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(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 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 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 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 } 99 100 static void misc_seq_stop(struct seq_file *seq, void *v) 101 { 102 mutex_unlock(&misc_mtx); 103 } 104 105 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 121 122 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 } 170 171 static struct class *misc_class; 172 173 static const struct file_operations misc_fops = { 174 .owner = THIS_MODULE, 175 .open = misc_open, 176 .llseek = noop_llseek, 177 }; 178 179 /** 180 * misc_register - register a miscellaneous device 181 * @misc: device structure 182 * 183 * Register a miscellaneous device with the kernel. If the minor 184 * number is set to %MISC_DYNAMIC_MINOR a minor number is assigned 185 * and placed in the minor field of the structure. For other cases 186 * the minor number requested is used. 187 * 188 * The structure passed is linked into the kernel and may not be 189 * destroyed until it has been unregistered. By default, an open() 190 * syscall to the device sets file->private_data to point to the 191 * structure. Drivers don't need open in fops for this. 192 * 193 * A zero is returned on success and a negative errno code for 194 * failure. 195 */ 196 197 int misc_register(struct miscdevice *misc) 198 { 199 dev_t dev; 200 int err = 0; 201 bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR); 202 203 INIT_LIST_HEAD(&misc->list); 204 205 mutex_lock(&misc_mtx); 206 207 if (is_dynamic) { 208 int i = misc_minor_alloc(); 209 210 if (i < 0) { 211 err = -EBUSY; 212 goto out; 213 } 214 misc->minor = i; 215 } else { 216 struct miscdevice *c; 217 218 list_for_each_entry(c, &misc_list, list) { 219 if (c->minor == misc->minor) { 220 err = -EBUSY; 221 goto out; 222 } 223 } 224 } 225 226 dev = MKDEV(MISC_MAJOR, misc->minor); 227 228 misc->this_device = 229 device_create_with_groups(misc_class, misc->parent, dev, 230 misc, misc->groups, "%s", misc->name); 231 if (IS_ERR(misc->this_device)) { 232 if (is_dynamic) { 233 misc_minor_free(misc->minor); 234 misc->minor = MISC_DYNAMIC_MINOR; 235 } 236 err = PTR_ERR(misc->this_device); 237 goto out; 238 } 239 240 /* 241 * Add it to the front, so that later devices can "override" 242 * earlier defaults 243 */ 244 list_add(&misc->list, &misc_list); 245 out: 246 mutex_unlock(&misc_mtx); 247 return err; 248 } 249 EXPORT_SYMBOL(misc_register); 250 251 /** 252 * misc_deregister - unregister a miscellaneous device 253 * @misc: device to unregister 254 * 255 * Unregister a miscellaneous device that was previously 256 * successfully registered with misc_register(). 257 */ 258 259 void misc_deregister(struct miscdevice *misc) 260 { 261 if (WARN_ON(list_empty(&misc->list))) 262 return; 263 264 mutex_lock(&misc_mtx); 265 list_del(&misc->list); 266 device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor)); 267 misc_minor_free(misc->minor); 268 mutex_unlock(&misc_mtx); 269 } 270 EXPORT_SYMBOL(misc_deregister); 271 272 static char *misc_devnode(const struct device *dev, umode_t *mode) 273 { 274 const struct miscdevice *c = dev_get_drvdata(dev); 275 276 if (mode && c->mode) 277 *mode = c->mode; 278 if (c->nodename) 279 return kstrdup(c->nodename, GFP_KERNEL); 280 return NULL; 281 } 282 283 static int __init misc_init(void) 284 { 285 int err; 286 struct proc_dir_entry *ret; 287 288 ret = proc_create_seq("misc", 0, NULL, &misc_seq_ops); 289 misc_class = class_create("misc"); 290 err = PTR_ERR(misc_class); 291 if (IS_ERR(misc_class)) 292 goto fail_remove; 293 294 err = -EIO; 295 if (register_chrdev(MISC_MAJOR, "misc", &misc_fops)) 296 goto fail_printk; 297 misc_class->devnode = misc_devnode; 298 return 0; 299 300 fail_printk: 301 pr_err("unable to get major %d for misc devices\n", MISC_MAJOR); 302 class_destroy(misc_class); 303 fail_remove: 304 if (ret) 305 remove_proc_entry("misc", NULL); 306 return err; 307 } 308 subsys_initcall(misc_init); 309