linux-kernel - Re: [PATCH 1/1] V4L: stk11xx, add a new webcam driver

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Message-ID: <466131CB.20301@free.fr>
Date:	Sat, 02 Jun 2007 11:00:59 +0200
From:	Thierry Merle <thierry.merle@...e.fr>
To:	Mauro Carvalho Chehab <mchehab@...radead.org>
CC:	video4linux-list@...hat.com, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Slaby <jirislaby@...il.com>
Subject: Re: [PATCH 1/1] V4L: stk11xx, add a new webcam driver



Mauro Carvalho Chehab a écrit :
>>> This seems to be an interesting approach.
>>>
>>>   
>>>       
>> Interesting but impossible to do for ioctl calls.
>> When the application does a ioctl(fd_of_mnt_video0,VIDIOC_G_FMT,&arg) 
>> for example, there is no way for the userspace helper to catch this ioctl.
>> The application could only open/read from the userspace helper's file 
>> /mnt/video0.
>> ioctl would still have to be done on the kernel device driver.
>> I thought also about a /proc interface for decompression algorithms (a 
>> helper would listen on a /proc file and write on another /proc file) but 
>> /proc is not designed for that kind of thing.
>> A separate library seems to be the simplest solution.
>>     
>
> There are some ways for this to work. For example, you may create a
> helper device for the daemon driver to bind, even requiring it to have
> root permission.
>
>   
Right, but I am afraid that complex userspace/kernelspace context 
changes breaks performance.
Nevertheless, I will start to specify the framework.
The helper daemon would link to the v4l2-apps/lib.
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