Re: [PATCH v6 1/2] xen/domain: unify domain ID allocation

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.05.2025 04:04, dmkhn@xxxxxxxxx wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx>
> 
> Currently, hypervisor code has two different non-system domain ID allocation
> implementations:
> 
>   (a) Sequential IDs allocation in dom0less Arm code based on max_init_domid;
> 
>   (b) Sequential IDs allocation in XEN_DOMCTL_createdomain; does not use
>       max_init_domid (both Arm and x86).
> 
> It makes sense to have a common helper code for such task across architectures
> (Arm and x86) and between dom0less / toolstack domU allocation.
> 
> Wrap the domain ID allocation as an arch-independent function domid_alloc() in
> common/domain.c based on rangeset.
> 
> Allocation algorithm:
> - If an explicit domain ID is provided, verify its availability and
>   use it if ID is not used;
> - Otherwise, perform an exhaustive search starting from the end of the used
>   domain ID range. domid_alloc() guarantees that two subsequent calls will
>   result in different IDs allocation.
While you properly retain original logic now, the above is not an accurate
description thereof, imo. To search "from the end" usually is understood as
a backwards search. Whereas what you mean is that the search starts off where
the last one finished, wrapping around when hitting the end of the valid
range.

Jan