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/smp_lock.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         lock_kernel();
  59         mutex_lock(&raw_mutex);
  60
  61         /*
  62          * All we need to do on open is check that the device is bound.
  63          */
  64         bdev = raw_devices[minor].binding;
  65         err = -ENODEV;
  66         if (!bdev)
  67                 goto out;
  68         igrab(bdev->bd_inode);
  69         err = blkdev_get(bdev, filp->f_mode);
  70         if (err)
  71                 goto out;
  72         err = bd_claim(bdev, raw_open);
  73         if (err)
  74                 goto out1;
  75         err = set_blocksize(bdev, bdev_logical_block_size(bdev));
  76         if (err)
  77                 goto out2;
  78         filp->f_flags |= O_DIRECT;
  79         filp->f_mapping = bdev->bd_inode->i_mapping;
  80         if (++raw_devices[minor].inuse == 1)
  81                 filp->f_path.dentry->d_inode->i_mapping =
  82                         bdev->bd_inode->i_mapping;
  83         filp->private_data = bdev;
  84         mutex_unlock(&raw_mutex);
  85         unlock_kernel();
  86         return 0;
  87
  88 out2:
  89         bd_release(bdev);
  90 out1:
  91         blkdev_put(bdev, filp->f_mode);
  92 out:
  93         mutex_unlock(&raw_mutex);
  94         unlock_kernel();
  95         return err;
  96 }
  97
  98 /*
  99  * When the final fd which refers to this character-special node is closed, we
 100  * make its ->mapping point back at its own i_data.
 101  */
 102 static int raw_release(struct inode *inode, struct file *filp)
 103 {
 104         const int minor= iminor(inode);
 105         struct block_device *bdev;
 106
 107         mutex_lock(&raw_mutex);
 108         bdev = raw_devices[minor].binding;
 109         if (--raw_devices[minor].inuse == 0) {
 110                 /* Here  inode->i_mapping == bdev->bd_inode->i_mapping  */
 111                 inode->i_mapping = &inode->i_data;
 112                 inode->i_mapping->backing_dev_info = &default_backing_dev_info;
 113         }
 114         mutex_unlock(&raw_mutex);
 115
 116         bd_release(bdev);
 117         blkdev_put(bdev, filp->f_mode);
 118         return 0;
 119 }
 120
 121 /*
 122  * Forward ioctls to the underlying block device.
 123  */
 124 static int
 125 raw_ioctl(struct inode *inode, struct file *filp,
 126                   unsigned int command, unsigned long arg)
 127 {
 128         struct block_device *bdev = filp->private_data;
 129
 130         return blkdev_ioctl(bdev, 0, command, arg);
 131 }
 132
 133 static int bind_set(int number, u64 major, u64 minor)
 134 {
 135         dev_t dev = MKDEV(major, minor);
 136         struct raw_device_data *rawdev;
 137         int err = 0;
 138
 139         if (number <= 0 || number >= MAX_RAW_MINORS)
 140                 return -EINVAL;
 141
 142         if (MAJOR(dev) != major || MINOR(dev) != minor)
 143                 return -EINVAL;
 144
 145         rawdev = &raw_devices[number];
 146
 147         /*
 148          * This is like making block devices, so demand the
 149          * same capability
 150          */
 151         if (!capable(CAP_SYS_ADMIN))
 152                 return -EPERM;
 153
 154         /*
 155          * For now, we don't need to check that the underlying
 156          * block device is present or not: we can do that when
 157          * the raw device is opened.  Just check that the
 158          * major/minor numbers make sense.
 159          */
 160
 161         if (MAJOR(dev) == 0 && dev != 0)
 162                 return -EINVAL;
 163
 164         mutex_lock(&raw_mutex);
 165         if (rawdev->inuse) {
 166                 mutex_unlock(&raw_mutex);
 167                 return -EBUSY;
 168         }
 169         if (rawdev->binding) {
 170                 bdput(rawdev->binding);
 171                 module_put(THIS_MODULE);
 172         }
 173         if (!dev) {
 174                 /* unbind */
 175                 rawdev->binding = NULL;
 176                 device_destroy(raw_class, MKDEV(RAW_MAJOR, number));
 177         } else {
 178                 rawdev->binding = bdget(dev);
 179                 if (rawdev->binding == NULL) {
 180                         err = -ENOMEM;
 181                 } else {
 182                         dev_t raw = MKDEV(RAW_MAJOR, number);
 183                         __module_get(THIS_MODULE);
 184                         device_destroy(raw_class, raw);
 185                         device_create(raw_class, NULL, raw, NULL,
 186                                       "raw%d", number);
 187                 }
 188         }
 189         mutex_unlock(&raw_mutex);
 190         return err;
 191 }
 192
 193 static int bind_get(int number, dev_t *dev)
 194 {
 195         struct raw_device_data *rawdev;
 196         struct block_device *bdev;
 197
 198         if (number <= 0 || number >= MAX_RAW_MINORS)
 199                 return -EINVAL;
 200
 201         rawdev = &raw_devices[number];
 202
 203         mutex_lock(&raw_mutex);
 204         bdev = rawdev->binding;
 205         *dev = bdev ? bdev->bd_dev : 0;
 206         mutex_unlock(&raw_mutex);
 207         return 0;
 208 }
 209
 210 /*
 211  * Deal with ioctls against the raw-device control interface, to bind
 212  * and unbind other raw devices.
 213  */
 214 static int raw_ctl_ioctl(struct inode *inode, struct file *filp,
 215                         unsigned int command, unsigned long arg)
 216 {
 217         struct raw_config_request rq;
 218         dev_t dev;
 219         int err;
 220
 221         switch (command) {
 222         case RAW_SETBIND:
 223                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
 224                         return -EFAULT;
 225
 226                 return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);
 227
 228         case RAW_GETBIND:
 229                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
 230                         return -EFAULT;
 231
 232                 err = bind_get(rq.raw_minor, &dev);
 233                 if (err)
 234                         return err;
 235
 236                 rq.block_major = MAJOR(dev);
 237                 rq.block_minor = MINOR(dev);
 238
 239                 if (copy_to_user((void __user *)arg, &rq, sizeof(rq)))
 240                         return -EFAULT;
 241
 242                 return 0;
 243         }
 244
 245         return -EINVAL;
 246 }
 247
 248 #ifdef CONFIG_COMPAT
 249 struct raw32_config_request {
 250         compat_int_t    raw_minor;
 251         compat_u64      block_major;
 252         compat_u64      block_minor;
 253 };
 254
 255 static long raw_ctl_compat_ioctl(struct file *file, unsigned int cmd,
 256                                 unsigned long arg)
 257 {
 258         struct raw32_config_request __user *user_req = compat_ptr(arg);
 259         struct raw32_config_request rq;
 260         dev_t dev;
 261         int err = 0;
 262
 263         switch (cmd) {
 264         case RAW_SETBIND:
 265                 if (copy_from_user(&rq, user_req, sizeof(rq)))
 266                         return -EFAULT;
 267
 268                 return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);
 269
 270         case RAW_GETBIND:
 271                 if (copy_from_user(&rq, user_req, sizeof(rq)))
 272                         return -EFAULT;
 273
 274                 err = bind_get(rq.raw_minor, &dev);
 275                 if (err)
 276                         return err;
 277
 278                 rq.block_major = MAJOR(dev);
 279                 rq.block_minor = MINOR(dev);
 280
 281                 if (copy_to_user(user_req, &rq, sizeof(rq)))
 282                         return -EFAULT;
 283
 284                 return 0;
 285         }
 286
 287         return -EINVAL;
 288 }
 289 #endif
 290
 291 static const struct file_operations raw_fops = {
 292         .read   =       do_sync_read,
 293         .aio_read =     generic_file_aio_read,
 294         .write  =       do_sync_write,
 295         .aio_write =    blkdev_aio_write,
 296         .open   =       raw_open,
 297         .release=       raw_release,
 298         .ioctl  =       raw_ioctl,
 299         .owner  =       THIS_MODULE,
 300 };
 301
 302 static const struct file_operations raw_ctl_fops = {
 303         .ioctl  =       raw_ctl_ioctl,
 304 #ifdef CONFIG_COMPAT
 305         .compat_ioctl = raw_ctl_compat_ioctl,
 306 #endif
 307         .open   =       raw_open,
 308         .owner  =       THIS_MODULE,
 309 };
 310
 311 static struct cdev raw_cdev;
 312
 313 static char *raw_devnode(struct device *dev, mode_t *mode)
 314 {
 315         return kasprintf(GFP_KERNEL, "raw/%s", dev_name(dev));
 316 }
 317
 318 static int __init raw_init(void)
 319 {
 320         dev_t dev = MKDEV(RAW_MAJOR, 0);
 321         int ret;
 322
 323         ret = register_chrdev_region(dev, MAX_RAW_MINORS, "raw");
 324         if (ret)
 325                 goto error;
 326
 327         cdev_init(&raw_cdev, &raw_fops);
 328         ret = cdev_add(&raw_cdev, dev, MAX_RAW_MINORS);
 329         if (ret) {
 330                 kobject_put(&raw_cdev.kobj);
 331                 goto error_region;
 332         }
 333
 334         raw_class = class_create(THIS_MODULE, "raw");
 335         if (IS_ERR(raw_class)) {
 336                 printk(KERN_ERR "Error creating raw class.\n");
 337                 cdev_del(&raw_cdev);
 338                 ret = PTR_ERR(raw_class);
 339                 goto error_region;
 340         }
 341         raw_class->devnode = raw_devnode;
 342         device_create(raw_class, NULL, MKDEV(RAW_MAJOR, 0), NULL, "rawctl");
 343
 344         return 0;
 345
 346 error_region:
 347         unregister_chrdev_region(dev, MAX_RAW_MINORS);
 348 error:
 349         return ret;
 350 }
 351
 352 static void __exit raw_exit(void)
 353 {
 354         device_destroy(raw_class, MKDEV(RAW_MAJOR, 0));
 355         class_destroy(raw_class);
 356         cdev_del(&raw_cdev);
 357         unregister_chrdev_region(MKDEV(RAW_MAJOR, 0), MAX_RAW_MINORS);
 358 }
 359
 360 module_init(raw_init);
 361 module_exit(raw_exit);
 362 MODULE_LICENSE("GPL");