Re: [PATCH v2] xen/arm, xen/common: Add Kconfig option to control Dom0 boot

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.07.2025 23:28, dmkhn@xxxxxxxxx wrote:
> On Mon, Jul 28, 2025 at 05:07:30PM +0000, Oleksii Moisieiev wrote:
>> This commit introduces a new Kconfig option, `CONFIG_DOM0_BOOT`, to
>> allow for building Xen without support for booting a regular domain (Dom0).
>> This functionality is primarily intended for the ARM architecture.
>>
>> A new Kconfig symbol, `HAS_DOM0`, has been added and is selected by
>> default for ARM and X86 architecture. This symbol signifies that an
>> architecture has the capability to support a Dom0.
>>
>> The `DOM0_BOOT` option depends on `HAS_DOM0` and defaults to 'y'. For
>> expert users, this option can be disabled (`CONFIG_EXPERT=y` and no
>> `CONFIG_DOM0_BOOT` in the config), which will compile out the Dom0
>> creation code on ARM. This is useful for embedded or dom0less-only
>> scenarios to reduce binary size and complexity.
>>
>> The ARM boot path has been updated to panic if it detects a non-dom0less
>> configuration while `CONFIG_DOM0_BOOT` is disabled, preventing an invalid
>> boot.
>>
>> Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@xxxxxxxx>
>>
>> ---
>>
>> ---
>>  xen/arch/arm/Kconfig        |  1 +
>>  xen/arch/arm/domain_build.c |  8 ++++++++
>>  xen/arch/arm/setup.c        | 14 ++++++++++----
>>  xen/arch/x86/Kconfig        |  1 +
>>  xen/common/Kconfig          | 11 +++++++++++
>>  5 files changed, 31 insertions(+), 4 deletions(-)
> 
> I think there should be changes in
>   include/xen/domain.h
> and
>   arch/arm/include/asm/setup.h
> to compile out declarations of dom0_max_vcpus() and create_dom0() under new
> CONFIG_DOM0_BOOT.

Adding #ifdef-ary just to hide declarations is often merely adding clutter,
without providing a clear benefit. I didn't check in this case, but I think
when making such a request you want to clarify what the gains would be of
adding more #ifdef.

Jan