On Thursday 29 July 2010 18:06:34 Laurent Pinchart wrote:
> The media_devnode structure provides support for registering and
> unregistering character devices using a dynamic major number. Reference
> counting is handled internally, making device drivers easier to write
> without having to solve the open/disconnect race condition issue over
> and over again.
>
> The code is based on video/v4l2-dev.c.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> ---
> drivers/media/Makefile | 8 +-
> drivers/media/media-devnode.c | 326 +++++++++++++++++++++++++++++++++++++++++
> include/media/media-devnode.h | 84 +++++++++++
> 3 files changed, 416 insertions(+), 2 deletions(-)
> create mode 100644 drivers/media/media-devnode.c
> create mode 100644 include/media/media-devnode.h
>
<snip>
> diff --git a/drivers/media/media-devnode.c b/drivers/media/media-devnode.c
> new file mode 100644
> index 0000000..6f5558c
> --- /dev/null
> +++ b/drivers/media/media-devnode.c
<snip>
> +/* 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 ENODEV 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 -ENODEV;
> + }
> + /* and increase the device refcount */
> + get_device(&mdev->dev);
> + mutex_unlock(&media_devnode_lock);
> + if (mdev->fops->open) {
> + ret = mdev->fops->open(filp);
> + if (ret) {
> + put_device(&mdev->dev);
> + return ret;
> + }
> + }
> +
> + filp->private_data = mdev;
This line should be moved up to before the if: that way the open op can rely
on private_data being setup correctly.
> + return 0;
> +}
<snip>
Regards,
Hans
--
Hans Verkuil - video4linux developer - sponsored by TANDBERG, part of Cisco
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