grub2: Support setting rootflags in config

The `AIMEEOS_DEFAULT_ROOTFLAGS` kconfig option can be used to set the
default value for the `rootflags` GRUB2 environment variable.  The value
of this variable will be passed along as command-line arguments to
whatever kernel is chosen at boot.

Since post-image scripts do not have access to kconfig option values, we
need to build the GRUB2 environment file in the
`GRUB2_INSTALL_IMAGES_CMDS` script fragment instead.

Config.in

@@ -30,3 +30,8 @@ config AIMEEOS_RPI
 	select BR2_TARGET_GRUB2_ARM_EFI
 	help
 	  Support running Aimee OS on Rasperry Pi devices
+
+config AIMEEOS_DEFAULT_ROOTFLAGS
+	string "Default kernel command line argumens"
+	help
+	  Additional command line arguments to pass to the kernel by default.

board/qemu/post-image.sh

@@ -3,16 +3,12 @@
 set -e
 
 BOARD_DIR=$(dirname "$0")
-GRUBENV="${BINARIES_DIR}"/efi-part/EFI/BOOT/grubenv
 
 genimage_tmp=$(mktemp -d)
 trap 'rm -rf "${genimage_tmp}"' EXIT
 
 mkdir -p  "${genimage_tmp}"/rootfs "${genimage_tmp}"/tmp
 
-grub-editenv "${GRUBENV}" set default=0
-grub-editenv "${GRUBENV}" set timeout=3
-
 cd "${BINARIES_DIR}"
 genimage \
 	--rootpath "${genimage_tmp}/rootfs" \

boot/grub2/gen-grub-cfg.sh

@@ -8,6 +8,6 @@ kernel_filename=$1
 cat > "${TARGET_DIR}"/boot/grub.cfg <<EOF
 menuentry "Aimee OS ${vers} (Buildroot ${br2_vers}) on \$dev" --class gnu-linux --id "id-\$partuuid" "\$dev" "\$partuuid" {
     set root="\$2"
-    linux "/boot/${kernel_filename}" root=PARTUUID=\$3 ro
+    linux "/boot/${kernel_filename}" root=PARTUUID=\$3 ro \$rootflags
 }
 EOF

external.mk

@@ -3,6 +3,10 @@ define AIMEEOS_GRUB2_INSTALL_IMAGES_CMDS
 $(foreach tuple, $(GRUB2_TUPLES-y), \
 	$(INSTALL) -D -m 0644 $(BR2_EXTERNAL_AIMEEOS_PATH)/boot/grub2/grub.cfg $(GRUB2_CFG_$(tuple))
 )
+grub-editenv $(BINARIES_DIR)/efi-part/EFI/BOOT/grubenv set \
+	default=0 \
+	timeout=3 \
+	rootflags=$(AIMEEOS_DEFAULT_ROOTFLAGS)
 endef
 GRUB2_INSTALL_IMAGES_CMDS += $(AIMEEOS_GRUB2_INSTALL_IMAGES_CMDS)