Re: [PATCH v6 07/22] iomap: teach iomap to read files with fsverity

Darrick J. Wong
2026-03-31T23:30:11Z

On Tue, Mar 31, 2026 at 11:28:08PM +0200, Andrey Albershteyn wrote:
> Obtain fsverity info for folios with file data and fsverity metadata.
> Filesystem can pass vi down to ioend and then to fsverity for
> verification. This is different from other filesystems ext4, f2fs, btrfs
> supporting fsverity, these filesystems don't need fsverity_info for
> reading fsverity metadata. While reading merkle tree iomap requires
> fsverity info to synthesize hashes for zeroed data block.
>
> fsverity metadata has two kinds of holes - ones in merkle tree and one
> after fsverity descriptor.
>
> Merkle tree holes are blocks full of hashes of zeroed data blocks. These
> are not stored on the disk but synthesized on the fly. This saves a bit
> of space for sparse files. Due to this iomap also need to lookup
> fsverity_info for folios with fsverity metadata. ->vi has a hash of the
> zeroed data block which will be used to fill the merkle tree block.
>
> The hole past descriptor is interpreted as end of metadata region. As we
> don't have EOF here we use this hole as an indication that rest of the
> folio is empty. This patch marks rest of the folio beyond fsverity
> descriptor as uptodate.
>
> For file data, fsverity needs to verify consistency of the whole file
> against the root hash, hashes of holes are included in the merkle tree.
> Verify them too.
>
> Issue reading of fsverity merkle tree on the fsverity inodes. This way
> metadata will be available at I/O completion time.
>
> Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>

Still looks fine, thanks for reducing the patch count :)
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
> fs/iomap/buffered-io.c | 41 +++++++++++++++++++++++++++++++++++++++--
> include/linux/iomap.h | 2 ++
> 2 files changed, 41 insertions(+), 2 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index a80fcb598cc8..7ac319618f8e 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -9,6 +9,7 @@
> #include <linux/swap.h>
> #include <linux/migrate.h>
> #include <linux/fserror.h>
> +#include <linux/fsverity.h>
> #include "internal.h"
> #include "trace.h"
>
> @@ -561,9 +562,27 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
> if (plen == 0)
> return 0;
>
> - /* zero post-eof blocks as the page may be mapped */
> - if (iomap_block_needs_zeroing(iter, pos)) {
> + /*
> + * Handling of fsverity "holes". We hit this for two case:
> + * 1. No need to go further, the hole after fsverity
> + * descriptor is the end of the fsverity metadata.
> + *
> + * 2. This folio contains merkle tree blocks which need to be
> + * synthesized. If we already have fsverity info (ctx->vi)
> + * synthesize these blocks.
> + */
> + if ((iomap->flags & IOMAP_F_FSVERITY) &&
> + iomap->type == IOMAP_HOLE) {
> + if (ctx->vi)
> + fsverity_fill_zerohash(folio, poff, plen,
> + ctx->vi);
> + iomap_set_range_uptodate(folio, poff, plen);
> + } else if (iomap_block_needs_zeroing(iter, pos)) {
> + /* zero post-eof blocks as the page may be mapped */
> folio_zero_range(folio, poff, plen);
> + if (ctx->vi &&
> + !fsverity_verify_blocks(ctx->vi, folio, plen, poff))
> + return -EIO;
> iomap_set_range_uptodate(folio, poff, plen);
> } else {
> if (!*bytes_submitted)
> @@ -614,6 +633,15 @@ void iomap_read_folio(const struct iomap_ops *ops,
>
> trace_iomap_readpage(iter.inode, 1);
>
> + /*
> + * Fetch fsverity_info for both data and fsverity metadata, as iomap
> + * needs zeroed hash for merkle tree block synthesis
> + */
> + ctx->vi = fsverity_get_info(iter.inode);
> + if (ctx->vi && iter.pos < i_size_read(iter.inode))
> + fsverity_readahead(ctx->vi, folio->index,
> + folio_nr_pages(folio));
> +
> while ((ret = iomap_iter(&iter, ops)) > 0)
> iter.status = iomap_read_folio_iter(&iter, ctx,
> &bytes_submitted);
> @@ -681,6 +709,15 @@ void iomap_readahead(const struct iomap_ops *ops,
>
> trace_iomap_readahead(rac->mapping->host, readahead_count(rac));
>
> + /*
> + * Fetch fsverity_info for both data and fsverity metadata, as iomap
> + * needs zeroed hash for merkle tree block synthesis
> + */
> + ctx->vi = fsverity_get_info(iter.inode);
> + if (ctx->vi && iter.pos < i_size_read(iter.inode))
> + fsverity_readahead(ctx->vi, readahead_index(rac),
> + readahead_count(rac));
> +
> while (iomap_iter(&iter, ops) > 0)
> iter.status = iomap_readahead_iter(&iter, ctx,
> &cur_bytes_submitted);
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 4506a99d5285..4d9202cae29f 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -435,6 +435,7 @@ struct iomap_ioend {
> loff_t io_offset; /* offset in the file */
> sector_t io_sector; /* start sector of ioend */
> void *io_private; /* file system private data */
> + struct fsverity_info *io_vi; /* fsverity info */
> struct bio io_bio; /* MUST BE LAST! */
> };
>
> @@ -509,6 +510,7 @@ struct iomap_read_folio_ctx {
> struct readahead_control *rac;
> void *read_ctx;
> loff_t read_ctx_file_offset;
> + struct fsverity_info *vi;
> };
>
> struct iomap_read_ops {
> --
> 2.51.2
>
>