board/chromebook/snow/mksd.sh

   1 #!/bin/sh
   2
   3 # This scripts makes a minimal bootable SD card image for the Chromebook.
   4 # The resulting file is called bootsd.img. It should be written directly
   5 # to the card:
   6 #
   7 #       SD=/dev/mmcblk1         # check your device name!
   8 #       dd if=output/images/bootsd.img of=$SD
   9 #
  10 # The partitions are created just large enough to hold the kernel and
  11 # the rootfs image. Most of the card will be empty, and the secondary
  12 # GPT will not be in its proper location.
  13
  14 # cgpt does not create protective MBR, and the kernel refuses to read
  15 # GPT unless there's some kind of MBR in sector 0. So we need parted
  16 # to write that single sector before doing anything with the GPT.
  17 cgpt=$HOST_DIR/usr/bin/cgpt
  18 parted=$HOST_DIR/usr/sbin/parted
  19 kernel=$BINARIES_DIR/uImage.kpart
  20 rootfs=$BINARIES_DIR/rootfs.ext2
  21
  22 run() { echo "$@"; "$@"; }
  23 die() { echo "$@" >&2; exit 1; }
  24 test -f $kernel || die "No kernel image found"
  25 test -f $rootfs || die "No rootfs image found"
  26 test -x $cgpt || die "cgpt not found (host-vboot-utils have not been built?)"
  27
  28 # True file sizes in bytes
  29 kernelsize=`stat -t $kernel | cut -d\  -f2`
  30 rootfssize=`stat -t $rootfs | cut -d\  -f2`
  31
  32 # The card is partitioned in sectors of 8KB.
  33 # 4 sectors are reserved for MBR+GPT. Their actual size turns out
  34 # to be 33 512-blocks which is just over 2 sectors, but we align
  35 # it to a nice round number.
  36 sec=8192
  37 kernelsec=$(((kernelsize+8191)>>13))
  38 rootfssec=$(((rootfssize+8191)>>13))
  39 headersec=4
  40
  41 # There is also a copy of MBR+GPT at the end of the image.
  42 # It's going to be useless but both tools assume it's there.
  43 imagesec=$((2*headersec+kernelsec+rootfssec))
  44 bootsd="$BINARIES_DIR/bootsd.img"
  45 run dd bs=$sec count=$imagesec if=/dev/zero of=$bootsd
  46
  47 # cgpt needs offsets and sizes in 512-blocks.
  48 block=512
  49 kernelstart=$((headersec<<4))
  50 kernelblocks=$((kernelsec<<4))
  51 rootfsblocks=$((rootfssec<<4))
  52 rootfsstart=$((kernelstart+kernelblocks))
  53
  54 # This command initializes both GPT and MBR
  55 run $parted -s $bootsd mklabel gpt
  56
  57 # The kernel partition must be marked as bootable, that's why -S -T -P
  58 run $cgpt add -i 1 -b $kernelstart -s $kernelblocks \
  59         -t kernel -l kernel \
  60         -S 1 -T 1 -P 10 $bootsd
  61
  62 # It does not really matter where the rootfs partition is located as long
  63 # as the kernel can find it.
  64 # However, if anything is changed here, kernel.args must be updated as well.
  65 run $cgpt add -i 2 -b $rootfsstart -s $rootfsblocks \
  66         -t data -l rootfs $bootsd
  67
  68 run dd bs=$block if=$kernel of=$bootsd seek=$kernelstart
  69 run dd bs=$block if=$rootfs of=$bootsd seek=$rootfsstart