The documentation says the write should return the number of bytes not
written on an error (0 means everything was written). Read provides a
buffer length and the return value should be the buffer length - bytes
actually read. Remove the incorrect FIXME's and return the correct
values.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>