1 files changed, 36 insertions, 9 deletions

diff --git a/meta/classes/bootimg.bbclass b/meta/classes/bootimg.bbclass
index b50202f68f..df3ee7315a 100644
--- a/meta/classes/bootimg.bbclass
+++ b/meta/classes/bootimg.bbclass
@@ -103,19 +103,46 @@ build_hddimg() {
                         grubefi_hddimg_populate
                 fi
 
-                # Determine the 1024 byte block count for the final image.
-                BLOCKS=`du --apparent-size -ks ${HDDDIR} | cut -f 1`
-                SIZE=`expr $BLOCKS + ${BOOTIMG_EXTRA_SPACE}`
+                # Calculate the size required for the final image including the
+                # data and filesystem overhead.
+                # Sectors: 512 bytes
+                #  Blocks: 1024 bytes
+
+                # Determine the sector count just for the data
+                SECTORS=$(expr $(du --apparent-size -ks ${HDDDIR} | cut -f 1) \* 2)
+
+                # Account for the filesystem overhead. This includes directory
+                # entries in the clusters as well as the FAT itself.
+                # Assumptions:
+                #   < 16 entries per directory
+                #   8.3 filenames only
+
+                # 32 bytes per dir entry
+                DIR_BYTES=$(expr $(find ${HDDDIR} | tail -n +2 | wc -l) \* 32)
+                # 32 bytes for every end-of-directory dir entry
+                DIR_BYTES=$(expr $DIR_BYTES + $(expr $(find ${HDDDIR} -type d | tail -n +2 | wc -l) \* 32))
+                # 4 bytes per FAT entry per sector of data
+                FAT_BYTES=$(expr $SECTORS \* 4)
+                # 4 bytes per FAT entry per end-of-cluster list
+                FAT_BYTES=$(expr $FAT_BYTES + $(expr $(find ${HDDDIR} -type d | tail -n +2 | wc -l) \* 4))
+
+                # Use a ceiling function to determine FS overhead in sectors
+                DIR_SECTORS=$(expr $(expr $DIR_BYTES + 511) / 512)
+                # There are two FATs on the image
+                FAT_SECTORS=$(expr $(expr $(expr $FAT_BYTES + 511) / 512) \* 2)
+                SECTORS=$(expr $SECTORS + $(expr $DIR_SECTORS + $FAT_SECTORS))
+
+                # Determine the final size in blocks accounting for some padding
+                BLOCKS=$(expr $(expr $SECTORS \* 2) + ${BOOTIMG_EXTRA_SPACE})
 
                 # Ensure total sectors is an integral number of sectors per
-                # track or mcopy will complain. Sectors are 512 bytes, and and
-                # we generate images with 32 sectors per track. This calculation
-                # is done in blocks, which are twice the size of sectors, thus
-                # the 16 instead of 32.
-                SIZE=$(expr $SIZE + $(expr 16 - $(expr $SIZE % 16)))
+                # track or mcopy will complain. Sectors are 512 bytes, and we
+                # generate images with 32 sectors per track. This calculation is
+                # done in blocks, thus the mod by 16 instead of 32.
+                BLOCKS=$(expr $BLOCKS + $(expr 16 - $(expr $BLOCKS % 16)))
 
                 IMG=${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.hddimg
-                mkdosfs -n ${BOOTIMG_VOLUME_ID} -S 512 -C ${IMG} ${SIZE}
+                mkdosfs -F 32 -n ${BOOTIMG_VOLUME_ID} -S 512 -C ${IMG} ${BLOCKS}
                 # Copy HDDDIR recursively into the image file directly
                 mcopy -i ${IMG} -s ${HDDDIR}/* ::/