On 11/17/2014 06:11 PM, Michael S. Tsirkin wrote: > On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote: >> On Mon, 17 Nov 2014 11:37:01 +0200 >> "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: >> >>> On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote: >>>> Buggy host may advertised buggy host features (a usual case is that host >>>> advertise a feature whose dependencies were missed). In this case, driver >>>> should detect and disable the buggy features by itself. >>>> >>>> This patch introduces driver specific sanitize_features() method which is >>>> called just before features finalizing to detect and disable buggy features >>>> advertised by host. >>>> >>>> Virtio-net will be the first user. >>>> >>>> Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx> >>>> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx> >>>> Cc: Cornelia Huck <cornelia.huck@xxxxxxxxxx> >>>> Cc: Wanlong Gao <gaowanlong@xxxxxxxxxxxxxx> >>>> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> >>> Hmm this conflicts with virtio 1.0 work: we drop >>> features as bitmap there. >> But that's an implementation detail, no? We'll still need a way for the >> driver to sanitize features, and I think this interface works just fine. > Now that you mention it, I don't think we do. > > The spec is quite explicit that devices must not expose invalid > combinations of features. > > Admittedly, BUG_ON isn't very friendly to hypervisors. > > But e.g. failing probe seems better than trying to work around > hypervisor bugs - otherwise we'll be stuck maintaining compatibility > with hypervisors forever. > I'm ok with failing the probe. But it won't cost big effort to workaround only features dependencies issue. I don't see how this block any further features implementation. Looking at virtio-net, it also depends on network core to fix NETIF_F_* dependencies. There seems no way to get rid of maintaining compatibility, e.g the workarounds for the buggy hypervisor without VIRTIO_F_ANY_LAYOUT support. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
