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raw.c

/*
 * linux/drivers/char/raw.c
 *
 * Front-end raw character devices.  These can be bound to any block
 * devices to provide genuine Unix raw character device semantics.
 *
 * We reserve minor number 0 for a control interface.  ioctl()s on this
 * device are used to bind the other minor numbers to block devices.
 */

#include <linux/init.h>
#include <linux/fs.h>
#include <linux/major.h>
#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/raw.h>
#include <linux/capability.h>
#include <linux/uio.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/mutex.h>

#include <asm/uaccess.h>

struct raw_device_data {
      struct block_device *binding;
      int inuse;
};

static struct class *raw_class;
static struct raw_device_data raw_devices[MAX_RAW_MINORS];
static DEFINE_MUTEX(raw_mutex);
static const struct file_operations raw_ctl_fops; /* forward declaration */

/*
 * Open/close code for raw IO.
 *
 * We just rewrite the i_mapping for the /dev/raw/rawN file descriptor to
 * point at the blockdev's address_space and set the file handle to use
 * O_DIRECT.
 *
 * Set the device's soft blocksize to the minimum possible.  This gives the
 * finest possible alignment and has no adverse impact on performance.
 */
static int raw_open(struct inode *inode, struct file *filp)
{
      const int minor = iminor(inode);
      struct block_device *bdev;
      int err;

      if (minor == 0) { /* It is the control device */
            filp->f_op = &raw_ctl_fops;
            return 0;
      }

      mutex_lock(&raw_mutex);

      /*
       * All we need to do on open is check that the device is bound.
       */
      bdev = raw_devices[minor].binding;
      err = -ENODEV;
      if (!bdev)
            goto out;
      igrab(bdev->bd_inode);
      err = blkdev_get(bdev, filp->f_mode, 0);
      if (err)
            goto out;
      err = bd_claim(bdev, raw_open);
      if (err)
            goto out1;
      err = set_blocksize(bdev, bdev_hardsect_size(bdev));
      if (err)
            goto out2;
      filp->f_flags |= O_DIRECT;
      filp->f_mapping = bdev->bd_inode->i_mapping;
      if (++raw_devices[minor].inuse == 1)
            filp->f_path.dentry->d_inode->i_mapping =
                  bdev->bd_inode->i_mapping;
      filp->private_data = bdev;
      mutex_unlock(&raw_mutex);
      return 0;

out2:
      bd_release(bdev);
out1:
      blkdev_put(bdev);
out:
      mutex_unlock(&raw_mutex);
      return err;
}

/*
 * When the final fd which refers to this character-special node is closed, we
 * make its ->mapping point back at its own i_data.
 */
static int raw_release(struct inode *inode, struct file *filp)
{
      const int minor= iminor(inode);
      struct block_device *bdev;

      mutex_lock(&raw_mutex);
      bdev = raw_devices[minor].binding;
      if (--raw_devices[minor].inuse == 0) {
            /* Here  inode->i_mapping == bdev->bd_inode->i_mapping  */
            inode->i_mapping = &inode->i_data;
            inode->i_mapping->backing_dev_info = &default_backing_dev_info;
      }
      mutex_unlock(&raw_mutex);

      bd_release(bdev);
      blkdev_put(bdev);
      return 0;
}

/*
 * Forward ioctls to the underlying block device.
 */
static int
raw_ioctl(struct inode *inode, struct file *filp,
              unsigned int command, unsigned long arg)
{
      struct block_device *bdev = filp->private_data;

      return blkdev_ioctl(bdev->bd_inode, NULL, command, arg);
}

static void bind_device(struct raw_config_request *rq)
{
      device_destroy(raw_class, MKDEV(RAW_MAJOR, rq->raw_minor));
      device_create(raw_class, NULL, MKDEV(RAW_MAJOR, rq->raw_minor),
                  "raw%d", rq->raw_minor);
}

/*
 * Deal with ioctls against the raw-device control interface, to bind
 * and unbind other raw devices.
 */
static int raw_ctl_ioctl(struct inode *inode, struct file *filp,
                  unsigned int command, unsigned long arg)
{
      struct raw_config_request rq;
      struct raw_device_data *rawdev;
      int err = 0;

      switch (command) {
      case RAW_SETBIND:
      case RAW_GETBIND:

            /* First, find out which raw minor we want */

            if (copy_from_user(&rq, (void __user *) arg, sizeof(rq))) {
                  err = -EFAULT;
                  goto out;
            }

            if (rq.raw_minor <= 0 || rq.raw_minor >= MAX_RAW_MINORS) {
                  err = -EINVAL;
                  goto out;
            }
            rawdev = &raw_devices[rq.raw_minor];

            if (command == RAW_SETBIND) {
                  dev_t dev;

                  /*
                   * This is like making block devices, so demand the
                   * same capability
                   */
                  if (!capable(CAP_SYS_ADMIN)) {
                        err = -EPERM;
                        goto out;
                  }

                  /*
                   * For now, we don't need to check that the underlying
                   * block device is present or not: we can do that when
                   * the raw device is opened.  Just check that the
                   * major/minor numbers make sense.
                   */

                  dev = MKDEV(rq.block_major, rq.block_minor);
                  if ((rq.block_major == 0 && rq.block_minor != 0) ||
                              MAJOR(dev) != rq.block_major ||
                              MINOR(dev) != rq.block_minor) {
                        err = -EINVAL;
                        goto out;
                  }

                  mutex_lock(&raw_mutex);
                  if (rawdev->inuse) {
                        mutex_unlock(&raw_mutex);
                        err = -EBUSY;
                        goto out;
                  }
                  if (rawdev->binding) {
                        bdput(rawdev->binding);
                        module_put(THIS_MODULE);
                  }
                  if (rq.block_major == 0 && rq.block_minor == 0) {
                        /* unbind */
                        rawdev->binding = NULL;
                        device_destroy(raw_class,
                                    MKDEV(RAW_MAJOR, rq.raw_minor));
                  } else {
                        rawdev->binding = bdget(dev);
                        if (rawdev->binding == NULL)
                              err = -ENOMEM;
                        else {
                              __module_get(THIS_MODULE);
                              bind_device(&rq);
                        }
                  }
                  mutex_unlock(&raw_mutex);
            } else {
                  struct block_device *bdev;

                  mutex_lock(&raw_mutex);
                  bdev = rawdev->binding;
                  if (bdev) {
                        rq.block_major = MAJOR(bdev->bd_dev);
                        rq.block_minor = MINOR(bdev->bd_dev);
                  } else {
                        rq.block_major = rq.block_minor = 0;
                  }
                  mutex_unlock(&raw_mutex);
                  if (copy_to_user((void __user *)arg, &rq, sizeof(rq))) {
                        err = -EFAULT;
                        goto out;
                  }
            }
            break;
      default:
            err = -EINVAL;
            break;
      }
out:
      return err;
}

static const struct file_operations raw_fops = {
      .read =     do_sync_read,
      .aio_read =       generic_file_aio_read,
      .write      =     do_sync_write,
      .aio_write =      generic_file_aio_write_nolock,
      .open =     raw_open,
      .release=   raw_release,
      .ioctl      =     raw_ioctl,
      .owner      =     THIS_MODULE,
};

static const struct file_operations raw_ctl_fops = {
      .ioctl      =     raw_ctl_ioctl,
      .open =     raw_open,
      .owner      =     THIS_MODULE,
};

static struct cdev raw_cdev;

static int __init raw_init(void)
{
      dev_t dev = MKDEV(RAW_MAJOR, 0);
      int ret;

      ret = register_chrdev_region(dev, MAX_RAW_MINORS, "raw");
      if (ret)
            goto error;

      cdev_init(&raw_cdev, &raw_fops);
      ret = cdev_add(&raw_cdev, dev, MAX_RAW_MINORS);
      if (ret) {
            kobject_put(&raw_cdev.kobj);
            goto error_region;
      }

      raw_class = class_create(THIS_MODULE, "raw");
      if (IS_ERR(raw_class)) {
            printk(KERN_ERR "Error creating raw class.\n");
            cdev_del(&raw_cdev);
            ret = PTR_ERR(raw_class);
            goto error_region;
      }
      device_create(raw_class, NULL, MKDEV(RAW_MAJOR, 0), "rawctl");

      return 0;

error_region:
      unregister_chrdev_region(dev, MAX_RAW_MINORS);
error:
      return ret;
}

static void __exit raw_exit(void)
{
      device_destroy(raw_class, MKDEV(RAW_MAJOR, 0));
      class_destroy(raw_class);
      cdev_del(&raw_cdev);
      unregister_chrdev_region(MKDEV(RAW_MAJOR, 0), MAX_RAW_MINORS);
}

module_init(raw_init);
module_exit(raw_exit);
MODULE_LICENSE("GPL");

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