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

[Ahmad Fatoum]

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.


> 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.

- 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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