Re: [Xen-devel] [PATCH] xen/pvhvm: If xen_platform_pci=0 is set don't blow up.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-12-04 at 11:18 +0000, Stefano Stabellini wrote:
> On Wed, 4 Dec 2013, Ian Campbell wrote:
> > On Wed, 2013-12-04 at 11:05 +0000, Stefano Stabellini wrote:
> > > On Wed, 4 Dec 2013, Ian Campbell wrote:
> > > > On Wed, 2013-12-04 at 10:51 +0000, Stefano Stabellini wrote:
> > > > > On Wed, 4 Dec 2013, Ian Campbell wrote:
> > > > > > > +bool xen_has_pv_devices(void)
> > > > > > > +{
> > > > > > > + if (!xen_domain())
> > > > > > > +         return false;
> > > > > > > +
> > > > > > > + if (xen_hvm_domain()) {
> > > > > > > +         /* User requested no unplug, so no PV drivers. */
> > > > > > > +         if (xen_emul_unplug & XEN_UNPLUG_NEVER)
> > > > > > > +                 return false;
> > > > > > 
> > > > > > I think you need
> > > > > >             if (xen_emul_unpug & XEN_UNPLUG_UNNECESSARY)
> > > > > >                     return true;
> > > > > > don't you?
> > > > > 
> > > > > XEN_UNPLUG_UNNECESSARY was introduced to enable the platform PCI 
> > > > > device
> > > > > even if it didn't respond properly to the unplug protocol.
> > > > > The corresponding parameter is called "unnecessary" because if you 
> > > > > pass
> > > > > it to the kernel you mean that it is unnecessary to unplug the 
> > > > > emulated
> > > > > devices but you can use the pv devices anyway.
> > > > > 
> > > > > So no, we shouldn't check for XEN_UNPLUG_UNNECESSARY here.
> > > > 
> > > > Oh, we will eventually fall through to the return true, so it does
> > > > actually work out OK.
> > > > 
> > > > I'd still be in favour of handling each option explicitly, for clarity.
> > > > Which means checking for XEN_UNPLUG_UNNECESSARY.
> > > 
> > > I think is wrong to check for any xen_emul_unpug options in this function.
> > > The xen_emul_unpug options should be used to set the right value of
> > > xen_platform_pci_unplug. (See my other reply.)
> > 
> > Whichever one we check we should still be checking explicitly for the
> > "unnecessary" case, for clarity if nothing else.
> 
> Sure, that is OK for me.
> In that case should we check for the full list of possible options?

We probably should. That probably means an extra
xen_has_pv_{disk,nic}_devices() which is the existing one plus the
specific checks?

> 
>             ide-disks -- unplug primary master IDE devices
>                       aux-ide-disks -- unplug non-primary-master IDE devices
>                       nics -- unplug network devices
>                       all -- unplug all emulated devices (NICs and IDE disks)
>                       unnecessary -- unplugging emulated devices is
>                               unnecessary even if the host did not respond to
>                               the unplug protocol
>                       never -- do not unplug even if version check succeeds



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