fs/cpio: new option to use dracut tool

Adds an option to invoke the dracut host tool, providing
a configuration file, instead of having a full cpio archive
of the whole target directory.

A default configuration file is provided. It assumes busybox init.
ideally, a different default should be used in case of systemd init, but
that's left for future work.

Signed-off-by: Thierry Bultel <thierry.bultel@linatsea.fr>
[arnout@mind.be: many changes]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[yann.morin.1998@free.fr: some additional fixups]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

fs/cpio/Config.in

@@ -7,6 +7,41 @@ config BR2_TARGET_ROOTFS_CPIO
 
 if BR2_TARGET_ROOTFS_CPIO
 
+choice
+	prompt "cpio type"
+	default BR2_TARGET_ROOTFS_CPIO_FULL
+
+config BR2_TARGET_ROOTFS_CPIO_FULL
+	bool "cpio the whole root filesystem"
+	help
+	  Build a cpio archive containing the whole the root filesystem.
+
+config BR2_TARGET_ROOTFS_CPIO_DRACUT
+	bool "Invoke dracut to make a partial initramfs"
+	select BR2_PACKAGE_HOST_DRACUT
+	help
+	  Build an additional initramfs using dracut. This only contains
+	  a subset of the rootfs, as determined by the configuration
+	  file.
+	  This can be useful to create a recovery system, for instance.
+
+endchoice
+
+if BR2_TARGET_ROOTFS_CPIO_DRACUT
+
+config BR2_TARGET_ROOTFS_CPIO_DRACUT_CONF_FILE
+	string "dracut configuration file"
+	default "fs/cpio/dracut.conf"
+	help
+	  Dracut configuration file. It determines which parts of the
+	  rootfs get included in the cpio image. See dracut.conf(5) or
+	  https://github.com/dracutdevs/dracut/blob/master/man/dracut.conf.5.asc
+
+	  The default configuration file is suitable for busybox init.
+	  It doesn't, however, pivot_root into a full rootfs.
+
+endif
+
 choice
 	prompt "Compression method"
 	default BR2_TARGET_ROOTFS_CPIO_NONE

fs/cpio/cpio.mk

@@ -36,6 +36,8 @@ ROOTFS_CPIO_DEPENDENCIES += host-cpio
 ROOTFS_CPIO_OPTS += --reproducible
 endif
 
+ifeq ($(BR2_TARGET_ROOTFS_CPIO_FULL),y)
+
 define ROOTFS_CPIO_CMD
 	cd $(TARGET_DIR) && \
 	find . \
@@ -44,6 +46,37 @@ define ROOTFS_CPIO_CMD
 	> $@
 endef
 
+else ifeq ($(BR2_TARGET_ROOTFS_CPIO_DRACUT),y)
+
+ROOTFS_CPIO_DEPENDENCIES += host-dracut
+
+ROOTFS_CPIO_DRACUT_CONF_FILE = $(call qstrip,$(BR2_TARGET_ROOTFS_CPIO_DRACUT_CONF_FILE))
+ifeq ($(BR_BUILDING):$(ROOTFS_CPIO_DRACUT_CONF_FILE),y:)
+$(error No dracut config file name specified, check your BR2_TARGET_ROOTFS_CPIO_DRACUT_CONF_FILE setting)
+endif
+
+ifeq ($(BR2_LINUX_KERNEL),y)
+ROOTFS_CPIO_DEPENDENCIES += linux
+ROOTFS_CPIO_OPTS += --kver $(LINUX_VERSION_PROBED)
+else
+ROOTFS_CPIO_OPTS += --no-kernel
+endif
+
+define ROOTFS_CPIO_CMD
+	mkdir -p $(ROOTFS_CPIO_DIR)/tmp
+	$(HOST_DIR)/bin/dracut \
+		$(ROOTFS_CPIO_OPTS) \
+		-c $(ROOTFS_CPIO_DRACUT_CONF_FILE) \
+		--sysroot $(TARGET_DIR) \
+		--tmpdir $(ROOTFS_CPIO_DIR)/tmp \
+		-M \
+		--force \
+		--no-compress \
+		$@
+endef
+
+endif #BR2_TARGET_ROOTFS_CPIO_DRACUT
+
 ifeq ($(BR2_TARGET_ROOTFS_CPIO_UIMAGE),y)
 ROOTFS_CPIO_DEPENDENCIES += host-uboot-tools
 define ROOTFS_CPIO_UBOOT_MKIMAGE

fs/cpio/dracut.conf

@@ -0,0 +1,92 @@
+#Simple dracut config for a system without systemd
+
+#Dracut configuration
+
+show_modules=yes
+i18n_install_all=no
+lvmconf=no
+mdadmconf=no
+early_microcode=no
+hostonly=no
+hostonly_cmdline=no
+use_fstab=no
+kernel_cmdline="rd.break=initqueue"
+do_strip=no
+
+# Dracut modules needed
+add_dracutmodules+=" \
+busybox-init
+"
+
+# Modules to ignore
+omit_dracutmodules+=" \
+bash \
+biosdevname \
+btrfs \
+bluetooth \
+busybox \
+caps \
+cifs \
+crypt \
+crypt-gpg \
+dash \
+dbus-broker \
+dbus-daemon \
+dm \
+dmraid \
+dmsquash-live-ntfs \
+dracut-systemd \
+fcoe \
+fcoe-uefi \
+fs-lib \
+iscsi \
+i18n \
+lvmmerge \
+lvm \
+lunmask \
+mdraid \
+memstrack \
+mksh \
+modsign \
+mount-root \
+multipath \
+nbd \
+network-legacy \
+network-wicked \
+nfs \
+nvdimm \
+nvmf \
+parse-lunmask \
+qemu \
+qemu-net \
+resume \
+rootfs-block \
+rngd \
+systemd \
+systemd-udevd \
+systemd-coredump \
+systemd-ask-password \
+systemd-timedated \
+systemd-rfkill \
+systemd-resolved \
+systemd-hostnamed \
+systemd-initrd \
+systemd-journald \
+systemd-ldconfig \
+systemd-networkd \
+systemd-timesyncd \
+systemd-veritysetup \
+systemd-modules-load \
+systemd-sysctl \
+systemd-repart \
+systemd-sysext \
+systemd-sysusers \
+systemd-tmpfiles \
+squash \
+ssh-client \
+stratis \
+tpm2-tss \
+udev-rules \
+url-lib \
+usrmount \
+"