Re: [PATCH v1 3/8] xen/domain: introduce domid_top

[Jan Beulich <jbeulich@suse.com>]

On 19.03.2025 00:36, dmkhn@proton.me wrote:
> Rename max_init_domid to domid_top to align with its usage in the code
> (Arm), where it represents the upper boundary of the non-system domain
> ID range.

I think I said before that I don't share this view of yours. The variable
is quite appropriately named; it's the further use you made of it in earlier
versions of work of yours in this area where the name ended up no longer
reflecting the purpose. Yet that's not a reason to change the name.

I'm unconvinced we actually need a variable tracking the largest known
non-system domain ID. The domain list is sorted, so obtaining that ID
should be reasonably easy and cheap without such a variable.

Furthermore such a variable would likely also need reducing when the
domain with the highest ID dies.

> --- a/xen/drivers/char/console.c
> +++ b/xen/drivers/char/console.c
> @@ -472,7 +472,7 @@ static void cf_check dump_console_ring_key(unsigned char key)
>   */
>  static unsigned int __read_mostly console_rx = 0;
>  
> -#define max_console_rx (max_init_domid + 1)
> +#define max_console_rx (domid_top + 1)

This use in particular is bogus. The intention here is to permit console
access only to (some?) domains created during boot. Making a (conceptual)
change here would require separate justification.

Jan