efi bootmenu

[Mark Kettenis]

> From: François Ozog <francois.ozog at linaro.org>
> Date: Wed, 29 Dec 2021 14:39:36 +0100
> 
> HI Simon
> 
> On Wed, 29 Dec 2021 at 14:36, Simon Glass <sjg at chromium.org> wrote:
> 
> > Hi François,
> >
> > On Tue, 28 Dec 2021 at 03:15, François Ozog <francois.ozog at linaro.org>
> > wrote:
> > >
> > >
> > >
> > > Le mar. 28 déc. 2021 à 09:32, Simon Glass <sjg at chromium.org> a écrit :
> > >>
> > >> Hi Masahisa,
> > >>
> > >> On Tue, 21 Dec 2021 at 00:37, Masahisa Kojima
> > >> <masahisa.kojima at linaro.org> wrote:
> > >> >
> > >> > Hi Takahiro,
> > >> >
> > >> > On Tue, 21 Dec 2021 at 11:47, Takahiro Akashi
> > >> > <takahiro.akashi at linaro.org> wrote:
> > >> > >
> > >> > > On Mon, Dec 20, 2021 at 06:25:05PM +0900, Masahisa Kojima wrote:
> > >> > > > Hi Heinrich, Ilias, Akashi-san,
> > >> > > >
> > >> > > > Ilias and I are now discussing to create efi bootmenu, almost
> > similar
> > >> > > > to UiApp in EDK2.
> > >> > >
> > >> > > Why not discuss this topic openly in ML?
> > >> >
> > >> > Yes, I included U-Boot ML.(Sorry, I should include from the the
> > beginning.)
> > >> >
> > >> > >
> > >> > > How is this feature related to Simon's bootmethod proposal?
> > >> >
> > >> > If I correctly understand Simon's bootmethod proposal,
> > >> > the difference is that efi bootmenu only targets to implement
> > >> > the menu based UI to select/edit/add/delete "Boot####" and
> > "BootOrder".
> > >>
> > >> Yes, EFI would be one of the bootmethods. Others would be U-Boot
> > >> scripts, Chrome OS, Android, etc. plus people might add custom ones.
> > >>
> > >> Also I am thinking that (perhaps) the bootdev part of the standard
> > >> boot thing could be used to provide boot devices for EFI.
> > >>
> > >> If we do have a bootmenu, I wonder if it could be generic, instead of
> > >> tied to EFI?
> > >
> > > EFI BootXXXX specify an array of device paths and boot options. A device
> > path is quite a unique construct despite its name.
> > > A device path is itself an array of elements, some elements can be a
> > file path , configuration information, or diverse metadata. An example of
> > configuration information element is UART baud,stop bits, parity along with
> > terminal (vt100, ansi…). Another device path element can cover IP address,
> > transport information (tcp, UDP and port number).
> > > The traditional EFI boot menu is quite crude and does not expose the
> > full capabilities of BootXXXX (lacks edit of boot options for instance!).
> > >
> > > In the long run we will need to leverage all the BootXXXX capabilities
> > and those are EFI specific while being OS agnostic.
> > > The other U-Boot boot methods (Android , ChromeOS…) are OS specific.
> > > The goals are thus very different and making a generic approach seems
> > quite compromised. If there is a fully generic framework available in the
> > future, it may be possible to integrate the EFI boot menu. But at least
> > there is a need to solve, code first, the EFI complexities to fuel the
> > generic architecture discussion.
> >
> > Despite this, the goal of standard boot is to encompass all of this
> > within U-Boot. I believe that it will be successful, even if the path
> > at present is a bit unclear.
> >
> So I would suggest we work bottom up. Starting by making EFI menu work,
> then extend it more generic or integrated it in a framework. Starting top
> down would require a long architecture process based on not enough known
> problems to solve for each environment.
> 

Well, whatever you do, please build something that works well with a
serial console.  EDK2 makes assumptions the terminal emulation on the
other side, insists on changing the colors to white on black and
relies on function keys that need escape sequences.  And escape
sequences over serial are always iffy since they depend on timing for
their interpretation.  You can do better for U-Boot.

Also, keep in mind that BootOrder and Boot#### only really work if
there is runtime EFI variable support.  So the boot menu should
include options to select a device to boot from and use the default
(removable media) bootloader from the ESP on that device.  And a way
to make this selection stick!  Pretty much all x86 EFI implementations
provide functionality like that.  I suppose this could be done by
populating the EFI variable store with appropriate Boot#### variables
and manipulating BootOrder.  But that would make it hard to generalize
the boot menu to non-EFI boot flows.