Re: V4L-DVB drivers and BKL

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

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 ?

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.

-- 
Regards,

Laurent Pinchart