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

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

[Tom Hale]

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?

Thanks in advance,

Tom

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

[Tom Rini]

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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?

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.

-- 
Tom

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

[Heinrich Schuchardt]

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
this. E.g.

HD(2,GPT,12345678-1234-5678-ABCD-123456789ABC,0x109000,0x32000)/File(\EFI\debian\shimx64.efi)

I think this approach should also be adopted for U-Boot when the file is
on a GPT partition.

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.
>

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

[AKASHI Takahiro]

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 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.
> > 
> 

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@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.
>> > 
>>