sdcard_image-rpi: Align SD partition and optimize final SD image

SD image file was 4G in size but actually the rootfs partition was only
60MB (ex.: rpi-basic-image).
The image file size is not fixed anymore but calculated inside this
class. In this way we will setup the partition for rootfs to fit the
ext file used as SDIMG_ROOTFS. By default the free space is calculated
with IMAGE_OVERHEAD_FACTOR which is by default 1.3. If more free space
is needed this can be overwritten.
IMAGE_ROOTFS_ALIGNMENT set at 4096. This should be the best value for a
SD card.

[GITHUB #20]
[GITHUB #59]

Signed-off-by: Andrei Gherzan <andrei@gherzan.ro>

1 files changed, 33 insertions, 14 deletions

diff --git a/classes/sdcard_image-rpi.bbclass b/classes/sdcard_image-rpi.bbclass
index 725355e..de96e50 100644
--- a/classes/sdcard_image-rpi.bbclass
+++ b/classes/sdcard_image-rpi.bbclass
@@ -3,22 +3,35 @@
 #
 # The disk layout used is:
 #
-#    0  - 1M                  - reserved for other data
-#    1M - BOOT_SPACE          - bootloader and kernel
-#    BOOT_SPACE - SDIMG_SIZE  - rootfs
+#    0                      -> IMAGE_ROOTFS_ALIGNMENT         - reserved for other data
+#    IMAGE_ROOTFS_ALIGNMENT -> BOOT_SPACE                     - bootloader and kernel
+#    BOOT_SPACE             -> SDIMG_SIZE                     - rootfs
 #
 
+#                                                     Default Free space = 1.3x
+#                                                     Use IMAGE_OVERHEAD_FACTOR to add more space
+#                                                     <--------->
+#            4KiB              20MiB           SDIMG_ROOTFS
+# <-----------------------> <----------> <---------------------->
+#  ------------------------ ------------ ------------------------ -------------------------------
+# | IMAGE_ROOTFS_ALIGNMENT | BOOT_SPACE | ROOTFS_SIZE            |     IMAGE_ROOTFS_ALIGNMENT    |
+#  ------------------------ ------------ ------------------------ -------------------------------
+# ^                        ^            ^                        ^                               ^
+# |                        |            |                        |                               |
+# 0                      4096     4KiB + 20MiB       4KiB + 20Mib + SDIMG_ROOTFS   4KiB + 20MiB + SDIMG_ROOTFS + 4KiB
+
+
 # Set kernel and boot loader
 IMAGE_BOOTLOADER ?= "bcm2835-bootfiles"
 
-# Default to 1.4GiB images
-SDIMG_SIZE ?= "4000"
-
 # Boot partition volume id
 BOOTDD_VOLUME_ID ?= "${MACHINE}"
 
-# Addional space for boot partition
-BOOT_SPACE ?= "20MiB"
+# Boot partition size [in KiB]
+BOOT_SPACE ?= "20480"
+
+# Set alignment to 4MB [in KiB]
+IMAGE_ROOTFS_ALIGNMENT = "4096"
 
 # Use an uncompressed ext3 by default as rootfs
 SDIMG_ROOTFS_TYPE ?= "ext3"
@@ -48,16 +61,22 @@ FATPAYLOAD ?= ""
 IMAGEDATESTAMP = "${@time.strftime('%Y.%m.%d',time.gmtime())}"
 
 IMAGE_CMD_rpi-sdimg () {
+
+        # Align partitions
+        BOOT_SPACE_ALIGNED=$(expr ${BOOT_SPACE} + ${IMAGE_ROOTFS_ALIGNMENT} - 1)
+        BOOT_SPACE_ALIGNED=$(expr ${BOOT_SPACE_ALIGNED} - ${BOOT_SPACE_ALIGNED} % ${IMAGE_ROOTFS_ALIGNMENT})
+        SDIMG_SIZE=$(expr ${BOOT_SPACE_ALIGNED} + $ROOTFS_SIZE + ${IMAGE_ROOTFS_ALIGNMENT})
+
         # Initialize sdcard image file
-        dd if=/dev/zero of=${SDIMG} bs=1 count=0 seek=$(expr 1000 \* 1000 \* ${SDIMG_SIZE})
+        dd if=/dev/zero of=${SDIMG} bs=1 count=0 seek=$(expr 1024 \* ${SDIMG_SIZE})
 
         # Create partition table
         parted -s ${SDIMG} mklabel msdos
         # Create boot partition and mark it as bootable
-        parted -s ${SDIMG} mkpart primary fat32 1MiB ${BOOT_SPACE}
+        parted -s ${SDIMG} unit KiB mkpart primary fat32 ${IMAGE_ROOTFS_ALIGNMENT} $(expr ${BOOT_SPACE_ALIGNED} \+ ${IMAGE_ROOTFS_ALIGNMENT})
         parted -s ${SDIMG} set 1 boot on
         # Create rootfs partition
-        parted -s ${SDIMG} mkpart primary ext2 ${BOOT_SPACE} 100%
+        parted -s ${SDIMG} unit KiB mkpart primary ext2 $(expr ${BOOT_SPACE_ALIGNED} \+ ${IMAGE_ROOTFS_ALIGNMENT}) 100%
         parted ${SDIMG} print
 
         # Create a vfat image with boot files
@@ -93,13 +112,13 @@ IMAGE_CMD_rpi-sdimg () {
         mcopy -i ${WORKDIR}/boot.img -v ${WORKDIR}//image-version-info ::
 
         # Burn Partitions
-        dd if=${WORKDIR}/boot.img of=${SDIMG} conv=notrunc seek=1 bs=1M && sync && sync
+        dd if=${WORKDIR}/boot.img of=${SDIMG} conv=notrunc seek=1 bs=$(expr ${IMAGE_ROOTFS_ALIGNMENT} \* 1024) && sync && sync
         # If SDIMG_ROOTFS_TYPE is a .xz file use xzcat
         if [[ "$SDIMG_ROOTFS_TYPE" == *.xz ]]
         then
-                xzcat ${SDIMG_ROOTFS} | dd of=${SDIMG} conv=notrunc seek=1 bs=${BOOT_SPACE} && sync && sync
+                xzcat ${SDIMG_ROOTFS} | dd of=${SDIMG} conv=notrunc seek=1 bs=$(expr 1024 \* ${BOOT_SPACE_ALIGNED}) && sync && sync
         else
-                dd if=${SDIMG_ROOTFS} of=${SDIMG} conv=notrunc seek=1 bs=${BOOT_SPACE} && sync && sync
+                dd if=${SDIMG_ROOTFS} of=${SDIMG} conv=notrunc seek=1 bs=$(expr 1024 \* ${BOOT_SPACE_ALIGNED} + ${IMAGE_ROOTFS_ALIGNMENT} \* 1024) && sync && sync
         fi
 }