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

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Date:	Sun, 3 May 2015 21:37:24 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Anssi Hannula <anssi.hannula@....fi>,
	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

On Mon, May 04, 2015 at 09:00:16AM +0800, Herbert Xu wrote:
> 
> Sorry for the confusion.  Please just revert my patch.
> 
> I was trying to figure out what was causing various crypto modules
> to be built-in in my test config and this was the latest change that
> *looked* as if it might have caused my problem.  Obviously I didn't
> test it properly after making that change.
> 
> It should just be reverted because if ext4 was built-in then you
> do want to have the crypto stuff built-in just in case the root fs
> was encrypted.

Whoops, I _just_ sent a pull request to Linus.  The patch as it stands
actually allows both behaviors, depending on whether you answer 'y' or
'm' to EXT4_ENCRYPTION question.  Given that one of the main purposes
of per-filesystem encryption is that we only have to encrypt the user
files, so the system files can remain unencrypted for performance
reasons[1], I can imagine scenarios where it's conceivable that
someone might want to keep the crypto as modules.  My main unhappiness
with the Kconfig option is that it's a bit user unfriendly/confusing
what it means for CONFIG_EXT4_ENCRYPTION to be 'y' versus 'm'.

So I may end up reverting it, but since I've already sent the pull
request to Linus, I'm going to sleep on this for a bit.

Cheers,
					- Ted

[1] Though not for Intel chips; Intel acceleration of AES is so fast
there you might as well encrypt everything; and for single-user
laptops I still recommend dm-crypt.  Unfortunately, there are some ARM
chips which either do not have hardware accelerated AES, or where
their hardware accleration is decidedly poor....
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