Re: [PATCH v3 1/3] qmp: Switch x-query-virtio-status back to numeric encoding

[Markus Armbruster <armbru@redhat.com>]

Hyman Huang <yong.huang@smartx.com> writes:

> x-query-virtio-status returns several sets of virtio feature and
> status flags.  It goes back to v7.2.0.
>
> In the initial commit 90c066cd682 (qmp: add QMP command
> x-query-virtio-status), we returned them as numbers, using virtio's
> well-known binary encoding.
>
> The next commit f3034ad71fc (qmp: decode feature & status bits in
> virtio-status) replaced the numbers by objects.  The objects represent
> bits QEMU knows symbolically, and any unknown bits numerically just like
> before.
>
> Commit 8a8287981d1 (hmp: add virtio commands) the matching HMP command

added the matching HMP command

> "info virtio" (and a few more, which aren't relevant here).
>
> The symbolic representation uses lists of strings.  The string format is
> undocumented.  The strings look like "WELL_KNOWN_SYMBOL: human readable
> explanation".
>
> This symbolic representation is nice for humans.  Machines it can save
> the trouble of decoding virtio's well-known binary encoding.
>
> 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.
>
> Revert the decoding for QMP, but keep it for HMP.
>
> This makes the QMP command easier to use for use cases where we
> don't need to decode, like the comparison above.  For use cases
> where we need to decode, we replace parsing undocumented strings by
> decoding virtio's well-known binary encoding.
>
> Incompatible change; acceptable because x-query-virtio-status does

Scratch "does".

> comes without a stability promise.
>
> Signed-off-by: Hyman Huang <yong.huang@smartx.com>

Acked-by: Markus Armbruster <armbru@redhat.com>