linux-kernel - Re: [RFC PATCH 2/4] media: Add Media Device Allocator API documentation

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Date:	Mon, 28 Mar 2016 15:14:35 -0600
From:	Shuah Khan <shuahkh@....samsung.com>
To:	Mauro Carvalho Chehab <mchehab@....samsung.com>
Cc:	laurent.pinchart@...asonboard.com, perex@...ex.cz, tiwai@...e.com,
	hans.verkuil@...co.com, chehabrafael@...il.com,
	javier@....samsung.com, jh1009.sung@...sung.com,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	alsa-devel@...a-project.org, Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [RFC PATCH 2/4] media: Add Media Device Allocator API
 documentation

On 03/28/2016 12:28 PM, Mauro Carvalho Chehab wrote:
> Em Fri, 25 Mar 2016 22:38:43 -0600
> Shuah Khan <shuahkh@....samsung.com> escreveu:
> 
>> Add Media Device Allocator API documentation.
> 
> Please merge this with the previous patch.

Yes. I will merge them.

-- Shuah
> 
>>
>> Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
>> ---
>>  include/media/media-dev-allocator.h | 32 ++++++++++++++++++++++++++++++++
>>  1 file changed, 32 insertions(+)
>>
>> diff --git a/include/media/media-dev-allocator.h b/include/media/media-dev-allocator.h
>> index 2932c90..174840c 100644
>> --- a/include/media/media-dev-allocator.h
>> +++ b/include/media/media-dev-allocator.h
>> @@ -20,6 +20,38 @@
>>  
>>  #ifdef CONFIG_MEDIA_CONTROLLER
>>  /**
>> + * DOC: Media Controller Device Allocator API
>> + * There are known problems with media device life time management. When media
>> + * device is released while an media ioctl is in progress, ioctls fail with
>> + * use-after-free errors and kernel hangs in some cases.
>> + * 
>> + * Media Device can be in any the following states:
>> + * 
>> + * - Allocated
>> + * - Registered (could be tied to more than one driver)
>> + * - Unregistered, not in use (media device file is not open)
>> + * - Unregistered, in use (media device file is not open)
>> + * - Released
>> + * 
>> + * When media device belongs to  more than one driver, registrations should be
>> + * refcounted to avoid unregistering when one of the drivers does unregister.
>> + * A refcount field in the struct media_device covers this case. Unregister on
>> + * a Media Allocator media device is a kref_put() call. The media device should
>> + * be unregistered only when the last unregister occurs.
>> + * 
>> + * When a media device is in use when it is unregistered, it should not be
>> + * released until the application exits when it detects the unregistered
>> + * status. Media device that is in use when it is unregistered is moved to
>> + * to_delete_list. When the last unregister occurs, media device is unregistered
>> + * and becomes an unregistered, still allocated device. Unregister marks the
>> + * device to be deleted.
>> + * 
>> + * When media device belongs to more than one driver, as both drivers could be
>> + * unbound/bound, driver should not end up getting stale media device that is
>> + * on its way out. Moving the unregistered media device to to_delete_list helps
>> + * this case as well.
>> + */
>> +/**
>>   * media_device_get() - Allocate and return global media device
>>   *
>>   * @mdev
> 
>