On 04/27/2016 10:43 AM, Lars-Peter Clausen wrote:
> Looks mostly good, a few comments.
>
> On 04/27/2016 05:08 AM, Shuah Khan wrote:
> [...]
>> @@ -428,7 +428,7 @@ static long media_device_ioctl(struct file *filp,
>> unsigned int cmd,
>> unsigned long arg)
>> {
>> struct media_devnode *devnode = media_devnode_data(filp);
>> - struct media_device *dev = to_media_device(devnode);
>
> Can we keep the helper macro, means we don't need to touch this code.
Yeah. I have been thinking about that as well. It avoids changes
and abstracts it.
>
>> + struct media_device *dev = devnode->media_dev;
>
> You need a lock to protect this from running concurrently with
> media_device_unregister() otherwise the struct might be freed while still in
> use.
>
Right. This needs to be protected.
>> long ret;
>>
>> switch (cmd) {
> [...]
>> @@ -725,21 +726,26 @@ int __must_check __media_device_register(struct
>> media_device *mdev,
>> {
>> int ret;
>>
>> + mdev->devnode = kzalloc(sizeof(struct media_devnode), GFP_KERNEL);
>
> sizeof(*mdev->devnode) is preferred kernel style,
Yeah. Force of habit, I keep forgetting it.
>
>> + if (!mdev->devnode)
>> + return -ENOMEM;
>> +
>> /* Register the device node. */
>> - mdev->devnode.fops = &media_device_fops;
>> - mdev->devnode.parent = mdev->dev;
>> - mdev->devnode.release = media_device_release;
>> + mdev->devnode->fops = &media_device_fops;
>> + mdev->devnode->parent = mdev->dev;
>> + mdev->devnode->media_dev = mdev;
>> + mdev->devnode->release = media_device_release;
>
> This should no longer be necessary. Just drop the release callback altogether.
It does nothing at the moment. I believe the intent is for this routine
to invoke any driver hooks if any at media_device level. It gets called
from media_devnode_release() which is the media_devnode->dev.release.
I will look into if it can be removed.
>
>>
>> /* Set version 0 to indicate user-space that the graph is static */
>> mdev->topology_version = 0;
>>
> [...]
>> @@ -813,8 +819,10 @@ void media_device_unregister(struct media_device *mdev)
>>
>> spin_unlock(&mdev->lock);
>>
>> - device_remove_file(&mdev->devnode.dev, &dev_attr_model);
>> - media_devnode_unregister(&mdev->devnode);
>> + device_remove_file(&mdev->devnode->dev, &dev_attr_model);
>> + media_devnode_unregister(mdev->devnode);
>> + /* kfree devnode is done via kobject_put() handler */
>> + mdev->devnode = NULL;
>
> mdev->devnode->media_dev needs to be set to NULL.
Yes. Thanks for catching it.
>
>>
>> dev_dbg(mdev->dev, "Media device unregistered\n");
>> }
>> diff --git a/drivers/media/media-devnode.c b/drivers/media/media-devnode.c
>> index 29409f4..9af9ba1 100644
>> --- a/drivers/media/media-devnode.c
>> +++ b/drivers/media/media-devnode.c
>> @@ -171,6 +171,9 @@ static int media_open(struct inode *inode, struct file
>> *filp)
>> mutex_unlock(&media_devnode_lock);
>> return -ENXIO;
>> }
>> +
>> + kobject_get(&mdev->kobj);
>
> This is not necessary, and if it was it would be prone to race condition as
> the last reference could be dropped before this line. But assigning the cdev
> parent makes sure that we always have a reference to the object while the
> open() callback is running.
I don't see cdev parent kobj get in cdev_get() which does kobject_get()
on cdev->kobj. Is that enough to get the reference?
cdev_add() gets the cdev parent kobj and cdev_del() puts it back. That is
the reason why I added a get here and put in media_release().
I can remove the get and put and test. Looks like I am not checking
kobject_get() return value which isn't good?
>
>> +
>> /* and increase the device refcount */
>> get_device(&mdev->dev);
>> mutex_unlock(&media_devnode_lock);
>> /*
> [...]
>> diff --git a/include/media/media-devnode.h b/include/media/media-devnode.h
>> index fe42f08..ba4bdaa 100644
>> --- a/include/media/media-devnode.h
>> +++ b/include/media/media-devnode.h
>> @@ -70,7 +70,9 @@ struct media_file_operations {
>> * @fops: pointer to struct &media_file_operations with media device ops
>> * @dev: struct device pointer for the media controller device
>> * @cdev: struct cdev pointer character device
>> + * @kobj: struct kobject
>> * @parent: parent device
>> + * @media_dev: media device
>> * @minor: device node minor number
>> * @flags: flags, combination of the MEDIA_FLAG_* constants
>> * @release: release callback called at the end of
>> media_devnode_release()
>> @@ -87,7 +89,9 @@ struct media_devnode {
>> /* sysfs */
>> struct device dev; /* media device */
>> struct cdev cdev; /* character device */
>> + struct kobject kobj; /* set as cdev parent kobj */
>
> You don't need a extra kobj. Just use the struct dev kobj.
Yeah I can use that as long as I can override the default release
function with media_devnode_free(). media_devnode should stick around
until the last app closes /dev/mediaX even if the media_device is no
longer registered. i.e media_ioctl should be able to check if devnode
is registered or not. I think I am missing something and don't understand
how struct dev kobj can be used.
>
>> struct device *parent; /* device parent */
>> + struct media_device *media_dev; /* media device for the devnode */
>>
>> /* device info */
>> int minor;
>
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