iomap: convert to in-iter iomap_next() model

This series implements a suggestion by Christoph for finishing the conversion
of iomap to an iterator model. This revives Matthew's previous RFC [1], which
had the same intention.

This series has no functional changes intended. Patch 1 introduces the new
->iomap_next() interface, and the rest is a mechanical conversion to the new
api. The patches are broken down as:

1) Patch 1: adds ->iomap_next() and an iomap_process() inline helper that
filesystems can use by passing in their direct begin/end helper functions

2) Patches 2 to 15: converts each filesystem to ->iomap_next()

3) Patch 16: Removes the legacy ->iomap_begin()/->iomap_end() path

4) Patch 17: Passes iomap_next_fn directly instead of struct iomap_ops

5) Patch 18: Updates the iomap documentation to match.

If needed, performance-critical callers can later inline the iteration into
the caller and avoid the indirect iomap_next_fn call on hot paths.

This series is submitted against Christian's vfs iomap tree, and is based
on top of the current head of his tree (commit f2727952b21d1).

Thanks,
Joanne

[1] https://lore.kernel.org/linux-fsdevel/20200728173216.7184...

Changelog
---------
v1: https://lore.kernel.org/linux-fsdevel/20260625024723.1611...
v1 -> v2:
* Implement conversion for all callers

Joanne Koong (18):
  iomap: add ->iomap_next() and iomap_process() helper
  xfs: convert iomap ops to ->iomap_next()
  btrfs: convert iomap ops to ->iomap_next()
  ntfs3: convert iomap ops to ->iomap_next()
  ntfs: convert iomap ops to ->iomap_next()
  ext4: convert iomap ops to ->iomap_next()
  erofs: convert iomap ops to ->iomap_next()
  zonefs: convert iomap ops to ->iomap_next()
  ext2: convert iomap ops to ->iomap_next()
  block: convert iomap ops to ->iomap_next()
  f2fs: convert iomap ops to ->iomap_next()
  gfs2: convert iomap ops to ->iomap_next()
  hpfs: convert iomap ops to ->iomap_next()
  fuse: convert iomap ops to ->iomap_next()
  exfat: convert iomap ops to ->iomap_next()
  iomap: remove ->iomap_begin()/->iomap_end() legacy path
  iomap: pass iomap_next_fn directly instead of struct iomap_ops
  Documentation: iomap: update docs to reflect iomap_next model

 Documentation/filesystems/iomap/design.rst    | 115 ++++++++++-----
 .../filesystems/iomap/operations.rst          |  60 ++++----
 Documentation/filesystems/iomap/porting.rst   |  22 ++-
 block/fops.c                                  |  14 +-
 fs/btrfs/direct-io.c                          |  14 +-
 fs/dax.c                                      |  47 ++++---
 fs/erofs/data.c                               |  30 ++--
 fs/erofs/internal.h                           |   3 +-
 fs/erofs/zmap.c                               |   9 +-
 fs/exfat/file.c                               |  18 +--
 fs/exfat/inode.c                              |   6 +-
 fs/exfat/iomap.c                              |  20 +--
 fs/exfat/iomap.h                              |   6 +-
 fs/ext2/ext2.h                                |   3 +-
 fs/ext2/file.c                                |   4 +-
 fs/ext2/inode.c                               |  12 +-
 fs/ext4/ext4.h                                |   6 +-
 fs/ext4/extents.c                             |  12 +-
 fs/ext4/file.c                                |  14 +-
 fs/ext4/inode.c                               |  23 +--
 fs/f2fs/data.c                                |   9 +-
 fs/f2fs/f2fs.h                                |   3 +-
 fs/f2fs/file.c                                |   4 +-
 fs/fuse/dax.c                                 |  16 ++-
 fs/fuse/file.c                                |  14 +-
 fs/fuse/virtio_fs.c                           |   2 +-
 fs/gfs2/aops.c                                |   6 +-
 fs/gfs2/bmap.c                                |  12 +-
 fs/gfs2/bmap.h                                |   3 +-
 fs/gfs2/file.c                                |   6 +-
 fs/gfs2/inode.c                               |   6 +-
 fs/hpfs/file.c                                |  10 +-
 fs/internal.h                                 |   1 -
 fs/iomap/buffered-io.c                        |  38 ++---
 fs/iomap/direct-io.c                          |   8 +-
 fs/iomap/fiemap.c                             |   8 +-
 fs/iomap/iter.c                               |  88 +++++++-----
 fs/iomap/seek.c                               |   8 +-
 fs/iomap/swapfile.c                           |   4 +-
 fs/ntfs/aops.c                                |   6 +-
 fs/ntfs/file.c                                |  24 ++--
 fs/ntfs/inode.c                               |   2 +-
 fs/ntfs/iomap.c                               |  58 +++++---
 fs/ntfs/iomap.h                               |  15 +-
 fs/ntfs3/file.c                               |  16 +--
 fs/ntfs3/inode.c                              |  16 ++-
 fs/ntfs3/ntfs_fs.h                            |   3 +-
 fs/remap_range.c                              |   6 +-
 fs/xfs/xfs_aops.c                             |   8 +-
 fs/xfs/xfs_file.c                             |  44 +++---
 fs/xfs/xfs_iomap.c                            | 105 ++++++++++----
 fs/xfs/xfs_iomap.h                            |  24 ++--
 fs/xfs/xfs_iops.c                             |   4 +-
 fs/xfs/xfs_reflink.c                          |   6 +-
 fs/zonefs/file.c                              |  32 +++--
 include/linux/dax.h                           |  18 ++-
 include/linux/fs.h                            |   7 +-
 include/linux/iomap.h                         | 131 ++++++++++++------
 58 files changed, 730 insertions(+), 479 deletions(-)

-- 
2.52.0