The previous patch 128cb1a to fix uninitialized data was incorrect and
did not initialize the padding space correctly. Furthermore, several
other cases in this function do not initialize their padding space
correctly.

Move initialization into some helper functions in a more robust way.
Signed-off-by: Justin Husted <sigstop@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>