[PATCH 0/2] iomap: ->iomap_end() error handling fixes

Brian Foster
2025-09-08T12:57:04Z

Hi all,

This is a couple small error handling fixes for ->iomap_end() errors
(via iomap_iter()). The immediate problem here was that the
->iomap_end() error return started overriding an iter.status error code,
which on ext4 happened to trigger dio fallback to buffered I/O in some
cases. Jan has actually fixed that separately in ext4 [1], but I wanted
to take an independent look at iomap to see if it is worth fixing as
well.

The more I poked around the more it seemed like it's more appropriate to
return the initial error code in iter.status if one is pending. I also
eventually noticed the DAX vs. reflink case documented in patch 2, which
further tweaks the error handling and supports the former reasoning.

These are separate patches because they are separate issues. This has
survived my testing since the RFC was posted and some Reviewed-by's have
trickled in, so there are no real changes for v1 other than adding those
tags. Thoughts, reviews, flames appreciated.

Brian

[1] https://lore.kernel.org/linux-ext4/20250901112739.32484-2-jack@suse.cz/

v1:
- Added R-b tags.
rfc: https://lore.kernel.org/linux-fsdevel/20250902150755.289469-1-bfoster@redhat.com/

Brian Foster (2):
iomap: prioritize iter.status error over ->iomap_end()
iomap: revert the iomap_iter pos on ->iomap_end() error

fs/iomap/iter.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)

--
2.51.0