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


  • To: dmkhn@xxxxxxxxx
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 26 Mar 2025 14:52:37 +0100
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  • Cc: andrew.cooper3@xxxxxxxxxx, anthony.perard@xxxxxxxxxx, julien@xxxxxxx, michal.orzel@xxxxxxx, roger.pau@xxxxxxxxxx, sstabellini@xxxxxxxxxx, dmukhin@xxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 26 Mar 2025 13:52:54 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 19.03.2025 00:36, dmkhn@xxxxxxxxx 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



 


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