Re: Boot from specified partition (or FS) UUID without knowing Device ID

[Heinrich Schuchardt]

Am 19. Februar 2022 02:51:10 MEZ schrieb AKASHI Takahiro <takahiro.akashi at linaro.org>:
>On Fri, Feb 18, 2022 at 06:41:18PM +0100, Heinrich Schuchardt wrote:
>> On 2/18/22 18:07, Tom Rini wrote:
>> > On Fri, Feb 18, 2022 at 02:01:41PM +0700, Tom Hale wrote:
>> > 
>> > > I want to have a fallback boot situation where boot is first tried from one
>> > > partition, and then from another partition (on a different device) if the
>> > > first partition isn't available (eg, if the first device fails).
>> > > 
>> > > Can I boot from a specific FS UUID or a partition UUID without knowing a
>> > > particular device ID?  (I'm not sure if my devices will always be detected
>> > > in a repeatable order).
>> > > 
>> > > Can fatload be used with only a partition UUID?  Or can I somehow get the
>> > > dev number from the UUID?
>> 
>> The UEFI boot manager uses device paths which comprise the partition
>> GUIDs. Currently we use the full device path.
>> 
>> Windows and efibootmgr just store the partition and the file path in
>> boot options and non-U-Boot UEFI implementation will work fine with
>
>What do you mean by "efibootmgr"?

It is the Linux program used to set boot options.

https://manpages.ubuntu.com/manpages/xenial/man8/efibootmgr.8.html

Best regards

Heinrich

>It sounds to be the name of U-Boot's implementation of UEFI Boot Manager.
>
>> this. E.g.
>> 
>> HD(2,GPT,12345678-1234-5678-ABCD-123456789ABC,0x109000,0x32000)/File(\EFI\debian\shimx64.efi)
>
>This is called a short path and already supported in U-Boot UEFI implementation.
>See efi_dp_find_obj().
>
>> I think this approach should also be adopted for U-Boot when the file is
>> on a GPT partition.
>
>To be clear, setting a device path in a boot option is not boot manager's
>responsibility, but efidebug's, at least for now.
>So even now, if efidebug is modified to allow for a short path, it should
>work with current "efibootmgr" (although I have never tried it before).
>
># FYI, the current implementation of creating a "full" device path from
># U-Boot's probe mechanism/DM has a fatal problem of uniqueness. I have
># mentioned the issue partially in my "removable media" support RFC but
># will have to address it fully in the future.
>
>-Takahiro Akashi
>
>> Would this solve your problem?
>> 
>> Best regards
>> 
>> Heinrich
>> 
>> > 
>> > As UUIDs are unique per device but our device probe order is (nominally,
>> > there's counter examples) static, this would be a more board specific
>> > way of going than knowing which media is which device.
>> > 
>>