Re: [Xen-devel] [PATCH v5.1 6/8] xen: destroy_hvm_domain: Try xendevicemodel_shutdown

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

Stefano Stabellini writes ("Re: [PATCH v5.1 6/8] xen: destroy_hvm_domain: Try 
xendevicemodel_shutdown"):
> On Fri, 20 Oct 2017, Ian Jackson wrote:
> > xc_interface_open etc. is not going to work if we have dropped
> > privilege, but xendevicemodel_shutdown will if everything is new
> > enough.
> > 
> > xendevicemodel_shutdown is only availabe in Xen 4.10 and later, so
> > provide a stub for earlier versions.
...
> > +    if (xen_dmod) {
> > +        rc = xendevicemodel_shutdown(xen_dmod, xen_domid, reason);
> > +        if (!rc) {
> > +            return;
> > +        }
> > +        perror("xendevicemodel_shutdown failed");
> 
> I don't think is a good idea to print an error because this is actually
> a normal condition when QEMU is build and run against an older Xen.
> Users might get confused when looking at the logs.

Oh.  Yes.  I wrote this before I provided the fallback stub in
xen_common.h, and therefore before I properly understood the approach
taken to fallbacks.  The fallback logic here is not correct.

> But it would be correct to print an error if errno != ENOTTY.

Indeed.

I have changed it to read like this:

    if (xen_dmod) {
        rc = xendevicemodel_shutdown(xen_dmod, xen_domid, reason);
        if (!rc) {
            return;
        }
        if (errno != ENOTTY /* old Xen */)
            perror("xendevicemodel_shutdown failed");
        /* well, try the old thing then */
    }

Thanks,
Ian.

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