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

[Julien Grall <julien@xxxxxxx>]

Hi Denis,

On 12/08/2025 23:30, 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()
This was a good catch from Jan. Has a unit-test been added for this issue?

Anyway, my reviewed-by holds.

Cheers,

--
Julien Grall