Re: [PATCH 04/11] fsverity: start consolidating pagecache code

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

On Thu, Jan 22, 2026 at 09:22:00AM +0100, Christoph Hellwig wrote:
> ext4 and f2fs are largely using the same code to read a page full
> of Merkle tree blocks from the page cache, and the upcoming xfs
> fsverity support would add another copy.
> 
> Move the ext4 code to fs/verity/ and use it in f2fs as well.  For f2fs
> this removes the previous f2fs-specific error injection, but otherwise
> the behavior remains unchanged.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/ext4/verity.c         | 17 +----------------
>  fs/f2fs/verity.c         | 17 +----------------
>  fs/verity/pagecache.c    | 38 ++++++++++++++++++++++++++++++++++++++
>  include/linux/fsverity.h |  3 +++
>  4 files changed, 43 insertions(+), 32 deletions(-)
>  create mode 100644 fs/verity/pagecache.c
> 
> diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c
> index 2ce4cf8a1e31..a071860ad36a 100644
> --- a/fs/ext4/verity.c
> +++ b/fs/ext4/verity.c
> @@ -361,23 +361,8 @@ static struct page *ext4_read_merkle_tree_page(struct inode *inode,
>  					       pgoff_t index,
>  					       unsigned long num_ra_pages)
>  {
> -	struct folio *folio;
> -
>  	index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
> -
> -	folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
> -	if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
> -		DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
> -
> -		if (!IS_ERR(folio))
> -			folio_put(folio);
> -		else if (num_ra_pages > 1)
> -			page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
> -		folio = read_mapping_folio(inode->i_mapping, index, NULL);
> -		if (IS_ERR(folio))
> -			return ERR_CAST(folio);
> -	}
> -	return folio_file_page(folio, index);
> +	return generic_read_merkle_tree_page(inode, index, num_ra_pages);
>  }
>  
>  static int ext4_write_merkle_tree_block(struct file *file, const void *buf,
> diff --git a/fs/f2fs/verity.c b/fs/f2fs/verity.c
> index c1c4d8044681..d37e584423af 100644
> --- a/fs/f2fs/verity.c
> +++ b/fs/f2fs/verity.c
> @@ -259,23 +259,8 @@ static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
>  					       pgoff_t index,
>  					       unsigned long num_ra_pages)
>  {
> -	struct folio *folio;
> -
>  	index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
> -
> -	folio = f2fs_filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
> -	if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
> -		DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
> -
> -		if (!IS_ERR(folio))
> -			folio_put(folio);
> -		else if (num_ra_pages > 1)
> -			page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
> -		folio = read_mapping_folio(inode->i_mapping, index, NULL);
> -		if (IS_ERR(folio))
> -			return ERR_CAST(folio);
> -	}
> -	return folio_file_page(folio, index);
> +	return generic_read_merkle_tree_page(inode, index, num_ra_pages);
>  }
>  
>  static int f2fs_write_merkle_tree_block(struct file *file, const void *buf,
> diff --git a/fs/verity/pagecache.c b/fs/verity/pagecache.c
> new file mode 100644
> index 000000000000..1efcdde20b73
> --- /dev/null
> +++ b/fs/verity/pagecache.c
> @@ -0,0 +1,38 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright 2019 Google LLC
> + */
> +
> +#include <linux/fsverity.h>
> +#include <linux/pagemap.h>
> +
> +/**
> + * generic_read_merkle_tree_page - generic ->read_merkle_tree_page helper
> + * @inode:	inode containing the Merkle tree
> + * @index:	0-based index of the page in the inode
> + * @num_ra_pages: The number of Merkle tree pages that should be prefetched.
> + *
> + * The caller needs to adjust @index from the Merkle-tree relative index passed
> + * to ->read_merkle_tree_page to the actual index where the Merkle tree is
> + * stored in the page cache for @inode.
> + */
> +struct page *generic_read_merkle_tree_page(struct inode *inode, pgoff_t index,
> +		unsigned long num_ra_pages)
> +{
> +	struct folio *folio;
> +
> +	folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);

Nice hoist, though I wonder -- as an exported fs function, should we be
checking that the returned folio doesn't cover EOF?  Not that any of the
users actually check that returned merkle tree folios fit that
criterion.

<shrug> as a pure hoist this is ok so
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> +	if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
> +		DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
> +
> +		if (!IS_ERR(folio))
> +			folio_put(folio);
> +		else if (num_ra_pages > 1)
> +			page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
> +		folio = read_mapping_folio(inode->i_mapping, index, NULL);
> +		if (IS_ERR(folio))
> +			return ERR_CAST(folio);
> +	}
> +	return folio_file_page(folio, index);
> +}
> +EXPORT_SYMBOL_GPL(generic_read_merkle_tree_page);
> diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
> index e22cf84fe83a..121703625cc8 100644
> --- a/include/linux/fsverity.h
> +++ b/include/linux/fsverity.h
> @@ -309,4 +309,7 @@ static inline int fsverity_file_open(struct inode *inode, struct file *filp)
>  
>  void fsverity_cleanup_inode(struct inode *inode);
>  
> +struct page *generic_read_merkle_tree_page(struct inode *inode, pgoff_t index,
> +		unsigned long num_ra_pages);
> +
>  #endif	/* _LINUX_FSVERITY_H */
> -- 
> 2.47.3
> 
>