From b4be2a30cfe86e7f081b2fd7ef72a7ec3b3645b2 Mon Sep 17 00:00:00 2001
From: Charles Duffy <charles@dyfis.net>
Date: Thu, 26 Oct 2017 12:36:10 -0500
Subject: [PATCH] Add off-by-default --rsyncable option

When active, this option compromises compression ratio and removes timestamps
from the generated cpio archive to minimize differences between subsequent
builds of the same content.

- Requires gzip with --rsyncable support (present in 1.8)
- Moves from BSD to GNU cpio for --reproducible option (requires 2.12)
---
 mkinitcpio | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/mkinitcpio b/mkinitcpio
index 42b8290..7f37137 100755
--- a/mkinitcpio
+++ b/mkinitcpio
@@ -21,7 +21,7 @@ _d_presets=mkinitcpio.d
 _optmoduleroot= _optgenimg=
 _optcompress= _opttargetdir=
 _optshowautomods=0 _optsavetree=0 _optshowmods=0
-_optquiet=1 _optcolor=1
+_optquiet=1 _optcolor=1 _optrsyncable=0
 _optskiphooks=() _optaddhooks=() _hooks=()  _optpreset=()
 declare -A _runhooks _addedmodules _modpaths _autodetect_cache
 
@@ -52,6 +52,7 @@ usage: ${0##*/} [options]
    -p, --preset <file>          Build specified preset from /etc/mkinitcpio.d
    -P, --allpresets             Process all preset files in /etc/mkinitcpio.d
    -r, --moduleroot <dir>       Root directory for modules (default: /)
+   -R, --rsyncable              Attempt to generate builds with smaller deltas
    -S, --skiphooks <hooks>      Skip specified hooks, comma-separated, during build
    -s, --save                   Save build directory. (default: no)
    -d, --generatedir <dir>      Write generated image into <dir>
@@ -205,6 +206,11 @@ build_image() {
         cat)
             unset COMPRESSION_OPTIONS
             ;;
+        gzip)
+            if (( _optrsyncable )); then
+                COMPRESSION_OPTIONS+=(--rsyncable)
+            fi
+            ;;
         xz)
             COMPRESSION_OPTIONS+=(--check=crc32)
             ;;
@@ -215,14 +221,21 @@ build_image() {
 
     cpio_opts=('-0' '-o' '-H' 'newc')
     (( _optquiet )) && cpio_opts+=('--quiet')
+    (( _optrsyncable )) && cpio_opts+=('--reproducible')
+    (( _optrsyncable )) && find "$BUILDROOT" -exec touch -d '@0' -- {} +
     if (( EUID != 0 )); then
         warning 'Not building as root, ownership cannot be preserved'
-        cpio_opts+=('-R' '0:0')
+        cpio_opts+=('-R' '+0:+0')
     fi
 
     pushd "$BUILDROOT" >/dev/null
     find -mindepth 1 -printf '%P\0' |
-            LANG=C bsdcpio "${cpio_opts[@]}" |
+            if (( _optrsyncable )); then
+                LC_COLLATE=C LC_CTYPE=C sort -z
+            else
+                cat
+            fi |
+            LANG=C cpio "${cpio_opts[@]}" |
             $compress "${COMPRESSION_OPTIONS[@]}" > "$out"
     pipesave=("${PIPESTATUS[@]}") # save immediately
     popd >/dev/null
@@ -315,10 +328,11 @@ process_preset() (
 trap 'cleanup 130' INT
 trap 'cleanup 143' TERM
 
-_opt_short='A:c:g:H:hk:nLMPp:r:S:sd:t:Vvz:'
+_opt_short='A:c:g:H:hk:nLMPp:r:RS:sd:t:Vvz:'
 _opt_long=('add:' 'addhooks:' 'config:' 'generate:' 'hookhelp:' 'help'
           'kernel:' 'listhooks' 'automods' 'moduleroot:' 'nocolor' 'allpresets'
-          'preset:' 'skiphooks:' 'save' 'generatedir:' 'builddir:' 'version' 'verbose' 'compress:')
+          'preset:' 'rsyncable' 'skiphooks:' 'save' 'generatedir:' 'builddir:'
+          'version' 'verbose' 'compress:')
 
 parseopts "$_opt_short" "${_opt_long[@]}" -- "$@" || exit 1
 set -- "${OPTRET[@]}"
@@ -407,6 +421,9 @@ while :; do
             shift
             _optmoduleroot=$1
             ;;
+        -R|--rsyncable)
+            _optrsyncable=1
+            ;;
         --)
             shift
             break 2
-- 
2.14.3