linux-kernel - Re: [PATCH v3 3/3] blk-crypto: show crypto capabilities in sysfs

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Message-ID: <YbOSLC9SNelqwD+g@sol.localdomain>
Date:   Fri, 10 Dec 2021 09:45:16 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-mmc@...r.kernel.org, Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH v3 3/3] blk-crypto: show crypto capabilities in sysfs

On Fri, Dec 10, 2021 at 09:29:41AM -0800, Bart Van Assche wrote:
> (c) This encoding enforces the restriction that data unit sizes are a power of
>     two. Is there anything fundamental in encryption that restricts data unit
>     sizes to a power of two? I don't know the answer myself.

Well, the data unit size has to evenly divide the size of the request (for
requests that have an encryption context which specifies that data unit size).
So if the data unit size was, say, 1536 bytes, then all requests would have to
be multiples of 1536 bytes.  That has a factor of 3 in it, so it would be
impossible to make any power-of-2 size request.  That sounds pretty impractical;
it's hard to see how and why we would ever support such a thing.

- Eric