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