On Thursday 01 April 2010 11:23:30 Laurent Pinchart wrote:
> Hi Hans,
>
> On Thursday 01 April 2010 10:01:10 Hans Verkuil wrote:
> > Hi all,
> >
> > I just read on LWN that the core kernel guys are putting more effort into
> > removing the BKL. We are still using it in our own drivers, mostly V4L.
> >
> > I added a BKL column to my driver list:
> >
> > http://www.linuxtv.org/wiki/index.php/V4L_framework_progress#Bridge_Drivers
> >
> > If you 'own' one of these drivers that still use BKL, then it would be nice
> > if you can try and remove the use of the BKL from those drivers.
> >
> > The other part that needs to be done is to move from using the .ioctl file
> > op to using .unlocked_ioctl. Very few drivers do that, but I suspect
> > almost no driver actually needs to use .ioctl.
>
> What about something like this patch as a first step ?
That doesn't fix anything. You just move the BKL from one place to another.
I don't see any benefit from that.
Regards,
Hans
>
> diff --git a/drivers/media/video/v4l2-dev.c b/drivers/media/video/v4l2-dev.c
> index 7090699..14e1b1c 100644
> --- a/drivers/media/video/v4l2-dev.c
> +++ b/drivers/media/video/v4l2-dev.c
> @@ -25,6 +25,7 @@
> #include <linux/init.h>
> #include <linux/kmod.h>
> #include <linux/slab.h>
> +#include <linux/smp_lock.h>
> #include <asm/uaccess.h>
> #include <asm/system.h>
>
> @@ -215,28 +216,22 @@ static unsigned int v4l2_poll(struct file *filp, struct
> poll_table_struct *poll)
> return vdev->fops->poll(filp, poll);
> }
>
> -static int v4l2_ioctl(struct inode *inode, struct file *filp,
> - unsigned int cmd, unsigned long arg)
> -{
> - struct video_device *vdev = video_devdata(filp);
> -
> - if (!vdev->fops->ioctl)
> - return -ENOTTY;
> - /* Allow ioctl to continue even if the device was unregistered.
> - Things like dequeueing buffers might still be useful. */
> - return vdev->fops->ioctl(filp, cmd, arg);
> -}
> -
> static long v4l2_unlocked_ioctl(struct file *filp,
> unsigned int cmd, unsigned long arg)
> {
> struct video_device *vdev = video_devdata(filp);
> + int ret = -ENOTTY;
>
> - if (!vdev->fops->unlocked_ioctl)
> - return -ENOTTY;
> /* Allow ioctl to continue even if the device was unregistered.
> Things like dequeueing buffers might still be useful. */
> - return vdev->fops->unlocked_ioctl(filp, cmd, arg);
> + if (vdev->fops->ioctl) {
> + lock_kernel();
> + ret = vdev->fops->ioctl(filp, cmd, arg);
> + unlock_kernel();
> + } else if (vdev->fops->unlocked_ioctl)
> + ret = vdev->fops->unlocked_ioctl(filp, cmd, arg);
> +
> + return ret;
> }
>
> #ifdef CONFIG_MMU
> @@ -323,22 +318,6 @@ static const struct file_operations v4l2_unlocked_fops =
> {
> .llseek = no_llseek,
> };
>
> -static const struct file_operations v4l2_fops = {
> - .owner = THIS_MODULE,
> - .read = v4l2_read,
> - .write = v4l2_write,
> - .open = v4l2_open,
> - .get_unmapped_area = v4l2_get_unmapped_area,
> - .mmap = v4l2_mmap,
> - .ioctl = v4l2_ioctl,
> -#ifdef CONFIG_COMPAT
> - .compat_ioctl = v4l2_compat_ioctl32,
> -#endif
> - .release = v4l2_release,
> - .poll = v4l2_poll,
> - .llseek = no_llseek,
> -};
> -
> /**
> * get_index - assign stream index number based on parent device
> * @vdev: video_device to assign index number to, vdev->parent should be
> assigned
> @@ -517,10 +496,7 @@ static int __video_register_device(struct video_device
> *vdev, int type, int nr,
> ret = -ENOMEM;
> goto cleanup;
> }
> - if (vdev->fops->unlocked_ioctl)
> - vdev->cdev->ops = &v4l2_unlocked_fops;
> - else
> - vdev->cdev->ops = &v4l2_fops;
> + vdev->cdev->ops = &v4l2_unlocked_fops;
> vdev->cdev->owner = vdev->fops->owner;
> ret = cdev_add(vdev->cdev, MKDEV(VIDEO_MAJOR, vdev->minor), 1);
> if (ret < 0) {
>
> A second step would be to replace lock_kernel/unlock_kernel with a
> V4L-specific lock, and the third step to push the lock into drivers.
>
>
--
Hans Verkuil - video4linux developer - sponsored by TANDBERG
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