xref: /linux/fs/char_dev.c (revision d67b569f5f620c0fb95d5212642746b7ba9d29e4) 
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 DECLARE_MUTEX(chrdevs_lock);
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 	down(&chrdevs_lock);
58 	for (i = 0; i < ARRAY_SIZE(chrdevs) ; i++) {
59 		for (cd = chrdevs[i]; cd; cd = cd->next) {
60 			/*
61 			 * if the current name, plus the 5 extra characters
62 			 * in the device line for this entry
63 			 * would run us off the page, we're done
64 			 */
65 			if ((len+strlen(cd->name) + 5) >= PAGE_SIZE)
66 				goto page_full;
67 
68 
69 			len += sprintf(page+len, "%3d %s\n",
70 				       cd->major, cd->name);
71 		}
72 	}
73 page_full:
74 	up(&chrdevs_lock);
75 
76 	return len;
77 }
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  */
90 static 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 = kmalloc(sizeof(struct char_device_struct), GFP_KERNEL);
99 	if (cd == NULL)
100 		return ERR_PTR(-ENOMEM);
101 
102 	memset(cd, 0, sizeof(struct char_device_struct));
103 
104 	down(&chrdevs_lock);
105 
106 	/* temporary */
107 	if (major == 0) {
108 		for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
109 			if (chrdevs[i] == NULL)
110 				break;
111 		}
112 
113 		if (i == 0) {
114 			ret = -EBUSY;
115 			goto out;
116 		}
117 		major = i;
118 		ret = major;
119 	}
120 
121 	cd->major = major;
122 	cd->baseminor = baseminor;
123 	cd->minorct = minorct;
124 	cd->name = name;
125 
126 	i = major_to_index(major);
127 
128 	for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
129 		if ((*cp)->major > major ||
130 		    ((*cp)->major == major && (*cp)->baseminor >= baseminor))
131 			break;
132 	if (*cp && (*cp)->major == major &&
133 	    (*cp)->baseminor < baseminor + minorct) {
134 		ret = -EBUSY;
135 		goto out;
136 	}
137 	cd->next = *cp;
138 	*cp = cd;
139 	up(&chrdevs_lock);
140 	return cd;
141 out:
142 	up(&chrdevs_lock);
143 	kfree(cd);
144 	return ERR_PTR(ret);
145 }
146 
147 static struct char_device_struct *
148 __unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
149 {
150 	struct char_device_struct *cd = NULL, **cp;
151 	int i = major_to_index(major);
152 
153 	down(&chrdevs_lock);
154 	for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
155 		if ((*cp)->major == major &&
156 		    (*cp)->baseminor == baseminor &&
157 		    (*cp)->minorct == minorct)
158 			break;
159 	if (*cp) {
160 		cd = *cp;
161 		*cp = cd->next;
162 	}
163 	up(&chrdevs_lock);
164 	return cd;
165 }
166 
167 int register_chrdev_region(dev_t from, unsigned count, const char *name)
168 {
169 	struct char_device_struct *cd;
170 	dev_t to = from + count;
171 	dev_t n, next;
172 
173 	for (n = from; n < to; n = next) {
174 		next = MKDEV(MAJOR(n)+1, 0);
175 		if (next > to)
176 			next = to;
177 		cd = __register_chrdev_region(MAJOR(n), MINOR(n),
178 			       next - n, name);
179 		if (IS_ERR(cd))
180 			goto fail;
181 	}
182 	return 0;
183 fail:
184 	to = n;
185 	for (n = from; n < to; n = next) {
186 		next = MKDEV(MAJOR(n)+1, 0);
187 		kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
188 	}
189 	return PTR_ERR(cd);
190 }
191 
192 int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
193 			const char *name)
194 {
195 	struct char_device_struct *cd;
196 	cd = __register_chrdev_region(0, baseminor, count, name);
197 	if (IS_ERR(cd))
198 		return PTR_ERR(cd);
199 	*dev = MKDEV(cd->major, cd->baseminor);
200 	return 0;
201 }
202 
203 int register_chrdev(unsigned int major, const char *name,
204 		    struct file_operations *fops)
205 {
206 	struct char_device_struct *cd;
207 	struct cdev *cdev;
208 	char *s;
209 	int err = -ENOMEM;
210 
211 	cd = __register_chrdev_region(major, 0, 256, name);
212 	if (IS_ERR(cd))
213 		return PTR_ERR(cd);
214 
215 	cdev = cdev_alloc();
216 	if (!cdev)
217 		goto out2;
218 
219 	cdev->owner = fops->owner;
220 	cdev->ops = fops;
221 	kobject_set_name(&cdev->kobj, "%s", name);
222 	for (s = strchr(kobject_name(&cdev->kobj),'/'); s; s = strchr(s, '/'))
223 		*s = '!';
224 
225 	err = cdev_add(cdev, MKDEV(cd->major, 0), 256);
226 	if (err)
227 		goto out;
228 
229 	cd->cdev = cdev;
230 
231 	return major ? 0 : cd->major;
232 out:
233 	kobject_put(&cdev->kobj);
234 out2:
235 	kfree(__unregister_chrdev_region(cd->major, 0, 256));
236 	return err;
237 }
238 
239 void unregister_chrdev_region(dev_t from, unsigned count)
240 {
241 	dev_t to = from + count;
242 	dev_t n, next;
243 
244 	for (n = from; n < to; n = next) {
245 		next = MKDEV(MAJOR(n)+1, 0);
246 		if (next > to)
247 			next = to;
248 		kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
249 	}
250 }
251 
252 int unregister_chrdev(unsigned int major, const char *name)
253 {
254 	struct char_device_struct *cd;
255 	cd = __unregister_chrdev_region(major, 0, 256);
256 	if (cd && cd->cdev)
257 		cdev_del(cd->cdev);
258 	kfree(cd);
259 	return 0;
260 }
261 
262 static DEFINE_SPINLOCK(cdev_lock);
263 
264 static struct kobject *cdev_get(struct cdev *p)
265 {
266 	struct module *owner = p->owner;
267 	struct kobject *kobj;
268 
269 	if (owner && !try_module_get(owner))
270 		return NULL;
271 	kobj = kobject_get(&p->kobj);
272 	if (!kobj)
273 		module_put(owner);
274 	return kobj;
275 }
276 
277 void cdev_put(struct cdev *p)
278 {
279 	if (p) {
280 		kobject_put(&p->kobj);
281 		module_put(p->owner);
282 	}
283 }
284 
285 /*
286  * Called every time a character special file is opened
287  */
288 int chrdev_open(struct inode * inode, struct file * filp)
289 {
290 	struct cdev *p;
291 	struct cdev *new = NULL;
292 	int ret = 0;
293 
294 	spin_lock(&cdev_lock);
295 	p = inode->i_cdev;
296 	if (!p) {
297 		struct kobject *kobj;
298 		int idx;
299 		spin_unlock(&cdev_lock);
300 		kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
301 		if (!kobj)
302 			return -ENXIO;
303 		new = container_of(kobj, struct cdev, kobj);
304 		spin_lock(&cdev_lock);
305 		p = inode->i_cdev;
306 		if (!p) {
307 			inode->i_cdev = p = new;
308 			inode->i_cindex = idx;
309 			list_add(&inode->i_devices, &p->list);
310 			new = NULL;
311 		} else if (!cdev_get(p))
312 			ret = -ENXIO;
313 	} else if (!cdev_get(p))
314 		ret = -ENXIO;
315 	spin_unlock(&cdev_lock);
316 	cdev_put(new);
317 	if (ret)
318 		return ret;
319 	filp->f_op = fops_get(p->ops);
320 	if (!filp->f_op) {
321 		cdev_put(p);
322 		return -ENXIO;
323 	}
324 	if (filp->f_op->open) {
325 		lock_kernel();
326 		ret = filp->f_op->open(inode,filp);
327 		unlock_kernel();
328 	}
329 	if (ret)
330 		cdev_put(p);
331 	return ret;
332 }
333 
334 void cd_forget(struct inode *inode)
335 {
336 	spin_lock(&cdev_lock);
337 	list_del_init(&inode->i_devices);
338 	inode->i_cdev = NULL;
339 	spin_unlock(&cdev_lock);
340 }
341 
342 static void cdev_purge(struct cdev *cdev)
343 {
344 	spin_lock(&cdev_lock);
345 	while (!list_empty(&cdev->list)) {
346 		struct inode *inode;
347 		inode = container_of(cdev->list.next, struct inode, i_devices);
348 		list_del_init(&inode->i_devices);
349 		inode->i_cdev = NULL;
350 	}
351 	spin_unlock(&cdev_lock);
352 }
353 
354 /*
355  * Dummy default file-operations: the only thing this does
356  * is contain the open that then fills in the correct operations
357  * depending on the special file...
358  */
359 struct file_operations def_chr_fops = {
360 	.open = chrdev_open,
361 };
362 
363 static struct kobject *exact_match(dev_t dev, int *part, void *data)
364 {
365 	struct cdev *p = data;
366 	return &p->kobj;
367 }
368 
369 static int exact_lock(dev_t dev, void *data)
370 {
371 	struct cdev *p = data;
372 	return cdev_get(p) ? 0 : -1;
373 }
374 
375 int cdev_add(struct cdev *p, dev_t dev, unsigned count)
376 {
377 	p->dev = dev;
378 	p->count = count;
379 	return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
380 }
381 
382 static void cdev_unmap(dev_t dev, unsigned count)
383 {
384 	kobj_unmap(cdev_map, dev, count);
385 }
386 
387 void cdev_del(struct cdev *p)
388 {
389 	cdev_unmap(p->dev, p->count);
390 	kobject_put(&p->kobj);
391 }
392 
393 
394 static void cdev_default_release(struct kobject *kobj)
395 {
396 	struct cdev *p = container_of(kobj, struct cdev, kobj);
397 	cdev_purge(p);
398 }
399 
400 static void cdev_dynamic_release(struct kobject *kobj)
401 {
402 	struct cdev *p = container_of(kobj, struct cdev, kobj);
403 	cdev_purge(p);
404 	kfree(p);
405 }
406 
407 static struct kobj_type ktype_cdev_default = {
408 	.release	= cdev_default_release,
409 };
410 
411 static struct kobj_type ktype_cdev_dynamic = {
412 	.release	= cdev_dynamic_release,
413 };
414 
415 struct cdev *cdev_alloc(void)
416 {
417 	struct cdev *p = kmalloc(sizeof(struct cdev), GFP_KERNEL);
418 	if (p) {
419 		memset(p, 0, sizeof(struct cdev));
420 		p->kobj.ktype = &ktype_cdev_dynamic;
421 		INIT_LIST_HEAD(&p->list);
422 		kobject_init(&p->kobj);
423 	}
424 	return p;
425 }
426 
427 void cdev_init(struct cdev *cdev, struct file_operations *fops)
428 {
429 	memset(cdev, 0, sizeof *cdev);
430 	INIT_LIST_HEAD(&cdev->list);
431 	cdev->kobj.ktype = &ktype_cdev_default;
432 	kobject_init(&cdev->kobj);
433 	cdev->ops = fops;
434 }
435 
436 static struct kobject *base_probe(dev_t dev, int *part, void *data)
437 {
438 	if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
439 		/* Make old-style 2.4 aliases work */
440 		request_module("char-major-%d", MAJOR(dev));
441 	return NULL;
442 }
443 
444 void __init chrdev_init(void)
445 {
446 	cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
447 }
448 
449 
450 /* Let modules do char dev stuff */
451 EXPORT_SYMBOL(register_chrdev_region);
452 EXPORT_SYMBOL(unregister_chrdev_region);
453 EXPORT_SYMBOL(alloc_chrdev_region);
454 EXPORT_SYMBOL(cdev_init);
455 EXPORT_SYMBOL(cdev_alloc);
456 EXPORT_SYMBOL(cdev_del);
457 EXPORT_SYMBOL(cdev_add);
458 EXPORT_SYMBOL(register_chrdev);
459 EXPORT_SYMBOL(unregister_chrdev);
460