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Date: Wed, 4 Feb 2026 10:00:03 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich Cc: dmukhin@xen.org, xen-devel@lists.xenproject.org, andrew.cooper3@citrix.com, anthony.perard@vates.tech, julien@xen.org, michal.orzel@amd.com, sstabellini@kernel.org, dmukhin@ford.com Subject: Re: [PATCH v4] xen/domain: introduce DOMID_ANY Message-ID: References: <20260109140747.195460-2-dmukhin@ford.com> <0e3a1af4-d87c-405c-a0a7-598929df3f4b@suse.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <0e3a1af4-d87c-405c-a0a7-598929df3f4b@suse.com> X-ClientProxiedBy: MR1P264CA0041.FRAP264.PROD.OUTLOOK.COM (2603:10a6:501:3e::33) To CH7PR03MB7860.namprd03.prod.outlook.com (2603:10b6:610:24e::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH7PR03MB7860:EE_|MN2PR03MB5231:EE_ X-MS-Office365-Filtering-Correlation-Id: d8cc4dc8-ff81-43ff-3dcc-08de63cbcb20 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024; 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> >> /* 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 withdrawn.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. Even if it's not passed into anything, does it make sense to guard them? The reserved domid values are already consumed, ie: cannot be reused in any way. It just seem to me like more ifdefery churn for no specific benefit. Thanks, Roger.