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

[Jürgen Groß <jgross@xxxxxxxx>]

On 28.10.24 11:50, Jan Beulich wrote:
> 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).
Okay, so back to my initial RFC variant then. :-)

Andrew, can you confirm you'd prefer that route?


Juergen

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