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

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