[PATCH v2 09/10] Documentation: efi: describe load options handling

[Ahmad Fatoum]

Hi,

On 10/15/26 2:13 PM, Marco Felsch wrote:
> On 26-10-15 13:19, Ahmad Fatoum wrote:
>> Hello Marco,
>>
>> On 10/15/26 1:08 PM, Marco Felsch wrote:
>>> On 26-10-15 11:18, Ahmad Fatoum wrote:
>>>> +To pass a ``root=`` option to a UKI, have :ref:`command_devlookup`
>>>> +generate it for the root partition, the same way ``global.bootm.appendroot``
>>>> +would, including the option name from ``global.bootm.root_param``:
>>>> +
>>>> +.. code-block:: sh
>>>> +
>>>> +  devlookup -v rootarg -k /dev/disk0.1
>>>> +  global efi.bootargs.root="${rootarg}"
>>>> +  bootm /boot/EFI/Linux/uki.efi
>>>
>>> Just a comment on this: devlookup can't be compared to the appendroot
>>> mechansim, due to the partition enumeration mismatch between barebox and
>>> linux, e.g. mmc block device partitions start at 0, whereas linux starts
>>> counting at 1.
>>>> On embedded devices booting from an MMC device the root=/dev/mmcblk*
>>> mechanism should be used if the device supports dual boot e.g. from SD
>>> and from eMMC.
>>
>> devlookup -k follows the same code paths appendroot would follow, so it
>> will be 1-indexed /dev/mmblkXpY if that's what appendroot would have
>> produced.
> 
> Ah, good to know, thanks.
> 
>>> Therefore I would have liked to see that the appendroot mechanism would
>>> be supported for UKIs as well which would stop the requirement of having
>>> different UKI profiles just to encode the different boot mediums.
>>
>> I believe barebox can't provide this universally.
>>
>> - On an x86 system with secure boot, the systemd-stub will ignore any
>> extra command-line arguments, except for the profile.
> 
> According the comment from system-stub, the cmdline is only ignored if
> the UKI already has a cmdline and we're in secure-boot:
> 
> ---8<---------8<---------8<---------8<---------8<---------8<---------8<--
> | * We'll suppress the custom cmdline if we are in Secure Boot mode, and if either there is already
> | * a cmdline baked into the UKI or we are in confidential VM mode. */ 
> ---8<---------8<---------8<---------8<---------8<---------8<---------8<--

If you have a good idea how to design the API for this, so it's not
confusing to users, go ahead.

Cheers,
Ahmad

> 
> Regards,
>   Marco
> 
>> - On the ARM systems with device tree, we may be able to cheat by
>> patching the DT, but I have not checked how Linux or systemd-boot handle
>> /chosen/bootargs if they are booted via EFI.
>>
>> Cheers,
>> Ahmad
>>
>>
>>>
>>> However, as said this is just a comment and doesn't block this patch:
>>>
>>> Reviewed-by: Marco Felsch <m.felsch at pengutronix.de>
>>>
>>>>  Drivers
>>>>  ^^^^^^^
>>>> diff --git a/Documentation/user/booting-linux.rst b/Documentation/user/booting-linux.rst
>>>> index 8e6f3bbbe9ce..dc7ac6dc8716 100644
>>>> --- a/Documentation/user/booting-linux.rst
>>>> +++ b/Documentation/user/booting-linux.rst
>>>> @@ -103,6 +103,9 @@ to the bootargs. Variables without a value are skipped:
>>>>  
>>>>    Kernel command line: ignore_loglevel console=ttyO0,115200 earlyprintk
>>>>  
>>>> +When booting an EFI-stubbed kernel as EFI application, the
>>>> +:ref:`EFI load options <efi_load_options>` precede the Linux bootargs.
>>>> +
>>>>  .. _bootargs_concat_order:
>>>>  
>>>>  Concatenation order
>>>> @@ -170,7 +173,8 @@ This takes the kernel from ``/mnt/mmc1/zImage`` (which could be an
>>>>  boot entries should always add Kernel command line parameters to variables with
>>>>  ``.dyn`` in it. These will be cleared before booting different boot entries.
>>>>  This is done so that following boot entries do not leak command line
>>>> -parameters from the previous boot entries.
>>>> +parameters from the previous boot entries. The same applies to the
>>>> +:ref:`EFI load options <efi_load_options>` in ``global.efi.bootargs.dyn.*``.
>>>>  
>>>>  This entry can be booted with ``boot mmc``. It can also be made the default by
>>>>  setting the :ref:`global.boot.default <magicvar_global_boot_default>` variable
>>>> -- 
>>>> 2.47.3
>>>>
>>>>
>>
>> -- 
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>>

-- 
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