The Btrfs pull request from Chris Mason mentions, "Has our merge window series of cleanups and fixes. These target a wide range of issues, but do include some important fixes for qgroups, O_DIRECT, and fsync handling. Jeff Mahoney moved around a few definitions to make them easier for userland to consume. Also whiteout support is included now that issues with overlayfs have been cleared up."
The RENAME_WHITEOUT is intended for use with OverlayFS when forming a stackable file-system. When doing a "whiteout" on Btrfs, it's used for hiding file(s) from the lower layer of the file-system stack.
Over in F2FS space, the Flash-Friendly File-System pull request brings more fixes. "In this round, as Ted pointed out, fscrypto allows one more key prefix given by filesystem to resolve backward compatibility issue. Other than that, we could fix several error handling flow by introducing fault injection facility. We've also achieved performance improvement in some workloads as well as a bunch of bug fixes."
Some of the F2FS specifics include the file-system specific prefix for fscrypto, a fault injection facility was added, speed-ups for fallocate/rm/preallocation, support for using per-CPU counters, and more.