Re: [PATCH v3 4/8] iomap: simplify ->read_folio_range() error handling for reads

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

On Thu, Nov 06, 2025 at 09:17:02AM -0800, Joanne Koong wrote:
> On Tue, Nov 4, 2025 at 5:50 PM Darrick J. Wong <djwong@kernel.org> wrote:
> >
> > On Tue, Nov 04, 2025 at 12:51:15PM -0800, Joanne Koong wrote:
> > > Instead of requiring that the caller calls iomap_finish_folio_read()
> > > even if the ->read_folio_range() callback returns an error, account for
> > > this internally in iomap instead, which makes the interface simpler and
> > > makes it match writeback's ->read_folio_range() error handling
> > > expectations.
> > >
> > > Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > ---
> > >  .../filesystems/iomap/operations.rst          |  7 +++--
> > >  fs/fuse/file.c                                | 10 ++-----
> > >  fs/iomap/buffered-io.c                        | 27 +++++++++----------
> > >  include/linux/iomap.h                         |  5 ++--
> > >  4 files changed, 20 insertions(+), 29 deletions(-)
> > >
> > > @@ -498,10 +497,10 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
> > >               } else {
> > >                       if (!*bytes_submitted)
> > >                               iomap_read_init(folio);
> > > -                     *bytes_submitted += plen;
> > >                       ret = ctx->ops->read_folio_range(iter, ctx, plen);
> > >                       if (ret)
> > >                               return ret;
> > > +                     *bytes_submitted += plen;
> >
> > Hrmm.  Is this the main change of this patch?  We don't increment
> > bytes_submitted if ->read_folio_range returns an error, which then means
> > that fuse doesn't have to call iomap_finish_folio_read to decrement
> > *bytes_submitted?
> >
> > (and apparently the bio read_folio_range can't fail so no changes are
> > needed there)
> 
> Yes, that is the motivation for the change. And to make the interface
> consistent with how the ->read_folio_iter() callback for writeback
> handles errors.

Cool!  I think I understand this well enough to say
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> 
> Thanks,
> Joanne
> 
> >
> > --D
>