support for package-customized images

ported from https://github.com/piotrminkina/docker-alpine/commit/0727c80559f4aa267b86e5cbe77028201f929e2f

added a -b option to extract alpine-base without dependencies

If /etc/issue, /etc/os-release, /etc/alpine-release are desirable, but
not all of alpine-base's dep, -b can be passed to extract an appropriate
set of these files directly.

The prime example use-case is in a container environment, where the init
system may not be appropriate.

builder/README.md

@@ -11,4 +11,6 @@ The builder takes several options:
 * `-s`: Outputs the `rootfs.tar.gz` to stdout.
 * `-c`: Adds the `apk-install` script to the resulting rootfs.
 * `-e`: Adds extra `edge/main` and `edge/testing` pins to the repositories file.
-* `-t <timzone>`: Set the timezone. Default is `UTC`.
+* `-t <timezone>`: Set the timezone. Default is `UTC`.
+* `-p <packages>`: Comma-separated packages list (`tzdata` is always installed). Default is `alpine-base`. 
+* `-b`: Extracts `alpine-base` to the rootfs without dependencies. For images slimmed down with `-p` which still want `/etc/*-release` and `/etc/issue`.

builder/scripts/mkimage-alpine.bash

@@ -16,7 +16,7 @@ set -eo pipefail; [[ "$TRACE" ]] && set -x
 }
 
 usage() {
-	printf >&2 '%s: [-r release] [-m mirror] [-s] [-e] [-c] [-t]\n' "$0" && exit 1
+	printf >&2 '%s: [-r release] [-m mirror] [-s] [-e] [-c] [-t timezone] [-p packages] [-b]\n' "$0" && exit 1
 }
 
 output_redirect() {
@@ -27,8 +27,8 @@ output_redirect() {
 	fi
 }
 
-build(){
-	declare mirror="$1" rel="$2" timezone="${3:-UTC}"
+build() {
+	declare mirror="$1" rel="$2" timezone="${3:-UTC}" packages="${4:-alpine-base}"
 	local repo="$mirror/$rel/main"
 	local arch="$(uname -m)"
 
@@ -40,7 +40,11 @@ build(){
 	# mkbase
 	{
 		apk --repository "$repo" --update-cache \
-			fetch --recursive --output "$tmp" alpine-base tzdata
+			fetch --recursive --output "$tmp" \
+			tzdata ${packages//,/ }
+		[[ "$ADD_BASELAYOUT" ]] && \
+			apk --repository "$repo" fetch --stdout alpine-base \
+				| tar -xvz -C "$rootfs" etc
 		apk --root "$rootfs" --allow-untrusted add --initdb "$tmp"/*.apk
 		cp -a "$rootfs/usr/share/zoneinfo/$timezone" "$rootfs/etc/localtime"
 		apk --root "$rootfs" del tzdata
@@ -57,27 +61,27 @@ build(){
 
 	# save
 	tar -z -f rootfs.tar.gz --numeric-owner -C "$rootfs" -c .
-	if [[ "$STDOUT" ]]; then
-		cat rootfs.tar.gz
-	else
-		return 0
-	fi
+	[[ "$STDOUT" ]] && cat rootfs.tar.gz
+
+	return 0
 }
 
 main() {
-	while getopts "hr:m:t:sec" opt; do
+	while getopts "hr:m:t:secp:b" opt; do
 		case $opt in
 			r) REL="$OPTARG";;
 			m) MIRROR="$OPTARG";;
 			s) STDOUT=1;;
 			e) REPO_EXTRA=1;;
 			t) TIMEZONE="$OPTARG";;
 			c) ADD_APK_SCRIPT=1;;
+			p) PACKAGES="$OPTARG";;
+			b) ADD_BASELAYOUT=1;;
 			*) usage;;
 		esac
 	done
 
-	build "$MIRROR" "$REL" "$TIMEZONE"
+	build "$MIRROR" "$REL" "$TIMEZONE" "$PACKAGES"
 }
 
 main "$@"