Re: [PATCH RFC 01/29] iomap: add iomap_writepages_unbound() to write beyond EOF

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

On Mon, Jul 28, 2025 at 10:30:05PM +0200, Andrey Albershteyn wrote:
> From: Andrey Albershteyn <aalbersh@redhat.com>
> 
> Add iomap_writepages_unbound() without limit in form of EOF. XFS
> will use this to write metadata (fs-verity Merkle tree) in range far
> beyond EOF.

...and I guess some day fscrypt might use it to encrypt merkle trees
too?

> Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
> ---
>  fs/iomap/buffered-io.c | 51 +++++++++++++++++++++++++++++++++++++++-----------
>  include/linux/iomap.h  |  3 +++
>  2 files changed, 43 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 3729391a18f3..7bef232254a3 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1881,18 +1881,10 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
>  	int error = 0;
>  	u32 rlen;
>  
> -	WARN_ON_ONCE(!folio_test_locked(folio));
> -	WARN_ON_ONCE(folio_test_dirty(folio));
> -	WARN_ON_ONCE(folio_test_writeback(folio));
> -
> -	trace_iomap_writepage(inode, pos, folio_size(folio));
> -
> -	if (!iomap_writepage_handle_eof(folio, inode, &end_pos)) {
> -		folio_unlock(folio);
> -		return 0;
> -	}
>  	WARN_ON_ONCE(end_pos <= pos);
>  
> +	trace_iomap_writepage(inode, pos, folio_size(folio));
> +
>  	if (i_blocks_per_folio(inode, folio) > 1) {
>  		if (!ifs) {
>  			ifs = ifs_alloc(inode, folio, 0);
> @@ -1956,6 +1948,23 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
>  	return error;
>  }
>  
> +/* Map pages bound by EOF */
> +static int iomap_writepage_map_eof(struct iomap_writepage_ctx *wpc,

iomap_writepage_map_within_eof ?

> +		struct writeback_control *wbc, struct folio *folio)
> +{
> +	int error;
> +	struct inode *inode = folio->mapping->host;
> +	u64 end_pos = folio_pos(folio) + folio_size(folio);
> +
> +	if (!iomap_writepage_handle_eof(folio, inode, &end_pos)) {
> +		folio_unlock(folio);
> +		return 0;
> +	}
> +
> +	error = iomap_writepage_map(wpc, wbc, folio);
> +	return error;
> +}
> +
>  int
>  iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
>  		struct iomap_writepage_ctx *wpc,
> @@ -1972,9 +1981,29 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
>  			PF_MEMALLOC))
>  		return -EIO;
>  
> +	wpc->ops = ops;
> +	while ((folio = writeback_iter(mapping, wbc, folio, &error))) {
> +		WARN_ON_ONCE(!folio_test_locked(folio));
> +		WARN_ON_ONCE(folio_test_dirty(folio));
> +		WARN_ON_ONCE(folio_test_writeback(folio));
> +
> +		error = iomap_writepage_map_eof(wpc, wbc, folio);
> +	}
> +	return iomap_submit_ioend(wpc, error);
> +}
> +EXPORT_SYMBOL_GPL(iomap_writepages);
> +
> +int
> +iomap_writepages_unbound(struct address_space *mapping, struct writeback_control *wbc,

Might want to leave a comment here explaining what's the difference
between the two iomap_writepages exports:

/*
 * Write dirty pages, including any beyond EOF.  This is solely for use
 * by files that allow post-EOF pagecache, which means fsverity.
 */

> +		struct iomap_writepage_ctx *wpc,
> +		const struct iomap_writeback_ops *ops)
> +{
> +	struct folio *folio = NULL;
> +	int error;
> +

...and you might want a:

	WARN_ON(!IS_VERITY(wpc->inode));

to keep it that way.

--D

>  	wpc->ops = ops;
>  	while ((folio = writeback_iter(mapping, wbc, folio, &error)))
>  		error = iomap_writepage_map(wpc, wbc, folio);
>  	return iomap_submit_ioend(wpc, error);
>  }
> -EXPORT_SYMBOL_GPL(iomap_writepages);
> +EXPORT_SYMBOL_GPL(iomap_writepages_unbound);
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 522644d62f30..4a0b5ebb79e9 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -464,6 +464,9 @@ void iomap_sort_ioends(struct list_head *ioend_list);
>  int iomap_writepages(struct address_space *mapping,
>  		struct writeback_control *wbc, struct iomap_writepage_ctx *wpc,
>  		const struct iomap_writeback_ops *ops);
> +int iomap_writepages_unbound(struct address_space *mapping,
> +		struct writeback_control *wbc, struct iomap_writepage_ctx *wpc,
> +		const struct iomap_writeback_ops *ops);
>  
>  /*
>   * Flags for direct I/O ->end_io:
> 
> -- 
> 2.50.0
> 
>