On Fri, Mar 15, 2024 at 3:51 PM Markus Armbruster <arm...@redhat.com> wrote:
> "Michael S. Tsirkin" <m...@redhat.com> writes:
>
> > On Wed, Mar 13, 2024 at 10:40:21AM +0100, Markus Armbruster wrote:
> >> I could be awkward for the use case described in PATCH 1's commit
> >> message:
> >>
> >> However, we sometimes want to compare features and status bits
> without
> >> caring for their exact meaning. Say we want to verify the
> correctness
> >> of the virtio negotiation between guest, QEMU, and OVS-DPDK. We
> can use
> >> QMP command x-query-virtio-status to retrieve vhost-user net device
> >> features, and the "ovs-vsctl list interface" command to retrieve
> >> interface features. Without commit f3034ad71fc, we could then
> simply
> >> compare the numbers. With this commit, we first have to map from
> the
> >> strings back to the numeric encoding.
> >
> > So, consider how guest kernel presents features then. Do you happen to
> know?
> > It's actually a binary string:
> >
> > static ssize_t features_show(struct device *_d,
> > struct device_attribute *attr, char *buf)
> > {
> > struct virtio_device *dev = dev_to_virtio(_d);
> > unsigned int i;
> > ssize_t len = 0;
> >
> > /* We actually represent this as a bitstring, as it could be
> > * arbitrary length in future. */
> > for (i = 0; i < sizeof(dev->features)*8; i++)
> > len += sysfs_emit_at(buf, len, "%c",
> > __virtio_test_bit(dev, i) ? '1' : '0');
> > len += sysfs_emit_at(buf, len, "\n");
> > return len;
> > }
> > static DEVICE_ATTR_RO(features);
>
> I'm willing to accept any reasonably compact representation of the bits
> that is easy to use for the comparison use case.
>
> I strongly prefer integers as long as their width suffices.
>
> Since out integers are limited to 64 bits, and you want us to design for
> more, we need something else.
>
> I'm fine with array of integers, but you don't like it.
>
> We generally avoid encoding stuff in strings, but using strings for
> "overwide" integers isn't as bad as using them for structured data. I
> guess I'd be okay with it.
>
> I'd use decimal simply to keep these "overwide" integers as close as
> possible to regular ones.
>
> If using base 2 enables string compare for the comparison use case,
> that's an argument for base 2.
>
> Hyman Huang, can you show us example output of "ovs-vsctl list
> interface"?
>
>
Here is the output of an active interface enable the dpdk feature:
# ovs-vsctl list interface port-testvm2pn8
_uuid: xxxx
admin_state: up
name: port-testvm2pn8
......
status: {features="0x000000017060a782", mode=client,
num_of_vrings="4"......}
Yong
--
Best regards
