debvm-create: install only one kernel image

The apt pattern ?or does not short-circuit. It installs any pattern
matching one of the arguments. On amd64, we thus get both the cloud and
the non-cloud variant.

There aren't that many good options to fix this, so the next best way is
using a hook and running apt again, which is suboptimal in terms of
repeated triggers, but likely the best we can do at present.

2 files changed, 59 insertions, 27 deletions

diff --git a/bin/debvm-create b/bin/debvm-create
index 637d613..c554165 100755
--- a/bin/debvm-create
+++ b/bin/debvm-create
@@ -72,7 +72,8 @@ cmdline and passes it as C<TERM> to B<agetty>.
 =item B<kernel>
 
 skips installing a linux kernel image.
-This can be useful to install a custom kernel or to install a different kernel variant than is selected by default.
+This can be useful to install a kernel without a package.
+If a kernel is installed via B<mmdebstrap> option C<--include>, automtatic kernel installation is automatically skipped.
 
 =item B<packagelists>
 
@@ -224,33 +225,8 @@ check_skip() {
 	esac
 }
 
-KERNEL_ARCH=$ARCHITECTURE
-case "$ARCHITECTURE" in
-	armhf)
-		KERNEL_ARCH=armmp
-	;;
-	hppa)
-		KERNEL_ARCH=parisc
-	;;
-	i386)
-		KERNEL_ARCH=686-pae
-	;;
-	mips64el)
-		KERNEL_ARCH=5kc-malta
-	;;
-	mipsel)
-		KERNEL_ARCH=4kc-malta
-	;;
-	ppc64)
-		KERNEL_ARCH=powerpc64
-	;;
-	ppc64el)
-		KERNEL_ARCH=powerpc64le
-	;;
-esac
-
 if ! check_skip kernel; then
-	set -- "--include=?not(?virtual)?or(?exact-name(linux-image-cloud-$KERNEL_ARCH),?exact-name(linux-image-$KERNEL_ARCH),?exact-name(linux-image-generic))" "$@"
+	set -- "--customize-hook=$SHARE_DIR/customize-kernel.sh" "$@"
 fi
 
 # construct mmdebstrap options as $@:
diff --git a/share/customize-kernel.sh b/share/customize-kernel.sh
new file mode 100755
index 0000000..fa94df7
--- /dev/null
+++ b/share/customize-kernel.sh
@@ -0,0 +1,56 @@
+#!/bin/sh
+#
+# Copyright 2022 Helmut Grohne <helmut@subdivi.de>
+# SPDX-License-Identifier: MIT
+#
+# This is a mmdebstrap customize hook that installs a kernel image. The name
+# of the kernel image depends on the architecture, derivative and release.
+
+set -eu
+
+TARGET="$1"
+
+if dpkg-query --root="$TARGET" --showformat='${db:Status-Status}\n' --show 'linux-image-*' 2>/dev/null | grep -q '^installed$'; then
+	exit 0
+fi
+
+ARCHITECTURE=$(cat "$TARGET/var/lib/dpkg/arch")
+
+KERNEL_ARCH="$ARCHITECTURE"
+case "$ARCHITECTURE" in
+	armhf)
+		KERNEL_ARCH=armmp
+	;;
+	hppa)
+		KERNEL_ARCH=parisc
+	;;
+	i386)
+		KERNEL_ARCH=686-pae
+	;;
+	mips64el)
+		KERNEL_ARCH=5kc-malta
+	;;
+	mipsel)
+		KERNEL_ARCH=4kc-malta
+	;;
+	ppc64)
+		KERNEL_ARCH=powerpc64
+	;;
+	ppc64el)
+		KERNEL_ARCH=powerpc64le
+	;;
+esac
+
+export APT_CONFIG="$MMDEBSTRAP_APT_CONFIG"
+
+if test "${MMDEBSTRAP_MODE:-}" = chrootless; then
+	set -- \
+		-oDPkg::Options::=--force-not-root \
+		-oDPkg::Options::=--force-script-chrootless \
+		-oDPkg::Options::=--root="$TARGET" \
+		-oDPkg::Options::=--log="$TARGET/var/log/dpkg.log"
+else
+	set -- -oDPkg::Chroot-Directory="$TARGET"
+fi
+
+apt-get --yes satisfy "$@" "linux-image-cloud-$KERNEL_ARCH | linux-image-$KERNEL_ARCH | linux-image-generic"