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
  24 #include <asm/uaccess.h>
  25
  26 struct raw_device_data {
  27         struct block_device *binding;
  28         int inuse;
  29 };
  30
  31 static struct class *raw_class;
  32 static struct raw_device_data raw_devices[MAX_RAW_MINORS];
  33 static DEFINE_MUTEX(raw_mutex);
  34 static const struct file_operations raw_ctl_fops; /* forward declaration */
  35
  36 /*
  37  * Open/close code for raw IO.
  38  *
  39  * We just rewrite the i_mapping for the /dev/raw/rawN file descriptor to
  40  * point at the blockdev's address_space and set the file handle to use
  41  * O_DIRECT.
  42  *
  43  * Set the device's soft blocksize to the minimum possible.  This gives the
  44  * finest possible alignment and has no adverse impact on performance.
  45  */
  46 static int raw_open(struct inode *inode, struct file *filp)
  47 {
  48         const int minor = iminor(inode);
  49         struct block_device *bdev;
  50         int err;
  51
  52         if (minor == 0) {       /* It is the control device */
  53                 filp->f_op = &raw_ctl_fops;
  54                 return 0;
  55         }
  56
  57         lock_kernel();
  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_hardsect_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         unlock_kernel();
  85         return 0;
  86
  87 out2:
  88         bd_release(bdev);
  89 out1:
  90         blkdev_put(bdev, filp->f_mode);
  91 out:
  92         mutex_unlock(&raw_mutex);
  93         return err;
  94 }
  95
  96 /*
  97  * When the final fd which refers to this character-special node is closed, we
  98  * make its ->mapping point back at its own i_data.
  99  */
 100 static int raw_release(struct inode *inode, struct file *filp)
 101 {
 102         const int minor= iminor(inode);
 103         struct block_device *bdev;
 104
 105         mutex_lock(&raw_mutex);
 106         bdev = raw_devices[minor].binding;
 107         if (--raw_devices[minor].inuse == 0) {
 108                 /* Here  inode->i_mapping == bdev->bd_inode->i_mapping  */
 109                 inode->i_mapping = &inode->i_data;
 110                 inode->i_mapping->backing_dev_info = &default_backing_dev_info;
 111         }
 112         mutex_unlock(&raw_mutex);
 113
 114         bd_release(bdev);
 115         blkdev_put(bdev, filp->f_mode);
 116         return 0;
 117 }
 118
 119 /*
 120  * Forward ioctls to the underlying block device.
 121  */
 122 static int
 123 raw_ioctl(struct inode *inode, struct file *filp,
 124                   unsigned int command, unsigned long arg)
 125 {
 126         struct block_device *bdev = filp->private_data;
 127
 128         return blkdev_ioctl(bdev, 0, command, arg);
 129 }
 130
 131 static void bind_device(struct raw_config_request *rq)
 132 {
 133         device_destroy(raw_class, MKDEV(RAW_MAJOR, rq->raw_minor));
 134         device_create(raw_class, NULL, MKDEV(RAW_MAJOR, rq->raw_minor), NULL,
 135                       "raw%d", rq->raw_minor);
 136 }
 137
 138 /*
 139  * Deal with ioctls against the raw-device control interface, to bind
 140  * and unbind other raw devices.
 141  */
 142 static int raw_ctl_ioctl(struct inode *inode, struct file *filp,
 143                         unsigned int command, unsigned long arg)
 144 {
 145         struct raw_config_request rq;
 146         struct raw_device_data *rawdev;
 147         int err = 0;
 148
 149         switch (command) {
 150         case RAW_SETBIND:
 151         case RAW_GETBIND:
 152
 153                 /* First, find out which raw minor we want */
 154
 155                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq))) {
 156                         err = -EFAULT;
 157                         goto out;
 158                 }
 159
 160                 if (rq.raw_minor <= 0 || rq.raw_minor >= MAX_RAW_MINORS) {
 161                         err = -EINVAL;
 162                         goto out;
 163                 }
 164                 rawdev = &raw_devices[rq.raw_minor];
 165
 166                 if (command == RAW_SETBIND) {
 167                         dev_t dev;
 168
 169                         /*
 170                          * This is like making block devices, so demand the
 171                          * same capability
 172                          */
 173                         if (!capable(CAP_SYS_ADMIN)) {
 174                                 err = -EPERM;
 175                                 goto out;
 176                         }
 177
 178                         /*
 179                          * For now, we don't need to check that the underlying
 180                          * block device is present or not: we can do that when
 181                          * the raw device is opened.  Just check that the
 182                          * major/minor numbers make sense.
 183                          */
 184
 185                         dev = MKDEV(rq.block_major, rq.block_minor);
 186                         if ((rq.block_major == 0 && rq.block_minor != 0) ||
 187                                         MAJOR(dev) != rq.block_major ||
 188                                         MINOR(dev) != rq.block_minor) {
 189                                 err = -EINVAL;
 190                                 goto out;
 191                         }
 192
 193                         mutex_lock(&raw_mutex);
 194                         if (rawdev->inuse) {
 195                                 mutex_unlock(&raw_mutex);
 196                                 err = -EBUSY;
 197                                 goto out;
 198                         }
 199                         if (rawdev->binding) {
 200                                 bdput(rawdev->binding);
 201                                 module_put(THIS_MODULE);
 202                         }
 203                         if (rq.block_major == 0 && rq.block_minor == 0) {
 204                                 /* unbind */
 205                                 rawdev->binding = NULL;
 206                                 device_destroy(raw_class,
 207                                                 MKDEV(RAW_MAJOR, rq.raw_minor));
 208                         } else {
 209                                 rawdev->binding = bdget(dev);
 210                                 if (rawdev->binding == NULL)
 211                                         err = -ENOMEM;
 212                                 else {
 213                                         __module_get(THIS_MODULE);
 214                                         bind_device(&rq);
 215                                 }
 216                         }
 217                         mutex_unlock(&raw_mutex);
 218                 } else {
 219                         struct block_device *bdev;
 220
 221                         mutex_lock(&raw_mutex);
 222                         bdev = rawdev->binding;
 223                         if (bdev) {
 224                                 rq.block_major = MAJOR(bdev->bd_dev);
 225                                 rq.block_minor = MINOR(bdev->bd_dev);
 226                         } else {
 227                                 rq.block_major = rq.block_minor = 0;
 228                         }
 229                         mutex_unlock(&raw_mutex);
 230                         if (copy_to_user((void __user *)arg, &rq, sizeof(rq))) {
 231                                 err = -EFAULT;
 232                                 goto out;
 233                         }
 234                 }
 235                 break;
 236         default:
 237                 err = -EINVAL;
 238                 break;
 239         }
 240 out:
 241         return err;
 242 }
 243
 244 static const struct file_operations raw_fops = {
 245         .read   =       do_sync_read,
 246         .aio_read =     generic_file_aio_read,
 247         .write  =       do_sync_write,
 248         .aio_write =    generic_file_aio_write_nolock,
 249         .open   =       raw_open,
 250         .release=       raw_release,
 251         .ioctl  =       raw_ioctl,
 252         .owner  =       THIS_MODULE,
 253 };
 254
 255 static const struct file_operations raw_ctl_fops = {
 256         .ioctl  =       raw_ctl_ioctl,
 257         .open   =       raw_open,
 258         .owner  =       THIS_MODULE,
 259 };
 260
 261 static struct cdev raw_cdev;
 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), NULL, "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");