Function fits_an_io_size 

fn fits_an_io_size(vid_offset: usize, data_offset: usize) -> bool

Returns whether the kernel’s io_init gives these offsets for some minimum I/O size.

It puts the data at the end of the VID header, rounded up to the minimum I/O size, a power of two. The offset of the VID header in its subpage must be a multiple of 4. This assumes that the subpage size is at least 4 bytes if the I/O size is.