f2fs-for-4.21-rc1 In this round, we've focused on bug fixes since Pixel devices have been shipping with f2fs. Some of them were related to hardware encryption support which are actually not an issue in mainline, but would be better to merge them in order to avoid potential bugs. Enhancement: - do GC sub-sections when the section is large - add a flag in ioctl(SHUTDOWN) to trigger fsck for QA - use kvmalloc() in order to give another chance to avoid ENOMEM Bug fix: - fix accessing memory boundaries in a malformed iamge - GC gives stale unencrypted block - GC counts in large sections - detect idle time more precisely - block allocation of DIO writes - race conditions between write_begin and write_checkpoint - allow GCs for node segments via ioctl() There are various clean-ups and minor bug fixes as well.