btrfs: subpage: introduce helpers to handle subpage delalloc locking

Three new helpers are introduced for the incoming subpage delalloc locking
change.

- btrfs_folio_set_writer_lock()
  This is to mark specified range with subpage specific writer lock.
  After calling this, the subpage range can be proper unlocked by
  btrfs_folio_end_writer_lock()

- btrfs_subpage_find_writer_locked()
  This is to find the writer locked subpage range in a page.
  With the help of btrfs_folio_set_writer_lock(), it can allow us to
  record and find previously locked subpage range without extra memory
  allocation.

- btrfs_folio_end_all_writers()
  This is for the locked_page of __extent_writepage(), as there may be
  multiple subpage delalloc ranges locked.

Reviewed-by: Johannes Thumshirn <[email protected]>
Reviewed-by: Naohiro Aota <[email protected]>
Signed-off-by: Qu Wenruo <[email protected]>
Signed-off-by: David Sterba <[email protected]>

0 files changed, 0 insertions, 0 deletions