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Date: Thu, 22 Jul 2010 20:30:21 +0300
From: Sakari Ailus <sakari.ailus@maxwell.research.nokia.com>
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To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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Subject: Re: [RFC/PATCH v2 06/10] media: Entities, pads and links enumeration
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Laurent Pinchart wrote:
> Hi Sakari,

Hello Laurent,

...
>>> +
>>> +struct media_user_pad {
>>> +	__u32 entity;		/* entity ID */
>>> +	__u8 index;		/* pad index */
>>> +	__u32 direction;	/* pad direction */
>>> +};
>>
>> Another small comment, I think you mentioned it yourself some time back
>>
>> :-): how about some reserved fields to these structures?
> 
> Very good point. Reserved fields are needed in media_user_entity and 
> media_user_links at least. For media_user_pad and media_user_link, we could do 
> without reserved fields if we add fields to media_user_links to store the size 
> of those structures.

The structure size is part of the ioctl number defined by the _IOC macro
so I'd go with reserved fields even for these structures. Otherwise
special handling would be required for these ioctls in a few places.

>>> +struct media_user_entity {
>>> +	__u32 id;
>>> +	char name[32];
>>> +	__u32 type;
>>> +	__u32 subtype;
>>> +	__u8 pads;
>>> +	__u32 links;
>>> +
>>> +	union {
>>> +		/* Node specifications */
>>> +		struct {
>>> +			__u32 major;
>>> +			__u32 minor;
>>> +		} v4l;
>>> +		struct {
>>> +			__u32 major;
>>> +			__u32 minor;
>>> +		} fb;
>>> +		int alsa;
>>> +		int dvb;
>>> +
>>> +		/* Sub-device specifications */
>>> +		/* Nothing needed yet */

This union could have a defined size as well, e.g. u8 blob[64] or something.

Regards,

-- 
Sakari Ailus
sakari.ailus@maxwell.research.nokia.com