linux-kernel - Re: [PATCH 01/29] fscrypt: Add in-place encryption mode

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Message-Id: <C622816B-E69F-4B81-9F37-E04E06CDC591@sigma-star.at>
Date:   Fri, 25 Nov 2016 13:09:05 +0100
From:   David Gstir <david@...ma-star.at>
To:     Eric Biggers <ebiggers@...gle.com>
Cc:     Richard Weinberger <richard@....at>, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        dedekind1@...il.com, adrian.hunter@...el.com, tytso@....edu,
        jaegeuk@...nel.org, wd@...x.de, sbabic@...x.de,
        dengler@...utronix.de, mhalcrow@...gle.com, hch@...radead.org
Subject: Re: [PATCH 01/29] fscrypt: Add in-place encryption mode

Eric,

> On 15.11.2016, at 19:14, Eric Biggers <ebiggers@...gle.com> wrote:
> 
> Hi,
> 
> On Sun, Nov 13, 2016 at 10:20:44PM +0100, Richard Weinberger wrote:
>> From: David Gstir <david@...ma-star.at>
>> 
>> ext4 and f2fs require a bounce page when encrypting pages. However, not
>> all filesystems will need that (eg. UBIFS). This is handled via a
>> flag on fscrypt_operations where a fs implementation can select in-place
>> encryption over using a bounce page (which is the default).
>> 
>> Signed-off-by: David Gstir <david@...ma-star.at>
>> Signed-off-by: Richard Weinberger <richard@....at>
> 
> The comment for fscrypt_encrypt_page() still says the following:
> 
> * Called on the page write path.  The caller must call
> * fscrypt_restore_control_page() on the returned ciphertext page to
> * release the bounce buffer and the encryption context.
> 
> It seems this isn't correct anymore.  

Yes, this is not true in all cases anymore. Will fix that.

> It also looks like the fscrypt_context
> never gets released in the case where the page is encrypted in-place.

You're right. I've already fixed that locally and will include it in the next patch set.

> Additionally, after this change the name of the flag FS_WRITE_PATH_FL is
> misleading, since it now really indicates the presence of a bounce buffer rather
> than the "write path".

I can see no use case for FS_WRITE_PATH_FL other than to indicate that the bounce buffer has to be free'd. Is there any reason why we should not just remove it and check the presence of a bounce buffer by a simple "if (ctx->w.bounce_page)" ?

Thanks,
David