Re: [PATCH v4 06/25] fsverity: hoist pagecache_read from f2fs/ext4 to fsverity

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

On Mon, Mar 09, 2026 at 08:23:21PM +0100, Andrey Albershteyn wrote:
> This is the same function to read from pageache. XFS will also need
> this, so move this to core fsverity.
> 
> Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>

This looks like a neat code reduction. :)
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/ext4/verity.c         | 32 +++-----------------------------
>  fs/f2fs/verity.c         | 30 +-----------------------------
>  fs/verity/pagecache.c    | 33 +++++++++++++++++++++++++++++++++
>  include/linux/fsverity.h |  2 ++
>  4 files changed, 39 insertions(+), 58 deletions(-)
> 
> diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c
> index 347945ac23a4..ac5c133f5529 100644
> --- a/fs/ext4/verity.c
> +++ b/fs/ext4/verity.c
> @@ -34,32 +34,6 @@ static inline loff_t ext4_verity_metadata_pos(const struct inode *inode)
>  	return round_up(inode->i_size, 65536);
>  }
>  
> -/*
> - * Read some verity metadata from the inode.  __vfs_read() can't be used because
> - * we need to read beyond i_size.
> - */
> -static int pagecache_read(struct inode *inode, void *buf, size_t count,
> -			  loff_t pos)
> -{
> -	while (count) {
> -		struct folio *folio;
> -		size_t n;
> -
> -		folio = read_mapping_folio(inode->i_mapping, pos >> PAGE_SHIFT,
> -					 NULL);
> -		if (IS_ERR(folio))
> -			return PTR_ERR(folio);
> -
> -		n = memcpy_from_file_folio(buf, folio, pos, count);
> -		folio_put(folio);
> -
> -		buf += n;
> -		pos += n;
> -		count -= n;
> -	}
> -	return 0;
> -}
> -
>  /*
>   * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
>   * kernel_write() can't be used because the file descriptor is readonly.
> @@ -311,8 +285,8 @@ static int ext4_get_verity_descriptor_location(struct inode *inode,
>  		goto bad;
>  	desc_size_pos -= sizeof(desc_size_disk);
>  
> -	err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
> -			     desc_size_pos);
> +	err = fsverity_pagecache_read(inode, &desc_size_disk,
> +				      sizeof(desc_size_disk), desc_size_pos);
>  	if (err)
>  		return err;
>  	desc_size = le32_to_cpu(desc_size_disk);
> @@ -352,7 +326,7 @@ static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
>  	if (buf_size) {
>  		if (desc_size > buf_size)
>  			return -ERANGE;
> -		err = pagecache_read(inode, buf, desc_size, desc_pos);
> +		err = fsverity_pagecache_read(inode, buf, desc_size, desc_pos);
>  		if (err)
>  			return err;
>  	}
> diff --git a/fs/f2fs/verity.c b/fs/f2fs/verity.c
> index b3b3e71604ac..5ea0a9b40443 100644
> --- a/fs/f2fs/verity.c
> +++ b/fs/f2fs/verity.c
> @@ -36,34 +36,6 @@ static inline loff_t f2fs_verity_metadata_pos(const struct inode *inode)
>  	return round_up(inode->i_size, 65536);
>  }
>  
> -/*
> - * Read some verity metadata from the inode.  __vfs_read() can't be used because
> - * we need to read beyond i_size.
> - */
> -static int pagecache_read(struct inode *inode, void *buf, size_t count,
> -			  loff_t pos)
> -{
> -	while (count) {
> -		size_t n = min_t(size_t, count,
> -				 PAGE_SIZE - offset_in_page(pos));
> -		struct page *page;
> -
> -		page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
> -					 NULL);
> -		if (IS_ERR(page))
> -			return PTR_ERR(page);
> -
> -		memcpy_from_page(buf, page, offset_in_page(pos), n);
> -
> -		put_page(page);
> -
> -		buf += n;
> -		pos += n;
> -		count -= n;
> -	}
> -	return 0;
> -}
> -
>  /*
>   * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
>   * kernel_write() can't be used because the file descriptor is readonly.
> @@ -248,7 +220,7 @@ static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
>  	if (buf_size) {
>  		if (size > buf_size)
>  			return -ERANGE;
> -		res = pagecache_read(inode, buf, size, pos);
> +		res = fsverity_pagecache_read(inode, buf, size, pos);
>  		if (res)
>  			return res;
>  	}
> diff --git a/fs/verity/pagecache.c b/fs/verity/pagecache.c
> index 1d94bf73f38c..ec65f60e657f 100644
> --- a/fs/verity/pagecache.c
> +++ b/fs/verity/pagecache.c
> @@ -78,3 +78,36 @@ void fsverity_folio_zero_hash(struct folio *folio, size_t poff, size_t plen,
>  				vi->tree_params.digest_size);
>  }
>  EXPORT_SYMBOL_GPL(fsverity_folio_zero_hash);
> +
> +/**
> + * fsverity_pagecache_read() - read page and copy data to buffer
> + * @inode:	copy from this inode's address space
> + * @buf:	buffer to copy to
> + * @count:	number of bytes to copy
> + * @pos:	position of the folio to copy from
> + *
> + * Read some verity metadata from the inode.  __vfs_read() can't be used because
> + * we need to read beyond i_size.
> + */
> +int fsverity_pagecache_read(struct inode *inode, void *buf, size_t count,
> +			  loff_t pos)
> +{
> +	while (count) {
> +		struct folio *folio;
> +		size_t n;
> +
> +		folio = read_mapping_folio(inode->i_mapping, pos >> PAGE_SHIFT,
> +					 NULL);
> +		if (IS_ERR(folio))
> +			return PTR_ERR(folio);
> +
> +		n = memcpy_from_file_folio(buf, folio, pos, count);
> +		folio_put(folio);
> +
> +		buf += n;
> +		pos += n;
> +		count -= n;
> +	}
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(fsverity_pagecache_read);
> diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
> index 1ca8de129323..53dc161e18c0 100644
> --- a/include/linux/fsverity.h
> +++ b/include/linux/fsverity.h
> @@ -327,5 +327,7 @@ void generic_readahead_merkle_tree(struct inode *inode, pgoff_t index,
>  				   unsigned long nr_pages);
>  void fsverity_folio_zero_hash(struct folio *folio, size_t poff, size_t plen,
>  			      struct fsverity_info *vi);
> +int fsverity_pagecache_read(struct inode *inode, void *buf, size_t count,
> +			    loff_t pos);
>  
>  #endif	/* _LINUX_FSVERITY_H */
> -- 
> 2.51.2
> 
>