live-image: pack full rootfs as initrd so PXE actually boots userspace

update-initramfs produces a boot stub (~50 MB) that expects to mount a
separate rootfs over squashfs/disk/NFS. Our PXE channel only ships
vmlinuz+initrd.img, so the stub had nothing to pivot to — kernel
finished hand-off and the system wedged with firmware, modules, and
userspace stranded in the 545 MB rootfs dir we never delivered.

Replace with an everything-in-initramfs build: cpio.zst the full
rootfs (minus /boot) as the initrd, add /init -> sbin/init for the
kernel's runtime entrypoint, materialize the kernel symlink into a
real file. Bump check-initrd floor to 200 MB and switch the firmware
grep from unmkinitramfs (boot-stub-specific) to zstd | cpio -t.

Also add cpio to the CI apt deps.

.gitea/workflows/e2e.yml

@@ -39,7 +39,7 @@ jobs:
             debootstrap squashfs-tools \
             systemd-ukify systemd-boot kmod bubblewrap \
             debian-archive-keyring python3-pip git zstd \
-            qemu-system-x86 qemu-utils \
+            qemu-system-x86 qemu-utils cpio \
             dnsmasq iperf3 ipxe-qemu
           # See release.yml for rationale — Ubuntu's apt mkosi is too old
           # to handle bookworm's non-free-firmware component correctly.

.gitea/workflows/release.yml

@@ -35,7 +35,7 @@ jobs:
           sudo apt-get install -y --no-install-recommends \
             debootstrap squashfs-tools dosfstools \
             systemd-ukify systemd-boot kmod bubblewrap \
-            debian-archive-keyring python3-pip git zstd
+            debian-archive-keyring python3-pip git zstd cpio
           # Ubuntu's apt-packaged mkosi is too old to wire
           # non-free-firmware shorthand through to debootstrap.
           # mkosi isn't published on PyPI under v24+ — install the

live-image/Makefile

@@ -12,38 +12,58 @@ REPO_ROOT := $(abspath ..)
 AGENT_BIN := $(REPO_ROOT)/bin/vetting-agent.linux-amd64
 MKOSI_EXTRA_AGENT := mkosi.extra/usr/local/sbin/vetting-agent
 
-.PHONY: all check-linux check-initrd agent clean
+.PHONY: all check-linux check-initrd repack-initrd agent clean
 all: check-linux $(MKOSI_EXTRA_AGENT)
 	mkosi --force build
+	$(MAKE) repack-initrd
 	$(MAKE) check-initrd
 
-# Fail the build if the initrd doesn't actually contain the firmware
-# blobs we need. Catches two failure modes:
-#   1. Packages didn't install (apt/bootstrap component misconfigured) —
-#      the size check trips.
-#   2. Packages installed but update-initramfs didn't pack them
-#      (MODULES=dep regression, initramfs-tools default drift) — the
-#      blob presence check trips.
-# Requires unmkinitramfs (from initramfs-tools on the build host).
+# mkosi + initramfs-tools produce a *boot stub* initrd (~50 MB) that
+# expects to mount a separate rootfs (squashfs / disk / NFS). Our PXE
+# channel only delivers vmlinuz+initrd.img, so there's nothing for the
+# stub to pivot to and boot wedges right after the kernel hands off.
+#
+# Fix: pack the entire rootfs as the initrd. Kernel unpacks the cpio.zst
+# into tmpfs and runs /init from it — no pivot, no live-boot, no rootfs
+# param. Size balloons to a few hundred MB but that's the real cost of
+# shipping firmware + modules + userspace in a diskless boot.
+repack-initrd:
+	@# Materialize symlinked kernel/initrd into real files so downstream
+	@# copies (release tarball) don't have to follow links.
+	@cp -fL build/vmlinuz build/vmlinuz.real && mv build/vmlinuz.real build/vmlinuz
+	@rm -f build/initrd.img build/initrd.img.old build/vmlinuz.old
+	@# Kernel execs /init from the unpacked initramfs. systemd-sysv puts
+	@# init at /sbin/init; add the top-level symlink the kernel looks for.
+	@[ -e build/init ] || ln -sf sbin/init build/init
+	@# Skip /boot: holds the old kernel + stub initrd, both superseded.
+	@# Write to a sibling temp path so find doesn't race with the
+	@# archive being written into the dir it's walking.
+	@cd build && \
+	 find . -path ./boot -prune -o -print0 \
+	 | cpio --null --create --format=newc --quiet \
+	 | zstd -T0 -10 -q > ../build.initrd.img.tmp
+	@mv build.initrd.img.tmp build/initrd.img
+
+# Fail the build if the repacked initrd doesn't actually contain the
+# firmware we need. Two failure modes:
+#   1. Packages didn't install (apt/bootstrap misconfigured) → size check.
+#   2. Packages installed but repack-initrd missed /lib/firmware → blob
+#      presence check.
+# cpio -t lists the archive; zstd -dc streams it without extracting.
 check-initrd:
-	@# build/initrd.img is a symlink into build/boot/; use wc -c (which
-	@# follows symlinks) to get the real byte count. `stat -c%s` without
-	@# -L returns the symlink's path length instead of the target size.
+	@# With repack-initrd the initrd is the full rootfs (cpio.zst), so
+	@# 200 MB is the floor — anything smaller means firmware/userspace
+	@# is missing or the repack step silently produced a stub.
 	@size=$$(wc -c < build/initrd.img); \
-	 min=$$((150 * 1024 * 1024)); \
+	 min=$$((200 * 1024 * 1024)); \
 	 if [ "$$size" -lt "$$min" ]; then \
-	   echo "ERROR: initrd.img is $$size bytes (< $$min) — firmware almost certainly missing."; \
-	   echo "       Check mkosi build log for missing packages or apt failures."; \
+	   echo "ERROR: initrd.img is $$size bytes (< $$min) — firmware/rootfs almost certainly missing."; \
+	   echo "       Check mkosi build log and repack-initrd output."; \
 	   exit 1; \
 	 fi
-	@tmp=$$(mktemp -d); \
-	 trap 'rm -rf "$$tmp"' EXIT; \
-	 unmkinitramfs build/initrd.img "$$tmp" >/dev/null 2>&1 || { \
-	   echo "ERROR: unmkinitramfs failed — initrd.img may be corrupt."; exit 1; }; \
-	 if ! find "$$tmp" -path '*lib/firmware/i915/tgl_guc*' -print -quit | grep -q .; then \
+	@if ! zstd -dc build/initrd.img | cpio -t --quiet 2>/dev/null | grep -q 'lib/firmware/i915/tgl_guc'; then \
 	   echo "ERROR: i915/tgl_guc firmware missing from initrd."; \
-	   echo "       Package installed but update-initramfs didn't pack /lib/firmware."; \
-	   echo "       Check MODULES= in /etc/initramfs-tools/initramfs.conf."; \
+	   echo "       firmware-misc-nonfree likely didn't install during bootstrap."; \
 	   exit 1; \
 	 fi
 	@echo "initrd.img OK ($$(du -hL build/initrd.img | cut -f1), i915 firmware present)"