media-devnode.c

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/*
 * Media device node
 *
 * Copyright (C) 2010 Nokia Corporation
 *
 * Based on drivers/media/video/v4l2_dev.c code authored by
 *  Mauro Carvalho Chehab <[email protected]> (version 2)
 *  Alan Cox, <[email protected]> (version 1)
 *
 * Contacts: Laurent Pinchart <[email protected]>
 *       Sakari Ailus <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * --
 *
 * Generic media device node infrastructure to register and unregister
 * character devices using a dynamic major number and proper reference
 * counting.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/errno.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/kmod.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/uaccess.h>

#include <media/media-devnode.h>

#define MEDIA_NUM_DEVICES   256
#define MEDIA_NAME      "media"

static dev_t media_dev_t;

/*
 *  Active devices
 */
static DEFINE_MUTEX(media_devnode_lock);
static DECLARE_BITMAP(media_devnode_nums, MEDIA_NUM_DEVICES);

/* Called when the last user of the media device exits. */
static void media_devnode_release(struct device *cd)
{
    struct media_devnode *mdev = to_media_devnode(cd);

    mutex_lock(&media_devnode_lock);

    /* Delete the cdev on this minor as well */
    cdev_del(&mdev->cdev);

    /* Mark device node number as free */
    clear_bit(mdev->minor, media_devnode_nums);

    mutex_unlock(&media_devnode_lock);

    /* Release media_devnode and perform other cleanups as needed. */
    if (mdev->release)
        mdev->release(mdev);
}

static struct bus_type media_bus_type = {
    .name = MEDIA_NAME,
};

static ssize_t media_read(struct file *filp, char __user *buf,
        size_t sz, loff_t *off)
{
    struct media_devnode *mdev = media_devnode_data(filp);

    if (!mdev->fops->read)
        return -EINVAL;
    if (!media_devnode_is_registered(mdev))
        return -EIO;
    return mdev->fops->read(filp, buf, sz, off);
}

static ssize_t media_write(struct file *filp, const char __user *buf,
        size_t sz, loff_t *off)
{
    struct media_devnode *mdev = media_devnode_data(filp);

    if (!mdev->fops->write)
        return -EINVAL;
    if (!media_devnode_is_registered(mdev))
        return -EIO;
    return mdev->fops->write(filp, buf, sz, off);
}

static unsigned int media_poll(struct file *filp,
                   struct poll_table_struct *poll)
{
    struct media_devnode *mdev = media_devnode_data(filp);

    if (!media_devnode_is_registered(mdev))
        return POLLERR | POLLHUP;
    if (!mdev->fops->poll)
        return DEFAULT_POLLMASK;
    return mdev->fops->poll(filp, poll);
}

static long media_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
    struct media_devnode *mdev = media_devnode_data(filp);

    if (!mdev->fops->ioctl)
        return -ENOTTY;

    if (!media_devnode_is_registered(mdev))
        return -EIO;

    return mdev->fops->ioctl(filp, cmd, arg);
}

/* Override for the open function */
static int media_open(struct inode *inode, struct file *filp)
{
    struct media_devnode *mdev;
    int ret;

    /* Check if the media device is available. This needs to be done with
     * the media_devnode_lock held to prevent an open/unregister race:
     * without the lock, the device could be unregistered and freed between
     * the media_devnode_is_registered() and get_device() calls, leading to
     * a crash.
     */
    mutex_lock(&media_devnode_lock);
    mdev = container_of(inode->i_cdev, struct media_devnode, cdev);
    /* return ENXIO if the media device has been removed
       already or if it is not registered anymore. */
    if (!media_devnode_is_registered(mdev)) {
        mutex_unlock(&media_devnode_lock);
        return -ENXIO;
    }
    /* and increase the device refcount */
    get_device(&mdev->dev);
    mutex_unlock(&media_devnode_lock);

    filp->private_data = mdev;

    if (mdev->fops->open) {
        ret = mdev->fops->open(filp);
        if (ret) {
            put_device(&mdev->dev);
            return ret;
        }
    }

    return 0;
}

/* Override for the release function */
static int media_release(struct inode *inode, struct file *filp)
{
    struct media_devnode *mdev = media_devnode_data(filp);
    int ret = 0;

    if (mdev->fops->release)
        mdev->fops->release(filp);

    /* decrease the refcount unconditionally since the release()
       return value is ignored. */
    put_device(&mdev->dev);
    filp->private_data = NULL;
    return ret;
}

static const struct file_operations media_devnode_fops = {
    .owner = THIS_MODULE,
    .read = media_read,
    .write = media_write,
    .open = media_open,
    .unlocked_ioctl = media_ioctl,
    .release = media_release,
    .poll = media_poll,
    .llseek = no_llseek,
};

int __must_check media_devnode_register(struct media_devnode *mdev)
{
    int minor;
    int ret;

    /* Part 1: Find a free minor number */
    mutex_lock(&media_devnode_lock);
    minor = find_next_zero_bit(media_devnode_nums, MEDIA_NUM_DEVICES, 0);
    if (minor == MEDIA_NUM_DEVICES) {
        mutex_unlock(&media_devnode_lock);
        pr_err("could not get a free minor\n");
        return -ENFILE;
    }

    set_bit(minor, media_devnode_nums);
    mutex_unlock(&media_devnode_lock);

    mdev->minor = minor;

    /* Part 2: Initialize and register the character device */
    cdev_init(&mdev->cdev, &media_devnode_fops);
    mdev->cdev.owner = mdev->fops->owner;

    ret = cdev_add(&mdev->cdev, MKDEV(MAJOR(media_dev_t), mdev->minor), 1);
    if (ret < 0) {
        pr_err("%s: cdev_add failed\n", __func__);
        goto error;
    }

    /* Part 3: Register the media device */
    mdev->dev.bus = &media_bus_type;
    mdev->dev.devt = MKDEV(MAJOR(media_dev_t), mdev->minor);
    mdev->dev.release = media_devnode_release;
    if (mdev->parent)
        mdev->dev.parent = mdev->parent;
    dev_set_name(&mdev->dev, "media%d", mdev->minor);
    ret = device_register(&mdev->dev);
    if (ret < 0) {
        pr_err("%s: device_register failed\n", __func__);
        goto error;
    }

    /* Part 4: Activate this minor. The char device can now be used. */
    set_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);

    return 0;

error:
    cdev_del(&mdev->cdev);
    clear_bit(mdev->minor, media_devnode_nums);
    return ret;
}

void media_devnode_unregister(struct media_devnode *mdev)
{
    /* Check if mdev was ever registered at all */
    if (!media_devnode_is_registered(mdev))
        return;

    mutex_lock(&media_devnode_lock);
    clear_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
    mutex_unlock(&media_devnode_lock);
    device_unregister(&mdev->dev);
}

/*
 *  Initialise media for linux
 */
static int __init media_devnode_init(void)
{
    int ret;

    pr_info("Linux media interface: v0.10\n");
    ret = alloc_chrdev_region(&media_dev_t, 0, MEDIA_NUM_DEVICES,
                  MEDIA_NAME);
    if (ret < 0) {
        pr_warn("unable to allocate major\n");
        return ret;
    }

    ret = bus_register(&media_bus_type);
    if (ret < 0) {
        unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
        pr_warn("bus_register failed\n");
        return -EIO;
    }

    return 0;
}

static void __exit media_devnode_exit(void)
{
    bus_unregister(&media_bus_type);
    unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
}

subsys_initcall(media_devnode_init);
module_exit(media_devnode_exit)

MODULE_AUTHOR("Laurent Pinchart <[email protected]>");
MODULE_DESCRIPTION("Device node registration for media drivers");
MODULE_LICENSE("GPL");