Have buildroot generate a root file system

Makefile

@@ -16,9 +16,11 @@ buildroot_srcdir := $(srcdir)/buildroot
 buildroot_initramfs_wrkdir := $(wrkdir)/buildroot_initramfs
 buildroot_initramfs_tar := $(buildroot_initramfs_wrkdir)/images/rootfs.tar
 buildroot_initramfs_config := $(confdir)/buildroot_initramfs_config
-
 buildroot_initramfs_sysroot_stamp := $(wrkdir)/.buildroot_initramfs_sysroot
 buildroot_initramfs_sysroot := $(wrkdir)/buildroot_initramfs_sysroot
+buildroot_rootfs_wrkdir := $(wrkdir)/buildroot_rootfs
+buildroot_rootfs_ext := $(buildroot_rootfs_wrkdir)/images/rootfs.ext4
+buildroot_rootfs_config := $(confdir)/buildroot_rootfs_config
 
 linux_srcdir := $(srcdir)/linux
 linux_wrkdir := $(wrkdir)/linux
@@ -77,8 +79,25 @@ $(buildroot_initramfs_tar): $(buildroot_srcdir) $(buildroot_initramfs_wrkdir)/.c
 	$(MAKE) -C $< RISCV=$(RISCV) PATH=$(PATH) O=$(buildroot_initramfs_wrkdir)
 
 .PHONY: buildroot_initramfs-menuconfig
-buildroot_initramfs-menuconfig: $(buildroot_srcdir)
+buildroot_initramfs-menuconfig: $(buildroot_initramfs_wrkdir)/.config $(buildroot_srcdir)
-	$(MAKE) -C $< O=$(buildroot_initramfs_wrkdir) menuconfig
+	$(MAKE) -C $(dir $<) O=$(buildroot_initramfs_wrkdir) menuconfig
+	$(MAKE) -C $(dir $<) O=$(buildroot_initramfs_wrkdir) savedefconfig
+	cp $(dir $<)/defconfig conf/buildroot_initramfs_config
+
+$(buildroot_rootfs_wrkdir)/.config: $(buildroot_srcdir)
+	rm -rf $(dir $@)
+	mkdir -p $(dir $@)
+	cp $(buildroot_rootfs_config) $@
+	$(MAKE) -C $< RISCV=$(RISCV) PATH=$(PATH) O=$(buildroot_rootfs_wrkdir) olddefconfig
+
+$(buildroot_rootfs_ext): $(buildroot_srcdir) $(buildroot_rootfs_wrkdir)/.config $(RISCV)/bin/$(target)-gcc $(buildroot_rootfs_config)
+	$(MAKE) -C $< RISCV=$(RISCV) PATH=$(PATH) O=$(buildroot_rootfs_wrkdir)
+
+.PHONY: buildroot_rootfs-menuconfig
+buildroot_rootfs-menuconfig: $(buildroot_rootfs_wrkdir)/.config $(buildroot_srcdir)
+	$(MAKE) -C $(dir $<) O=$(buildroot_rootfs_wrkdir) menuconfig
+	$(MAKE) -C $(dir $<) O=$(buildroot_rootfs_wrkdir) savedefconfig
+	cp $(dir $<)/defconfig conf/buildroot_rootfs_config
 
 $(buildroot_initramfs_sysroot_stamp): $(buildroot_initramfs_tar)
 	mkdir -p $(buildroot_initramfs_sysroot)
@@ -164,9 +183,8 @@ $(qemu): $(qemu_srcdir)
 	$(MAKE) -C $(qemu_wrkdir) install
 	touch -c $@
 
-$(rootfs):
+$(rootfs): $(buildroot_rootfs_ext)
-	truncate --size=1G $@
+	cp $< $@
-	mkfs.ext4 $@
 
 .PHONY: buildroot_initramfs_sysroot vmlinux bbl
 buildroot_initramfs_sysroot: $(buildroot_initramfs_sysroot)

conf/buildroot_rootfs_config

@@ -0,0 +1,81 @@
+BR2_riscv64=y
+BR2_TOOLCHAIN_EXTERNAL=y
+BR2_TOOLCHAIN_EXTERNAL_PATH="$(RISCV)"
+BR2_TOOLCHAIN_EXTERNAL_CUSTOM_PREFIX="$(ARCH)-unknown-linux-gnu"
+BR2_TOOLCHAIN_EXTERNAL_GCC_7=y
+BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_6=y
+BR2_TOOLCHAIN_EXTERNAL_CUSTOM_GLIBC=y
+# BR2_TOOLCHAIN_EXTERNAL_INET_RPC is not set
+BR2_TOOLCHAIN_EXTERNAL_CXX=y
+BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y
+BR2_TARGET_GENERIC_ROOT_PASSWD="sifive"
+BR2_SYSTEM_DHCP="eth0"
+BR2_PACKAGE_BUSYBOX_SHOW_OTHERS=y
+BR2_PACKAGE_FFMPEG=y
+BR2_PACKAGE_FFMPEG_GPL=y
+BR2_PACKAGE_BONNIE=y
+BR2_PACKAGE_CACHE_CALIBRATOR=y
+BR2_PACKAGE_DHRYSTONE=y
+BR2_PACKAGE_LMBENCH=y
+BR2_PACKAGE_LTP_TESTSUITE=y
+BR2_PACKAGE_RAMSMP=y
+BR2_PACKAGE_RAMSPEED=y
+BR2_PACKAGE_STRESS_NG=y
+BR2_PACKAGE_WHETSTONE=y
+BR2_PACKAGE_PCIUTILS=y
+BR2_PACKAGE_MSMTP=y
+BR2_PACKAGE_MUTT=y
+BR2_PACKAGE_MUTT_IMAP=y
+BR2_PACKAGE_MUTT_POP3=y
+BR2_PACKAGE_BASH=y
+BR2_PACKAGE_WHICH=y
+BR2_PACKAGE_COREUTILS=y
+BR2_PACKAGE_UTIL_LINUX=y
+BR2_PACKAGE_UTIL_LINUX_BINARIES=y
+BR2_PACKAGE_UTIL_LINUX_AGETTY=y
+BR2_PACKAGE_UTIL_LINUX_BFS=y
+BR2_PACKAGE_UTIL_LINUX_CHFN_CHSH=y
+BR2_PACKAGE_UTIL_LINUX_CRAMFS=y
+BR2_PACKAGE_UTIL_LINUX_EJECT=y
+BR2_PACKAGE_UTIL_LINUX_FALLOCATE=y
+BR2_PACKAGE_UTIL_LINUX_FDFORMAT=y
+BR2_PACKAGE_UTIL_LINUX_FINDFS=y
+BR2_PACKAGE_UTIL_LINUX_FSCK=y
+BR2_PACKAGE_UTIL_LINUX_HWCLOCK=y
+BR2_PACKAGE_UTIL_LINUX_KILL=y
+BR2_PACKAGE_UTIL_LINUX_LAST=y
+BR2_PACKAGE_UTIL_LINUX_LINE=y
+BR2_PACKAGE_UTIL_LINUX_LOGIN_UTILS=y
+BR2_PACKAGE_UTIL_LINUX_LOSETUP=y
+BR2_PACKAGE_UTIL_LINUX_LSBLK=y
+BR2_PACKAGE_UTIL_LINUX_MESG=y
+BR2_PACKAGE_UTIL_LINUX_MINIX=y
+BR2_PACKAGE_UTIL_LINUX_MORE=y
+BR2_PACKAGE_UTIL_LINUX_MOUNT=y
+BR2_PACKAGE_UTIL_LINUX_MOUNTPOINT=y
+BR2_PACKAGE_UTIL_LINUX_NEWGRP=y
+BR2_PACKAGE_UTIL_LINUX_NOLOGIN=y
+BR2_PACKAGE_UTIL_LINUX_NSENTER=y
+BR2_PACKAGE_UTIL_LINUX_PARTX=y
+BR2_PACKAGE_UTIL_LINUX_PIVOT_ROOT=y
+BR2_PACKAGE_UTIL_LINUX_RAW=y
+BR2_PACKAGE_UTIL_LINUX_RENAME=y
+BR2_PACKAGE_UTIL_LINUX_RESET=y
+BR2_PACKAGE_UTIL_LINUX_SCHEDUTILS=y
+BR2_PACKAGE_UTIL_LINUX_SETPRIV=y
+BR2_PACKAGE_UTIL_LINUX_SETTERM=y
+BR2_PACKAGE_UTIL_LINUX_SWITCH_ROOT=y
+BR2_PACKAGE_UTIL_LINUX_TUNELP=y
+BR2_PACKAGE_UTIL_LINUX_UL=y
+BR2_PACKAGE_UTIL_LINUX_UNSHARE=y
+BR2_PACKAGE_UTIL_LINUX_UTMPDUMP=y
+BR2_PACKAGE_UTIL_LINUX_UUIDD=y
+BR2_PACKAGE_UTIL_LINUX_VIPW=y
+BR2_PACKAGE_UTIL_LINUX_WALL=y
+BR2_PACKAGE_UTIL_LINUX_WDCTL=y
+BR2_PACKAGE_UTIL_LINUX_WRITE=y
+BR2_PACKAGE_UTIL_LINUX_ZRAMCTL=y
+BR2_TARGET_ROOTFS_EXT2=y
+BR2_TARGET_ROOTFS_EXT2_4=y
+BR2_TARGET_ROOTFS_EXT2_EXTRA_BLOCKS=10240
+# BR2_TARGET_ROOTFS_TAR is not set