Re: [Xen-devel] [PATCH 3/4] xen: introduce an event channel for buffered io event notifications

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2011-11-15 at 17:20 +0000, Stefano Stabellini wrote:
> On Tue, 15 Nov 2011, Ian Campbell wrote:
> > > +    xc_get_hvm_param(xen_xc, xen_domid, HVM_PARAM_BUFIOREQ_EVTCHN,
> > > +            &bufioreq_evtchn);
> > > +    rc = xc_evtchn_bind_interdomain(state->xce_handle, xen_domid,
> > > +            (uint32_t)bufioreq_evtchn);
> > > +    if (rc == -1) {
> > > +        fprintf(stderr, "bind interdomain ioctl error %d\n", errno);
> > > +        return -1;
> > > +    }
> > > +    state->bufioreq_local_port = rc;
> > 
> > Does this fallback gracefully on hypervisors which don't have this new
> > hvm param? It doesn't look like it but perhaps I'm missing something.
> 
> No, it does not.
> However upstream Qemu doesn't work very well with Xen 4.1 anyway, the
> first Xen release that is going to support it will be Xen 4.2 that
> should have this feature.

In which case I think you need to handle the resultant error from
xc_get_hvm_param() gracefully with a suitable error message which says
something along those lines.

Ian.


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