Re: [PATCH v3 05/35] fsverity: introduce fsverity_folio_zero_hash()

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Feb 18, 2026 at 12:19:05AM +0100, Andrey Albershteyn wrote:
> Helper to pre-fill folio with hashes of empty blocks. This will be used
> by XFS to synthesize blocks full of zero hashes on the fly.
> 
> Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
> ---
>  fs/verity/pagecache.c    | 22 ++++++++++++++++++++++
>  include/linux/fsverity.h |  9 +++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/fs/verity/pagecache.c b/fs/verity/pagecache.c
> index 73f03b48d42d..7642a7a09dfb 100644
> --- a/fs/verity/pagecache.c
> +++ b/fs/verity/pagecache.c
> @@ -2,6 +2,7 @@
>  /*
>   * Copyright 2019 Google LLC
>   */
> +#include "fsverity_private.h"
>  
>  #include <linux/export.h>
>  #include <linux/fsverity.h>
> @@ -62,3 +63,24 @@ loff_t fsverity_metadata_offset(const struct inode *inode)
>  	return roundup(i_size_read(inode), mapping_max_folio_size_supported());
>  }
>  EXPORT_SYMBOL_GPL(fsverity_metadata_offset);
> +
> +/**
> + * fsverity_folio_zero_hash() - fill folio with hashes of zero data block
> + * @folio:	folio to fill
> + * @poff:	offset in the folio to start
> + * @plen:	length of the range to fill with hashes
> + * @vi:		fsverity info
> + */
> +void fsverity_folio_zero_hash(struct folio *folio, size_t poff, size_t plen,
> +			      struct fsverity_info *vi)
> +{
> +	size_t offset = poff;
> +
> +	WARN_ON_ONCE(!IS_ALIGNED(poff, vi->tree_params.digest_size));
> +	WARN_ON_ONCE(!IS_ALIGNED(plen, vi->tree_params.digest_size));
> +
> +	for (; offset < (poff + plen); offset += vi->tree_params.digest_size)
> +		memcpy_to_folio(folio, offset, vi->tree_params.zero_digest,
> +				vi->tree_params.digest_size);
> +}
> +EXPORT_SYMBOL_GPL(fsverity_folio_zero_hash);
> diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
> index 278c6340849f..addee462dcc2 100644
> --- a/include/linux/fsverity.h
> +++ b/include/linux/fsverity.h
> @@ -215,6 +215,8 @@ bool fsverity_verify_blocks(struct fsverity_info *vi, struct folio *folio,
>  void fsverity_verify_bio(struct fsverity_info *vi, struct bio *bio);
>  void fsverity_enqueue_verify_work(struct work_struct *work);
>  loff_t fsverity_metadata_offset(const struct inode *inode);
> +void fsverity_folio_zero_hash(struct folio *folio, size_t poff, size_t plen,
> +			      struct fsverity_info *vi);
>  
>  #else /* !CONFIG_FS_VERITY */
>  
> @@ -302,6 +304,13 @@ static inline loff_t fsverity_metadata_offset(const struct inode *inode)
>  	return ULLONG_MAX;
>  }
>  
> +static inline void fsverity_folio_zero_hash(struct folio *folio, size_t poff,
> +					    size_t plen,
> +					    struct fsverity_info *vi)
> +{
> +	WARN_ON_ONCE(1);
> +}

/me wonders if something this deep in the IO path really needs a stub
version?  Otherwise this looks ok to me, in the "vaguely familiar from
long ago" sense. :/

--D

> +
>  #endif	/* !CONFIG_FS_VERITY */
>  
>  static inline bool fsverity_verify_folio(struct fsverity_info *vi,
> -- 
> 2.51.2
> 
>