xref: /kernel/linux/linux-5.10/drivers/char/misc.c (revision 8c2ecf20) 
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 */
57static LIST_HEAD(misc_list);
58static DEFINE_MUTEX(misc_mtx);
59
60/*
61 * Assigned numbers, used for dynamic minors
62 */
63#define DYNAMIC_MINORS 64 /* like dynamic majors */
64static DECLARE_BITMAP(misc_minors, DYNAMIC_MINORS);
65
66#ifdef CONFIG_PROC_FS
67static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
68{
69	mutex_lock(&misc_mtx);
70	return seq_list_start(&misc_list, *pos);
71}
72
73static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos)
74{
75	return seq_list_next(v, &misc_list, pos);
76}
77
78static void misc_seq_stop(struct seq_file *seq, void *v)
79{
80	mutex_unlock(&misc_mtx);
81}
82
83static int misc_seq_show(struct seq_file *seq, void *v)
84{
85	const struct miscdevice *p = list_entry(v, struct miscdevice, list);
86
87	seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : "");
88	return 0;
89}
90
91
92static const struct seq_operations misc_seq_ops = {
93	.start = misc_seq_start,
94	.next  = misc_seq_next,
95	.stop  = misc_seq_stop,
96	.show  = misc_seq_show,
97};
98#endif
99
100static int misc_open(struct inode *inode, struct file *file)
101{
102	int minor = iminor(inode);
103	struct miscdevice *c;
104	int err = -ENODEV;
105	const struct file_operations *new_fops = NULL;
106
107	mutex_lock(&misc_mtx);
108
109	list_for_each_entry(c, &misc_list, list) {
110		if (c->minor == minor) {
111			new_fops = fops_get(c->fops);
112			break;
113		}
114	}
115
116	if (!new_fops) {
117		mutex_unlock(&misc_mtx);
118		request_module("char-major-%d-%d", MISC_MAJOR, minor);
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		if (!new_fops)
128			goto fail;
129	}
130
131	/*
132	 * Place the miscdevice in the file's
133	 * private_data so it can be used by the
134	 * file operations, including f_op->open below
135	 */
136	file->private_data = c;
137
138	err = 0;
139	replace_fops(file, new_fops);
140	if (file->f_op->open)
141		err = file->f_op->open(inode, file);
142fail:
143	mutex_unlock(&misc_mtx);
144	return err;
145}
146
147static struct class *misc_class;
148
149static const struct file_operations misc_fops = {
150	.owner		= THIS_MODULE,
151	.open		= misc_open,
152	.llseek		= noop_llseek,
153};
154
155/**
156 *	misc_register	-	register a miscellaneous device
157 *	@misc: device structure
158 *
159 *	Register a miscellaneous device with the kernel. If the minor
160 *	number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
161 *	and placed in the minor field of the structure. For other cases
162 *	the minor number requested is used.
163 *
164 *	The structure passed is linked into the kernel and may not be
165 *	destroyed until it has been unregistered. By default, an open()
166 *	syscall to the device sets file->private_data to point to the
167 *	structure. Drivers don't need open in fops for this.
168 *
169 *	A zero is returned on success and a negative errno code for
170 *	failure.
171 */
172
173int misc_register(struct miscdevice *misc)
174{
175	dev_t dev;
176	int err = 0;
177	bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
178
179	INIT_LIST_HEAD(&misc->list);
180
181	mutex_lock(&misc_mtx);
182
183	if (is_dynamic) {
184		int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
185
186		if (i >= DYNAMIC_MINORS) {
187			err = -EBUSY;
188			goto out;
189		}
190		misc->minor = DYNAMIC_MINORS - i - 1;
191		set_bit(i, misc_minors);
192	} else {
193		struct miscdevice *c;
194
195		list_for_each_entry(c, &misc_list, list) {
196			if (c->minor == misc->minor) {
197				err = -EBUSY;
198				goto out;
199			}
200		}
201	}
202
203	dev = MKDEV(MISC_MAJOR, misc->minor);
204
205	misc->this_device =
206		device_create_with_groups(misc_class, misc->parent, dev,
207					  misc, misc->groups, "%s", misc->name);
208	if (IS_ERR(misc->this_device)) {
209		if (is_dynamic) {
210			int i = DYNAMIC_MINORS - misc->minor - 1;
211
212			if (i < DYNAMIC_MINORS && i >= 0)
213				clear_bit(i, misc_minors);
214			misc->minor = MISC_DYNAMIC_MINOR;
215		}
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}
229EXPORT_SYMBOL(misc_register);
230
231/**
232 *	misc_deregister - unregister a miscellaneous device
233 *	@misc: device to unregister
234 *
235 *	Unregister a miscellaneous device that was previously
236 *	successfully registered with misc_register().
237 */
238
239void misc_deregister(struct miscdevice *misc)
240{
241	int i = DYNAMIC_MINORS - misc->minor - 1;
242
243	if (WARN_ON(list_empty(&misc->list)))
244		return;
245
246	mutex_lock(&misc_mtx);
247	list_del(&misc->list);
248	device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor));
249	if (i < DYNAMIC_MINORS && i >= 0)
250		clear_bit(i, misc_minors);
251	mutex_unlock(&misc_mtx);
252}
253EXPORT_SYMBOL(misc_deregister);
254
255static char *misc_devnode(struct device *dev, umode_t *mode)
256{
257	struct miscdevice *c = dev_get_drvdata(dev);
258
259	if (mode && c->mode)
260		*mode = c->mode;
261	if (c->nodename)
262		return kstrdup(c->nodename, GFP_KERNEL);
263	return NULL;
264}
265
266static int __init misc_init(void)
267{
268	int err;
269	struct proc_dir_entry *ret;
270
271	ret = proc_create_seq("misc", 0, NULL, &misc_seq_ops);
272	misc_class = class_create(THIS_MODULE, "misc");
273	err = PTR_ERR(misc_class);
274	if (IS_ERR(misc_class))
275		goto fail_remove;
276
277	err = -EIO;
278	if (register_chrdev(MISC_MAJOR, "misc", &misc_fops))
279		goto fail_printk;
280	misc_class->devnode = misc_devnode;
281	return 0;
282
283fail_printk:
284	pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
285	class_destroy(misc_class);
286fail_remove:
287	if (ret)
288		remove_proc_entry("misc", NULL);
289	return err;
290}
291subsys_initcall(misc_init);
292