bootimg: Account for FAT filesystem overhead in image size
Fixes [YOCTO #1852]
The bootimg class wasn't accounting for non-trivial amount of space
required by the directory entries and FATs for the FAT filesystem.
This patch attempts to make an accurate prediction of FAT overhead and
adjusts the image size accordingly. It assumes no more than 16 directory
entries per directory (which fit in a single sector). It also assumes
8.3 filenames. With the ceiling functions rounding up to full sectors
and tracks, these assumptions seem reasonable.
In order to ensure the calculations are accurate, this patch forces the
FAT size to 32, rather than allowing mkdosfs to automatically select 12,
16, or 32 depending on the image being built.
Tested by setting BOOTIMG_EXTRA_SPACE=0 and building core-image-minimal
and core-image-sato for fri2-noemgd from meta-intel.
Signed-off-by: Darren Hart <dvhart@linux.intel.com> CC: Saul Wold <sgw@linux.intel.com>
