On Thu, Jun 25, 2026 at 02:07:57PM +0200, Christoph Hellwig wrote:
> Currently the iomap buffered read path tries to build up read context
> (i.e. bios for the typical block based case) over multiple iomaps as
> long as the sector matches. This does not take into account files
> that can map to multiple different devices. While this could be fixed
> by a bdev check in iomap_bio_read_folio_range, the building up of I/O
> over iomaps actually was a problem for the not yet merged ext2 iomap
> port, as that does want to send out I/O at the end of an indirect
> block mapped range.
This really puts the onus on block-mapped filesystems (e.g. ext2) to
merge adjacent maps into extents. Granted they *probably* already have
been doing that.
> So instead of adding more checks move over to a model where a bio only
> spans a single iomap. Change ->submit_read to be called after each
> iteration, and pass a force argument to indicate that the bio must
> be submitted set on the last iteration. Switch the bio based users
> to always submit, while keeping the single submit for fuse.
Is fuse the sole reason for the "force" parameter to exist? I wonder if
fuse could drop its submit_read function and call fuse_send_readpages
after the iomap_read{ahead,folio} function returns?
--D
> Fixes: dfeab2e95a75 ("erofs: add multiple device support")
> Reported-by: Kelu Ye <[email protected]>
> Reported-by: Yifan Zhao <[email protected]>
> Signed-off-by: Christoph Hellwig <[email protected]>
> Tested-by: Yifan Zhao <[email protected]>
> ---
> fs/exfat/iomap.c | 2 +-
> fs/fuse/file.c | 6 +++++-
> fs/iomap/bio.c | 6 ++++--
> fs/iomap/buffered-io.c | 21 +++++++++++++--------
> fs/ntfs/aops.c | 2 +-
> fs/ntfs3/inode.c | 2 +-
> fs/xfs/xfs_aops.c | 3 ++-
> include/linux/iomap.h | 2 +-
> 8 files changed, 28 insertions(+), 16 deletions(-)
>
> diff --git a/fs/exfat/iomap.c b/fs/exfat/iomap.c
> index 190fc6471f84..c428a949120e 100644
> --- a/fs/exfat/iomap.c
> +++ b/fs/exfat/iomap.c
> @@ -251,7 +251,7 @@ static void exfat_iomap_read_end_io(struct bio *bio)
> }
>
> static void exfat_iomap_bio_submit_read(const struct iomap_iter *iter,
> - struct iomap_read_folio_ctx *ctx)
> + struct iomap_read_folio_ctx *ctx, bool force)
> {
> iomap_bio_submit_read_endio(iter, ctx, exfat_iomap_read_end_io);
> }
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index e052a0d44dee..6fa3b1f55c95 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -982,13 +982,17 @@ static int fuse_iomap_read_folio_range_async(const
> struct iomap_iter *iter,
> }
>
> static void fuse_iomap_submit_read(const struct iomap_iter *iter,
> - struct iomap_read_folio_ctx *ctx)
> + struct iomap_read_folio_ctx *ctx, bool force)
> {
> struct fuse_fill_read_data *data = ctx->read_ctx;
>
> + if (!force)
> + return;
> +
> if (data->ia)
> fuse_send_readpages(data->ia, data->file, data->nr_bytes,
> data->fc->async_read);
> + ctx->read_ctx = NULL;
> }
>
> static const struct iomap_read_ops fuse_iomap_read_ops = {
> diff --git a/fs/iomap/bio.c b/fs/iomap/bio.c
> index 0f31e35567b4..6aca1cd0622c 100644
> --- a/fs/iomap/bio.c
> +++ b/fs/iomap/bio.c
> @@ -87,11 +87,13 @@ void iomap_bio_submit_read_endio(const struct iomap_iter
> *iter,
> if (iter->iomap.flags & IOMAP_F_INTEGRITY)
> fs_bio_integrity_alloc(bio);
> submit_bio(bio);
> +
> + ctx->read_ctx = NULL;
> }
> EXPORT_SYMBOL_GPL(iomap_bio_submit_read_endio);
>
> static void iomap_bio_submit_read(const struct iomap_iter *iter,
> - struct iomap_read_folio_ctx *ctx)
> + struct iomap_read_folio_ctx *ctx, bool force)
> {
> return iomap_bio_submit_read_endio(iter, ctx, iomap_read_end_io);
> }
> @@ -116,7 +118,7 @@ static void iomap_read_alloc_bio(const struct iomap_iter
> *iter,
>
> /* Submit the existing range if there was one. */
> if (ctx->read_ctx)
> - ctx->ops->submit_read(iter, ctx);
> + ctx->ops->submit_read(iter, ctx, true);
>
> /* Same as readahead_gfp_mask: */
> if (ctx->rac)
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 8d4806dc46d4..b1c3da8a97dc 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -524,6 +524,13 @@ static void iomap_read_end(struct folio *folio, size_t
> bytes_submitted)
> }
> }
>
> +static void iomap_submit_read(struct iomap_iter *iter,
> + struct iomap_read_folio_ctx *ctx, bool force)
> +{
> + if (ctx->read_ctx && ctx->ops->submit_read)
> + ctx->ops->submit_read(iter, ctx, force);
> +}
> +
> static int iomap_read_folio_iter(struct iomap_iter *iter,
> struct iomap_read_folio_ctx *ctx, size_t *bytes_submitted)
> {
> @@ -642,12 +649,11 @@ void iomap_read_folio(const struct iomap_ops *ops,
> fsverity_readahead(ctx->vi, folio->index,
> folio_nr_pages(folio));
>
> - while ((ret = iomap_iter(&iter, ops)) > 0)
> + while ((ret = iomap_iter(&iter, ops)) > 0) {
> iter.status = iomap_read_folio_iter(&iter, ctx,
> &bytes_submitted);
> -
> - if (ctx->read_ctx && ctx->ops->submit_read)
> - ctx->ops->submit_read(&iter, ctx);
> + iomap_submit_read(&iter, ctx, !iter.iomap.length);
> + }
>
> if (ctx->cur_folio)
> iomap_read_end(ctx->cur_folio, bytes_submitted);
> @@ -718,12 +724,11 @@ void iomap_readahead(const struct iomap_ops *ops,
> fsverity_readahead(ctx->vi, readahead_index(rac),
> readahead_count(rac));
>
> - while (iomap_iter(&iter, ops) > 0)
> + while (iomap_iter(&iter, ops) > 0) {
> iter.status = iomap_readahead_iter(&iter, ctx,
> &cur_bytes_submitted);
> -
> - if (ctx->read_ctx && ctx->ops->submit_read)
> - ctx->ops->submit_read(&iter, ctx);
> + iomap_submit_read(&iter, ctx, !iter.iomap.length);
> + }
>
> if (ctx->cur_folio)
> iomap_read_end(ctx->cur_folio, cur_bytes_submitted);
> diff --git a/fs/ntfs/aops.c b/fs/ntfs/aops.c
> index f2bb56506046..f7bd55275d8c 100644
> --- a/fs/ntfs/aops.c
> +++ b/fs/ntfs/aops.c
> @@ -38,7 +38,7 @@ static void ntfs_iomap_read_end_io(struct bio *bio)
> }
>
> static void ntfs_iomap_bio_submit_read(const struct iomap_iter *iter,
> - struct iomap_read_folio_ctx *ctx)
> + struct iomap_read_folio_ctx *ctx, bool force)
> {
> iomap_bio_submit_read_endio(iter, ctx, ntfs_iomap_read_end_io);
> }
> diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
> index f9600aba1548..cd05faebb806 100644
> --- a/fs/ntfs3/inode.c
> +++ b/fs/ntfs3/inode.c
> @@ -607,7 +607,7 @@ static void ntfs_iomap_read_end_io(struct bio *bio)
> }
>
> static void ntfs_iomap_bio_submit_read(const struct iomap_iter *iter,
> - struct iomap_read_folio_ctx *ctx)
> + struct iomap_read_folio_ctx *ctx, bool force)
> {
> iomap_bio_submit_read_endio(iter, ctx, ntfs_iomap_read_end_io);
> }
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 51293b6f331f..1b9a55e2f4a7 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -758,7 +758,8 @@ xfs_vm_bmap(
> static void
> xfs_bio_submit_read(
> const struct iomap_iter *iter,
> - struct iomap_read_folio_ctx *ctx)
> + struct iomap_read_folio_ctx *ctx,
> + bool force)
> {
> struct bio *bio = ctx->read_ctx;
>
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 56b43d594e6e..4d8893b02aaf 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -528,7 +528,7 @@ struct iomap_read_ops {
> * This is optional.
> */
> void (*submit_read)(const struct iomap_iter *iter,
> - struct iomap_read_folio_ctx *ctx);
> + struct iomap_read_folio_ctx *ctx, bool force);
>
> /*
> * Optional, allows filesystem to specify own bio_set, so new bio's
> --
> 2.53.0
>
>
