scripts/combined-image.sh

   1 #!/bin/sh
   2
   3 BLKSZ=65536
   4
   5 [ -f "$1" -a -f "$2" ] || {
   6         echo "Usage: $0 <kernel image> <rootfs image> [output file]"
   7         exit 1
   8 }
   9
  10 IMAGE=${3:-openwrt-combined.img}
  11
  12 # Make sure provided images are 64k aligned.
  13 kern="${IMAGE}.kernel"
  14 root="${IMAGE}.rootfs"
  15 dd if="$1" of="$kern" bs=$BLKSZ conv=sync 2>/dev/null
  16 dd if="$2" of="$root" bs=$BLKSZ conv=sync 2>/dev/null
  17
  18 # Calculate md5sum over combined kernel and rootfs image.
  19 md5=$(cat "$kern" "$root" | md5sum -)
  20
  21 # Write image header followed by kernel and rootfs image.
  22 # The header is padded to 64k, format is:
  23 #  CI               magic word ("Combined Image")
  24 #  <kernel length>  length of kernel encoded as zero padded 8 digit hex
  25 #  <rootfs length>  length of rootfs encoded as zero padded 8 digit hex
  26 #  <md5sum>         checksum of the combined kernel and rootfs image
  27 ( printf "CI%08x%08x%32s" \
  28         $(stat -c "%s" "$kern") $(stat -c "%s" "$root") "${md5%% *}" | \
  29         dd bs=$BLKSZ conv=sync;
  30   cat "$kern" "$root"
  31 ) > ${IMAGE} 2>/dev/null
  32
  33 # Clean up.
  34 rm -f "$kern" "$root"