On Mon, 2009-11-09 at 19:00 +0000, Jamie Lokier wrote: > Adam Litke wrote: > > + s->stats.pswapin = has_feature(dev, VIRTIO_BALLOON_F_RPT_SWAP_OUT) > > ? > > + dev->stats.pswapin : -1; > > (etc.) > > Why not simply have the guest fill in the unused fields with -1, and > say that's how "no meaningful value" is represented in the ABI? > > All guests have to know about all those fields anyway, for the > structure layout. Is there any benefit to specifying feature bits in > advance over simply storing -1 there?
This holds true for fields that exist but might not be supported by a guest, but what about the case where we add a new field? In that case, qemu and the guest may disagree on the structure layout. -- Thanks, Adam
