f2fs_io: support gc_range command

This patch supports a new sub-command 'gc_range' in f2fs_io to trigger
gc to move blocks in specified range via F2FS_IOC_GARBAGE_COLLECT_RANGE
ioctl.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2 files changed