Provide, and use, a buildah script to construct zbm-builder images

Using buildah directly provides flexibility that can not be achieved
with a Dockerfile. It also prevents the layer problem that bloats image
sizes, avoiding the need to squash the image.

Closes #230.

releng/docker/README.md

@@ -15,8 +15,28 @@ the commands should work just as well by substituting `docker` for `podman`.
 
 # Creating a ZFSBootMenu Builder Image
 
-The provided `Dockerfile` automates creation of the ZFSBootMenu builder image.
-From this directory, simply run
+The script `image-build.sh` uses `buildah` to construct a ZBM builder image.
+This is the preferred way to construct the image and may, in the future,
+provide features not available with a `podman build` workflow. The script
+requires a single argument, the tag to use when naming the image.
+
+An optional second argument is a Git commit-like reference (a hash or tag) that
+will be recorded as `/etc/zbm-commit-hash` in the image. The contents of this
+file are used to checkout a specific state of the ZFSBootMenu repository. If
+the tag is unspecified on the command line, the build script will attempt to
+capture a reference to the current HEAD commit if the image is built in an
+active git repository. If a commit-like name is not provided and cannot be
+discovered, no default will be recorded and containers will attempt to build
+from the current `master`.
+
+The `image-build.sh` script expects to be run from the root of the ZFSBootMenu
+tree by default. From there, the path `releng/docker/zbm-build.sh` defines the
+entrypoint for build containers. To run the `image-build.sh` script from
+another directory, simply set the `ZBM_BUILDER` environment variable to the
+location of the `zbm-build.sh` script to use.
+
+For those without access to `buildah`, the `Dockerfile` will also create of a
+ZFSBootMenu builder image. From this directory, simply run
 
 ```sh
 podman build --squash -t zbm .
@@ -34,10 +54,10 @@ the latest release version packaged for Void; manually editing the `Dockerfile`
 to add new dependencies may be necessary until a new release is packaged.
 
 The builder image does **not** contain a ZFSBootMenu installation or a copy of
-the upstream git repository. Instead, the image contains a build script,
-installed as `/zbm-build.sh`, that runs by default. The script ensures that a
-ZFSBootMenu repository is available in a running container and invokes
-`generate-zbm` to build images.
+the upstream git repository. Instead, the entrypoint `/zbm-build.sh` will fetch
+a ZFSBootMenu archive when the container is instantiated (or allow a local copy
+to be bind-mounted) and, as noted above, attempt to check out a specific commit
+based on the contents of `/etc/zbm-commit-hash`.
 
 # Running a ZFSBootMenu Builder Container
 

releng/docker/image-build.sh

@@ -0,0 +1,73 @@
+#!/bin/sh
+# vim: softtabstop=2 shiftwidth=2 expandtab
+
+set -o errexit
+
+# A tag for the image is required
+tag="${1}"
+if [ -z "${tag}" ]; then
+  echo "USAGE: $0 <tag> [zbm-commit-like]"
+  exit 1
+fi
+
+# If a commit hash is unspecified, try to pull HEAD from git
+zbm_commit_hash="$2"
+if [ -z "${zbm_commit_hash}" ]; then
+  if ! zbm_commit_hash="$(git rev-parse HEAD 2>/dev/null)"; then
+    unset zbm_commit_hash
+  fi
+fi
+
+if [ -z "${ZBM_BUILDER}" ]; then
+  ZBM_BUILDER="./releng/docker/zbm-build.sh"
+fi
+
+if [ ! -r "${ZBM_BUILDER}" ]; then
+  echo "ERROR: cannot find build script at ${ZBM_BUILDER}"
+  echo "Run from ZFSBootMenu root or override \$ZBM_BUILDER"
+  exit 1
+fi
+
+maintainer="ZFSBootMenu Team, https://zfsbootmenu.org"
+container="$(buildah from voidlinux/voidlinux:latest)"
+
+buildah config --label author="${maintainer}" "${container}"
+
+# Make sure image is up to date
+buildah run "${container}" xbps-install -Syu xbps
+buildah run "${container}" xbps-install -yu
+
+# Prefer an LTS version over whatever Void thinks is current
+buildah run "${container}" sh -c "cat > /etc/xbps.d/10-nolinux.conf" <<-EOF
+	ignorepkg=linux
+	ignorepkg=linux-headers
+EOF
+
+# Install ZFSBootMenu dependencies and components necessary to build images
+buildah run "${container}" \
+  sh -c 'xbps-query -Rp run_depends zfsbootmenu | xargs xbps-install -y'
+buildah run "${container}" xbps-install -y \
+  linux5.10 linux5.10-headers gummiboot-efistub curl yq-go bash kbd terminus-font
+
+# Remove headers and development toolchain, but keep binutils for objcopy
+buildah run "${container}" sh -c 'echo "ignorepkg=dkms" > /etc/xbps.d/10-nodkms.conf'
+buildah run "${container}" xbps-pkgdb -m manual binutils
+buildah run "${container}" xbps-remove -Roy linux5.10-headers dkms
+buildah run "${container}" sh -c 'rm -f /var/cache/xbps/*'
+
+# Record a commit hash if one is available
+if [ -n "${zbm_commit_hash}" ]; then
+  echo "${zbm_commit_hash}" | \
+    buildah run "${container}" sh -c 'cat > /etc/zbm-commit-hash'
+fi
+
+buildah copy "${container}" "${ZBM_BUILDER}" /zbm-build.sh
+buildah run "${container}" chmod 755 /zbm-build.sh
+
+buildah config \
+  --workingdir / \
+  --entrypoint '[ "/zbm-build.sh" ]' \
+  --cmd '[ ]' \
+  "${container}"
+
+buildah commit --rm "${container}" "${tag}"

releng/make-binary.sh

@@ -26,17 +26,13 @@ esac
 
 buildtag="${2:-localhost/zbm-builder:$(date '+%Y%m%d')}"
 if ! podman inspect "${buildtag}" >/dev/null 2>&1; then
-  if ! bldctx="$( realpath -e releng/docker )"; then
-    error "missing releng/docker, cannot create image ${buildtag}"
-  fi
-
-  build_args=( "--squash" )
+  build_args=( "${buildtag}" )
 
-  if ZBM_COMMIT_HASH="$(git rev-parse HEAD)" && [ -n "${ZBM_COMMIT_HASH}" ]; then
-    build_args+=( "--build-arg=ZBM_COMMIT_HASH=${ZBM_COMMIT_HASH}" )
+  if [ -n "${ZBM_COMMIT_HASH}" ]; then
+    build_args+=( "${ZBM_COMMIT_HASH}" )
   fi
 
-  if ! podman build -t "${buildtag}" "${build_args[@]}" "${bldctx}"; then
+  if ! ./releng/docker/image-build.sh "${build_args[@]}"; then
     error "failed to create builder image"
   fi
 fi