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