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