xref: /openbmc/linux/drivers/char/misc.c (revision 9d56dd3b083a3bec56e9da35ce07baca81030b03)
1 /*
2  * linux/drivers/char/misc.c
3  *
4  * Generic misc open routine by Johan Myreen
5  *
6  * Based on code from Linus
7  *
8  * Teemu Rantanen's Microsoft Busmouse support and Derrick Cole's
9  *   changes incorporated into 0.97pl4
10  *   by Peter Cervasio (pete%q106fm.uucp@wupost.wustl.edu) (08SEP92)
11  *   See busmouse.c for particulars.
12  *
13  * Made things a lot mode modular - easy to compile in just one or two
14  * of the misc drivers, as they are now completely independent. Linus.
15  *
16  * Support for loadable modules. 8-Sep-95 Philip Blundell <pjb27@cam.ac.uk>
17  *
18  * Fixed a failing symbol register to free the device registration
19  *		Alan Cox <alan@lxorguk.ukuu.org.uk> 21-Jan-96
20  *
21  * Dynamic minors and /proc/mice by Alessandro Rubini. 26-Mar-96
22  *
23  * Renamed to misc and miscdevice to be more accurate. Alan Cox 26-Mar-96
24  *
25  * Handling of mouse minor numbers for kerneld:
26  *  Idea by Jacques Gelinas <jack@solucorp.qc.ca>,
27  *  adapted by Bjorn Ekwall <bj0rn@blox.se>
28  *  corrected by Alan Cox <alan@lxorguk.ukuu.org.uk>
29  *
30  * Changes for kmod (from kerneld):
31  *	Cyrus Durgin <cider@speakeasy.org>
32  *
33  * Added devfs support. Richard Gooch <rgooch@atnf.csiro.au>  10-Jan-1998
34  */
35 
36 #include <linux/module.h>
37 
38 #include <linux/fs.h>
39 #include <linux/errno.h>
40 #include <linux/miscdevice.h>
41 #include <linux/kernel.h>
42 #include <linux/major.h>
43 #include <linux/slab.h>
44 #include <linux/mutex.h>
45 #include <linux/proc_fs.h>
46 #include <linux/seq_file.h>
47 #include <linux/stat.h>
48 #include <linux/init.h>
49 #include <linux/device.h>
50 #include <linux/tty.h>
51 #include <linux/kmod.h>
52 
53 /*
54  * Head entry for the doubly linked miscdevice list
55  */
56 static LIST_HEAD(misc_list);
57 static DEFINE_MUTEX(misc_mtx);
58 
59 /*
60  * Assigned numbers, used for dynamic minors
61  */
62 #define DYNAMIC_MINORS 64 /* like dynamic majors */
63 static DECLARE_BITMAP(misc_minors, DYNAMIC_MINORS);
64 
65 #ifdef CONFIG_PROC_FS
66 static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
67 {
68 	mutex_lock(&misc_mtx);
69 	return seq_list_start(&misc_list, *pos);
70 }
71 
72 static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos)
73 {
74 	return seq_list_next(v, &misc_list, pos);
75 }
76 
77 static void misc_seq_stop(struct seq_file *seq, void *v)
78 {
79 	mutex_unlock(&misc_mtx);
80 }
81 
82 static int misc_seq_show(struct seq_file *seq, void *v)
83 {
84 	const struct miscdevice *p = list_entry(v, struct miscdevice, list);
85 
86 	seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : "");
87 	return 0;
88 }
89 
90 
91 static const struct seq_operations misc_seq_ops = {
92 	.start = misc_seq_start,
93 	.next  = misc_seq_next,
94 	.stop  = misc_seq_stop,
95 	.show  = misc_seq_show,
96 };
97 
98 static int misc_seq_open(struct inode *inode, struct file *file)
99 {
100 	return seq_open(file, &misc_seq_ops);
101 }
102 
103 static const struct file_operations misc_proc_fops = {
104 	.owner	 = THIS_MODULE,
105 	.open    = misc_seq_open,
106 	.read    = seq_read,
107 	.llseek  = seq_lseek,
108 	.release = seq_release,
109 };
110 #endif
111 
112 static int misc_open(struct inode * inode, struct file * file)
113 {
114 	int minor = iminor(inode);
115 	struct miscdevice *c;
116 	int err = -ENODEV;
117 	const struct file_operations *old_fops, *new_fops = NULL;
118 
119 	mutex_lock(&misc_mtx);
120 
121 	list_for_each_entry(c, &misc_list, list) {
122 		if (c->minor == minor) {
123 			new_fops = fops_get(c->fops);
124 			break;
125 		}
126 	}
127 
128 	if (!new_fops) {
129 		mutex_unlock(&misc_mtx);
130 		request_module("char-major-%d-%d", MISC_MAJOR, minor);
131 		mutex_lock(&misc_mtx);
132 
133 		list_for_each_entry(c, &misc_list, list) {
134 			if (c->minor == minor) {
135 				new_fops = fops_get(c->fops);
136 				break;
137 			}
138 		}
139 		if (!new_fops)
140 			goto fail;
141 	}
142 
143 	err = 0;
144 	old_fops = file->f_op;
145 	file->f_op = new_fops;
146 	if (file->f_op->open) {
147 		err=file->f_op->open(inode,file);
148 		if (err) {
149 			fops_put(file->f_op);
150 			file->f_op = fops_get(old_fops);
151 		}
152 	}
153 	fops_put(old_fops);
154 fail:
155 	mutex_unlock(&misc_mtx);
156 	return err;
157 }
158 
159 static struct class *misc_class;
160 
161 static const struct file_operations misc_fops = {
162 	.owner		= THIS_MODULE,
163 	.open		= misc_open,
164 };
165 
166 /**
167  *	misc_register	-	register a miscellaneous device
168  *	@misc: device structure
169  *
170  *	Register a miscellaneous device with the kernel. If the minor
171  *	number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
172  *	and placed in the minor field of the structure. For other cases
173  *	the minor number requested is used.
174  *
175  *	The structure passed is linked into the kernel and may not be
176  *	destroyed until it has been unregistered.
177  *
178  *	A zero is returned on success and a negative errno code for
179  *	failure.
180  */
181 
182 int misc_register(struct miscdevice * misc)
183 {
184 	struct miscdevice *c;
185 	dev_t dev;
186 	int err = 0;
187 
188 	INIT_LIST_HEAD(&misc->list);
189 
190 	mutex_lock(&misc_mtx);
191 	list_for_each_entry(c, &misc_list, list) {
192 		if (c->minor == misc->minor) {
193 			mutex_unlock(&misc_mtx);
194 			return -EBUSY;
195 		}
196 	}
197 
198 	if (misc->minor == MISC_DYNAMIC_MINOR) {
199 		int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
200 		if (i >= DYNAMIC_MINORS) {
201 			mutex_unlock(&misc_mtx);
202 			return -EBUSY;
203 		}
204 		misc->minor = DYNAMIC_MINORS - i - 1;
205 		set_bit(i, misc_minors);
206 	}
207 
208 	dev = MKDEV(MISC_MAJOR, misc->minor);
209 
210 	misc->this_device = device_create(misc_class, misc->parent, dev,
211 					  misc, "%s", misc->name);
212 	if (IS_ERR(misc->this_device)) {
213 		int i = DYNAMIC_MINORS - misc->minor - 1;
214 		if (i < DYNAMIC_MINORS && i >= 0)
215 			clear_bit(i, misc_minors);
216 		err = PTR_ERR(misc->this_device);
217 		goto out;
218 	}
219 
220 	/*
221 	 * Add it to the front, so that later devices can "override"
222 	 * earlier defaults
223 	 */
224 	list_add(&misc->list, &misc_list);
225  out:
226 	mutex_unlock(&misc_mtx);
227 	return err;
228 }
229 
230 /**
231  *	misc_deregister - unregister a miscellaneous device
232  *	@misc: device to unregister
233  *
234  *	Unregister a miscellaneous device that was previously
235  *	successfully registered with misc_register(). Success
236  *	is indicated by a zero return, a negative errno code
237  *	indicates an error.
238  */
239 
240 int misc_deregister(struct miscdevice *misc)
241 {
242 	int i = DYNAMIC_MINORS - misc->minor - 1;
243 
244 	if (list_empty(&misc->list))
245 		return -EINVAL;
246 
247 	mutex_lock(&misc_mtx);
248 	list_del(&misc->list);
249 	device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor));
250 	if (i < DYNAMIC_MINORS && i >= 0)
251 		clear_bit(i, misc_minors);
252 	mutex_unlock(&misc_mtx);
253 	return 0;
254 }
255 
256 EXPORT_SYMBOL(misc_register);
257 EXPORT_SYMBOL(misc_deregister);
258 
259 static char *misc_devnode(struct device *dev, mode_t *mode)
260 {
261 	struct miscdevice *c = dev_get_drvdata(dev);
262 
263 	if (mode && c->mode)
264 		*mode = c->mode;
265 	if (c->nodename)
266 		return kstrdup(c->nodename, GFP_KERNEL);
267 	return NULL;
268 }
269 
270 static int __init misc_init(void)
271 {
272 	int err;
273 
274 #ifdef CONFIG_PROC_FS
275 	proc_create("misc", 0, NULL, &misc_proc_fops);
276 #endif
277 	misc_class = class_create(THIS_MODULE, "misc");
278 	err = PTR_ERR(misc_class);
279 	if (IS_ERR(misc_class))
280 		goto fail_remove;
281 
282 	err = -EIO;
283 	if (register_chrdev(MISC_MAJOR,"misc",&misc_fops))
284 		goto fail_printk;
285 	misc_class->devnode = misc_devnode;
286 	return 0;
287 
288 fail_printk:
289 	printk("unable to get major %d for misc devices\n", MISC_MAJOR);
290 	class_destroy(misc_class);
291 fail_remove:
292 	remove_proc_entry("misc", NULL);
293 	return err;
294 }
295 subsys_initcall(misc_init);
296