[oe-commits] Darren Hart : bootimg: Account for FAT filesystem overhead in image size

[git at git.openembedded.org]

Module: openembedded-core.git
Branch: 2011-1
Commit: 96c64075246b2252962cee1e8b6db4b139022f87
URL:    http://git.openembedded.org/?p=openembedded-core.git&a=commit;h=96c64075246b2252962cee1e8b6db4b139022f87

Author: Darren Hart <dvhart at linux.intel.com>
Date:   Wed Apr 11 10:51:11 2012 -0700

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.

(From OE-Core rev: 68aa18609c10a3ae2f738930c933fa2a95ce8959)

Signed-off-by: Darren Hart <dvhart at linux.intel.com>
CC: Saul Wold <sgw at linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie at linuxfoundation.org>

Backported to edison by Darren Hart.

Signed-off-by: Darren Hart <dvhart at linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie at linuxfoundation.org>

---

 meta/classes/bootimg.bbclass |   45 +++++++++++++++++++++++++++++++++--------
 1 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/meta/classes/bootimg.bbclass b/meta/classes/bootimg.bbclass
index bcae2ae..c2d43c8 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}/* ::/