ext4: refactor partial block zero-out for iomap conversion

From: Zhang Yi <yi.zhang@huawei.com>

Changes since v3:
 - In patch 04, fix the comments of ext4_block_zero_range().
 - Add patch 09, ensure zeroed partial blocks are persisted in SYNC mode
   for ext4_punch_hole() and ext4_zero_range(), This can resolve the
   breaks in the guarantee of data-ordered mode caused by patch 05, as
   pointed out by Sashiko.
 - Add patch 10, unify the inconsistent SYNC mode checks in all
   fallocate paths.
 - In patch 12, fix two issues related to updating the file size in
   error paths, as pointed out by Sashiko.

Changes since v2:
 - Drop patch 02 in v2 because it will not be used in the later iomap
   conversion.
 - In patch 08, modify ext4_alloc_file_blocks() to zero out EOF block
   when new_size is larger than old_size, preventing the exposure of
   stale data when the user performs fallocate starting within the
   old_size. This was pointed out by Sashiko.
 - In patch 08, add checks for the return value of
   ext4_block_zero_eof().
 - Add patches 09 and 10, move pagecache_isize_extended() out of an
   active journal handle as well to prevent opposite lock ordering.
   This was pointed out by Sashiko.
 - In patch 11, add a check for IOCB_NOWAIT, which was also pointed out
   by Sashiko.

Changes since v1:
 - In patch 04, rename ext4_block_get_zero_range() to
   ext4_load_tail_bh() and drop the unused 'length' parameter as Jan
   suggested.
 - In patch 06, modify the commit message, add another reason to drop
   data=ordered mode when zeroing partial blocks in ext4_punch_hole()
   and ext4_punch_hole() as Jan pointed out.
 - In patch 10, modify the commit message, explain the race condition
   between the buffered write and mmap write that pointed out by Jan.
 - Collect reviewed tags from Jan.

v3: https://lore.kernel.org/linux-ext4/20260326111054.907252-...
v2: https://lore.kernel.org/linux-ext4/20260325072850.3997161...
v1: https://lore.kernel.org/linux-ext4/20260310014101.4140698...

Original cover letter:

This patch series extracted from my iomap conversion v2 series[1]. It
refactors the ext4 zero partial block code path in preparation for
converting buffered I/O to the iomap infrastructure. The main changes
are:

[1] https://lore.kernel.org/linux-ext4/20260203062523.3869120...

1. Introduce ext4_block_zero_eof(): Extend and rename
   ext4_block_truncate_page() to handle post-EOF partial block zeroing
   for both append writes and truncate operations.
2. Separate ordered data handling: Move data=ordered mode handling from
   __ext4_block_zero_page_range to ext4_block_zero_eof(). Only truncate
   and post-EOF append write/fallocate paths need ordered data mode,
   hole punching and zero range paths don't need ordered data handling.
3. Split journal mode handling: Extract
   ext4_block_journalled_zero_range() from
   __ext4_block_zero_page_range() for data=journal mode, leaving
   ext4_block_do_zero_range() for data=ordered/writeback modes.
4. Refactor ext4_alloc_file_blocks(): Change parameters to loff_t byte
   granularity to simplify callers and prepares removing the zero call
   from the allocation loop for unaligned append writes.
5. Remove handle parameters: Stop passing handle_t * to zero functions.
   Make ext4_block_journalled_zero_range() start its own handle, and
   move zero operations outside active handles. This is required because
   iomap uses "folio lock -> transaction start" lock ordering, opposite
   to the current lock ordering.
6. Centralize zeroing in ext4_write_checks(): Move all post-EOF partial
   block zeroing to ext4_write_checks() so it applies to both regular
   buffered writes and the upcoming iomap path.

Thanks
Yi.

Zhang Yi (13):
  ext4: add did_zero output parameter to ext4_block_zero_page_range()
  ext4: rename and extend ext4_block_truncate_page()
  ext4: factor out journalled block zeroing range
  ext4: rename ext4_block_zero_page_range() to ext4_block_zero_range()
  ext4: move ordered data handling out of ext4_block_do_zero_range()
  ext4: remove handle parameters from zero partial block functions
  ext4: pass allocate range as loff_t to ext4_alloc_file_blocks()
  ext4: move zero partial block range functions out of active handle
  ext4: ensure zeroed partial blocks are persisted in SYNC mode
  ext4: unify SYNC mode checks in fallocate paths
  ext4: remove ctime/mtime update from ext4_alloc_file_blocks()
  ext4: move pagecache_isize_extended() out of active handle
  ext4: zero post-EOF partial block before appending write

 fs/ext4/ext4.h    |   5 +-
 fs/ext4/extents.c | 163 ++++++++++++++-------------
 fs/ext4/file.c    |  17 +++
 fs/ext4/inode.c   | 273 +++++++++++++++++++++++++++++-----------------
 4 files changed, 278 insertions(+), 180 deletions(-)

-- 
2.52.0