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

[Marco Felsch]

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<--

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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