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