[PATCH] videodev: fix sysfs kobj ref count

["David Ellingsworth" <david@xxxxxxxxxxxxxxxxx>]

This patch duplicates the behavior seen by char_dev in videodev.
Please apply.

char_dev handles the kobject reference count as follows:
     1. Initializes it to 1 in device_register.
     2. Increments it in chrdev_open
     3. Decrements it in __fput(see fs/file_table.c) after the
file_operations.release callback
     4. Decrements it in device_unregister

videodev currently handles the kobject reference count as follows:
     1. Initializes it to 1 in device_register.
     2. Decrements it in device_unregister.

With this patch, videodev will handle the kobject reference count as follows:
     1. Initialize it to 1 in device_register.
     2. Increment it in video_open.
     3. Decrement it in video_close.
     4. Decrement it in device_unregister.

This allows the following sequences of events before the kobject ref
count reaches 0 and the sysfs release callback is called.
     1. device_register
     2. video_open
     3. video_close
     4. device_unregister

- and -

     1. device_register
     2. video_open
     3. device_unregister
     4. video_close

Once videodev has been converted to use the char_dev api, video_open
and video_close may be removed. Until then they are needed to mimic
char_dev's behavior and ensure that the sysfs callback occurs at the
appropriate time.

Regards,

David Ellingsworth

From 354f72d4ed5861813b1509d437e551c19f8a6aca Mon Sep 17 00:00:00 2001
From: David Ellingsworth <david@xxxxxxxxxxxxxxxxx>
Date: Tue, 1 Jul 2008 16:04:26 -0400
Subject: [PATCH] videodev: fix sysfs kobj ref count


Signed-off-by: David Ellingsworth <david@xxxxxxxxxxxxxxxxx>
---
 drivers/media/video/videodev.c |   52 ++++++++++++++++++++++++++--------------
 include/media/v4l2-dev.h       |    1 +
 2 files changed, 35 insertions(+), 18 deletions(-)

diff --git a/drivers/media/video/videodev.c b/drivers/media/video/videodev.c
index 0d52819..0ef51b8 100644
--- a/drivers/media/video/videodev.c
+++ b/drivers/media/video/videodev.c
@@ -406,17 +406,23 @@ void video_device_release(struct video_device *vfd)
 }
 EXPORT_SYMBOL(video_device_release);
 
+/*
+ *	Active devices
+ */
+
+static struct video_device *video_device[VIDEO_NUM_DEVICES];
+static DEFINE_MUTEX(videodev_lock);
+
 static void video_release(struct device *cd)
 {
 	struct video_device *vfd = container_of(cd, struct video_device,
 								class_dev);
 
-#if 1
-	/* needed until all drivers are fixed */
-	if (!vfd->release)
-		return;
-#endif
-	vfd->release(vfd);
+	mutex_lock(&videodev_lock);
+	if (vfd->release)
+		vfd->release(vfd);
+	video_device[vfd->minor] = NULL;
+	mutex_unlock(&videodev_lock);
 }
 
 static struct device_attribute video_device_attrs[] = {
@@ -431,19 +437,30 @@ static struct class video_class = {
 	.dev_release = video_release,
 };
 
-/*
- *	Active devices
- */
-
-static struct video_device *video_device[VIDEO_NUM_DEVICES];
-static DEFINE_MUTEX(videodev_lock);
-
 struct video_device* video_devdata(struct file *file)
 {
 	return video_device[iminor(file->f_path.dentry->d_inode)];
 }
 EXPORT_SYMBOL(video_devdata);
 
+static int video_close(struct inode *inode, struct file *file)
+{
+	unsigned int minor = iminor(inode);
+	int err = 0;
+	struct video_device *vfl;
+
+	mutex_lock(&videodev_lock);
+	vfl = video_device[minor];
+
+	if (vfl->fops && vfl->fops->release)
+		err = vfl->fops->release(inode, file);
+
+	mutex_unlock(&videodev_lock);
+	kobject_put(&vfl->class_dev.kobj);
+
+	return err;
+}
+
 /*
  *	Open a video device - FIXME: Obsoleted
  */
@@ -469,8 +486,8 @@ static int video_open(struct inode *inode, struct file *file)
 		}
 	}
 	old_fops = file->f_op;
-	file->f_op = fops_get(vfl->fops);
-	if(file->f_op->open)
+	file->f_op = fops_get(&vfl->priv_fops);
+	if(file->f_op->open && kobject_get(&vfl->class_dev.kobj))
 		err = file->f_op->open(inode,file);
 	if (err) {
 		fops_put(file->f_op);
@@ -2175,6 +2192,8 @@ int video_register_device_index(struct video_device *vfd, int type, int nr,
 	}
 
 	vfd->index = ret;
+	vfd->priv_fops = *vfd->fops;
+	vfd->priv_fops.release = video_close;
 
 	mutex_unlock(&videodev_lock);
 	mutex_init(&vfd->lock);
@@ -2221,13 +2240,10 @@ EXPORT_SYMBOL(video_register_device_index);
 
 void video_unregister_device(struct video_device *vfd)
 {
-	mutex_lock(&videodev_lock);
 	if(video_device[vfd->minor]!=vfd)
 		panic("videodev: bad unregister");
 
-	video_device[vfd->minor]=NULL;
 	device_unregister(&vfd->class_dev);
-	mutex_unlock(&videodev_lock);
 }
 EXPORT_SYMBOL(video_unregister_device);
 
diff --git a/include/media/v4l2-dev.h b/include/media/v4l2-dev.h
index 3c93414..d4fe617 100644
--- a/include/media/v4l2-dev.h
+++ b/include/media/v4l2-dev.h
@@ -342,6 +342,7 @@ void *priv;
 	/* for videodev.c intenal usage -- please don't touch */
 	int users;                     /* video_exclusive_{open|close} ... */
 	struct mutex lock;             /* ... helper function uses these   */
+	struct file_operations priv_fops; /* video_close */
 };
 
 /* Class-dev to video-device */
-- 
1.5.5.1

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