret = -EBUSY;
114            goto out;
115        }
116        major = i;
117        ret = major;
118    }
119
120    cd->major = major;
121    cd->baseminor = baseminor;
122    cd->minorct = minorct;
123    strlcpy(cd->name, name, sizeof(cd->name));
124
125    i = major_to_index(major);
126
127    for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
128        if ((*cp)->major > major ||
129            ((*cp)->major == major &&
130             (((*cp)->baseminor >= baseminor) ||
131              ((*cp)->baseminor + (*cp)->minorct > baseminor))))
132            break;
133
134    /* Check for overlapping minor ranges. */
135    if (*cp && (*cp)->major == major) {
136        int old_min = (*cp)->baseminor;
137        int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
138        int new_min = baseminor;
139        int new_max = baseminor + minorct - 1;
140
141        /* New driver overlaps from the left. */
142        if (new_max >= old_min && new_max <= old_max) {
143            ret = -EBUSY;
144            goto out;
145        }
146
147        /* New driver overlaps from the right. */
148        if (new_min <= old_max && new_min >= old_min) {
149            ret = -EBUSY;
150            goto out;
151        }
152    }
153
154    cd->next = *cp;
155    *cp = cd;
156    mutex_unlock(&chrdevs_lock);
157    return cd;
158out:
159    mutex_unlock(&chrdevs_lock);
160    kfree(cd);
161    return ERR_PTR(ret);
162}
163
164static struct char_device_struct *
165__unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
166{
167    struct char_device_struct *cd = NULL, **cp;
168    int i = major_to_index(major);
169
170    mutex_lock(&chrdevs_lock);
171    for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
172        if ((*cp)->major == major &&
173            (*cp)->baseminor == baseminor &&
174            (*cp)->minorct == minorct)
175            break;
176    if (*cp) {
177        cd = *cp;
178        *cp = cd->next;
179    }
180    mutex_unlock(&chrdevs_lock);
181    return cd;
182}
183
184/**
185 * register_chrdev_region() - register a range of device numbers
186 * @from: the first in the desired range of device numbers; must include
187 * the major number.
188 * @count: the number of consecutive device numbers required
189 * @name: the name of the device or driver.
190 *
191 * Return value is zero on success, a negative error code on failure.
192 */
193int register_chrdev_region(dev_t from, unsigned count, const char *name)
194{
195    struct char_device_struct *cd;
196    dev_t to = from + count;
197    dev_t n, next;
198
199    for (n = from; n < to; n = next) {
200        next = MKDEV(MAJOR(n)+1, 0);
201        if (next > to)
202            next = to;
203        cd = __register_chrdev_region(MAJOR(n), MINOR(n),
204                   next - n, name);
205        if (IS_ERR(cd))
206            goto fail;
207    }
208    return 0;
209fail:
210    to = n;
211    for (n = from; n < to; n = next) {
212        next = MKDEV(MAJOR(n)+1, 0);
213        kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
214    }
215    return PTR_ERR(cd);
216}
217
218/**
219 * alloc_chrdev_region() - register a range of char device numbers
220 * @dev: output parameter for first assigned number
221 * @baseminor: first of the requested range of minor numbers
222 * @count: the number of minor numbers required
223 * @name: the name of the associated device or driver
224 *
225 * Allocates a range of char device numbers. The major number will be
226 * chosen dynamically, and returned (along with the first minor number)
227 * in @dev. Returns zero or a negative error code.
228 */
229int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
230            const char *name)
231{
232    struct char_device_struct *cd;
233    cd = __register_chrdev_region(0, baseminor, count, name);
234    if (IS_ERR(cd))
235        return PTR_ERR(cd);
236    *dev = MKDEV(cd->major, cd->baseminor);
237    return 0;
238}
239
240/**
241 * __register_chrdev() - create and register a cdev occupying a range of minors
242 * @major: major device number or 0 for dynamic allocation
243 * @baseminor: first of the requested range of minor numbers
244 * @count: the number of minor numbers required
245 * @name: name of this range of devices
246 * @fops: file operations associated with this devices
247 *
248 * If @major == 0 this functions will dynamically allocate a major and return
249 * its number.
250 *
251 * If @major > 0 this function will attempt to reserve a device with the given
252 * major number and will return zero on success.
253 *
254 * Returns a -ve errno on failure.
255 *
256 * The name of this device has nothing to do with the name of the device in
257 * /dev. It only helps to keep track of the different owners of devices. If
258 * your module name has only one type of devices it's ok to use e.g. the name
259 * of the module here.
260 */
261int __register_chrdev(unsigned int major, unsigned int baseminor,
262              unsigned int count, const char *name,
263              const struct file_operations *fops)
264{
265    struct char_device_struct *cd;
266    struct cdev *cdev;
267    int err = -ENOMEM;
268
269    cd = __register_chrdev_region(major, baseminor, count, name);
270    if (IS_ERR(cd))
271        return PTR_ERR(cd);
272    
273    cdev = cdev_alloc();
274    if (!cdev)
275        goto out2;
276
277    cdev->owner = fops->owner;
278    cdev->ops = fops;
279    kobject_set_name(&cdev->kobj, "%s", name);
280        
281    err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
282    if (err)
283        goto out;
284
285    cd->cdev = cdev;
286
287    return major ? 0 : cd->major;
288out:
289    kobject_put(&cdev->kobj);
290out2:
291    kfree(__unregister_chrdev_region(cd->major, baseminor, count));
292    return err;
293}
294
295/**
296 * unregister_chrdev_region() - return a range of device numbers
297 * @from: the first in the range of numbers to unregister
298 * @count: the number of device numbers to unregister
299 *
300 * This function will unregister a range of @count device numbers,
301 * starting with @from. The caller should normally be the one who
302 * allocated those numbers in the first place...
303 */
304void unregister_chrdev_region(dev_t from, unsigned count)
305{
306    dev_t to = from + count;
307    dev_t n, next;
308
309    for (n = from; n < to; n = next) {
310        next = MKDEV(MAJOR(n)+1, 0);
311        if (next > to)
312            next = to;
313        kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
314    }
315}
316
317/**
318 * __unregister_chrdev - unregister and destroy a cdev
319 * @major: major device number
320 * @baseminor: first of the range of minor numbers
321 * @count: the number of minor numbers this cdev is occupying
322 * @name: name of this range of devices
323 *
324 * Unregister and destroy the cdev occupying the region described by
325 * @major, @baseminor and @count. This function undoes what
326 * __register_chrdev() did.
327 */
328void __unregister_chrdev(unsigned int major, unsigned int baseminor,
329             unsigned int count, const char *name)
330{
331    struct char_device_struct *cd;
332
333    cd = __unregister_chrdev_region(major, baseminor, count);
334    if (cd && cd->cdev)
335        cdev_del(cd->cdev);
336    kfree(cd);
337}
338
339static DEFINE_SPINLOCK(cdev_lock);
340
341static struct kobject *cdev_get(struct cdev *p)
342{
343    struct module *owner = p->owner;
344    struct kobject *kobj;
345
346    if (owner && !try_module_get(owner))
347        return NULL;
348    kobj = kobject_get(&p->kobj);
349    if (!kobj)
350        module_put(owner);
351    return kobj;
352}
353
354void cdev_put(struct cdev *p)
355{
356    if (p) {
357        struct module *owner = p->owner;
358        kobject_put(&p->kobj);
359        module_put(owner);
360    }
361}
362
363/*
364 * Called every time a character special file is opened
365 */
366static int chrdev_open(struct inode *inode, struct file *filp)
367{
368    struct cdev *p;
369    struct cdev *new = NULL;
370    int ret = 0;
371
372    spin_lock(&cdev_lock);
373    p = inode->i_cdev;
374    if (!p) {
375        struct kobject *kobj;
376        int idx;
377        spin_unlock(&cdev_lock);
378        kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
379        if (!kobj)
380            return -ENXIO;
381        new = container_of(kobj, struct cdev, kobj);
382        spin_lock(&cdev_lock);
383        /* Check i_cdev again in case somebody beat us to it while
384           we dropped the lock. */
385        p = inode->i_cdev;
386        if (!p) {
387            inode->i_cdev = p = new;
388            list_add(&inode->i_devices, &p->list);
389            new = NULL;
390        } else if (!cdev_get(p))
391            ret = -ENXIO;
392    } else if (!cdev_get(p))
393        ret = -ENXIO;
394    spin_unlock(&cdev_lock);
395    cdev_put(new);
396    if (ret)
397        return ret;
398
399    ret = -ENXIO;
400    filp->f_op = fops_get(p->ops);
401    if (!filp->f_op)
402        goto out_cdev_put;
403
404    if (filp->f_op->open) {
405        ret = filp->f_op->open(inode,filp);
406        if (ret)
407            goto out_cdev_put;
408    }
409
410    return 0;
411
412 out_cdev_put:
413    cdev_put(p);
414    return ret;
415}
416
417int cdev_index(struct inode *inode)
418{
419    int idx;
420    struct kobject *kobj;
421
422    kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
423    if (!kobj)
424        return -1;
425    kobject_put(kobj);
426    return idx;
427}
428
429void cd_forget(struct inode *inode)
430{
431    spin_lock(&cdev_lock);
432    list_del_init(&inode->i_devices);
433    inode->i_cdev = NULL;
434    spin_unlock(&cdev_lock);
435}
436
437static void cdev_purge(struct cdev *cdev)
438{
439    spin_lock(&cdev_lock);
440    while (!list_empty(&cdev->list)) {
441        struct inode *inode;
442        inode = container_of(cdev->list.next, struct inode, i_devices);
443        list_del_init(&inode->i_devices);
444        inode->i_cdev = NULL;
445    }
446    spin_unlock(&cdev_lock);
447}
448
449/*
450 * Dummy default file-operations: the only thing this does
451 * is contain the open that then fills in the correct operations
452 * depending on the special file...
453 */
454const struct file_operations def_chr_fops = {
455    .open = chrdev_open,
456};
457
458static struct kobject *exact_match(dev_t dev, int *part, void *data)
459{
460    struct cdev *p = data;
461    return &p->kobj;
462}
463
464static int exact_lock(dev_t dev, void *data)
465{
466    struct cdev *p = data;
467    return cdev_get(p) ? 0 : -1;
468}
469
470/**
471 * cdev_add() - add a char device to the system
472 * @p: the cdev structure for the device
473 * @dev: the first device number for which this device is responsible
474 * @count: the number of consecutive minor numbers corresponding to this
475 * device
476 *
477 * cdev_add() adds the device represented by @p to the system, making it
478 * live immediately. A negative error code is returned on failure.
479 */
480int cdev_add(struct cdev *p, dev_t dev, unsigned count)
481{
482    p->dev = dev;
483    p->count = count;
484    return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
485}
486
487static void cdev_unmap(dev_t dev, unsigned count)
488{
489    kobj_unmap(cdev_map, dev, count);
490}
491
492/**
493 * cdev_del() - remove a cdev from the system
494 * @p: the cdev structure to be removed
495 *
496 * cdev_del() removes @p from the system, possibly freeing the structure
497 * itself.
498 */
499void cdev_del(struct cdev *p)
500{
501    cdev_unmap(p->dev, p->count);
502    kobject_put(&p->kobj);
503}
504
505
506static void cdev_default_release(struct kobject *kobj)
507{
508    struct cdev *p = container_of(kobj, struct cdev, kobj);
509    cdev_purge(p);
510}
511
512static void cdev_dynamic_release(struct kobject *kobj)
513{
514    struct cdev *p = container_of(kobj, struct cdev, kobj);
515    cdev_purge(p);
516    kfree(p);
517}
518
519static struct kobj_type ktype_cdev_default = {
520    .release = cdev_default_release,
521};
522
523static struct kobj_type ktype_cdev_dynamic = {
524    .release = cdev_dynamic_release,
525};
526
527/**
528 * cdev_alloc() - allocate a cdev structure
529 *
530 * Allocates and returns a cdev structure, or NULL on failure.
531 */
532struct cdev *cdev_alloc(void)
533{
534    struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
535    if (p) {
536        INIT_LIST_HEAD(&p->list);
537        kobject_init(&p->kobj, &ktype_cdev_dynamic);
538    }
539    return p;
540}
541
542/**
543 * cdev_init() - initialize a cdev structure
544 * @cdev: the structure to initialize
545 * @fops: the file_operations for this device
546 *
547 * Initializes @cdev, remembering @fops, making it ready to add to the
548 * system with cdev_add().
549 */
550void cdev_init(struct cdev *cdev, const struct file_operations *fops)
551{
552    memset(cdev, 0, sizeof *cdev);
553    INIT_LIST_HEAD(&cdev->list);
554    kobject_init(&cdev->kobj, &ktype_cdev_default);
555    cdev->ops = fops;
556}
557
558static struct kobject *base_probe(dev_t dev, int *part, void *data)
559{
560    if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
561        /* Make old-style 2.4 aliases work */
562        request_module("char-major-%d", MAJOR(dev));
563    return NULL;
564}
565
566void __init chrdev_init(void)
567{
568    cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
569    bdi_init(&directly_mappable_cdev_bdi);
570}
571
572
573/* Let modules do char dev stuff */
574EXPORT_SYMBOL(register_chrdev_region);
575EXPORT_SYMBOL(unregister_chrdev_region);
576EXPORT_SYMBOL(alloc_chrdev_region);
577EXPORT_SYMBOL(cdev_init);
578EXPORT_SYMBOL(cdev_alloc);
579EXPORT_SYMBOL(cdev_del);
580EXPORT_SYMBOL(cdev_add);
581EXPORT_SYMBOL(cdev_index);
582EXPORT_SYMBOL(__register_chrdev);
583EXPORT_SYMBOL(__unregister_chrdev);
584EXPORT_SYMBOL(directly_mappable_cdev_bdi);
585

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