xref: /openbmc/linux/drivers/char/misc.c (revision eafd52e6)
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, used for dynamic minors
62  */
63 #define DYNAMIC_MINORS 128 /* like dynamic majors */
64 static DEFINE_IDA(misc_minors_ida);
65 
misc_minor_alloc(void)66 static int misc_minor_alloc(void)
67 {
68 	int ret;
69 
70 	ret = ida_alloc_max(&misc_minors_ida, DYNAMIC_MINORS - 1, GFP_KERNEL);
71 	if (ret >= 0) {
72 		ret = DYNAMIC_MINORS - ret - 1;
73 	} else {
74 		ret = ida_alloc_range(&misc_minors_ida, MISC_DYNAMIC_MINOR + 1,
75 				      MINORMASK, GFP_KERNEL);
76 	}
77 	return ret;
78 }
79 
misc_minor_free(int minor)80 static void misc_minor_free(int minor)
81 {
82 	if (minor < DYNAMIC_MINORS)
83 		ida_free(&misc_minors_ida, DYNAMIC_MINORS - minor - 1);
84 	else if (minor > MISC_DYNAMIC_MINOR)
85 		ida_free(&misc_minors_ida, minor);
86 }
87 
88 #ifdef CONFIG_PROC_FS
misc_seq_start(struct seq_file * seq,loff_t * pos)89 static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
90 {
91 	mutex_lock(&misc_mtx);
92 	return seq_list_start(&misc_list, *pos);
93 }
94 
misc_seq_next(struct seq_file * seq,void * v,loff_t * pos)95 static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos)
96 {
97 	return seq_list_next(v, &misc_list, pos);
98 }
99 
misc_seq_stop(struct seq_file * seq,void * v)100 static void misc_seq_stop(struct seq_file *seq, void *v)
101 {
102 	mutex_unlock(&misc_mtx);
103 }
104 
misc_seq_show(struct seq_file * seq,void * v)105 static int misc_seq_show(struct seq_file *seq, void *v)
106 {
107 	const struct miscdevice *p = list_entry(v, struct miscdevice, list);
108 
109 	seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : "");
110 	return 0;
111 }
112 
113 
114 static const struct seq_operations misc_seq_ops = {
115 	.start = misc_seq_start,
116 	.next  = misc_seq_next,
117 	.stop  = misc_seq_stop,
118 	.show  = misc_seq_show,
119 };
120 #endif
121 
misc_open(struct inode * inode,struct file * file)122 static int misc_open(struct inode *inode, struct file *file)
123 {
124 	int minor = iminor(inode);
125 	struct miscdevice *c = NULL, *iter;
126 	int err = -ENODEV;
127 	const struct file_operations *new_fops = NULL;
128 
129 	mutex_lock(&misc_mtx);
130 
131 	list_for_each_entry(iter, &misc_list, list) {
132 		if (iter->minor != minor)
133 			continue;
134 		c = iter;
135 		new_fops = fops_get(iter->fops);
136 		break;
137 	}
138 
139 	if (!new_fops) {
140 		mutex_unlock(&misc_mtx);
141 		request_module("char-major-%d-%d", MISC_MAJOR, minor);
142 		mutex_lock(&misc_mtx);
143 
144 		list_for_each_entry(iter, &misc_list, list) {
145 			if (iter->minor != minor)
146 				continue;
147 			c = iter;
148 			new_fops = fops_get(iter->fops);
149 			break;
150 		}
151 		if (!new_fops)
152 			goto fail;
153 	}
154 
155 	/*
156 	 * Place the miscdevice in the file's
157 	 * private_data so it can be used by the
158 	 * file operations, including f_op->open below
159 	 */
160 	file->private_data = c;
161 
162 	err = 0;
163 	replace_fops(file, new_fops);
164 	if (file->f_op->open)
165 		err = file->f_op->open(inode, file);
166 fail:
167 	mutex_unlock(&misc_mtx);
168 	return err;
169 }
170 
misc_devnode(const struct device * dev,umode_t * mode)171 static char *misc_devnode(const struct device *dev, umode_t *mode)
172 {
173 	const struct miscdevice *c = dev_get_drvdata(dev);
174 
175 	if (mode && c->mode)
176 		*mode = c->mode;
177 	if (c->nodename)
178 		return kstrdup(c->nodename, GFP_KERNEL);
179 	return NULL;
180 }
181 
182 static const struct class misc_class = {
183 	.name		= "misc",
184 	.devnode	= misc_devnode,
185 };
186 
187 static const struct file_operations misc_fops = {
188 	.owner		= THIS_MODULE,
189 	.open		= misc_open,
190 	.llseek		= noop_llseek,
191 };
192 
193 /**
194  *	misc_register	-	register a miscellaneous device
195  *	@misc: device structure
196  *
197  *	Register a miscellaneous device with the kernel. If the minor
198  *	number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
199  *	and placed in the minor field of the structure. For other cases
200  *	the minor number requested is used.
201  *
202  *	The structure passed is linked into the kernel and may not be
203  *	destroyed until it has been unregistered. By default, an open()
204  *	syscall to the device sets file->private_data to point to the
205  *	structure. Drivers don't need open in fops for this.
206  *
207  *	A zero is returned on success and a negative errno code for
208  *	failure.
209  */
210 
misc_register(struct miscdevice * misc)211 int misc_register(struct miscdevice *misc)
212 {
213 	dev_t dev;
214 	int err = 0;
215 	bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
216 
217 	INIT_LIST_HEAD(&misc->list);
218 
219 	mutex_lock(&misc_mtx);
220 
221 	if (is_dynamic) {
222 		int i = misc_minor_alloc();
223 
224 		if (i < 0) {
225 			err = -EBUSY;
226 			goto out;
227 		}
228 		misc->minor = i;
229 	} else {
230 		struct miscdevice *c;
231 
232 		list_for_each_entry(c, &misc_list, list) {
233 			if (c->minor == misc->minor) {
234 				err = -EBUSY;
235 				goto out;
236 			}
237 		}
238 	}
239 
240 	dev = MKDEV(MISC_MAJOR, misc->minor);
241 
242 	misc->this_device =
243 		device_create_with_groups(&misc_class, misc->parent, dev,
244 					  misc, misc->groups, "%s", misc->name);
245 	if (IS_ERR(misc->this_device)) {
246 		if (is_dynamic) {
247 			misc_minor_free(misc->minor);
248 			misc->minor = MISC_DYNAMIC_MINOR;
249 		}
250 		err = PTR_ERR(misc->this_device);
251 		goto out;
252 	}
253 
254 	/*
255 	 * Add it to the front, so that later devices can "override"
256 	 * earlier defaults
257 	 */
258 	list_add(&misc->list, &misc_list);
259  out:
260 	mutex_unlock(&misc_mtx);
261 	return err;
262 }
263 EXPORT_SYMBOL(misc_register);
264 
265 /**
266  *	misc_deregister - unregister a miscellaneous device
267  *	@misc: device to unregister
268  *
269  *	Unregister a miscellaneous device that was previously
270  *	successfully registered with misc_register().
271  */
272 
misc_deregister(struct miscdevice * misc)273 void misc_deregister(struct miscdevice *misc)
274 {
275 	if (WARN_ON(list_empty(&misc->list)))
276 		return;
277 
278 	mutex_lock(&misc_mtx);
279 	list_del(&misc->list);
280 	device_destroy(&misc_class, MKDEV(MISC_MAJOR, misc->minor));
281 	misc_minor_free(misc->minor);
282 	mutex_unlock(&misc_mtx);
283 }
284 EXPORT_SYMBOL(misc_deregister);
285 
misc_init(void)286 static int __init misc_init(void)
287 {
288 	int err;
289 	struct proc_dir_entry *ret;
290 
291 	ret = proc_create_seq("misc", 0, NULL, &misc_seq_ops);
292 	err = class_register(&misc_class);
293 	if (err)
294 		goto fail_remove;
295 
296 	err = -EIO;
297 	if (register_chrdev(MISC_MAJOR, "misc", &misc_fops))
298 		goto fail_printk;
299 	return 0;
300 
301 fail_printk:
302 	pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
303 	class_unregister(&misc_class);
304 fail_remove:
305 	if (ret)
306 		remove_proc_entry("misc", NULL);
307 	return err;
308 }
309 subsys_initcall(misc_init);
310