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/module.h>
  16 #include <linux/raw.h>
  17 #include <linux/capability.h>
  18 #include <linux/uio.h>
  19 #include <linux/cdev.h>
  20 #include <linux/device.h>
  21 #include <linux/mutex.h>
  22 #include <linux/gfp.h>
  23 #include <linux/compat.h>
  24
  25 #include <asm/uaccess.h>
  26
  27 struct raw_device_data {
  28         struct block_device *binding;
  29         int inuse;
  30 };
  31
  32 static struct class *raw_class;
  33 static struct raw_device_data raw_devices[MAX_RAW_MINORS];
  34 static DEFINE_MUTEX(raw_mutex);
  35 static const struct file_operations raw_ctl_fops; /* forward declaration */
  36
  37 /*
  38  * Open/close code for raw IO.
  39  *
  40  * We just rewrite the i_mapping for the /dev/raw/rawN file descriptor to
  41  * point at the blockdev's address_space and set the file handle to use
  42  * O_DIRECT.
  43  *
  44  * Set the device's soft blocksize to the minimum possible.  This gives the
  45  * finest possible alignment and has no adverse impact on performance.
  46  */
  47 static int raw_open(struct inode *inode, struct file *filp)
  48 {
  49         const int minor = iminor(inode);
  50         struct block_device *bdev;
  51         int err;
  52
  53         if (minor == 0) {       /* It is the control device */
  54                 filp->f_op = &raw_ctl_fops;
  55                 return 0;
  56         }
  57
  58         mutex_lock(&raw_mutex);
  59
  60         /*
  61          * All we need to do on open is check that the device is bound.
  62          */
  63         bdev = raw_devices[minor].binding;
  64         err = -ENODEV;
  65         if (!bdev)
  66                 goto out;
  67         igrab(bdev->bd_inode);
  68         err = blkdev_get(bdev, filp->f_mode);
  69         if (err)
  70                 goto out;
  71         err = bd_claim(bdev, raw_open);
  72         if (err)
  73                 goto out1;
  74         err = set_blocksize(bdev, bdev_logical_block_size(bdev));
  75         if (err)
  76                 goto out2;
  77         filp->f_flags |= O_DIRECT;
  78         filp->f_mapping = bdev->bd_inode->i_mapping;
  79         if (++raw_devices[minor].inuse == 1)
  80                 filp->f_path.dentry->d_inode->i_mapping =
  81                         bdev->bd_inode->i_mapping;
  82         filp->private_data = bdev;
  83         mutex_unlock(&raw_mutex);
  84         return 0;
  85
  86 out2:
  87         bd_release(bdev);
  88 out1:
  89         blkdev_put(bdev, filp->f_mode);
  90 out:
  91         mutex_unlock(&raw_mutex);
  92         return err;
  93 }
  94
  95 /*
  96  * When the final fd which refers to this character-special node is closed, we
  97  * make its ->mapping point back at its own i_data.
  98  */
  99 static int raw_release(struct inode *inode, struct file *filp)
 100 {
 101         const int minor= iminor(inode);
 102         struct block_device *bdev;
 103
 104         mutex_lock(&raw_mutex);
 105         bdev = raw_devices[minor].binding;
 106         if (--raw_devices[minor].inuse == 0) {
 107                 /* Here  inode->i_mapping == bdev->bd_inode->i_mapping  */
 108                 inode->i_mapping = &inode->i_data;
 109                 inode->i_mapping->backing_dev_info = &default_backing_dev_info;
 110         }
 111         mutex_unlock(&raw_mutex);
 112
 113         bd_release(bdev);
 114         blkdev_put(bdev, filp->f_mode);
 115         return 0;
 116 }
 117
 118 /*
 119  * Forward ioctls to the underlying block device.
 120  */
 121 static long
 122 raw_ioctl(struct file *filp, unsigned int command, unsigned long arg)
 123 {
 124         struct block_device *bdev = filp->private_data;
 125         return blkdev_ioctl(bdev, 0, command, arg);
 126 }
 127
 128 static int bind_set(int number, u64 major, u64 minor)
 129 {
 130         dev_t dev = MKDEV(major, minor);
 131         struct raw_device_data *rawdev;
 132         int err = 0;
 133
 134         if (number <= 0 || number >= MAX_RAW_MINORS)
 135                 return -EINVAL;
 136
 137         if (MAJOR(dev) != major || MINOR(dev) != minor)
 138                 return -EINVAL;
 139
 140         rawdev = &raw_devices[number];
 141
 142         /*
 143          * This is like making block devices, so demand the
 144          * same capability
 145          */
 146         if (!capable(CAP_SYS_ADMIN))
 147                 return -EPERM;
 148
 149         /*
 150          * For now, we don't need to check that the underlying
 151          * block device is present or not: we can do that when
 152          * the raw device is opened.  Just check that the
 153          * major/minor numbers make sense.
 154          */
 155
 156         if (MAJOR(dev) == 0 && dev != 0)
 157                 return -EINVAL;
 158
 159         mutex_lock(&raw_mutex);
 160         if (rawdev->inuse) {
 161                 mutex_unlock(&raw_mutex);
 162                 return -EBUSY;
 163         }
 164         if (rawdev->binding) {
 165                 bdput(rawdev->binding);
 166                 module_put(THIS_MODULE);
 167         }
 168         if (!dev) {
 169                 /* unbind */
 170                 rawdev->binding = NULL;
 171                 device_destroy(raw_class, MKDEV(RAW_MAJOR, number));
 172         } else {
 173                 rawdev->binding = bdget(dev);
 174                 if (rawdev->binding == NULL) {
 175                         err = -ENOMEM;
 176                 } else {
 177                         dev_t raw = MKDEV(RAW_MAJOR, number);
 178                         __module_get(THIS_MODULE);
 179                         device_destroy(raw_class, raw);
 180                         device_create(raw_class, NULL, raw, NULL,
 181                                       "raw%d", number);
 182                 }
 183         }
 184         mutex_unlock(&raw_mutex);
 185         return err;
 186 }
 187
 188 static int bind_get(int number, dev_t *dev)
 189 {
 190         struct raw_device_data *rawdev;
 191         struct block_device *bdev;
 192
 193         if (number <= 0 || number >= MAX_RAW_MINORS)
 194                 return -EINVAL;
 195
 196         rawdev = &raw_devices[number];
 197
 198         mutex_lock(&raw_mutex);
 199         bdev = rawdev->binding;
 200         *dev = bdev ? bdev->bd_dev : 0;
 201         mutex_unlock(&raw_mutex);
 202         return 0;
 203 }
 204
 205 /*
 206  * Deal with ioctls against the raw-device control interface, to bind
 207  * and unbind other raw devices.
 208  */
 209 static long raw_ctl_ioctl(struct file *filp, unsigned int command,
 210                           unsigned long arg)
 211 {
 212         struct raw_config_request rq;
 213         dev_t dev;
 214         int err;
 215
 216         switch (command) {
 217         case RAW_SETBIND:
 218                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
 219                         return -EFAULT;
 220
 221                 return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);
 222
 223         case RAW_GETBIND:
 224                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
 225                         return -EFAULT;
 226
 227                 err = bind_get(rq.raw_minor, &dev);
 228                 if (err)
 229                         return err;
 230
 231                 rq.block_major = MAJOR(dev);
 232                 rq.block_minor = MINOR(dev);
 233
 234                 if (copy_to_user((void __user *)arg, &rq, sizeof(rq)))
 235                         return -EFAULT;
 236
 237                 return 0;
 238         }
 239
 240         return -EINVAL;
 241 }
 242
 243 #ifdef CONFIG_COMPAT
 244 struct raw32_config_request {
 245         compat_int_t    raw_minor;
 246         compat_u64      block_major;
 247         compat_u64      block_minor;
 248 };
 249
 250 static long raw_ctl_compat_ioctl(struct file *file, unsigned int cmd,
 251                                 unsigned long arg)
 252 {
 253         struct raw32_config_request __user *user_req = compat_ptr(arg);
 254         struct raw32_config_request rq;
 255         dev_t dev;
 256         int err = 0;
 257
 258         switch (cmd) {
 259         case RAW_SETBIND:
 260                 if (copy_from_user(&rq, user_req, sizeof(rq)))
 261                         return -EFAULT;
 262
 263                 return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);
 264
 265         case RAW_GETBIND:
 266                 if (copy_from_user(&rq, user_req, sizeof(rq)))
 267                         return -EFAULT;
 268
 269                 err = bind_get(rq.raw_minor, &dev);
 270                 if (err)
 271                         return err;
 272
 273                 rq.block_major = MAJOR(dev);
 274                 rq.block_minor = MINOR(dev);
 275
 276                 if (copy_to_user(user_req, &rq, sizeof(rq)))
 277                         return -EFAULT;
 278
 279                 return 0;
 280         }
 281
 282         return -EINVAL;
 283 }
 284 #endif
 285
 286 static const struct file_operations raw_fops = {
 287         .read           = do_sync_read,
 288         .aio_read       = generic_file_aio_read,
 289         .write          = do_sync_write,
 290         .aio_write      = blkdev_aio_write,
 291         .fsync          = blkdev_fsync,
 292         .open           = raw_open,
 293         .release        = raw_release,
 294         .unlocked_ioctl = raw_ioctl,
 295         .owner          = THIS_MODULE,
 296 };
 297
 298 static const struct file_operations raw_ctl_fops = {
 299         .unlocked_ioctl = raw_ctl_ioctl,
 300 #ifdef CONFIG_COMPAT
 301         .compat_ioctl   = raw_ctl_compat_ioctl,
 302 #endif
 303         .open           = raw_open,
 304         .owner          = THIS_MODULE,
 305 };
 306
 307 static struct cdev raw_cdev;
 308
 309 static char *raw_devnode(struct device *dev, mode_t *mode)
 310 {
 311         return kasprintf(GFP_KERNEL, "raw/%s", dev_name(dev));
 312 }
 313
 314 static int __init raw_init(void)
 315 {
 316         dev_t dev = MKDEV(RAW_MAJOR, 0);
 317         int ret;
 318
 319         ret = register_chrdev_region(dev, MAX_RAW_MINORS, "raw");
 320         if (ret)
 321                 goto error;
 322
 323         cdev_init(&raw_cdev, &raw_fops);
 324         ret = cdev_add(&raw_cdev, dev, MAX_RAW_MINORS);
 325         if (ret) {
 326                 kobject_put(&raw_cdev.kobj);
 327                 goto error_region;
 328         }
 329
 330         raw_class = class_create(THIS_MODULE, "raw");
 331         if (IS_ERR(raw_class)) {
 332                 printk(KERN_ERR "Error creating raw class.\n");
 333                 cdev_del(&raw_cdev);
 334                 ret = PTR_ERR(raw_class);
 335                 goto error_region;
 336         }
 337         raw_class->devnode = raw_devnode;
 338         device_create(raw_class, NULL, MKDEV(RAW_MAJOR, 0), NULL, "rawctl");
 339
 340         return 0;
 341
 342 error_region:
 343         unregister_chrdev_region(dev, MAX_RAW_MINORS);
 344 error:
 345         return ret;
 346 }
 347
 348 static void __exit raw_exit(void)
 349 {
 350         device_destroy(raw_class, MKDEV(RAW_MAJOR, 0));
 351         class_destroy(raw_class);
 352         cdev_del(&raw_cdev);
 353         unregister_chrdev_region(MKDEV(RAW_MAJOR, 0), MAX_RAW_MINORS);
 354 }
 355
 356 module_init(raw_init);
 357 module_exit(raw_exit);
 358 MODULE_LICENSE("GPL");