Re: [PATCH v2 03/18] lib/crc32: expose whether the lib is really optimized at runtime

Ard Biesheuvel
2024-10-25T20:32:27Z

On Fri, 25 Oct 2024 at 21:15, Eric Biggers <ebiggers@kernel.org> wrote:
>
> From: Eric Biggers <ebiggers@google.com>
>
> Make the CRC32 library export some flags that indicate which CRC32
> functions are actually executing optimized code at runtime. Set these
> correctly from the architectures that implement the CRC32 functions.
>
> This will be used to determine whether the crc32[c]-$arch shash
> algorithms should be registered in the crypto API. btrfs could also
> start using these flags instead of the hack that it currently uses where
> it parses the crypto_shash_driver_name.
>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
> arch/arm64/lib/crc32-glue.c | 15 +++++++++++++++
> arch/riscv/lib/crc32-riscv.c | 15 +++++++++++++++
> include/linux/crc32.h | 15 +++++++++++++++
> lib/crc32.c | 5 +++++
> 4 files changed, 50 insertions(+)
>
...
> diff --git a/include/linux/crc32.h b/include/linux/crc32.h
> index 58c632533b08..bf26d454b60d 100644
> --- a/include/linux/crc32.h
> +++ b/include/linux/crc32.h
> @@ -35,10 +35,25 @@ static inline u32 __pure __crc32c_le(u32 crc, const u8 *p, size_t len)
> if (IS_ENABLED(CONFIG_CRC32_ARCH))
> return crc32c_le_arch(crc, p, len);
> return crc32c_le_base(crc, p, len);
> }
>
> +/*
> + * crc32_optimizations contains flags that indicate which CRC32 library
> + * functions are using architecture-specific optimizations. Unlike
> + * IS_ENABLED(CONFIG_CRC32_ARCH) it takes into account the different CRC32
> + * variants and also whether any needed CPU features are available at runtime.
> + */
> +#define CRC32_LE_OPTIMIZATION BIT(0) /* crc32_le() is optimized */
> +#define CRC32_BE_OPTIMIZATION BIT(1) /* crc32_be() is optimized */
> +#define CRC32C_OPTIMIZATION BIT(2) /* __crc32c_le() is optimized */
> +#if IS_ENABLED(CONFIG_CRC32_ARCH)
> +extern u32 crc32_optimizations;
> +#else
> +#define crc32_optimizations 0
> +#endif
> +

Wouldn't it be cleaner to add a new library function for this, instead
of using a global variable?

> /**
> * crc32_le_combine - Combine two crc32 check values into one. For two
> * sequences of bytes, seq1 and seq2 with lengths len1
> * and len2, crc32_le() check values were calculated
> * for each, crc1 and crc2.
> diff --git a/lib/crc32.c b/lib/crc32.c
> index 47151624332e..194de73f30f8 100644
> --- a/lib/crc32.c
> +++ b/lib/crc32.c
> @@ -336,5 +336,10 @@ u32 __pure crc32_be_base(u32 crc, const u8 *p, size_t len)
> {
> return crc32_be_generic(crc, p, len, crc32table_be, CRC32_POLY_BE);
> }
> #endif
> EXPORT_SYMBOL(crc32_be_base);
> +
> +#if IS_ENABLED(CONFIG_CRC32_ARCH)
> +u32 crc32_optimizations;
> +EXPORT_SYMBOL(crc32_optimizations);
> +#endif
> --
> 2.47.0
>
>