Re: [PATCH v16 1/4] xen/domain: unify domain ID allocation

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.08.2025 00:30, dmkhn@xxxxxxxxx wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx> 
> 
> Currently, there are two different domain ID allocation implementations:
> 
>   1) Sequential IDs allocation in dom0less Arm code based on max_init_domid;
> 
>   2) Sequential IDs allocation in XEN_DOMCTL_createdomain; does not use
>      max_init_domid (both Arm and x86).
> 
> The domain ID allocation covers dom0 or late hwdom, predefined domains,
> post-boot domains, excluding Xen system domains (domid >=
> DOMID_FIRST_RESERVED).
> 
> It makes sense to have a common helper code for such task across architectures
> (Arm and x86) and between dom0less / toolstack domU allocation.
> 
> Note, fixing dependency on max_init_domid is out of scope of this patch.
> 
> Wrap the domain ID allocation as an arch-independent function domid_alloc() in
> new common/domid.c based on the bitmap.
> 
> Allocation algorithm:
> - If an explicit domain ID is provided, verify its availability and use it if
>   ID is not used;
> - If DOMID_INVALID is provided, search the range [1..DOMID_FIRST_RESERVED-1],
>   starting from the last used ID.
>   Implementation guarantees that two consecutive calls will never return the
>   same ID. ID#0 is reserved for the first boot domain (currently, dom0) and
>   excluded from the allocation range.
> 
> Remove is_free_domid() helper as it is not needed now.
> 
> No functional change intended.
> 
> Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
> Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
> Reviewed-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
> ---
> Changes since v15:
> - fixup for check after the first pass in the bitarray in domid_alloc()
> - trivial renaming for the local variable in domid_alloc()
> - kept Julien's R-b, added Alejandro's R-b

Just to mention: My take is that this kind of a fix ought to invalidate all
earlier R-b. It's not just a cosmetic change, after all.

Jan