Changes for 4.19: - iomap: support inline data, page done callbacks, and partial dio writes to support gfs2 - iomap: add library functions for page cache reads and writes in preparation to remove buffer heads from xfs. - Use extent maps to track pagecache page status instead of bufferhead state. - Refactor pagecache read and write paths to use the new iomap library functions, which enable us to drop the old bufferhead code for pagesize == blocksize filesystems. - Set up parallel per-block-per-page metadata to track subpage information that was tracked by buffer heads, which enables us to drop the old bufferhead code for pagesize > blocksize filesystems. - Tie a deferred ops control structure to a transaction so that we can take advantage of an upper-level dfops without having to plumb pointer passing through the code. - Refactor the deferred ops code to track deferred ops as part of the transaction structure (instead of as a separate data structure) so that we can simplify the scoping rules around defer_ops. - Refactor twisty delwri buffer submission code to avoid deadlocks. - Shorten and fix indenting problems in the scrub code. - Detect obviously bad summary counts at mount and fix them. - Various fixes and cleanups.