Re: [PATCH 15/31] media: dvb-frontend invoke enable/disable_source handlers

From: Shuah Khan <shuahkh@osg.samsung.com>
To: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
	Mauro Carvalho Chehab <mchehab@osg.samsung.com>
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	Shuah Khan <shuahkh@osg.samsung.com>
Subject: Re: [PATCH 15/31] media: dvb-frontend invoke enable/disable_source handlers
Date: Thu, 28 Jan 2016 09:59:38 -0700	[thread overview]
Message-ID: <56AA48FA.7070203@osg.samsung.com> (raw)
In-Reply-To: <20160128160711.029f3faf@lxorguk.ukuu.org.uk>

On 01/28/2016 09:07 AM, One Thousand Gnomes wrote:
> On Thu, 28 Jan 2016 13:53:04 -0200
> Mauro Carvalho Chehab <mchehab@osg.samsung.com> wrote:
> 
>> Em Wed,  6 Jan 2016 13:27:04 -0700
>> Shuah Khan <shuahkh@osg.samsung.com> escreveu:
>>
>>> Checking for tuner availability from frontend thread start
>>> disrupts video stream. Change to check for tuner and start
>>> pipeline from frontend open instead and stop pipeline from
>>> frontend release.  
>>
>> That's wrong, as DVB can be opened on read-only mode, where
>> it won't be changing anything.

Correct. Please check the code. Tuner availability check is
done when the device is opened in Write mode in the following
conditional.

       if ((file->f_flags & O_ACCMODE) != O_RDONLY) {

>>
>> Also, I don't think POSIX allows to return an error like EBUSY
>> on open:
>> 	http://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html
> 
> It doesn't document all the errors you may return. Quite a lot of
> kernel drivers return EBUSY when they are "single open" things.
> 
> POSIX documents certain cases that *must* error and what the error code
> is. It documents certain possible failures and what their error code is.
> Beyond that it's up to you.
> 

Returning EBUSY clearly indicates the reason why the device
can't be opened in this case.

thanks,
-- Shuah

-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@osg.samsung.com | (970) 217-8978