linux-kernel - Re: [v4l-dvb-maintainer] [patch, -git] drivers/media build fix fo r modular builds

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Message-ID: <4818F4EE.8050004@linuxtv.org>
Date:	Wed, 30 Apr 2008 18:38:38 -0400
From:	mkrufky@...uxtv.org
To:	xyzzy@...akeasy.org
Cc:	akpm@...ux-foundation.org, sfr@...b.auug.org.au,
	video4linux-list@...hat.com, torvalds@...ux-foundation.org,
	efault@....de, linux-kernel@...r.kernel.org, mchehab@...radead.org,
	linux-dvb-maintainer@...uxtv.org, mingo@...e.hu, sam@...nborg.org,
	davem@...emloft.net
Subject: Re: [v4l-dvb-maintainer] [patch, -git] drivers/media build fix fo
	r modular builds

Trent Piepho wrote:
> On Wed, 30 Apr 2008, Andrew Morton wrote:
>   
>> Does this make it feel better?
>>
>> --- a/drivers/media/video/tuner-core.c~a
>> +++ a/drivers/media/video/tuner-core.c
>> @@ -40,11 +40,11 @@
>>  	typeof(&FUNCTION) __a = symbol_request(FUNCTION); \
>>  	if (__a) { \
>>  		__r = (int) __a(ARGS); \
>> +		symbol_put(FUNCTION); \
>>  	} else { \
>>  		printk(KERN_ERR "TUNER: Unable to find " \
>>  				"symbol "#FUNCTION"()\n"); \
>>  	} \
>> -	symbol_put(FUNCTION); \
>>  	__r; \
>>  })
>>     
>
> Should the symbol_put be done at all?  When I wrote the code this is based
> on, it would check if FUNCTION failed or not.  If it failed, the symbol
was
> put.  But if it worked, then one was returned a handle into FUNCTION's
> module, and so the symbol was not put.  If it was, the module's refcount
> would be zero but the caller would have a handle into the module.
>
> So if FUNCTION does anything that creates references to the module, and it
> doesn't inc it's own refcount, then the symbol_put shouldn't be done.
>
>   
Trent,

The symbol_put is correct in this case.  This macro above is called 
"tuner_symbol_probe" , used only within tuner-core.c

This macro is used to call the probe function of a tuner sub-module 
(tea5761, tea5767, tda8290).  Regardless of whether the probe succeeds 
or fails, we do the symbol_put.  If the probe succeeds, tuner-core will 
proceed to dvb_attach(that_tuner_attach, params), which does the actual 
module use count increase.

Regards,

Mike
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