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Date:   Tue, 22 Dec 2020 00:55:39 -0800
From:   Eric Biggers <ebiggers@kernel.org>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        David Sterba <dsterba@suse.com>,
        Paul Crowley <paulcrowley@google.com>
Subject: Re: [PATCH v2 09/11] crypto: blake2s - share the "shash" API
 boilerplate code
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On Sat, Dec 19, 2020 at 01:01:53AM +0100, Jason A. Donenfeld wrote:
> Hey Eric,
> 
> The solution you've proposed at the end of your email is actually kind
> of similar to what we do with curve25519. Check out
> include/crypto/curve25519.h. The critical difference between that and
> the blake proposal is that it's in the header for curve25519, so the
> indirection disappears.
> 
> Could we do that with headers for blake?
> 

That doesn't look too similar, since most of include/crypto/curve25519.h is just
for the library API.  curve25519_generate_secret() is shared, but it's only a
few lines of code and there's no function pointer argument.

Either way, it would be possible to add __blake2s_update() and __blake2s_final()
(taking a blake2s_compress_t argument) to include/crypto/internal/blake2s.h, and
make these used by (and inlined into) both the library and shash functions.

Note, that's mostly separate from the question of whether blake2s_helpers.ko
should exist, since that depends on whether we want the functions in it to get
inlined into every shash implementation or not.  I don't really have a strong
preference.  They did seem long enough to make them out-of-line; however,
indirect calls are bad too.  If we go with inlining, then the shash helper
functions (crypto_blake2s_{setkey,init,update,final}()) would just be inline
functions in include/crypto/internal/blake2s.h too, similar to sha256_base.h,
and they would get compiled into both blake2s_generic.ko and blake2s-${arch}.ko.

- Eric