Re: [PATCH v3 04/18] crypto: crc32 - don't unnecessarily register arch algorithms

[Ard Biesheuvel <ardb@kernel.org>]

On Sun, 3 Nov 2024 at 23:32, Eric Biggers <ebiggers@kernel.org> wrote:
>
> From: Eric Biggers <ebiggers@google.com>
>
> Instead of registering the crc32-$arch and crc32c-$arch algorithms if
> the arch-specific code was built, only register them when that code was
> built *and* is not falling back to the base implementation at runtime.
>
> This avoids confusing users like btrfs which checks the shash driver
> name to determine whether it is crc32c-generic.
>
> (It would also make sense to change btrfs to test the crc32_optimization
> flags itself, so that it doesn't have to use the weird hack of parsing
> the driver name.  This change still makes sense either way though.)
>
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

> ---
>  crypto/crc32_generic.c  | 8 ++++++--
>  crypto/crc32c_generic.c | 8 ++++++--
>  2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/crypto/crc32_generic.c b/crypto/crc32_generic.c
> index cc064ea8240e..783a30b27398 100644
> --- a/crypto/crc32_generic.c
> +++ b/crypto/crc32_generic.c
> @@ -155,19 +155,23 @@ static struct shash_alg algs[] = {{
>         .base.cra_ctxsize       = sizeof(u32),
>         .base.cra_module        = THIS_MODULE,
>         .base.cra_init          = crc32_cra_init,
>  }};
>
> +static int num_algs;
> +
>  static int __init crc32_mod_init(void)
>  {
>         /* register the arch flavor only if it differs from the generic one */
> -       return crypto_register_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH));
> +       num_algs = 1 + ((crc32_optimizations() & CRC32_LE_OPTIMIZATION) != 0);
> +
> +       return crypto_register_shashes(algs, num_algs);
>  }
>
>  static void __exit crc32_mod_fini(void)
>  {
> -       crypto_unregister_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH));
> +       crypto_unregister_shashes(algs, num_algs);
>  }
>
>  subsys_initcall(crc32_mod_init);
>  module_exit(crc32_mod_fini);
>
> diff --git a/crypto/crc32c_generic.c b/crypto/crc32c_generic.c
> index 04b03d825cf4..985da981d6e2 100644
> --- a/crypto/crc32c_generic.c
> +++ b/crypto/crc32c_generic.c
> @@ -195,19 +195,23 @@ static struct shash_alg algs[] = {{
>         .base.cra_ctxsize       = sizeof(struct chksum_ctx),
>         .base.cra_module        = THIS_MODULE,
>         .base.cra_init          = crc32c_cra_init,
>  }};
>
> +static int num_algs;
> +
>  static int __init crc32c_mod_init(void)
>  {
>         /* register the arch flavor only if it differs from the generic one */
> -       return crypto_register_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH));
> +       num_algs = 1 + ((crc32_optimizations() & CRC32C_OPTIMIZATION) != 0);
> +
> +       return crypto_register_shashes(algs, num_algs);
>  }
>
>  static void __exit crc32c_mod_fini(void)
>  {
> -       crypto_unregister_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH));
> +       crypto_unregister_shashes(algs, num_algs);
>  }
>
>  subsys_initcall(crc32c_mod_init);
>  module_exit(crc32c_mod_fini);
>
> --
> 2.47.0
>
>