On Wed, Jan 11, 2012 at 07:30:34AM -0600, Anthony Liguori wrote: > On 01/10/2012 06:25 PM, Rusty Russell wrote: > >On Tue, 10 Jan 2012 19:03:36 +0200, "Michael S. Tsirkin"<mst@xxxxxxxxxx> wrote: > >>On Wed, Dec 21, 2011 at 11:03:25AM +1030, Rusty Russell wrote: > >>>Yes. The idea that we can alter fields in the device-specific config > >>>area is flawed. There may be cases where it doesn't matter, but as an > >>>idea it was holed to begin with. > >>> > >>>We can reduce probability by doing a double read to check, but there are > >>>still cases where it will fail. > >> > >>Okay - want me to propose an interface for that? > > > >Had a brief chat with BenH (CC'd). > > > >I think we should deprecate writing to the config space. Only balloon > >does it AFAICT, and I can't quite figure out *why* it has an 'active' > >field. This solves half the problem, of sync guest writes. For the > >other half, I suggest a generation counter; odd means inconsistent. The > >guest can poll. > > > >BenH also convinced me we should finally make the config space LE if > >we're going to change things. Since PCI is the most common transport, > >guest-endian confuses people. And it sucks for really weird machines > > I think the more important thing to do is require accesses to > integers in the config space to always be aligned and to use the > appropriate accessor. Non-integer fields should be restricted to > byte access. > > That limits config space entries to 32-bit but also means that there > is no need for a generation counter. It's also easier to deal with > endian conversion that way. This is similar to what we have now. But it's still buggy: e.g. if guest updates MAC byte by byte, we have no way to know when it's done doing so. > But it means the backend code ends up being much simpler to write > (because it behaves more like a normal PCI device). > > If we're already making the change, the endianness ought to be a feature bit. > > >We should also change the ring (to a single ring, I think). > > Ack. > > >Descriptors > >to 24 bytes long (8 byte cookie, 8 byte addr, 4 byte len, 4 byte flags). > >We might be able to squeeze it into 20 bytes but that means packing. We > >should support inline, chained or indirect. Let the other side ack by > >setting flag, cookie and len (if written). > > > >Moreover, I think we should make all these changes at once (at least, in > >the spec). That makes it a big change, and it'll take longer to > >develop, but makes it easy in the long run to differentiate legacy and > >modern virtio. > > Ack. Long live virtio2! :-) > > Regards, > > Anthony Liguori > > > > >Thoughts? > >Rusty. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
