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 66 static int misc_minor_alloc(int minor) 67 { 68 int ret = 0; 69 70 if (minor == MISC_DYNAMIC_MINOR) { 71 /* allocate free id */ 72 ret = ida_alloc_max(&misc_minors_ida, DYNAMIC_MINORS - 1, GFP_KERNEL); 73 if (ret >= 0) { 74 ret = DYNAMIC_MINORS - ret - 1; 75 } else { 76 ret = ida_alloc_range(&misc_minors_ida, MISC_DYNAMIC_MINOR + 1, 77 MINORMASK, GFP_KERNEL); 78 } 79 } else { 80 /* specific minor, check if it is in dynamic or misc dynamic range */ 81 if (minor < DYNAMIC_MINORS) { 82 minor = DYNAMIC_MINORS - minor - 1; 83 ret = ida_alloc_range(&misc_minors_ida, minor, minor, GFP_KERNEL); 84 } else if (minor > MISC_DYNAMIC_MINOR) { 85 ret = ida_alloc_range(&misc_minors_ida, minor, minor, GFP_KERNEL); 86 } else { 87 /* case of non-dynamic minors, no need to allocate id */ 88 ret = 0; 89 } 90 } 91 return ret; 92 } 93 94 static void misc_minor_free(int minor) 95 { 96 if (minor < DYNAMIC_MINORS) 97 ida_free(&misc_minors_ida, DYNAMIC_MINORS - minor - 1); 98 else if (minor > MISC_DYNAMIC_MINOR) 99 ida_free(&misc_minors_ida, minor); 100 } 101 102 #ifdef CONFIG_PROC_FS 103 static void *misc_seq_start(struct seq_file *seq, loff_t *pos) 104 { 105 mutex_lock(&misc_mtx); 106 return seq_list_start(&misc_list, *pos); 107 } 108 109 static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos) 110 { 111 return seq_list_next(v, &misc_list, pos); 112 } 113 114 static void misc_seq_stop(struct seq_file *seq, void *v) 115 { 116 mutex_unlock(&misc_mtx); 117 } 118 119 static int misc_seq_show(struct seq_file *seq, void *v) 120 { 121 const struct miscdevice *p = list_entry(v, struct miscdevice, list); 122 123 seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : ""); 124 return 0; 125 } 126 127 128 static const struct seq_operations misc_seq_ops = { 129 .start = misc_seq_start, 130 .next = misc_seq_next, 131 .stop = misc_seq_stop, 132 .show = misc_seq_show, 133 }; 134 #endif 135 136 static int misc_open(struct inode *inode, struct file *file) 137 { 138 int minor = iminor(inode); 139 struct miscdevice *c = NULL, *iter; 140 int err = -ENODEV; 141 const struct file_operations *new_fops = NULL; 142 143 mutex_lock(&misc_mtx); 144 145 list_for_each_entry(iter, &misc_list, list) { 146 if (iter->minor != minor) 147 continue; 148 c = iter; 149 new_fops = fops_get(iter->fops); 150 break; 151 } 152 153 if (!new_fops) { 154 mutex_unlock(&misc_mtx); 155 request_module("char-major-%d-%d", MISC_MAJOR, minor); 156 mutex_lock(&misc_mtx); 157 158 list_for_each_entry(iter, &misc_list, list) { 159 if (iter->minor != minor) 160 continue; 161 c = iter; 162 new_fops = fops_get(iter->fops); 163 break; 164 } 165 if (!new_fops) 166 goto fail; 167 } 168 169 /* 170 * Place the miscdevice in the file's 171 * private_data so it can be used by the 172 * file operations, including f_op->open below 173 */ 174 file->private_data = c; 175 176 err = 0; 177 replace_fops(file, new_fops); 178 if (file->f_op->open) 179 err = file->f_op->open(inode, file); 180 fail: 181 mutex_unlock(&misc_mtx); 182 return err; 183 } 184 185 static char *misc_devnode(const struct device *dev, umode_t *mode) 186 { 187 const struct miscdevice *c = dev_get_drvdata(dev); 188 189 if (mode && c->mode) 190 *mode = c->mode; 191 if (c->nodename) 192 return kstrdup(c->nodename, GFP_KERNEL); 193 return NULL; 194 } 195 196 static const struct class misc_class = { 197 .name = "misc", 198 .devnode = misc_devnode, 199 }; 200 201 static const struct file_operations misc_fops = { 202 .owner = THIS_MODULE, 203 .open = misc_open, 204 .llseek = noop_llseek, 205 }; 206 207 /** 208 * misc_register - register a miscellaneous device 209 * @misc: device structure 210 * 211 * Register a miscellaneous device with the kernel. If the minor 212 * number is set to %MISC_DYNAMIC_MINOR a minor number is assigned 213 * and placed in the minor field of the structure. For other cases 214 * the minor number requested is used. 215 * 216 * The structure passed is linked into the kernel and may not be 217 * destroyed until it has been unregistered. By default, an open() 218 * syscall to the device sets file->private_data to point to the 219 * structure. Drivers don't need open in fops for this. 220 * 221 * A zero is returned on success and a negative errno code for 222 * failure. 223 */ 224 225 int misc_register(struct miscdevice *misc) 226 { 227 dev_t dev; 228 int err = 0; 229 bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR); 230 231 INIT_LIST_HEAD(&misc->list); 232 233 mutex_lock(&misc_mtx); 234 235 if (is_dynamic) { 236 int i = misc_minor_alloc(misc->minor); 237 238 if (i < 0) { 239 err = -EBUSY; 240 goto out; 241 } 242 misc->minor = i; 243 } else { 244 struct miscdevice *c; 245 int i; 246 247 list_for_each_entry(c, &misc_list, list) { 248 if (c->minor == misc->minor) { 249 err = -EBUSY; 250 goto out; 251 } 252 } 253 254 i = misc_minor_alloc(misc->minor); 255 if (i < 0) { 256 err = -EBUSY; 257 goto out; 258 } 259 } 260 261 dev = MKDEV(MISC_MAJOR, misc->minor); 262 263 misc->this_device = 264 device_create_with_groups(&misc_class, misc->parent, dev, 265 misc, misc->groups, "%s", misc->name); 266 if (IS_ERR(misc->this_device)) { 267 misc_minor_free(misc->minor); 268 if (is_dynamic) { 269 misc->minor = MISC_DYNAMIC_MINOR; 270 } 271 err = PTR_ERR(misc->this_device); 272 goto out; 273 } 274 275 /* 276 * Add it to the front, so that later devices can "override" 277 * earlier defaults 278 */ 279 list_add(&misc->list, &misc_list); 280 out: 281 mutex_unlock(&misc_mtx); 282 return err; 283 } 284 EXPORT_SYMBOL(misc_register); 285 286 /** 287 * misc_deregister - unregister a miscellaneous device 288 * @misc: device to unregister 289 * 290 * Unregister a miscellaneous device that was previously 291 * successfully registered with misc_register(). 292 */ 293 294 void misc_deregister(struct miscdevice *misc) 295 { 296 if (WARN_ON(list_empty(&misc->list))) 297 return; 298 299 mutex_lock(&misc_mtx); 300 list_del(&misc->list); 301 device_destroy(&misc_class, MKDEV(MISC_MAJOR, misc->minor)); 302 misc_minor_free(misc->minor); 303 mutex_unlock(&misc_mtx); 304 } 305 EXPORT_SYMBOL(misc_deregister); 306 307 static int __init misc_init(void) 308 { 309 int err; 310 struct proc_dir_entry *ret; 311 312 ret = proc_create_seq("misc", 0, NULL, &misc_seq_ops); 313 err = class_register(&misc_class); 314 if (err) 315 goto fail_remove; 316 317 err = -EIO; 318 if (register_chrdev(MISC_MAJOR, "misc", &misc_fops)) 319 goto fail_printk; 320 return 0; 321 322 fail_printk: 323 pr_err("unable to get major %d for misc devices\n", MISC_MAJOR); 324 class_unregister(&misc_class); 325 fail_remove: 326 if (ret) 327 remove_proc_entry("misc", NULL); 328 return err; 329 } 330 subsys_initcall(misc_init); 331