f2fs-for-5.1-rc1 We've continued mainly to fix bugs in this round, as f2fs has been shipped in more devices. Especially, we've focused on stabilizing checkpoint=disable feature, and provided some interfaces for QA. Enhancement: - expose FS_NOCOW_FL for pin_file - run discard jobs at unmount time with timeout - tune discarding thread to avoid idling which consumes power - some checking codes to address vulnerabilities - give random value to i_generation - shutdown with more flags for QA Bug fix: - clean up stale objects when mount is failed along with checkpoint=disable - fix system being stuck due to wrong count by atomic writes - handle some corrupted disk cases - fix a deadlock in f2fs_read_inline_dir We've also added some minor build errors and clean-up patches.