Re: [PATCH] Fix fallout from DOMID_ANY ABI breakage

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, May 27, 2026 at 05:57:58PM +0100, Andrew Cooper wrote:
> Commit 23e2479ff9de ("xen/domain: introduce DOMID_ANY") broke at least:
> 
>  * xenstored domains
>  * The Python bindings
>  * The Ocaml bindings (i.e XAPI, and therefore XenServer/XCP-ng)
> 
> by causing Xen to reject 0 (the wildcard sentinel for decades) and
> DOMID_INVALID (a recently introduced wildcard sentinel) without adjusting the
> callers of xc_domain_create().
> 
> Under other circumstances I'd revert, but xenstored has gained a dependent use
> of DOMID_ANY.
> 
> Fix up the remaining in-tree callers, which covers init-xenstore-domain and
> the python bindings.  The Ocaml bindings, like libxc itself, expose this ABI
> detail to their caller, so need fixing individually.

I think this will also affect the rust crate(s), even when those don't
use the libxc bindings.

> 
> Leave a very clear message in CHANGELOG.md that all external callers need
> altering.
> 
> Fixes: 23e2479ff9de ("xen/domain: introduce DOMID_ANY")
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

> ---
> CC: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> CC: Michal Orzel <michal.orzel@xxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Julien Grall <julien@xxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Juergen Gross <jgross@xxxxxxxx>
> CC: Denis Mukhin <dmukhin@xxxxxxxx>
> CC: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> 
> Both Roger and I said no to the DOMID_ANY change.  We both think that there is
> still insufficient justification to be adding it as a new constant.  Next time
> it's going to be a straight nack.
> ---
>  CHANGELOG.md                         | 4 ++++
>  tools/helpers/init-xenstore-domain.c | 2 +-
>  tools/python/xen/lowlevel/xc/xc.c    | 2 +-
>  3 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/CHANGELOG.md b/CHANGELOG.md
> index 25f5a192ed48..1b54acf912a5 100644
> --- a/CHANGELOG.md
> +++ b/CHANGELOG.md
> @@ -7,6 +7,10 @@ The format is based on [Keep a 
> Changelog](https://keepachangelog.com/en/1.0.0/)
>  ## [4.22.0 
> UNRELEASED](https://xenbits.xenproject.org/gitweb/?p=xen.git;a=shortlog;h=staging)
>  - TBD
>  
>  ### Changed
> + - Users of xc_domain_create() must now pass DOMID_ANY to obtain an
> +   automatically allocated domid.  The prior sentinel values (0 since the
> +   birth of Xen, and DOMID_INVALID since Xen 4.21) now no longer represent a
> +   wildcard input.

Maybe also mention XEN_DOMCTL_createdomain explicitly, to notice is
not only the callers of libxc that needs adjustment, but also users of
the hypercall itself not going through libxc.

Thanks, Roger.