Initial commit

compress.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+# Copies raspi3.img into compr.img, resulting in many consecutive zero bytes
+# which are nicely compressible.
+
+set -e
+
+qemu-img create -f raw compr.img 1000M
+
+# copy partition table from raspi3.img
+sfdisk --quiet --dump raspi3.img | sfdisk --quiet compr.img
+
+readarray rmappings < <(sudo kpartx -asv raspi3.img)
+readarray cmappings < <(sudo kpartx -asv compr.img)
+
+# copy the vfat boot partition as-is
+set -- ${rmappings[0]}
+rboot="$3"
+set -- ${cmappings[0]}
+cboot="$3"
+sudo dd if=/dev/mapper/${rboot?} of=/dev/mapper/${cboot?} bs=5M status=none
+
+# copy the ext4 root partition in a space-saving way
+set -- ${rmappings[1]}
+rroot="$3"
+set -- ${cmappings[1]}
+croot="$3"
+sudo e2fsck -y -f /dev/mapper/${rroot?}
+sudo resize2fs /dev/mapper/${rroot?} 700M
+sudo e2image -rap /dev/mapper/${rroot?} /dev/mapper/${croot?}
+
+sudo kpartx -ds raspi3.img
+sudo kpartx -ds compr.img
+
+bzip2 -k -9 -f compr.img