Re: [PATCH v3 4/5] xen/console: remove max_init_domid dependency

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.05.2025 22:12, dmkhn@xxxxxxxxx wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx>
> 
> The physical console input rotation depends on max_init_domid symbol, which is
> managed differently across architectures.
> 
> Instead of trying to manage max_init_domid in the arch-common code the console
> input rotation code can be reworked by removing dependency on max_init_domid
> entirely.

... at the expense of doing (worst case) 32k iterations just to find nothing
(else). Iirc it was to avoid this why max_init_domid was introduced.

> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -2460,6 +2460,35 @@ void domid_free(domid_t domid)
>      spin_unlock(&domid_lock);
>  }
>  
> +/*
> + * Find the ID of the next possible console owner domain.
> + *
> + * @return Domain ID: DOMID_XEN or non-system domain IDs within
> + * the range of [0..CONFIG_MAX_DOMID-1].
> + */
> +domid_t domid_find_with_input_allowed(domid_t hint)
> +{
> +    struct domain *d;

const?

> +    domid_t domid = DOMID_XEN;
> +
> +    spin_lock(&domlist_update_lock);

Why this heavy lock? Other functions iterating the list just use the RCU
read lock.

Jan