Re: [RFC v4 2/4] crypto: Introduce CRYPTO_ALG_BULK flag

Herbert Xu
2016-06-15T06:50:22Z

On Wed, Jun 15, 2016 at 02:27:04PM +0800, Baolin Wang wrote:
>
> After some investigation, I still think we should divide the bulk
> request from dm-crypt into small request (each one is 512bytes) if
> this algorithm is not support bulk mode (like CBC). We have talked
> with dm-crypt
> maintainers why dm-crypt always use 512 bytes as one request size in
> below thread, could you please check it?
> http://www.kernelhub.org/?p=2&msg=907022

That link only points to an email about an oops.

Diggin through that thread, the only objection I have seen is about
the fact that you have to generate a fresh IV for each sector, which
is precisely what I'm suggesting that you do.

IOW, implement the IV generators in the crypto API, and then you can
easily generate a new IV (if necessary) for each sector.

> That means if we move the IV handling into crypto API, we still can
> not use bulk interface for all algorithm, for example we still need to
> read/write with 512 bytes for CBC, you can't use 4k or more block on
> CBC (and most other encryption modes). If only a part of 4k block is
> written (and then system crash happens), CBC would corrupt the block
> completely. It means if we map one whole bio with bulk interface in
> dm-crypt, we need to divide into every 512 bytes requests in crypto
> layer. So I don't think we can handle every algorithm with bulk
> interface just moving the IV handling into crypto API. Thanks.

Of course you would do CBC in 512-byte blocks, but my point is that
you should do this in a crypto API algorithm, rather than dm-crypt
as we do now. Once you implement that then dm-crypt can treat
every algorithm as if they supported bulk processing.

Cheers,
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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