linux-kernel - Re: Warnings from silentoldconfig (Re: [GIT PULL] PCI updates for v3.11)

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Date:	Tue, 06 Aug 2013 10:20:15 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	"Yann E. MORIN" <yann.morin.1998@...e.fr>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kbuild <linux-kbuild@...r.kernel.org>
Subject: Re: Warnings from silentoldconfig (Re: [GIT PULL] PCI updates for
 v3.11)

On 6.8.2013 00:58, Yann E. MORIN wrote:
> On 2013-08-05 10:39 +0200, Michal Marek spake thusly:
>> Added Yann and the linux-kbuild list to CC. Reproducer:
>>
>>   git checkout 1fe0135
>>   make mrproper
>>   make allmodconfig
>>   make silentoldconfig
>>   git checkout aa8032b
>>   make allmodconfig
>>   make silentoldconfig
>>
>> conf_write_autoconf() first calls conf_split_config() to generate the
>> include/config/**.h hierarchy, then generates include/config/auto.conf.
>> For some reason, conf_split_config() reads include/config/auto.conf,
>> which may not exist yet or may be out of date. Yann, can anything break
>> if we simply do not read that file from conf_split_config(), like this?
>>
>> diff --git a/scripts/kconfig/confdata.c b/scripts/kconfig/confdata.c
>> index c55c227..8c90835 100644
>> --- a/scripts/kconfig/confdata.c
>> +++ b/scripts/kconfig/confdata.c
>> @@ -829,16 +829,12 @@ next:
>>  
>>  static int conf_split_config(void)
>>  {
>> -	const char *name;
>>  	char path[PATH_MAX+1];
>>  	char *s, *d, c;
>>  	struct symbol *sym;
>>  	struct stat sb;
>>  	int res, i, fd;
>>  
>> -	name = conf_get_autoconfig_name();
>> -	conf_read_simple(name, S_DEF_AUTO);
>> -
>>  	if (chdir("include/config"))
>>  		return 1;
[...]
> 
> What I understand of the code is that, we're reading auto.conf with
> the S_DEF_AUTO flag, which is expected to set the SYMBOL_DEF_AUTO flags
> to symbols read from auto.conf.
> 
> This is then used by conf_split_config to detect symbols that have
> changed.

Ah, _that_ is why it's there.

[...]
> The two following tests do not invlolve the HOTPLUG_PCI_.* symbols
> on purpose, and involve a pristine master c095ba7:
> 
>     $ make allmodconfig
>     $ make silentoldconfig
>     $ make silentoldconfig
>     $ make silentoldconfig
> 
>   - Without Michal's proposed change, unaffected symbols are not
>     touched. For example, mtime and ctime for zswap.h are not changed
>     after the second and third silentoldconfig.
> 
>   - With Michal's proposed change, then mtime and ctime for zswap.h are
>     changed after each silentoldconfig, even though CONFIG_ZSWAP was not
>     changed.

Yes, I only did a simple diff -rq between two generated include/config
directories and did not think about mtimes.


> One solution would be to read auto.conf *before* we fuzz around symbols,
> not after. We should probably read auto.conf just after we read .config.

Maybe the safest solution would be to silence the warning if def ==
S_DEF_AUTO. Because auto.conf is only read by kconfig in
conf_split_config(), when it is expected to be out of date.

Michal
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