linux-ext4 - Re: [PATCH v2] Revert "ext4 crypto: fix to check feature status before get policy"

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Message-ID: <20191031164550.GF16197@mit.edu>
Date:   Thu, 31 Oct 2019 12:45:50 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        Douglas Anderson <dianders@...omium.org>,
        Gwendal Grignou <gwendal@...omium.org>,
        Ryo Hashimoto <hashimoto@...omium.org>, groeck@...omium.org,
        apronin@...omium.org, sukhomlinov@...gle.com,
        Chao Yu <chao@...nel.org>
Subject: Re: [PATCH v2] Revert "ext4 crypto: fix to check feature status
 before get policy"

On Wed, Oct 30, 2019 at 02:51:38PM -0700, Eric Biggers wrote:
> From: Douglas Anderson <dianders@...omium.org>
> 
> This reverts commit 0642ea2409f3 ("ext4 crypto: fix to check feature
> status before get policy").
> 
> The commit made a clear and documented ABI change that is not backward
> compatible.  There exists userspace code [1][2] that relied on the old
> behavior and is now broken.
> 
> While we could entertain the idea of updating the userspace code to
> handle the ABI change, it's my understanding that in general ABI
> changes that break userspace are frowned upon (to put it nicely).

The rule is that if someone complains, we have to revert.  Douglas's
email counts as a complaint, so we should revert.  That being said, if
ChromeOS (userspace) changes to using /sys/fs/ext4/features/encryption
to determine whether or not the kernel supports encryption, then we
can in the future change the error code to make things consistent with
f2fs.

This looks good, I'll pull it into ext4 git tree.

						- Ted