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