Re: [Buildroot] [PATCH v3 4/7] fs/iso9660: add support for hybrid image using Grub bootloader on BIOS and EFI

From: "Yann E. MORIN" <yann.morin.1998@free.fr>
To: Kory Maincent <kory.maincent@bootlin.com>
Cc: thomas.petazzoni@bootlin.com, buildroot@buildroot.org
Subject: Re: [Buildroot] [PATCH v3 4/7] fs/iso9660: add support for hybrid image using Grub bootloader on BIOS and EFI
Date: Mon, 27 Sep 2021 23:05:14 +0200	[thread overview]
Message-ID: <20210927210514.GF1504958@scaer> (raw)
In-Reply-To: <20210923155726.87851-5-kory.maincent@bootlin.com>

Köry, All,

On 2021-09-23 17:57 +0200, Kory Maincent spake thusly:
> Add support for building an hybrid ISO9660 image compatible with legacy
> and UEFI BIOS.
> The option -eltorito-alt-boot need to be used in the xorriso command
> to generate the hybrid image.

So I was wondering why you had to rename the variables, and why you
split the values with -eltorito-alt-boot right in between...

As I understand it from the xorriso command line, -eltorito-alt-boot
basically means "OK, we're done with the previous boot parameters, now
we start a new set of boot parameters", so the order of options *is*
important.

Right?

Furthermore, -eltorito-alt-boot and -no-emul-boot are not conflicting,
because the former is really this separator as discussed above, while
the latter specifies the type of the current boot image.

Right?

(For my information: how many such alternate boot parameters can we
define: is it limited to just two, or can we add more?)

> Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
> ---
[--SNIP--]
> diff --git a/fs/iso9660/iso9660.mk b/fs/iso9660/iso9660.mk
> index 921efa1b02..9c2535d102 100644
> --- a/fs/iso9660/iso9660.mk
> +++ b/fs/iso9660/iso9660.mk
[--SNIP--]
> @@ -151,24 +156,32 @@ endif # ROOTFS_ISO9660_USE_INITRD
>  
>  ROOTFS_ISO9660_OPTS += \
>  	-J \
> -	-R \
> -	-no-emul-boot
> +	-R
>  
> -ifeq ($(BR2_TARGET_ROOTFS_ISO9660_BIOS_BOOTLOADER),y)
> -ROOTFS_ISO9660_OPTS += \
> +ROOTFS_ISO9660_BOOTLOADER_OPTS_BIOS = \

    ROOTFS_ISO9660_OPTS_BIOS

> +	-b $(ROOTFS_ISO9660_BOOT_IMAGE) \
> +	-no-emul-boot \
>  	-boot-load-size 4 \
> -	-boot-info-table \
> -	-b $(ROOTFS_ISO9660_BOOT_IMAGE)
> -endif
> +	-boot-info-table

You are also reordering the remaining options. Is that really necessary?
Or is it for symmetry with the EFI case where the "image" option comes
first?

> -ifeq ($(BR2_TARGET_ROOTFS_ISO9660_EFI_BOOTLOADER),y)
> -ROOTFS_ISO9660_OPTS += \
> -	--efi-boot $(ROOTFS_ISO9660_EFI_PARTITION)
> +ROOTFS_ISO9660_BOOTLOADER_OPTS_EFI = \

    ROOTFS_ISO9660_OPTS_EFI

> +	--efi-boot $(ROOTFS_ISO9660_EFI_PARTITION) \
> +	-no-emul-boot
> +
> +ifeq ($(BR2_TARGET_ROOTFS_ISO9660_BIOS_BOOTLOADER)$(BR2_TARGET_ROOTFS_ISO9660_EFI_BOOTLOADER),yy)
> +ROOTFS_ISO9660_BOOTLOADER_OPTS = $(ROOTFS_ISO9660_BOOTLOADER_OPTS_BIOS)
> +ROOTFS_ISO9660_BOOTLOADER_OPTS += -eltorito-alt-boot
> +ROOTFS_ISO9660_BOOTLOADER_OPTS += $(ROOTFS_ISO9660_BOOTLOADER_OPTS_EFI)

Hmmm This is pretty ugly... What about:

    ROOTFS_ISO9660_OPTS += \
        $(ROOTFS_ISO9660_OPTS_BIOS) \
        -eltorito-alt-boot \
        $(ROOTFS_ISO9660_OPTS_EFI)

Also, does BIOS really has to come before EFI? If so, why?

> +else ifeq ($(BR2_TARGET_ROOTFS_ISO9660_BIOS_BOOTLOADER),y)
> +ROOTFS_ISO9660_BOOTLOADER_OPTS = $(ROOTFS_ISO9660_BOOTLOADER_OPTS_BIOS)

    ROOTFS_ISO9660_OPTS += $(ROOTFS_ISO9660_OPTS_BIOS)

> +else ifeq ($(BR2_TARGET_ROOTFS_ISO9660_EFI_BOOTLOADER),y)
> +ROOTFS_ISO9660_BOOTLOADER_OPTS = $(ROOTFS_ISO9660_BOOTLOADER_OPTS_EFI)

    ROOTFS_ISO9660_OPTS += $(ROOTFS_ISO9660_OPTS_EFI)

>  endif
>  
>  define ROOTFS_ISO9660_CMD
>  	$(HOST_DIR)/bin/xorriso -as mkisofs \
>  		$(ROOTFS_ISO9660_OPTS) \
> +		$(ROOTFS_ISO9660_BOOTLOADER_OPTS) \

And thus you don't need the new variable here.

Regards,
Yann E. MORIN.

>  		-o $@ $(ROOTFS_ISO9660_TMP_TARGET_DIR)
>  endef
>  
> -- 
> 2.25.1
> 
> _______________________________________________
> buildroot mailing list
> buildroot@lists.buildroot.org
> https://lists.buildroot.org/mailman/listinfo/buildroot

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