Re: [libvirt] [PATCH] SpaprVio addresses are 32-bit, not 64-bit

On Fri, Jun 14, 2019 at 01:45:24PM +0200, Andrea Bolognani wrote: > On Tue, 2019-06-04 at 11:38 +1000, David Gibson wrote: > > spapr-vio addresses are used on POWER platform qemu guests, which are based > > on the PAPR specification. PAPR specifies a number of virtual devices (but > > not virtio protocol) which are addressed in an abstract namespace. > > > > Currently, libvirt encodes these addresses as 64-bit values. This is not > > correct: spapr-vio addresses are, and always have been 32-bit. That's true > > both by the PAPR specification and the qemu implementation. > > > > Therefore, change this in libvirt. > > > > This looks like it would be a breaking change, but it actually isn't. > > Because these have always been 32-bit at the lower levels, any attempt to > > use a value here > 0xffffffff would always have failed in any case, this > > will just make it fail earlier and more clearly. > > Thanks for providing this patch, and sorry for taking a while to get > back to you about it. > > Unfortunately there's one major issue with your approach: even though > it's true that a spapr-vio address that can't be represented as a > 32-bit value would always have been rejected by QEMU and so the guest > would never have been able to start, refusing to parse the value > altogether would cause such a guest to disappear completely from > libvirt. We don't consider this to be acceptable, because we want to > give users a chance to fix their guests that doesn't involve poking > at the filesystem behind libvirt's back.