Re: [virtio] Re: [virtio-comment] [PATCH v10 09/10] admin: conformance clauses

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Mar 08, 2023 at 03:02:05PM +0100, Jiri Pirko wrote:
> Wed, Mar 08, 2023 at 02:44:08PM CET, david.edmondson@oracle.com wrote:
> >Jiri Pirko <jiri@nvidia.com> writes:
> >
> >> Wed, Mar 08, 2023 at 01:59:10PM CET, david.edmondson@oracle.com wrote:
> >>>"Michael S. Tsirkin" <mst@redhat.com> writes:
> >>>
> >>>> On Tue, Mar 07, 2023 at 11:04:33AM +0000, David Edmondson wrote:
> >>>>> "Michael S. Tsirkin" <mst@redhat.com> writes:
> >>>>> > +The driver MAY block use of VIRTIO_ADMIN_CMD_LIST_QUERY and
> >>>>> > +VIRTIO_ADMIN_CMD_LIST_USE by issuing VIRTIO_ADMIN_CMD_LIST_USE
> >>>>> > +with respective bits cleared in \field{command_specific_data}.
> >>>>> 
> >>>>> This runs contrary to the assertion "The list of supported commands MUST
> >>>>> NOT shrink", given that a driver is told to assume that
> >>>>> VIRTIO_ADMIN_CMD_LIST_QUERY and VIRTIO_ADMIN_CMD_LIST_USE are the only
> >>>>> commands initially available.
> >>>>
> >>>> Commands are still available just disabled, the meaning of
> >>>> "MUST NOT shrink" is clarified by the following:
> >>>>
> >>>> 	> > +after reporting a given command as supported through
> >>>> 	> > +VIRTIO_ADMIN_CMD_LIST_QUERY the device MUST NOT later report it
> >>>> 	> > +as unsupported.
> >>>> I will stick an "i.e." there to make it hopefully clearer.
> >>>
> >>>This puzzles me.
> >>>
> >>>I can see the point of blocking LIST_USE, but not of blocking
> >>
> >> What is that point, I'm curious.
> >
> >I might restrict the commands permitted by a device before handing it
> >off to some subordinate less trusted code.
> 
> Hmm, that is theoretical, or is there a usecase for that?
> 

Maybe there will be a future version replacing VIRTIO_ADMIN_CMD_LIST_QUERY
with a different command. Then we start with a device supporting
both VIRTIO_ADMIN_CMD_LIST_QUERY and the new VIRTIO_ADMIN_FOO,
and we block VIRTIO_ADMIN_CMD_LIST_QUERY for testing, to make sure driver
is able to handle future devices without VIRTIO_ADMIN_CMD_LIST_QUERY.


> >
> >>
> >>>LIST_QUERY. What's the purpose of this?
> >>
> >> I think that this might be just for the sake of treating all
> >> commands equally.
> >>
> >>
> >>>-- 
> >>>Time is waiting to explain, why refuse?
> >>>
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