efivars

[Ruben Safir]

On Thu, Sep 23, 2021 at 09:11:32AM +0200, FMDF wrote:
> On Wed, 22 Sep 2021, 08:22 Ruben Safir, <ruben at mrbrklyn.com> wrote:
> 
> > What is this for?
> >
> > efivarfs on /sys/firmware/efi/efivars type efivarfs
> >
> > why would the OS need to know anything about the UEFI
> > boot loader once it is up and running?
> >
> 
> I think you are still making confusion: UEFI bootloaders and UEFI are two
> different entities.
> 
> UEFI bootloaders (like Grub2) 

Grub is not a UEFI bootloader.  Actually, with UEFI, you don't need
grub.  UEFI has effectively moved the boot loader to the system
firmware.  Grub2 is a secondary bootloader, and it is not really needed.

https://bbs.archlinux.org/viewtopic.php?id=229634
https://archived.forum.manjaro.org/t/can-i-use-pure-uefi-without-grub/21367/2


> serve the purpose to locate, pass kernel
> options  and platform information to the kernel that themselves are going
> to boot.
> 
> Instead the UEFI is an interface between the running OS and the platform
> firmware.
>

Yeah - that is what I am discovering!  Why do I need that?  If the SAME
OS is run from BIOS, it doesn't exist like that.


> UEFI defines two types of services: boot services and runtime services.
> 
> After booting is done, via UEFI boot services and eventually UEFI
> bootloaders, the OS does not need anymore the bootloader and the UEFI boot
> services.
> 
> Instead the OS needs UEFI runtime services to talk to the platform
> firmware. 

What is that?  The kernel is on the Metal.  It is talking directly to
the hardware.

> For example, if OS cannot talk to the platform via UEFI, it
> cannot even shutdown the system

That is another issue.  I don't even want to get into why my HP
workstations don't shutdown properly.

It doesn't need UEFI to shutdown.  It has been able to do that for over
25 years.


> (obviously there is much more than simply
> shutting down). How can an OS know that you've attached a plug and play
> device if it cannot talk to the platform firmware?
> 
What are you talking about?  The Kernel doesn't need UEFI to know a
device is attached and to autoload a kernel module and talk to it.

It causes an interupt and announces itself on the systembus.

What do you think those thousands of hardware choices are about when you 
compile the kernel?

BIOS systems can do that 100%.  And then there is other hardware, like
ARM.

It is useless to for me to argue what I would want to have happen.  I
have no say and nobody cares about my opinion.  I do want to know what
it is doing, though, and why I can't install a UEFI boot system from a
thumdrive that loads in BIOS mode.

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