On Tue, Nov 18, 2014 at 11:23:49AM +0800, Jason Wang wrote: > 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" <[email protected]> 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 <[email protected]> > >>>> Cc: Michael S. Tsirkin <[email protected]> > >>>> Cc: Cornelia Huck <[email protected]> > >>>> Cc: Wanlong Gao <[email protected]> > >>>> Signed-off-by: Jason Wang <[email protected]> > >>> 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.
>From experience, second-guessing user always adds maintainance. > 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. That code is common for all drivers, so it was moved to core. > There seems no way to get rid of maintaining compatibility, e.g the > workarounds for the buggy hypervisor without VIRTIO_F_ANY_LAYOUT support. Right - because too many hypervisors shipped without it, it's too much work to fix them all. No such motivation here, right? -- MST -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
