linux-kernel - Re: [PATCH 15/31] media: dvb-frontend invoke enable/disable

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Message-ID: <20160128160711.029f3faf@lxorguk.ukuu.org.uk>
Date:	Thu, 28 Jan 2016 16:07:11 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Mauro Carvalho Chehab <mchehab@....samsung.com>
Cc:	Shuah Khan <shuahkh@....samsung.com>, tiwai@...e.com,
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Subject: Re: [PATCH 15/31] media: dvb-frontend invoke enable/disable_source
 handlers

On Thu, 28 Jan 2016 13:53:04 -0200
Mauro Carvalho Chehab <mchehab@....samsung.com> wrote:

> Em Wed,  6 Jan 2016 13:27:04 -0700
> Shuah Khan <shuahkh@....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.
> 
> 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.

Alan