mke2fs.c: add an option: -d root-directory

This option is used for adding the files from a given directory (the
root-directory) to the filesystem, it is similiar to genext2fs, but
genext2fs doesn't fully support ext4.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Reviewed-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2 files changed