fix: embed grub finder configuration

Helps GRUB find the ShredOS volume when it otherwise cannot (such as when the IMG is used with Ventoy in BIOS)

Signed-off-by: desertwitch <24509509+desertwitch@users.noreply.github.com>

board/shredos/embed/README

@@ -0,0 +1,16 @@
+This file is embedded into the GRUB bootloaders at build-time
+Helps GRUB find our ShredOS volume when it cannot (Ventoy BIOS)
+There is no point to put it anywhere on the USB - so don't do that.
+
+Keep consistent with BR2_TARGET_ROOTFS_ISO9660_GRUB2_EFI_IDENT_FILE
+when building any configurations that build both an ISO and the IMG.
+
+Do not use the version file as identification file though, because
+the ISO9660 filesystem does not have it (but has the needed grub.cfg),
+so you should always use a unique file not otherwise used for anything.
+
+Also ensure it is in a location where users cannot delete it by accident.
+
+Note that contrary to the GNU manual the BIOS bootloader seems to need an
+explicit "configfile" directive, otherwise the Buildroot static prefix takes
+precedence over the actual found volume path (which may be entirely different).

board/shredos/embed/grub.cfg

@@ -0,0 +1,3 @@
+search --file --set=root /boot/buildroot
+set prefix=($root)/boot/grub
+configfile $prefix/grub.cfg

board/shredos/genimage.cfg

@@ -4,6 +4,7 @@ image boot.vfat {
                 file boot/bzImage           { image = 'bzImage' }
                 file boot/grub/grub.cfg     { image = 'grub.cfg' }
                 file boot/version.txt       { image = 'version.txt' }
+                file boot/buildroot         { image = '/dev/null' }
                 file EFI/BOOT/bootx64.efi   { image = 'bootx64.efi' }
                 file EFI/BOOT/grub.cfg      { image = 'grub.cfg' }
                 file shredos.ico            { image = 'shredos.ico' }

board/shredos/genimage_i586.cfg

@@ -4,6 +4,7 @@ image boot.vfat {
                 file boot/bzImage            { image = 'bzImage' }
                 file boot/grub/grub.cfg      { image = 'grub.cfg' }
                 file boot/version.txt        { image = 'version.txt' }
+                file boot/buildroot          { image = '/dev/null' }
                 file EFI/BOOT/bootia32.efi   { image = 'bootia32.efi' }
                 file EFI/BOOT/grub.cfg       { image = 'grub.cfg' }
                 file shredos.ico             { image = 'shredos.ico' }

configs/shredos_defconfig

@@ -175,7 +175,9 @@ BR2_TARGET_GRUB2=y
 BR2_TARGET_GRUB2_I386_PC=y
 BR2_TARGET_GRUB2_X86_64_EFI=y
 BR2_TARGET_GRUB2_BUILTIN_MODULES_PC="boot linux ext2 fat squash4 part_msdos part_gpt normal progress biosdisk all_video video_cirrus video_bochs net tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_PC="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_BUILTIN_MODULES_EFI="boot linux ext2 fat squash4 part_msdos part_gpt normal progress efi_gop efi_uga all_video video_cirrus video_bochs net efinet tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile iso9660"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_EFI="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_INSTALL_TOOLS=y
 BR2_TARGET_SYSLINUX=y
 BR2_PACKAGE_HOST_E2FSPROGS=y

configs/shredos_i586_defconfig

@@ -172,7 +172,9 @@ BR2_TARGET_GRUB2=y
 BR2_TARGET_GRUB2_I386_PC=y
 BR2_TARGET_GRUB2_I386_EFI=y
 BR2_TARGET_GRUB2_BUILTIN_MODULES_PC="boot linux ext2 fat squash4 part_msdos part_gpt normal progress biosdisk all_video video_cirrus video_bochs net tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_PC="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_BUILTIN_MODULES_EFI="boot linux ext2 fat squash4 part_msdos part_gpt normal progress efi_gop efi_uga all_video video_cirrus video_bochs net efinet tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile iso9660"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_EFI="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_INSTALL_TOOLS=y
 BR2_TARGET_SYSLINUX=y
 BR2_PACKAGE_HOST_E2FSPROGS=y

configs/shredos_img_defconfig

@@ -165,13 +165,14 @@ BR2_PACKAGE_UTIL_LINUX_SU=y
 BR2_PACKAGE_UTIL_LINUX_SULOGIN=y
 BR2_TARGET_ROOTFS_CPIO_LZMA=y
 BR2_TARGET_ROOTFS_INITRAMFS=y
-# BR2_TARGET_ROOTFS_ISO9660_INITRD is not set
 # BR2_TARGET_ROOTFS_TAR is not set
 BR2_TARGET_GRUB2=y
 BR2_TARGET_GRUB2_I386_PC=y
 BR2_TARGET_GRUB2_X86_64_EFI=y
 BR2_TARGET_GRUB2_BUILTIN_MODULES_PC="boot linux ext2 fat squash4 part_msdos part_gpt normal progress biosdisk all_video video_cirrus video_bochs net tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_PC="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_BUILTIN_MODULES_EFI="boot linux ext2 fat squash4 part_msdos part_gpt normal progress efi_gop efi_uga all_video video_cirrus video_bochs net efinet tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_EFI="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_INSTALL_TOOLS=y
 BR2_PACKAGE_HOST_E2FSPROGS=y
 BR2_PACKAGE_HOST_GENIMAGE=y

configs/shredos_img_i586_defconfig

@@ -162,13 +162,14 @@ BR2_PACKAGE_UTIL_LINUX_SU=y
 BR2_PACKAGE_UTIL_LINUX_SULOGIN=y
 BR2_TARGET_ROOTFS_CPIO_LZMA=y
 BR2_TARGET_ROOTFS_INITRAMFS=y
-# BR2_TARGET_ROOTFS_ISO9660_INITRD is not set
 # BR2_TARGET_ROOTFS_TAR is not set
 BR2_TARGET_GRUB2=y
 BR2_TARGET_GRUB2_I386_PC=y
 BR2_TARGET_GRUB2_I386_EFI=y
 BR2_TARGET_GRUB2_BUILTIN_MODULES_PC="boot linux ext2 fat squash4 part_msdos part_gpt normal progress biosdisk all_video video_cirrus video_bochs net tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_PC="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_BUILTIN_MODULES_EFI="boot linux ext2 fat squash4 part_msdos part_gpt normal progress efi_gop efi_uga all_video video_cirrus video_bochs net efinet tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_EFI="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_INSTALL_TOOLS=y
 BR2_PACKAGE_HOST_E2FSPROGS=y
 BR2_PACKAGE_HOST_GENIMAGE=y

configs/shredos_iso_aio_defconfig

@@ -174,6 +174,7 @@ BR2_TARGET_ROOTFS_ISO9660_HYBRID=y
 BR2_TARGET_GRUB2=y
 BR2_TARGET_GRUB2_X86_64_EFI=y
 BR2_TARGET_GRUB2_BUILTIN_MODULES_EFI="boot linux ext2 fat squash4 part_msdos part_gpt normal progress efi_gop efi_uga all_video video_cirrus video_bochs net efinet tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile iso9660"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_EFI="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_INSTALL_TOOLS=y
 BR2_TARGET_SYSLINUX=y
 BR2_PACKAGE_HOST_E2FSPROGS=y

configs/shredos_iso_aio_i586_defconfig

@@ -171,6 +171,7 @@ BR2_TARGET_ROOTFS_ISO9660_HYBRID=y
 BR2_TARGET_GRUB2=y
 BR2_TARGET_GRUB2_I386_EFI=y
 BR2_TARGET_GRUB2_BUILTIN_MODULES_EFI="boot linux ext2 fat squash4 part_msdos part_gpt normal progress efi_gop efi_uga all_video video_cirrus video_bochs net efinet tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile iso9660"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_EFI="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_INSTALL_TOOLS=y
 BR2_TARGET_SYSLINUX=y
 BR2_PACKAGE_HOST_E2FSPROGS=y

configs/shredos_iso_defconfig

@@ -167,12 +167,12 @@ BR2_TARGET_ROOTFS_CPIO_LZMA=y
 BR2_TARGET_ROOTFS_INITRAMFS=y
 BR2_TARGET_ROOTFS_ISO9660=y
 BR2_TARGET_ROOTFS_ISO9660_BOTH=y
-# BR2_TARGET_ROOTFS_ISO9660_INITRD is not set
 BR2_TARGET_ROOTFS_ISO9660_HYBRID=y
 # BR2_TARGET_ROOTFS_TAR is not set
 BR2_TARGET_GRUB2=y
 BR2_TARGET_GRUB2_X86_64_EFI=y
 BR2_TARGET_GRUB2_BUILTIN_MODULES_EFI="boot linux ext2 fat squash4 part_msdos part_gpt normal progress efi_gop efi_uga all_video video_cirrus video_bochs net efinet tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile iso9660"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_EFI="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_INSTALL_TOOLS=y
 BR2_TARGET_SYSLINUX=y
 BR2_PACKAGE_HOST_E2FSPROGS=y

configs/shredos_iso_i586_defconfig

@@ -164,12 +164,12 @@ BR2_TARGET_ROOTFS_CPIO_LZMA=y
 BR2_TARGET_ROOTFS_INITRAMFS=y
 BR2_TARGET_ROOTFS_ISO9660=y
 BR2_TARGET_ROOTFS_ISO9660_BOTH=y
-# BR2_TARGET_ROOTFS_ISO9660_INITRD is not set
 BR2_TARGET_ROOTFS_ISO9660_HYBRID=y
 # BR2_TARGET_ROOTFS_TAR is not set
 BR2_TARGET_GRUB2=y
 BR2_TARGET_GRUB2_I386_EFI=y
 BR2_TARGET_GRUB2_BUILTIN_MODULES_EFI="boot linux ext2 fat squash4 part_msdos part_gpt normal progress efi_gop efi_uga all_video video_cirrus video_bochs net efinet tftp gzio test eval read true gfxterm gfxterm_menu gfxmenu gfxterm_background png usb usb_keyboard search configfile iso9660"
+BR2_TARGET_GRUB2_BUILTIN_CONFIG_EFI="board/shredos/embed/grub.cfg"
 BR2_TARGET_GRUB2_INSTALL_TOOLS=y
 BR2_TARGET_SYSLINUX=y
 BR2_PACKAGE_HOST_E2FSPROGS=y

fs/iso9660/Config.in

@@ -120,7 +120,7 @@ config BR2_TARGET_ROOTFS_ISO9660_GRUB2_EFI_IDENT_FILE
 	string "Grub2 identification file (EFI)"
 	depends on (BR2_TARGET_ROOTFS_ISO9660_GRUB2 || BR2_TARGET_ROOTFS_ISO9660_BOTH) \
 		&& BR2_TARGET_ROOTFS_ISO9660_EFI_BOOTLOADER
-	default "/buildroot"
+	default "/boot/buildroot"
 	help
 	  Use this option to provide a custom name for the identification
 	  file that is added to the ISO9660 filesystem, so the EFI bootloader