On 11/18/2014 07:04 PM, Michael S. Tsirkin wrote: > 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" <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. > 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? > Right, will post the patch that just fail the probe of virtio-net. Thanks _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
