efivars

[FMDF]

On Thu, 23 Sep 2021, 09:22 FMDF, <fmdefrancesco at gmail.com> wrote:

> On Thu, 23 Sep 2021, 09:11 FMDF, <fmdefrancesco at gmail.com> 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) 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.
>>
>> 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. For example, if OS cannot talk to the platform via UEFI, it
>> cannot even shutdown the system (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?
>>
>> Fabio
>>
>
> For sake of completeness and for better understanding that OS need UEFI,
> but not necessarily EFI bootloaders, please read the following document:
>
> https://www.kernel.org/doc/html/latest/admin-guide/efi-stub.html
>
> Linux can boot without bootloaders, but it still needs to use UEFI at
> runtime.
>
> Fabio
>


While at this, please read also:

https://www.kernel.org/doc/html/latest/arm/uefi.html
https://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface
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