linux-ext4 - Re: ext4 crypto: Do not select from EXT4_FS

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Message-ID: <554668EE.4000808@iki.fi>
Date:	Sun, 03 May 2015 21:29:02 +0300
From:	Anssi Hannula <anssi.hannula@....fi>
To:	Theodore Ts'o <tytso@....edu>
CC:	Herbert Xu <herbert@...dor.apana.org.au>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, Michael Halcrow <mhalcrow@...gle.com>
Subject: Re: ext4 crypto: Do not select from EXT4_FS_ENCRYPTION

03.05.2015, 20:53, Theodore Ts'o kirjoitti:
> On Sun, May 03, 2015 at 03:34:14PM +0300, Anssi Hannula wrote:
>> Hi,
>>
>> 01.05.2015, 03:18, Herbert Xu kirjoitti:
>>> This patch adds a tristate EXT4_ENCRYPTION to do the selections
>>> for EXT4_FS_ENCRYPTION because selecting from a bool causes all
>>> the selected options to be built-in, even if EXT4 itself is a
>>> module.
>>
>> Hmm, are you sure?
>>
>> Since CONFIG_EXT4_FS_ENCRYPTION itself depends on CONFIG_EXT4_FS, the
>> selector for the selected options becomes (CONFIG_EXT4_FS_ENCRYPTION &&
>> CONFIG_EXT4_FS && CONFIG_BLOCK).
>>
>> Per my testing on git master (without this patch), if EXT4_FS=m and
>> EXT4_FS_ENCRYPTION=y, both "built-in" and "module" options are allowed
>> for the selected options (checked CONFIG_ENCRYPTED_KEYS myself).
> 
> I believe the situation which is causing concern is when someone wants
> to build a kernel where EXT4_FS=y, but they want the cryptographic
> algorithms to be modules.  In that case, since EXT4_FS_ENCRYPTION is
> 'y', it forces the all of the crypto modules to be built into the
> kernel, and so it forecloses that option from someone who is building
> or packaging a kernel.

Ah, OK, so not "EXT4 itself as a module" like the commit message said :)

For the situation you described I don't see a better solution either.

-- 
Anssi Hannula

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