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Re: [RFC PATCH] kern/dl: Add module version check

From: Thomas Schmitt
Subject: Re: [RFC PATCH] kern/dl: Add module version check
Date: Wed, 21 Dec 2022 10:43:56 +0100


Pete Batard wrote:
> > unlike what is the case for UEFI, one can not expect
> > to be able to pick all the GRUB core files needed to convert a GRUB
> > based ISO bootable media to a GRUB based USB bootable media [...]
> > Typically, one of the
> > missing files will be a 'core.img' that can work for USB BIOS boot of a
> > MBR partitioned FAT or NTFS media, and that even a GRUB based ISOHybrid
> > image will not readily provide.

Zhang Boyang wrote:
> The situation is, for BIOS boot, there is no grub core file in ISO
> because it's written to sectors instead of files? Did I understand
> correctly?

I think it is rather about the fact that GRUB equipped hybrid ISOs boot
on legacy BIOS from USB stick via the MBR code (~440 byte) to the
El Torito boot image, which is in charge for booting from optical media.
In grub-mkrescue ISOs it is called
The MBR code is taken by grub-mkrescue.c from the file "boot_hybrid.img"
in source_dirs[GRUB_INSTALL_PLATFORM_I386_PC].

So no core.img is needed and the filesystem module set can be sparse,
because the filesystem type is known from which GRUB will read its further

Pete Batard wrote:
> > Rufus usually recommends to write such images in what it calls
> > "ISO mode" (shorthand for "ISO extraction mode") with the ISO content
> > extracted to a FAT or NTFS file system and with a GRUB core.img
> > bootloader

Maybe one should not only put a copy of the EFI boot image's /EFI/BOOT
tree into grub-mkrescue ISOs but also an outdoor pack with the GRUB
equipment that is needed to make bootable a USB stick with FAT or NTFS.
(The filesystem modules are included in Pete Batard's proposal for the
 /EFI/BOOT tree. But the disk MBR image and core.img are not.)

Zhang Boyang wrote:
> test whether that commit (052e6068be62) breaks Rufus
> (e.g. Rufus with latest git GRUB, to boot Debian ISO).

Debian ISOs still boot on legacy BIOS via ISOLINUX.
Archlinux, Ubuntu, Fedora, and others meanwhile use GRUB in their ISOs for
both, legacy BIOS and EFI.

I think that in any case an ISO made by grub-mkrescue should be tested.
Maybe a distro developer is here who uses it for making a full fledged
installation ISO or a live ISO.

Have a nice day :)


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