xref: /openbmc/linux/drivers/char/misc.c (revision e2f1cf25)
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/mutex.h>
44 #include <linux/proc_fs.h>
45 #include <linux/seq_file.h>
46 #include <linux/stat.h>
47 #include <linux/init.h>
48 #include <linux/device.h>
49 #include <linux/tty.h>
50 #include <linux/kmod.h>
51 #include <linux/gfp.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 *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 	/*
144 	 * Place the miscdevice in the file's
145 	 * private_data so it can be used by the
146 	 * file operations, including f_op->open below
147 	 */
148 	file->private_data = c;
149 
150 	err = 0;
151 	replace_fops(file, new_fops);
152 	if (file->f_op->open)
153 		err = file->f_op->open(inode,file);
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 	.llseek		= noop_llseek,
165 };
166 
167 /**
168  *	misc_register	-	register a miscellaneous device
169  *	@misc: device structure
170  *
171  *	Register a miscellaneous device with the kernel. If the minor
172  *	number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
173  *	and placed in the minor field of the structure. For other cases
174  *	the minor number requested is used.
175  *
176  *	The structure passed is linked into the kernel and may not be
177  *	destroyed until it has been unregistered. By default, an open()
178  *	syscall to the device sets file->private_data to point to the
179  *	structure. Drivers don't need open in fops for this.
180  *
181  *	A zero is returned on success and a negative errno code for
182  *	failure.
183  */
184 
185 int misc_register(struct miscdevice * misc)
186 {
187 	dev_t dev;
188 	int err = 0;
189 	bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
190 
191 	INIT_LIST_HEAD(&misc->list);
192 
193 	mutex_lock(&misc_mtx);
194 
195 	if (is_dynamic) {
196 		int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
197 		if (i >= DYNAMIC_MINORS) {
198 			err = -EBUSY;
199 			goto out;
200 		}
201 		misc->minor = DYNAMIC_MINORS - i - 1;
202 		set_bit(i, misc_minors);
203 	} else {
204 		struct miscdevice *c;
205 
206 		list_for_each_entry(c, &misc_list, list) {
207 			if (c->minor == misc->minor) {
208 				err = -EBUSY;
209 				goto out;
210 			}
211 		}
212 	}
213 
214 	dev = MKDEV(MISC_MAJOR, misc->minor);
215 
216 	misc->this_device =
217 		device_create_with_groups(misc_class, misc->parent, dev,
218 					  misc, misc->groups, "%s", misc->name);
219 	if (IS_ERR(misc->this_device)) {
220 		if (is_dynamic) {
221 			int i = DYNAMIC_MINORS - misc->minor - 1;
222 
223 			if (i < DYNAMIC_MINORS && i >= 0)
224 				clear_bit(i, misc_minors);
225 			misc->minor = MISC_DYNAMIC_MINOR;
226 		}
227 		err = PTR_ERR(misc->this_device);
228 		goto out;
229 	}
230 
231 	/*
232 	 * Add it to the front, so that later devices can "override"
233 	 * earlier defaults
234 	 */
235 	list_add(&misc->list, &misc_list);
236  out:
237 	mutex_unlock(&misc_mtx);
238 	return err;
239 }
240 
241 /**
242  *	misc_deregister - unregister a miscellaneous device
243  *	@misc: device to unregister
244  *
245  *	Unregister a miscellaneous device that was previously
246  *	successfully registered with misc_register(). Success
247  *	is indicated by a zero return, a negative errno code
248  *	indicates an error.
249  */
250 
251 int misc_deregister(struct miscdevice *misc)
252 {
253 	int i = DYNAMIC_MINORS - misc->minor - 1;
254 
255 	if (WARN_ON(list_empty(&misc->list)))
256 		return -EINVAL;
257 
258 	mutex_lock(&misc_mtx);
259 	list_del(&misc->list);
260 	device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor));
261 	if (i < DYNAMIC_MINORS && i >= 0)
262 		clear_bit(i, misc_minors);
263 	mutex_unlock(&misc_mtx);
264 	return 0;
265 }
266 
267 EXPORT_SYMBOL(misc_register);
268 EXPORT_SYMBOL(misc_deregister);
269 
270 static char *misc_devnode(struct device *dev, umode_t *mode)
271 {
272 	struct miscdevice *c = dev_get_drvdata(dev);
273 
274 	if (mode && c->mode)
275 		*mode = c->mode;
276 	if (c->nodename)
277 		return kstrdup(c->nodename, GFP_KERNEL);
278 	return NULL;
279 }
280 
281 static int __init misc_init(void)
282 {
283 	int err;
284 
285 #ifdef CONFIG_PROC_FS
286 	proc_create("misc", 0, NULL, &misc_proc_fops);
287 #endif
288 	misc_class = class_create(THIS_MODULE, "misc");
289 	err = PTR_ERR(misc_class);
290 	if (IS_ERR(misc_class))
291 		goto fail_remove;
292 
293 	err = -EIO;
294 	if (register_chrdev(MISC_MAJOR,"misc",&misc_fops))
295 		goto fail_printk;
296 	misc_class->devnode = misc_devnode;
297 	return 0;
298 
299 fail_printk:
300 	printk("unable to get major %d for misc devices\n", MISC_MAJOR);
301 	class_destroy(misc_class);
302 fail_remove:
303 	remove_proc_entry("misc", NULL);
304 	return err;
305 }
306 subsys_initcall(misc_init);
307