[dm-devel] [PATCH] dm verity: log the hash algorithm implementation

[Ard Biesheuvel]

On Thu, 6 Dec 2018 at 05:54, Eric Biggers <ebiggers at kernel.org> wrote:
>
> From: Eric Biggers <ebiggers at google.com>
>
> Log the hash algorithm's driver name when a dm-verity target is created.
> This will help people determine whether the expected implementation is
> being used.  It can make an enormous difference; e.g., SHA-256 on ARM
> can be 8x faster with the crypto extensions than without.  It can also
> be useful to know if an implementation using an external crypto
> accelerator is being used instead of a software implementation.
>
> Example message:
>
> [   35.281945] device-mapper: verity: sha256 using implementation "sha256-ce"
>
> We've already found the similar message in fs/crypto/keyinfo.c to be
> very useful.
>
> Signed-off-by: Eric Biggers <ebiggers at google.com>

Acked-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>

> ---
>  drivers/md/dm-verity-target.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> index fc65f0dedf7f..f4c31ffaa88e 100644
> --- a/drivers/md/dm-verity-target.c
> +++ b/drivers/md/dm-verity-target.c
> @@ -1040,6 +1040,15 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
>                 v->tfm = NULL;
>                 goto bad;
>         }
> +
> +       /*
> +        * dm-verity performance can vary greatly depending on which hash
> +        * algorithm implementation is used.  Help people debug performance
> +        * problems by logging the ->cra_driver_name.
> +        */
> +       DMINFO("%s using implementation \"%s\"", v->alg_name,
> +              crypto_hash_alg_common(v->tfm)->base.cra_driver_name);
> +
>         v->digest_size = crypto_ahash_digestsize(v->tfm);
>         if ((1 << v->hash_dev_block_bits) < v->digest_size * 2) {
>                 ti->error = "Digest size too big";
> --
> 2.19.2
>