1 files changed, 36 insertions, 9 deletions

diff --git a/meta/classes/bootimg.bbclass b/meta/classes/bootimg.bbclass
index bcae2aeab1..c2d43c86ee 100644
--- a/meta/classes/bootimg.bbclass
+++ b/meta/classes/bootimg.bbclass
@@ -62,19 +62,46 @@ build_boot_bin() {
 
         install -m 444 ${STAGING_LIBDIR}/syslinux/ldlinux.sys ${HDDDIR}/ldlinux.sys
 
-        # 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}/* ::/