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Re: [PATCH v4] xen/domain: introduce DOMID_ANY
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>, dmukhin@xxxxxxx
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 4 Feb 2026 08:56:10 +0100
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, andrew.cooper3@xxxxxxxxxx, anthony.perard@xxxxxxxxxx, julien@xxxxxxx, michal.orzel@xxxxxxx, sstabellini@xxxxxxxxxx, dmukhin@xxxxxxxx
- Delivery-date: Wed, 04 Feb 2026 07:56:17 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 04.02.2026 08:49, Roger Pau Monné wrote:
> On Fri, Jan 09, 2026 at 06:07:48AM -0800, dmukhin@xxxxxxx wrote:
>> --- a/xen/include/public/xen.h
>> +++ b/xen/include/public/xen.h
>> @@ -608,6 +608,11 @@ DEFINE_XEN_GUEST_HANDLE(mmuext_op_t);
>> /* DOMID_INVALID is used to identify pages with unknown owner. */
>> #define DOMID_INVALID xen_mk_uint(0x7FF4)
>>
>> +#if defined(__XEN__) || defined(__XEN_TOOLS__)
>> +/* Domain ID allocator: search [1..DOMID_FIRST_RESERVED-1] range. */
>> +#define DOMID_ANY xen_mk_uint(0x7FF5)
>> +#endif
>
> I would attempt to word the comment in a more generic way. While this
> is now only used for the domain ID allocator, it's likely to gain more
> uses going forward (Juergen already expressed interest):
>
> "DOMID_ANY is used to signal no specific domid requested. Handler
> should pick a valid domid, or handle it as a broadcast value depending
> on the context."
+1
> Also, I would remove the tools guards, I think once a DOMID_ constant
> is allocated it becomes part of the public ABI, and it cannot be
> withdrawn. See for example DOMID_IDLE: it's only used internally in
> the hypervisor AFAICT, yet the define is fully visible in the
> headers.
It was me to ask for it to be guarded like this. DOMID_IDLE (and perhaps
others) not being guarded (at least for IDLE: by just __XEN__) imo was a
mistake. That mistake may in fact be correctable, if we could prove that
the ID cannot usefully be passed into anywhere.
Jan
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