sys-kernel/vanilla-kernel: Enable qemu-based testing

Run a quick test whether the built kernel can boot a simple distribution
based on Tiny Core Linux.

Signed-off-by: Michał Górny <mgorny@gentoo.org>

sys-kernel/vanilla-kernel/Manifest

@@ -1,3 +1,5 @@
 DIST linux-5.4.3-arch1.i686.config 241295 BLAKE2B 795b6286bd1e7dc6aa5c1428e7bf08c204ce6c8cbee57863e9f64f8990790cc4398a7d062b54c89b1b80640f02a40fce028d9397725db0f968e8028b0611a20f SHA512 8c7387ded21c02b9cffee0e6d61a7040c44deae21764f743f7719f0d1c7adf684f6b62a501fe31709787ba741859e55fc3b8a3d3d27e52c09f2d8604212bf0a7
 DIST linux-5.4.4.arch1-1.amd64.config 241587 BLAKE2B 71db76bf30a8d7f4dc680399b9f9fbb4236d1938bb86e23eb1ab236a667a959fc1cff788f7e432c43a6173e1bac4e20f3a6c3391d84275d46f1f66bd338bf538 SHA512 34d66658963dbd72fa3e96f2c5d5bccafb781fa14f6ebafe7859953929ba2fbb112f1435ca68cec8389d789cf0efa81d5fc0f5ac6dfa23a704348ab83709e9db
 DIST linux-5.4.6.tar.xz 109454640 BLAKE2B 8619492fedd4ae489a811561f72285b69deb827bb1db1f65be2a128d3bcbb69bdeec6b73650e1e8f72b18e5016c2df092bc77ee38be756d35f2903ecf0db1687 SHA512 9e1153e80303d6d5016856a25f3757259a3a428bad11208192315088d1f1a09957f5b8e966ab8cb5842ce1a740760f87474066294f8b410e9c44c810838bcdac
+DIST tinycorelinux-10.1-amd64.qcow2 16842752 BLAKE2B e013e76503c335739a9623c0901ca791937a0e6b177854535cadec1e2c2cd2df588283ed3128cf652595f32264fbfe5b3bd3a8c97665fd4da344e308535be366 SHA512 c3aeb20ff8769da9211694b7f701907cc7ae7582cdfad2c2fdc008d97ebcbd9dc08245b4e8f8450e1cb304bd705345a11fe79f901a47979fee91443841d55641
+DIST tinycorelinux-10.1-x86.qcow2 14876672 BLAKE2B 3c760eb7438b13261e52ecfaa33a53649ced95f1ab40aae52134b8cdc31a16d7aa0d6a6dd716e268ed148e9d77a10b7c700b141b61d70c82d271ffe88e8e2a3c SHA512 9964538dc42f232a11949f74b61d46422ea5da3bdc253a217119bd0b8a750c40fd2da0b07157067be9ac0226472614f210a1248114df0d331df390979867a895

sys-kernel/vanilla-kernel/vanilla-kernel-5.4.6-r1.ebuild

@@ -6,6 +6,7 @@ EAPI=7
 inherit mount-boot savedconfig toolchain-funcs
 
 MY_P=linux-${PV}
+TCL_VER=10.1
 AMD64_CONFIG_VER=5.4.4.arch1-1
 AMD64_CONFIG_HASH=f101331956bb37080dce191ca789a5c44fac9e69
 I686_CONFIG_VER=5.4.3-arch1
@@ -17,17 +18,24 @@ SRC_URI="https://cdn.kernel.org/pub/linux/kernel/v5.x/${MY_P}.tar.xz
 	amd64? (
 		https://git.archlinux.org/svntogit/packages.git/plain/trunk/config?h=packages/linux&id=${AMD64_CONFIG_HASH}
 			-> linux-${AMD64_CONFIG_VER}.amd64.config
+		test? (
+			https://dev.gentoo.org/~mgorny/dist/tinycorelinux-${TCL_VER}-amd64.qcow2
+		)
 	)
 	x86? (
 		https://git.archlinux32.org/packages/plain/core/linux/config.i686?id=${I686_CONFIG_HASH}
 			-> linux-${I686_CONFIG_VER}.i686.config
+		test? (
+			https://dev.gentoo.org/~mgorny/dist/tinycorelinux-${TCL_VER}-x86.qcow2
+		)
 	)"
 S=${WORKDIR}/${MY_P}
 
 LICENSE="GPL-2"
 SLOT="${PV}"
 KEYWORDS="~amd64 ~x86"
-IUSE="+initramfs"
+IUSE="+initramfs test"
+RESTRICT="!test? ( test ) test? ( userpriv )"
 
 # install-DEPEND actually
 # note: we need installkernel with initramfs support!
@@ -39,7 +47,13 @@ RDEPEND="
 	initramfs? ( >=sys-kernel/dracut-049-r2 )"
 BDEPEND="
 	sys-devel/bc
-	virtual/libelf"
+	virtual/libelf
+	test? (
+		dev-tcltk/expect
+		sys-kernel/dracut
+		amd64? ( app-emulation/qemu[qemu_softmmu_targets_x86_64] )
+		x86? ( app-emulation/qemu[qemu_softmmu_targets_i386] )
+	)"
 
 pkg_pretend() {
 	mount-boot_pkg_pretend
@@ -112,7 +126,60 @@ src_compile() {
 }
 
 src_test() {
-	:
+	local image_arch=${ARCH}
+	local kern_arch=x86
+	local qemu_arch=$(usex amd64 x86_64 i386)
+
+	emake O="${WORKDIR}"/build "${MAKEARGS[@]}" \
+		INSTALL_MOD_PATH="${T}" modules_install
+
+	dracut \
+		--conf /dev/null \
+		--confdir /dev/null \
+		--no-hostonly \
+		--kmoddir "${T}/lib/modules/${PV}" \
+		"${T}/initrd" "${PV}" || die
+	cp "${DISTDIR}/tinycorelinux-${TCL_VER}-${image_arch}.qcow2" \
+		"${T}/fs.qcow2" || die
+
+	cd "${T}" || die
+	cat > run.sh <<-EOF || die
+		#!/bin/sh
+		exec qemu-system-${qemu_arch} \
+			-m 256M \
+			-display none \
+			-no-reboot \
+			-kernel '${WORKDIR}/build/arch/${kern_arch}/boot/bzImage' \
+			-initrd '${T}/initrd' \
+			-serial mon:stdio \
+			-hda '${T}/fs.qcow2' \
+			-append 'root=/dev/sda console=ttyS0,115200n8'
+	EOF
+	chmod +x run.sh || die
+	# TODO: initramfs does not let core finish starting on some systems,
+	# figure out how to make it better at that
+	expect - <<-EOF || die "Booting kernel failed"
+		set timeout 900
+		spawn ./run.sh
+		expect {
+			"Kernel panic" {
+				send_error "\n* Kernel panic"
+				exit 1
+			}
+			"Entering emergency mode" {
+				send_error "\n* Initramfs failed to start the system"
+				exit 1
+			}
+			"Core 10.1" {
+				send_error "\n* Booted to login"
+				exit 0
+			}
+			timeout {
+				send_error "\n* Kernel boot timed out"
+				exit 2
+			}
+		}
+	EOF
 }
 
 src_install() {