Re: [PATCH 01/13] btrfs: introduce a pure data checksum checking helper

[Christoph Hellwig <hch@infradead.org>]

> +/*
> + * Verify the checksum for a single sector without any extra action that
> + * depend on the type of I/O.
> + */
> +int btrfs_check_data_sector(struct btrfs_fs_info *fs_info, struct page *page,
> +			    u32 pgoff, u8 *csum_expected)
> +{
> +	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
> +	char *kaddr;
> +	const u32 len = fs_info->sectorsize;
> +	const u32 csum_size = fs_info->csum_size;
> +	u8 csum[BTRFS_CSUM_SIZE];
> +
> +	ASSERT(pgoff + len <= PAGE_SIZE);
> +
> +	kaddr = kmap_local_page(page) + pgoff;
> +	shash->tfm = fs_info->csum_shash;
> +
> +	crypto_shash_digest(shash, kaddr, len, csum);
> +	kunmap_local(kaddr);

Nit: the ->tfm assignment can move out of the kmap section.  Otherwise
this looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>