Compare file sizes of snaps and xdelta3 diffs with and without mksquashfs' -no-fragments option

analyze-nofrag.sh

#!/bin/bash

set -e

resquash_snap()
{
	orig_snap="$1"
	new_snap="$(basename "$orig_snap" .snap)-nofrag.snap"
	tmp=$(mktemp -d resquash.XXXXXXXXXX)
	dir="${tmp}/unsquashed"

	unsquashfs -d "$dir" "$orig_snap" > /dev/null
	fstime=$(unsquashfs -fstime "$orig_snap")
	mksquashfs "$dir" "$new_snap" -noappend -comp xz -all-root -no-xattrs -no-fragments -fstime "$fstime" > /dev/null
	rm -rf "$tmp"

	printf "%s" "$new_snap"
}

generate_delta()
{
	orig="$1"
	new="$2"
	out="$(basename "$orig" .snap)-to-$(basename "$new" .snap).xdelta3"

	xdelta3 -s "$orig" "$new" "$out"
	printf "%s" "$out"
}

if [ "$#" -lt 2 ]; then
	echo "Usage: $0 <OLDEST_SNAP> <NEWER_SNAP> [NEWER_SNAP] ..." 1>&2
	exit 1
fi

prev=
prev_resquash=
for cur in "$@"; do
	echo "### Resquashing $cur with no fragments"
	cur_resquash=$(resquash_snap "$(basename "$cur")")
	if [ -n "$prev" ]; then
		delta=$(generate_delta "$prev" "$cur")
		delta_resquash=$(generate_delta "$prev_resquash" "$cur_resquash")
		du -h "$cur" "$cur_resquash" "$delta" "$delta_resquash"
	else
		du -h "$cur" "$cur_resquash"
	fi
	prev="$cur"
	prev_resquash="$cur_resquash"
done