1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * linux/drivers/char/misc.c
4  *
5  * Generic misc open routine by Johan Myreen
6  *
7  * Based on code from Linus
8  *
9  * Teemu Rantanen's Microsoft Busmouse support and Derrick Cole's
10  *   changes incorporated into 0.97pl4
11  *   by Peter Cervasio (pete%q106fm.uucp@wupost.wustl.edu) (08SEP92)
12  *   See busmouse.c for particulars.
13  *
14  * Made things a lot mode modular - easy to compile in just one or two
15  * of the misc drivers, as they are now completely independent. Linus.
16  *
17  * Support for loadable modules. 8-Sep-95 Philip Blundell <pjb27@cam.ac.uk>
18  *
19  * Fixed a failing symbol register to free the device registration
20  *		Alan Cox <alan@lxorguk.ukuu.org.uk> 21-Jan-96
21  *
22  * Dynamic minors and /proc/mice by Alessandro Rubini. 26-Mar-96
23  *
24  * Renamed to misc and miscdevice to be more accurate. Alan Cox 26-Mar-96
25  *
26  * Handling of mouse minor numbers for kerneld:
27  *  Idea by Jacques Gelinas <jack@solucorp.qc.ca>,
28  *  adapted by Bjorn Ekwall <bj0rn@blox.se>
29  *  corrected by Alan Cox <alan@lxorguk.ukuu.org.uk>
30  *
31  * Changes for kmod (from kerneld):
32  *	Cyrus Durgin <cider@speakeasy.org>
33  *
34  * Added devfs support. Richard Gooch <rgooch@atnf.csiro.au>  10-Jan-1998
35  */
36 
37 #include <linux/module.h>
38 
39 #include <linux/fs.h>
40 #include <linux/errno.h>
41 #include <linux/miscdevice.h>
42 #include <linux/kernel.h>
43 #include <linux/major.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 #include <linux/gfp.h>
53 
54 /*
55  * Head entry for the doubly linked miscdevice list
56  */
57 static LIST_HEAD(misc_list);
58 static DEFINE_MUTEX(misc_mtx);
59 
60 /*
61  * Assigned numbers.
62  */
63 static DEFINE_IDA(misc_minors_ida);
64 
65 static int misc_minor_alloc(int minor)
66 {
67 	int ret = 0;
68 
69 	if (minor == MISC_DYNAMIC_MINOR) {
70 		/* allocate free id */
71 		ret = ida_alloc_range(&misc_minors_ida, MISC_DYNAMIC_MINOR + 1,
72 				      MINORMASK, GFP_KERNEL);
73 	} else {
74 		ret = ida_alloc_range(&misc_minors_ida, minor, minor, GFP_KERNEL);
75 	}
76 	return ret;
77 }
78 
79 static void misc_minor_free(int minor)
80 {
81 	ida_free(&misc_minors_ida, minor);
82 }
83 
84 #ifdef CONFIG_PROC_FS
85 static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
86 {
87 	mutex_lock(&misc_mtx);
88 	return seq_list_start(&misc_list, *pos);
89 }
90 
91 static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos)
92 {
93 	return seq_list_next(v, &misc_list, pos);
94 }
95 
96 static void misc_seq_stop(struct seq_file *seq, void *v)
97 {
98 	mutex_unlock(&misc_mtx);
99 }
100 
101 static int misc_seq_show(struct seq_file *seq, void *v)
102 {
103 	const struct miscdevice *p = list_entry(v, struct miscdevice, list);
104 
105 	seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : "");
106 	return 0;
107 }
108 
109 
110 static const struct seq_operations misc_seq_ops = {
111 	.start = misc_seq_start,
112 	.next  = misc_seq_next,
113 	.stop  = misc_seq_stop,
114 	.show  = misc_seq_show,
115 };
116 #endif
117 
118 static int misc_open(struct inode *inode, struct file *file)
119 {
120 	int minor = iminor(inode);
121 	struct miscdevice *c = NULL, *iter;
122 	int err = -ENODEV;
123 	const struct file_operations *new_fops = NULL;
124 
125 	mutex_lock(&misc_mtx);
126 
127 	list_for_each_entry(iter, &misc_list, list) {
128 		if (iter->minor != minor)
129 			continue;
130 		c = iter;
131 		new_fops = fops_get(iter->fops);
132 		break;
133 	}
134 
135 	if (!new_fops) {
136 		mutex_unlock(&misc_mtx);
137 		request_module("char-major-%d-%d", MISC_MAJOR, minor);
138 		mutex_lock(&misc_mtx);
139 
140 		list_for_each_entry(iter, &misc_list, list) {
141 			if (iter->minor != minor)
142 				continue;
143 			c = iter;
144 			new_fops = fops_get(iter->fops);
145 			break;
146 		}
147 		if (!new_fops)
148 			goto fail;
149 	}
150 
151 	/*
152 	 * Place the miscdevice in the file's
153 	 * private_data so it can be used by the
154 	 * file operations, including f_op->open below
155 	 */
156 	file->private_data = c;
157 
158 	err = 0;
159 	replace_fops(file, new_fops);
160 	if (file->f_op->open)
161 		err = file->f_op->open(inode, file);
162 fail:
163 	mutex_unlock(&misc_mtx);
164 	return err;
165 }
166 
167 static char *misc_devnode(const struct device *dev, umode_t *mode)
168 {
169 	const struct miscdevice *c = dev_get_drvdata(dev);
170 
171 	if (mode && c->mode)
172 		*mode = c->mode;
173 	if (c->nodename)
174 		return kstrdup(c->nodename, GFP_KERNEL);
175 	return NULL;
176 }
177 
178 static const struct class misc_class = {
179 	.name		= "misc",
180 	.devnode	= misc_devnode,
181 };
182 
183 static const struct file_operations misc_fops = {
184 	.owner		= THIS_MODULE,
185 	.open		= misc_open,
186 	.llseek		= noop_llseek,
187 };
188 
189 /**
190  *	misc_register	-	register a miscellaneous device
191  *	@misc: device structure
192  *
193  *	Register a miscellaneous device with the kernel. If the minor
194  *	number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
195  *	and placed in the minor field of the structure. For other cases
196  *	the minor number requested is used.
197  *
198  *	The structure passed is linked into the kernel and may not be
199  *	destroyed until it has been unregistered. By default, an open()
200  *	syscall to the device sets file->private_data to point to the
201  *	structure. Drivers don't need open in fops for this.
202  *
203  *	A zero is returned on success and a negative errno code for
204  *	failure.
205  */
206 
207 int misc_register(struct miscdevice *misc)
208 {
209 	dev_t dev;
210 	int err = 0;
211 	bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
212 
213 	INIT_LIST_HEAD(&misc->list);
214 
215 	mutex_lock(&misc_mtx);
216 
217 	if (is_dynamic) {
218 		int i = misc_minor_alloc(misc->minor);
219 
220 		if (i < 0) {
221 			err = -EBUSY;
222 			goto out;
223 		}
224 		misc->minor = i;
225 	} else {
226 		struct miscdevice *c;
227 		int i;
228 
229 		list_for_each_entry(c, &misc_list, list) {
230 			if (c->minor == misc->minor) {
231 				err = -EBUSY;
232 				goto out;
233 			}
234 		}
235 
236 		i = misc_minor_alloc(misc->minor);
237 		if (i < 0) {
238 			err = -EBUSY;
239 			goto out;
240 		}
241 	}
242 
243 	dev = MKDEV(MISC_MAJOR, misc->minor);
244 
245 	misc->this_device =
246 		device_create_with_groups(&misc_class, misc->parent, dev,
247 					  misc, misc->groups, "%s", misc->name);
248 	if (IS_ERR(misc->this_device)) {
249 		misc_minor_free(misc->minor);
250 		if (is_dynamic) {
251 			misc->minor = MISC_DYNAMIC_MINOR;
252 		}
253 		err = PTR_ERR(misc->this_device);
254 		goto out;
255 	}
256 
257 	/*
258 	 * Add it to the front, so that later devices can "override"
259 	 * earlier defaults
260 	 */
261 	list_add(&misc->list, &misc_list);
262  out:
263 	mutex_unlock(&misc_mtx);
264 	return err;
265 }
266 EXPORT_SYMBOL(misc_register);
267 
268 /**
269  *	misc_deregister - unregister a miscellaneous device
270  *	@misc: device to unregister
271  *
272  *	Unregister a miscellaneous device that was previously
273  *	successfully registered with misc_register().
274  */
275 
276 void misc_deregister(struct miscdevice *misc)
277 {
278 	if (WARN_ON(list_empty(&misc->list)))
279 		return;
280 
281 	mutex_lock(&misc_mtx);
282 	list_del(&misc->list);
283 	device_destroy(&misc_class, MKDEV(MISC_MAJOR, misc->minor));
284 	misc_minor_free(misc->minor);
285 	mutex_unlock(&misc_mtx);
286 }
287 EXPORT_SYMBOL(misc_deregister);
288 
289 static int __init misc_init(void)
290 {
291 	int err;
292 	struct proc_dir_entry *ret;
293 
294 	ret = proc_create_seq("misc", 0, NULL, &misc_seq_ops);
295 	err = class_register(&misc_class);
296 	if (err)
297 		goto fail_remove;
298 
299 	err = -EIO;
300 	if (__register_chrdev(MISC_MAJOR, 0, MINORMASK + 1, "misc", &misc_fops))
301 		goto fail_printk;
302 	return 0;
303 
304 fail_printk:
305 	pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
306 	class_unregister(&misc_class);
307 fail_remove:
308 	if (ret)
309 		remove_proc_entry("misc", NULL);
310 	return err;
311 }
312 subsys_initcall(misc_init);
313