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/gfp.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 long
 125 raw_ioctl(struct file *filp, unsigned int command, unsigned long arg)
 126 {
 127         struct block_device *bdev = filp->private_data;
 128         int ret;
 129
 130         lock_kernel();
 131         ret = blkdev_ioctl(bdev, 0, command, arg);
 132         unlock_kernel();
 133
 134         return ret;
 135 }
 136
 137 static void bind_device(struct raw_config_request *rq)
 138 {
 139         device_destroy(raw_class, MKDEV(RAW_MAJOR, rq->raw_minor));
 140         device_create(raw_class, NULL, MKDEV(RAW_MAJOR, rq->raw_minor), NULL,
 141                       "raw%d", rq->raw_minor);
 142 }
 143
 144 /*
 145  * Deal with ioctls against the raw-device control interface, to bind
 146  * and unbind other raw devices.
 147  */
 148 static long raw_ctl_ioctl(struct file *filp, unsigned int command,
 149                           unsigned long arg)
 150 {
 151         struct raw_config_request rq;
 152         struct raw_device_data *rawdev;
 153         int err = 0;
 154
 155         lock_kernel();
 156         switch (command) {
 157         case RAW_SETBIND:
 158         case RAW_GETBIND:
 159
 160                 /* First, find out which raw minor we want */
 161
 162                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq))) {
 163                         err = -EFAULT;
 164                         goto out;
 165                 }
 166
 167                 if (rq.raw_minor <= 0 || rq.raw_minor >= MAX_RAW_MINORS) {
 168                         err = -EINVAL;
 169                         goto out;
 170                 }
 171                 rawdev = &raw_devices[rq.raw_minor];
 172
 173                 if (command == RAW_SETBIND) {
 174                         dev_t dev;
 175
 176                         /*
 177                          * This is like making block devices, so demand the
 178                          * same capability
 179                          */
 180                         if (!capable(CAP_SYS_ADMIN)) {
 181                                 err = -EPERM;
 182                                 goto out;
 183                         }
 184
 185                         /*
 186                          * For now, we don't need to check that the underlying
 187                          * block device is present or not: we can do that when
 188                          * the raw device is opened.  Just check that the
 189                          * major/minor numbers make sense.
 190                          */
 191
 192                         dev = MKDEV(rq.block_major, rq.block_minor);
 193                         if ((rq.block_major == 0 && rq.block_minor != 0) ||
 194                                         MAJOR(dev) != rq.block_major ||
 195                                         MINOR(dev) != rq.block_minor) {
 196                                 err = -EINVAL;
 197                                 goto out;
 198                         }
 199
 200                         mutex_lock(&raw_mutex);
 201                         if (rawdev->inuse) {
 202                                 mutex_unlock(&raw_mutex);
 203                                 err = -EBUSY;
 204                                 goto out;
 205                         }
 206                         if (rawdev->binding) {
 207                                 bdput(rawdev->binding);
 208                                 module_put(THIS_MODULE);
 209                         }
 210                         if (rq.block_major == 0 && rq.block_minor == 0) {
 211                                 /* unbind */
 212                                 rawdev->binding = NULL;
 213                                 device_destroy(raw_class,
 214                                                 MKDEV(RAW_MAJOR, rq.raw_minor));
 215                         } else {
 216                                 rawdev->binding = bdget(dev);
 217                                 if (rawdev->binding == NULL)
 218                                         err = -ENOMEM;
 219                                 else {
 220                                         __module_get(THIS_MODULE);
 221                                         bind_device(&rq);
 222                                 }
 223                         }
 224                         mutex_unlock(&raw_mutex);
 225                 } else {
 226                         struct block_device *bdev;
 227
 228                         mutex_lock(&raw_mutex);
 229                         bdev = rawdev->binding;
 230                         if (bdev) {
 231                                 rq.block_major = MAJOR(bdev->bd_dev);
 232                                 rq.block_minor = MINOR(bdev->bd_dev);
 233                         } else {
 234                                 rq.block_major = rq.block_minor = 0;
 235                         }
 236                         mutex_unlock(&raw_mutex);
 237                         if (copy_to_user((void __user *)arg, &rq, sizeof(rq))) {
 238                                 err = -EFAULT;
 239                                 goto out;
 240                         }
 241                 }
 242                 break;
 243         default:
 244                 err = -EINVAL;
 245                 break;
 246         }
 247 out:
 248         unlock_kernel();
 249         return err;
 250 }
 251
 252 static const struct file_operations raw_fops = {
 253         .read           = do_sync_read,
 254         .aio_read       = generic_file_aio_read,
 255         .write          = do_sync_write,
 256         .aio_write      = blkdev_aio_write,
 257         .fsync          = blkdev_fsync,
 258         .open           = raw_open,
 259         .release        = raw_release,
 260         .unlocked_ioctl = raw_ioctl,
 261         .owner          = THIS_MODULE,
 262 };
 263
 264 static const struct file_operations raw_ctl_fops = {
 265         .unlocked_ioctl = raw_ctl_ioctl,
 266         .open           = raw_open,
 267         .owner          = THIS_MODULE,
 268 };
 269
 270 static struct cdev raw_cdev;
 271
 272 static char *raw_devnode(struct device *dev, mode_t *mode)
 273 {
 274         return kasprintf(GFP_KERNEL, "raw/%s", dev_name(dev));
 275 }
 276
 277 static int __init raw_init(void)
 278 {
 279         dev_t dev = MKDEV(RAW_MAJOR, 0);
 280         int ret;
 281
 282         ret = register_chrdev_region(dev, MAX_RAW_MINORS, "raw");
 283         if (ret)
 284                 goto error;
 285
 286         cdev_init(&raw_cdev, &raw_fops);
 287         ret = cdev_add(&raw_cdev, dev, MAX_RAW_MINORS);
 288         if (ret) {
 289                 kobject_put(&raw_cdev.kobj);
 290                 goto error_region;
 291         }
 292
 293         raw_class = class_create(THIS_MODULE, "raw");
 294         if (IS_ERR(raw_class)) {
 295                 printk(KERN_ERR "Error creating raw class.\n");
 296                 cdev_del(&raw_cdev);
 297                 ret = PTR_ERR(raw_class);
 298                 goto error_region;
 299         }
 300         raw_class->devnode = raw_devnode;
 301         device_create(raw_class, NULL, MKDEV(RAW_MAJOR, 0), NULL, "rawctl");
 302
 303         return 0;
 304
 305 error_region:
 306         unregister_chrdev_region(dev, MAX_RAW_MINORS);
 307 error:
 308         return ret;
 309 }
 310
 311 static void __exit raw_exit(void)
 312 {
 313         device_destroy(raw_class, MKDEV(RAW_MAJOR, 0));
 314         class_destroy(raw_class);
 315         cdev_del(&raw_cdev);
 316         unregister_chrdev_region(MKDEV(RAW_MAJOR, 0), MAX_RAW_MINORS);
 317 }
 318
 319 module_init(raw_init);
 320 module_exit(raw_exit);
 321 MODULE_LICENSE("GPL");