raw.c

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/*
 * 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 <linux/gfp.h>
#include <linux/compat.h>
#include <linux/vmalloc.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;
static DEFINE_MUTEX(raw_mutex);
static const struct file_operations raw_ctl_fops; /* forward declaration */

static int max_raw_minors = MAX_RAW_MINORS;

module_param(max_raw_minors, int, 0);
MODULE_PARM_DESC(max_raw_minors, "Maximum number of raw devices (1-65536)");

/*
 * 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 | FMODE_EXCL, raw_open);
    if (err)
        goto out;
    err = set_blocksize(bdev, bdev_logical_block_size(bdev));
    if (err)
        goto out1;
    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;

out1:
    blkdev_put(bdev, filp->f_mode | FMODE_EXCL);
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);

    blkdev_put(bdev, filp->f_mode | FMODE_EXCL);
    return 0;
}

/*
 * Forward ioctls to the underlying block device.
 */
static long
raw_ioctl(struct file *filp, unsigned int command, unsigned long arg)
{
    struct block_device *bdev = filp->private_data;
    return blkdev_ioctl(bdev, 0, command, arg);
}

static int bind_set(int number, u64 major, u64 minor)
{
    dev_t dev = MKDEV(major, minor);
    struct raw_device_data *rawdev;
    int err = 0;

    if (number <= 0 || number >= max_raw_minors)
        return -EINVAL;

    if (MAJOR(dev) != major || MINOR(dev) != minor)
        return -EINVAL;

    rawdev = &raw_devices[number];

    /*
     * This is like making block devices, so demand the
     * same capability
     */
    if (!capable(CAP_SYS_ADMIN))
        return -EPERM;

    /*
     * 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.
     */

    if (MAJOR(dev) == 0 && dev != 0)
        return -EINVAL;

    mutex_lock(&raw_mutex);
    if (rawdev->inuse) {
        mutex_unlock(&raw_mutex);
        return -EBUSY;
    }
    if (rawdev->binding) {
        bdput(rawdev->binding);
        module_put(THIS_MODULE);
    }
    if (!dev) {
        /* unbind */
        rawdev->binding = NULL;
        device_destroy(raw_class, MKDEV(RAW_MAJOR, number));
    } else {
        rawdev->binding = bdget(dev);
        if (rawdev->binding == NULL) {
            err = -ENOMEM;
        } else {
            dev_t raw = MKDEV(RAW_MAJOR, number);
            __module_get(THIS_MODULE);
            device_destroy(raw_class, raw);
            device_create(raw_class, NULL, raw, NULL,
                      "raw%d", number);
        }
    }
    mutex_unlock(&raw_mutex);
    return err;
}

static int bind_get(int number, dev_t *dev)
{
    struct raw_device_data *rawdev;
    struct block_device *bdev;

    if (number <= 0 || number >= MAX_RAW_MINORS)
        return -EINVAL;

    rawdev = &raw_devices[number];

    mutex_lock(&raw_mutex);
    bdev = rawdev->binding;
    *dev = bdev ? bdev->bd_dev : 0;
    mutex_unlock(&raw_mutex);
    return 0;
}

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

    switch (command) {
    case RAW_SETBIND:
        if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
            return -EFAULT;

        return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);

    case RAW_GETBIND:
        if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
            return -EFAULT;

        err = bind_get(rq.raw_minor, &dev);
        if (err)
            return err;

        rq.block_major = MAJOR(dev);
        rq.block_minor = MINOR(dev);

        if (copy_to_user((void __user *)arg, &rq, sizeof(rq)))
            return -EFAULT;

        return 0;
    }

    return -EINVAL;
}

#ifdef CONFIG_COMPAT
struct raw32_config_request {
    compat_int_t    raw_minor;
    compat_u64  block_major;
    compat_u64  block_minor;
};

static long raw_ctl_compat_ioctl(struct file *file, unsigned int cmd,
                unsigned long arg)
{
    struct raw32_config_request __user *user_req = compat_ptr(arg);
    struct raw32_config_request rq;
    dev_t dev;
    int err = 0;

    switch (cmd) {
    case RAW_SETBIND:
        if (copy_from_user(&rq, user_req, sizeof(rq)))
            return -EFAULT;

        return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);

    case RAW_GETBIND:
        if (copy_from_user(&rq, user_req, sizeof(rq)))
            return -EFAULT;

        err = bind_get(rq.raw_minor, &dev);
        if (err)
            return err;

        rq.block_major = MAJOR(dev);
        rq.block_minor = MINOR(dev);

        if (copy_to_user(user_req, &rq, sizeof(rq)))
            return -EFAULT;

        return 0;
    }

    return -EINVAL;
}
#endif

static const struct file_operations raw_fops = {
    .read       = do_sync_read,
    .aio_read   = generic_file_aio_read,
    .write      = do_sync_write,
    .aio_write  = blkdev_aio_write,
    .fsync      = blkdev_fsync,
    .open       = raw_open,
    .release    = raw_release,
    .unlocked_ioctl = raw_ioctl,
    .llseek     = default_llseek,
    .owner      = THIS_MODULE,
};

static const struct file_operations raw_ctl_fops = {
    .unlocked_ioctl = raw_ctl_ioctl,
#ifdef CONFIG_COMPAT
    .compat_ioctl   = raw_ctl_compat_ioctl,
#endif
    .open       = raw_open,
    .owner      = THIS_MODULE,
    .llseek     = noop_llseek,
};

static struct cdev raw_cdev;

static char *raw_devnode(struct device *dev, umode_t *mode)
{
    return kasprintf(GFP_KERNEL, "raw/%s", dev_name(dev));
}

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

    if (max_raw_minors < 1 || max_raw_minors > 65536) {
        printk(KERN_WARNING "raw: invalid max_raw_minors (must be"
            " between 1 and 65536), using %d\n", MAX_RAW_MINORS);
        max_raw_minors = MAX_RAW_MINORS;
    }

    raw_devices = vzalloc(sizeof(struct raw_device_data) * max_raw_minors);
    if (!raw_devices) {
        printk(KERN_ERR "Not enough memory for raw device structures\n");
        ret = -ENOMEM;
        goto error;
    }

    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) {
        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;
    }
    raw_class->devnode = raw_devnode;
    device_create(raw_class, NULL, MKDEV(RAW_MAJOR, 0), NULL, "rawctl");

    return 0;

error_region:
    unregister_chrdev_region(dev, max_raw_minors);
error:
    vfree(raw_devices);
    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");