[PATCH 0/2] Import environment variables from FIT configuration

[Quentin Schulz]

Hi Lukas,

On 7/2/24 1:01 PM, Lukas Funke wrote:
> Hi Quentin,
> 
> On 02.07.2024 11:16, Quentin Schulz wrote:
>> Hi Lukas,
>>
>> On 7/2/24 8:48 AM, lukas.funke-oss at weidmueller.com wrote:
>>> From: Lukas Funke <lukas.funke at weidmueller.com>
>>>
>>>
>>> This series enables U-Boot to import environment variables from the
>>> selectd FIT configuration. One use-case is that the overall build 
>>> process
>>> enriches the FIT configuration node with dm-verity information which
>>> should be injected into the kernel commandline. U-Boot will then read
>>> these (possibly signed) environment variables and put them into the
>>> actual Kernel commandline using variable replacement
>>> (see CONFIG_BOOTARGS_SUBST).
>>>
>>> Example:
>>>
>>> Config:
>>> CONFIG_BOOTARGS_SUBST=y
>>> CONFIG_ENV_IMPORT_FIT_CONF=y
>>>
>>> FIT:
>>>      configurations {
>>>          default = "conf-1";
>>>              conf-1 {
>>>                  kernel = "kernel-1";
>>>                  fdt = "fdt-1";
>>>                  env,dm-verity-args = "dm-mod.create=...";
>>>                  env,bar = "someothervalue";
>>>              };
>>>      };
>>>
>>> U-Boot cmdline:
>>> => env set bootargs="rootfstype=squashfs root=/dev/xyz 
>>> ${dm-verity-args} ro"
>>> => boot
>>>
>>> Kernel cmdline:
>>> Kernel command line: rootfstype=squashfs ... dm-mod.create= ...
>>>
>>>
>>
>> I think FIT supports storing U-Boot scripts and running those via 
>> `source` command (usually the file extension is .scr).
>>
>> I do not know if there's support for automatically loading this .scr 
>> as part of a config node though, but if there isn't I guess it'd make 
>> more sense to support this case than to come up with yet another 
>> implementation?
>>
>> What do you think?
> 
> I wasn't aware of this, thanks for pointing it out!
> 
> This patch was mainly inspired by the dm-vertiy use-case which requires 
> just env-variables and no (complex) scripts.
> 
> There is currently no mechanism to source/run such scripts automatically.
> 
> How would you distinguish between scripts that should run automatically 
> und scripts which are sourced by a specific board/shell-script 
> implementation? I guess there are good reasons to not run such scripts 

Scripts in conf would be automatically run? Scripts not in conf needs to 
be executed via `source` command for example?

Not sure what to do if you want a script linked to a conf but not run 
automatically though (and what would be the use-case?). I guess you 
could have a script automatically run (so in conf node) that sets a 
variable to know where to look for the other script that isn't 
automatically executed?

> per default. I would also change current behaviour. For env variables I 
> see no harm.
> 

If the env properties in the FIT image are part of the checksum and 
signature of the conf node, which is necessary for secure boot, I guess 
"no harm" fits the bill.

Cheers,
Quentin