Filesystems readable by grub

Posted Jul 18, 2024 20:43 UTC (Thu) by mrugiero (guest, #153040)
In reply to: Filesystems readable by grub by epa
Parent article: Giving bootloaders the boot with nmbl

So, you have a VFAT fs from which you load the bootloader and then cripple the other filesystem just to be able to put the kernel to boot inside it when you can... just put the kernel on the VFAT fs and not have a driver for a crippled version of a complex fs, in turn adding complexity for the special case.
Just use the EFI partition.

Filesystems readable by grub

Posted Jul 26, 2024 8:51 UTC (Fri) by epa (subscriber, #39769) [Link] (5 responses)

Yeah, that works too. Require the kernel to be on VFAT so grub can stay simple. I was still thinking in terms of a single partition. I think that reimplementing many different filesystems inside grub is a path to madness. But I must admit that people are doing it and they’ve made it mostly work so far.

Filesystems readable by grub

Posted Jul 26, 2024 17:16 UTC (Fri) by Wol (subscriber, #4433) [Link] (4 responses)

That then means you have to have VFAT on a system which may not run Windows.

If VFAT is required for UEFI, then okay, otherwise you have Grub enforcing a requirement of a special filesystem solely for Grub. THAT is the problem here - Grub wants to work with what's available, and there is no requirement for a computer to run Windows, there is no requirement for a computer to run UEFI, therefore Grub doesn't want to require it.

Cheers,
Wol

Filesystems readable by grub

Posted Jul 27, 2024 8:30 UTC (Sat) by jem (subscriber, #24231) [Link] (3 responses)

This has nothing to do with Windows. VFAT is the only file system UEFI understands, and the UEFI firmware expects to read executables from a VFAT formatted system partition at boot.

The old BIOS firmware is practically dead by now(*), so UEFI is also required for Linux; no difference from Windows there either.

(*) All "normal" x86_64 computers are shipped with UEFI firmware these days. Yes, BIOS emulation is still a a thing, but it would be silly thing for a distribution to enforce the use of it.

Filesystems readable by grub

Posted Jul 27, 2024 20:43 UTC (Sat) by Wol (subscriber, #4433) [Link] (2 responses)

> This has nothing to do with Windows. VFAT is the only file system UEFI understands, and the UEFI firmware expects to read executables from a VFAT formatted system partition at boot.

That is not, actually, true.

Witness Apple hardware, which afaik uses UEFI, but does not (unless we bugger about with it) have any VFAT partitions.

The specification states that UEFI *must* understand VFAT. It does not say that it's not allowed to understand anything else.

Which means if Grub is to boot linux on an Apple system it should/needs to understand Apple's disk formats. And who's to say Grub is running on a UEFI systsm anyway.

That's the point - Grub does not want to demand that there is a VFAT partition, because there is a quite possible scenario that it is the only software making that demand, and it doesn't want to be in that position. (And that position is - I believe - the case for all modern Apple systems.)

Cheers,
Wol

Filesystems readable by grub

Posted Jul 28, 2024 10:04 UTC (Sun) by jem (subscriber, #24231) [Link] (1 responses)

Ok, let's put it this way: the only thing UEFI firmware implementations have in common is that they can read from a VFAT file system. And that's typically the only file system UEFI firmware implementations know of. So if we are talking about the general case, i.e. how distro makers are going to set up booting so that it works on all UEFI machines, VFAT is the only choice. I admit that it may be possible for the kernel images to be placed on some other partition, if a boot loader is able to read from it. But the way UEFI normally works requires a VFAT partition anyway.

> Which means if Grub is to boot linux on an Apple system it should/needs to understand Apple's disk formats.

Not at all, my ca 2011 MacBook Air boots Linux the standard UEFI way, by loading systemd-boot and the kernel image from the EFI System Partition, which is a VFAT file system. Maybe macOS is started differently; I don't know and I don't care.

>And who's to say Grub is running on a UEFI systsm anyway.

True. I stopped using Grub about ten years ago, when I discovered that the kernel image can be loaded directly by UEFI. In this case, the over-engineered, hard to configure piece of software called Grub is relegated to being just a chooser application. There are better alternatives for this task, like systemd-boot.

Filesystems readable by grub

Posted Jul 28, 2024 13:42 UTC (Sun) by Wol (subscriber, #4433) [Link]

> There are better alternatives for this task, like systemd-boot.

: -)

Cheers,
Wol