Re: [PATCH 3/6] xen: add new domctl get_changed_domain

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.10.2024 15:10, Juergen Gross wrote:
> Add a new domctl sub-function to get data of a domain having changed
> state (this is needed by Xenstore).
> 
> The returned state just contains the domid, the domain unique id,
> and some flags (existing, shutdown, dying).
> 
> In order to enable Xenstore stubdom being built for multiple Xen
> versions, make this domctl stable.  For stable domctls the
> interface_version is specific to the respective domctl op and it is an
> in/out parameter: On input the caller is specifying the desired version
> of the op, while on output the hypervisor will return the used version
> (this will be at max the caller supplied version, but might be lower in
> case the hypervisor doesn't support this version).
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> V1:
> - use a domctl subop for the new interface (Jan Beulich)

Just as a preliminary reply: With Andrew's stabilization plans I'm not
sure this, in particular including ...

> @@ -1236,7 +1237,37 @@ struct xen_domctl_dt_overlay {
>  };
>  #endif
>  
> +/*
> + * XEN_DOMCTL_get_domain_state (stable interface)
> + *
> + * Get state information of a domain.
> + *
> + * In case domain is DOMID_INVALID, return information about a domain having
> + * changed state and reset the state change indicator for that domain. This
> + * function is usable only by a domain having registered the VIRQ_DOM_EXC
> + * event (normally Xenstore).
> + *
> + * Supported interface versions: 0x00000000
> + */
> +#define XEN_DOMCTL_GETDOMSTATE_VERS_MAX    0
> +struct xen_domctl_get_domain_state {
> +    domid_t domid;
> +    uint16_t state;
> +#define XEN_DOMCTL_GETDOMSTATE_STATE_EXIST     0x0001  /* Domain is 
> existing. */
> +#define XEN_DOMCTL_GETDOMSTATE_STATE_SHUTDOWN  0x0002  /* Shutdown finished. 
> */
> +#define XEN_DOMCTL_GETDOMSTATE_STATE_DYING     0x0004  /* Domain dying. */
> +    uint32_t pad1;           /* Returned as 0. */
> +    uint64_t unique_id;      /* Unique domain identifier. */
> +    uint64_t pad2[6];        /* Returned as 0. */
> +};
> +
>  struct xen_domctl {
> +/*
> + * Stable domctl ops:
> + * interface_version is per cmd, hypervisor can support multiple versions
> + * and will return used version (at max caller supplied value) in
> + * interface_version on return.
> + */

... this (ab)use of the interface version, is the way to go. I think
we want a brand new hypercall, with stability just like most other
hypercalls have it. Backwards-incompatible interface changes then
simply aren't allowed (as in: require a new sub-op instead).

Jan