Re: [PATCH v3 4/4] xen/arm: Prevent Dom0 to be loaded when using dom0less

[Julien Grall <julien@xxxxxxx>]

On 12/04/2021 11:52, Luca Fancellu wrote:
> This patch prevents the dom0 to be loaded skipping its
> building and going forward to build domUs when the dom0
> kernel is not found and at least one domU is present.
>
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> ---
> v3 changes:
> - Rephrase documentation
> ---
>   docs/features/dom0less.pandoc |  7 +++---
>   xen/arch/arm/setup.c          | 42 ++++++++++++++++++++++++++++++++---
>   2 files changed, 43 insertions(+), 6 deletions(-)
>
> diff --git a/docs/features/dom0less.pandoc b/docs/features/dom0less.pandoc
> index d798596cdf..c9edb529e1 100644
> --- a/docs/features/dom0less.pandoc
> +++ b/docs/features/dom0less.pandoc
> @@ -16,9 +16,10 @@ Multiboot specification has been extended to allow for 
> multiple domains
>   to be passed to Xen. See docs/misc/arm/device-tree/booting.txt for more
>   information about the Multiboot specification and how to use it.
>   
> -Currently, a control domain ("dom0") is still required, but in the
> -future it will become unnecessary when all domains are created
> -directly from Xen. Instead of waiting for the control domain to be fully
> +Currently, a control domain ("dom0") is still required to manage the DomU
> +domains, but the system can start also without dom0 if the Device Tree
> +doesn't specify the dom0 kernel and it declares one or more domUs.
> +Instead of waiting for the control domain (when declared) to be fully
>   booted and the Xen tools to become available, domains created by Xen
>   this way are started right away in parallel. Hence, their boot time is
>   typically much shorter.
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index b405f58996..ecc4f0ae98 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -793,6 +793,38 @@ static void __init setup_mm(void)
>   }
>   #endif
>   
> +static bool __init is_dom0less_mode(void)
> +{
> +    struct bootmodules *mods = &bootinfo.modules;
> +    struct bootmodule *mod;
> +    unsigned int i;
> +    bool dom0found = false;
> +    bool domUfound = false;
> +
> +    /* Look into the bootmodules */
> +    for ( i = 0 ; i < mods->nr_mods ; i++ )
> +    {
> +        mod = &mods->module[i];
> +        /* Find if dom0 and domU kernels are present */
> +        if ( mod->kind == BOOTMOD_KERNEL )
> +        {
> +            if ( mod->domU == false )
> +            {
> +                dom0found = true;
> +                break;
> +            }
> +            else
> +                domUfound = true;
> +        }
> +    }
> +
> +    /*
> +     * If there is no dom0 kernel but at least one domU, then we are in
> +     * dom0less mode
NIT: missing full stop.

Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

--
Julien Grall