drivers/char/raw.c

   1 /*
   2  * linux/drivers/char/raw.c
   3  *
   4  * Front-end raw character devices.  These can be bound to any block
   5  * devices to provide genuine Unix raw character device semantics.
   6  *
   7  * We reserve minor number 0 for a control interface.  ioctl()s on this
   8  * device are used to bind the other minor numbers to block devices.
   9  */
  10
  11 #include <linux/init.h>
  12 #include <linux/fs.h>
  13 #include <linux/major.h>
  14 #include <linux/blkdev.h>
  15 #include <linux/backing-dev.h>
  16 #include <linux/module.h>
  17 #include <linux/raw.h>
  18 #include <linux/capability.h>
  19 #include <linux/uio.h>
  20 #include <linux/cdev.h>
  21 #include <linux/device.h>
  22 #include <linux/mutex.h>
  23 #include <linux/gfp.h>
  24 #include <linux/compat.h>
  25 #include <linux/vmalloc.h>
  26
  27 #include <asm/uaccess.h>
  28
  29 struct raw_device_data {
  30         struct block_device *binding;
  31         int inuse;
  32 };
  33
  34 static struct class *raw_class;
  35 static struct raw_device_data *raw_devices;
  36 static DEFINE_MUTEX(raw_mutex);
  37 static const struct file_operations raw_ctl_fops; /* forward declaration */
  38
  39 static int max_raw_minors = MAX_RAW_MINORS;
  40
  41 module_param(max_raw_minors, int, 0);
  42 MODULE_PARM_DESC(max_raw_minors, "Maximum number of raw devices (1-65536)");
  43
  44 /*
  45  * Open/close code for raw IO.
  46  *
  47  * We just rewrite the i_mapping for the /dev/raw/rawN file descriptor to
  48  * point at the blockdev's address_space and set the file handle to use
  49  * O_DIRECT.
  50  *
  51  * Set the device's soft blocksize to the minimum possible.  This gives the
  52  * finest possible alignment and has no adverse impact on performance.
  53  */
  54 static int raw_open(struct inode *inode, struct file *filp)
  55 {
  56         const int minor = iminor(inode);
  57         struct block_device *bdev;
  58         int err;
  59
  60         if (minor == 0) {       /* It is the control device */
  61                 filp->f_op = &raw_ctl_fops;
  62                 return 0;
  63         }
  64
  65         mutex_lock(&raw_mutex);
  66
  67         /*
  68          * All we need to do on open is check that the device is bound.
  69          */
  70         bdev = raw_devices[minor].binding;
  71         err = -ENODEV;
  72         if (!bdev)
  73                 goto out;
  74         igrab(bdev->bd_inode);
  75         err = blkdev_get(bdev, filp->f_mode | FMODE_EXCL, raw_open);
  76         if (err)
  77                 goto out;
  78         err = set_blocksize(bdev, bdev_logical_block_size(bdev));
  79         if (err)
  80                 goto out1;
  81         filp->f_flags |= O_DIRECT;
  82         filp->f_mapping = bdev->bd_inode->i_mapping;
  83         if (++raw_devices[minor].inuse == 1)
  84                 file_inode(filp)->i_mapping =
  85                         bdev->bd_inode->i_mapping;
  86         filp->private_data = bdev;
  87         mutex_unlock(&raw_mutex);
  88         return 0;
  89
  90 out1:
  91         blkdev_put(bdev, filp->f_mode | FMODE_EXCL);
  92 out:
  93         mutex_unlock(&raw_mutex);
  94         return err;
  95 }
  96
  97 /*
  98  * When the final fd which refers to this character-special node is closed, we
  99  * make its ->mapping point back at its own i_data.
 100  */
 101 static int raw_release(struct inode *inode, struct file *filp)
 102 {
 103         const int minor= iminor(inode);
 104         struct block_device *bdev;
 105
 106         mutex_lock(&raw_mutex);
 107         bdev = raw_devices[minor].binding;
 108         if (--raw_devices[minor].inuse == 0)
 109                 /* Here  inode->i_mapping == bdev->bd_inode->i_mapping  */
 110                 inode->i_mapping = &inode->i_data;
 111         mutex_unlock(&raw_mutex);
 112
 113         blkdev_put(bdev, filp->f_mode | FMODE_EXCL);
 114         return 0;
 115 }
 116
 117 /*
 118  * Forward ioctls to the underlying block device.
 119  */
 120 static long
 121 raw_ioctl(struct file *filp, unsigned int command, unsigned long arg)
 122 {
 123         struct block_device *bdev = filp->private_data;
 124         return blkdev_ioctl(bdev, 0, command, arg);
 125 }
 126
 127 static int bind_set(int number, u64 major, u64 minor)
 128 {
 129         dev_t dev = MKDEV(major, minor);
 130         struct raw_device_data *rawdev;
 131         int err = 0;
 132
 133         if (number <= 0 || number >= max_raw_minors)
 134                 return -EINVAL;
 135
 136         if (MAJOR(dev) != major || MINOR(dev) != minor)
 137                 return -EINVAL;
 138
 139         rawdev = &raw_devices[number];
 140
 141         /*
 142          * This is like making block devices, so demand the
 143          * same capability
 144          */
 145         if (!capable(CAP_SYS_ADMIN))
 146                 return -EPERM;
 147
 148         /*
 149          * For now, we don't need to check that the underlying
 150          * block device is present or not: we can do that when
 151          * the raw device is opened.  Just check that the
 152          * major/minor numbers make sense.
 153          */
 154
 155         if (MAJOR(dev) == 0 && dev != 0)
 156                 return -EINVAL;
 157
 158         mutex_lock(&raw_mutex);
 159         if (rawdev->inuse) {
 160                 mutex_unlock(&raw_mutex);
 161                 return -EBUSY;
 162         }
 163         if (rawdev->binding) {
 164                 bdput(rawdev->binding);
 165                 module_put(THIS_MODULE);
 166         }
 167         if (!dev) {
 168                 /* unbind */
 169                 rawdev->binding = NULL;
 170                 device_destroy(raw_class, MKDEV(RAW_MAJOR, number));
 171         } else {
 172                 rawdev->binding = bdget(dev);
 173                 if (rawdev->binding == NULL) {
 174                         err = -ENOMEM;
 175                 } else {
 176                         dev_t raw = MKDEV(RAW_MAJOR, number);
 177                         __module_get(THIS_MODULE);
 178                         device_destroy(raw_class, raw);
 179                         device_create(raw_class, NULL, raw, NULL,
 180                                       "raw%d", number);
 181                 }
 182         }
 183         mutex_unlock(&raw_mutex);
 184         return err;
 185 }
 186
 187 static int bind_get(int number, dev_t *dev)
 188 {
 189         struct raw_device_data *rawdev;
 190         struct block_device *bdev;
 191
 192         if (number <= 0 || number >= max_raw_minors)
 193                 return -EINVAL;
 194
 195         rawdev = &raw_devices[number];
 196
 197         mutex_lock(&raw_mutex);
 198         bdev = rawdev->binding;
 199         *dev = bdev ? bdev->bd_dev : 0;
 200         mutex_unlock(&raw_mutex);
 201         return 0;
 202 }
 203
 204 /*
 205  * Deal with ioctls against the raw-device control interface, to bind
 206  * and unbind other raw devices.
 207  */
 208 static long raw_ctl_ioctl(struct file *filp, unsigned int command,
 209                           unsigned long arg)
 210 {
 211         struct raw_config_request rq;
 212         dev_t dev;
 213         int err;
 214
 215         switch (command) {
 216         case RAW_SETBIND:
 217                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
 218                         return -EFAULT;
 219
 220                 return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);
 221
 222         case RAW_GETBIND:
 223                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
 224                         return -EFAULT;
 225
 226                 err = bind_get(rq.raw_minor, &dev);
 227                 if (err)
 228                         return err;
 229
 230                 rq.block_major = MAJOR(dev);
 231                 rq.block_minor = MINOR(dev);
 232
 233                 if (copy_to_user((void __user *)arg, &rq, sizeof(rq)))
 234                         return -EFAULT;
 235
 236                 return 0;
 237         }
 238
 239         return -EINVAL;
 240 }
 241
 242 #ifdef CONFIG_COMPAT
 243 struct raw32_config_request {
 244         compat_int_t    raw_minor;
 245         compat_u64      block_major;
 246         compat_u64      block_minor;
 247 };
 248
 249 static long raw_ctl_compat_ioctl(struct file *file, unsigned int cmd,
 250                                 unsigned long arg)
 251 {
 252         struct raw32_config_request __user *user_req = compat_ptr(arg);
 253         struct raw32_config_request rq;
 254         dev_t dev;
 255         int err = 0;
 256
 257         switch (cmd) {
 258         case RAW_SETBIND:
 259                 if (copy_from_user(&rq, user_req, sizeof(rq)))
 260                         return -EFAULT;
 261
 262                 return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);
 263
 264         case RAW_GETBIND:
 265                 if (copy_from_user(&rq, user_req, sizeof(rq)))
 266                         return -EFAULT;
 267
 268                 err = bind_get(rq.raw_minor, &dev);
 269                 if (err)
 270                         return err;
 271
 272                 rq.block_major = MAJOR(dev);
 273                 rq.block_minor = MINOR(dev);
 274
 275                 if (copy_to_user(user_req, &rq, sizeof(rq)))
 276                         return -EFAULT;
 277
 278                 return 0;
 279         }
 280
 281         return -EINVAL;
 282 }
 283 #endif
 284
 285 static const struct file_operations raw_fops = {
 286         .read_iter      = blkdev_read_iter,
 287         .write_iter     = blkdev_write_iter,
 288         .fsync          = blkdev_fsync,
 289         .open           = raw_open,
 290         .release        = raw_release,
 291         .unlocked_ioctl = raw_ioctl,
 292         .llseek         = default_llseek,
 293         .owner          = THIS_MODULE,
 294 };
 295
 296 static const struct file_operations raw_ctl_fops = {
 297         .unlocked_ioctl = raw_ctl_ioctl,
 298 #ifdef CONFIG_COMPAT
 299         .compat_ioctl   = raw_ctl_compat_ioctl,
 300 #endif
 301         .open           = raw_open,
 302         .owner          = THIS_MODULE,
 303         .llseek         = noop_llseek,
 304 };
 305
 306 static struct cdev raw_cdev;
 307
 308 static char *raw_devnode(struct device *dev, umode_t *mode)
 309 {
 310         return kasprintf(GFP_KERNEL, "raw/%s", dev_name(dev));
 311 }
 312
 313 static int __init raw_init(void)
 314 {
 315         dev_t dev = MKDEV(RAW_MAJOR, 0);
 316         int ret;
 317
 318         if (max_raw_minors < 1 || max_raw_minors > 65536) {
 319                 printk(KERN_WARNING "raw: invalid max_raw_minors (must be"
 320                         " between 1 and 65536), using %d\n", MAX_RAW_MINORS);
 321                 max_raw_minors = MAX_RAW_MINORS;
 322         }
 323
 324         raw_devices = vzalloc(sizeof(struct raw_device_data) * max_raw_minors);
 325         if (!raw_devices) {
 326                 printk(KERN_ERR "Not enough memory for raw device structures\n");
 327                 ret = -ENOMEM;
 328                 goto error;
 329         }
 330
 331         ret = register_chrdev_region(dev, max_raw_minors, "raw");
 332         if (ret)
 333                 goto error;
 334
 335         cdev_init(&raw_cdev, &raw_fops);
 336         ret = cdev_add(&raw_cdev, dev, max_raw_minors);
 337         if (ret) {
 338                 goto error_region;
 339         }
 340
 341         raw_class = class_create(THIS_MODULE, "raw");
 342         if (IS_ERR(raw_class)) {
 343                 printk(KERN_ERR "Error creating raw class.\n");
 344                 cdev_del(&raw_cdev);
 345                 ret = PTR_ERR(raw_class);
 346                 goto error_region;
 347         }
 348         raw_class->devnode = raw_devnode;
 349         device_create(raw_class, NULL, MKDEV(RAW_MAJOR, 0), NULL, "rawctl");
 350
 351         return 0;
 352
 353 error_region:
 354         unregister_chrdev_region(dev, max_raw_minors);
 355 error:
 356         vfree(raw_devices);
 357         return ret;
 358 }
 359
 360 static void __exit raw_exit(void)
 361 {
 362         device_destroy(raw_class, MKDEV(RAW_MAJOR, 0));
 363         class_destroy(raw_class);
 364         cdev_del(&raw_cdev);
 365         unregister_chrdev_region(MKDEV(RAW_MAJOR, 0), max_raw_minors);
 366 }
 367
 368 module_init(raw_init);
 369 module_exit(raw_exit);
 370 MODULE_LICENSE("GPL");