Re: [virtio-dev] [PATCH v10 08/10] admin: command list discovery

[Jiri Pirko <jiri@nvidia.com>]

Thu, Mar 02, 2023 at 02:05:22PM CET, mst@redhat.com wrote:
>Add commands to find out which commands does each group support,
>as well as enable their use by driver.
>This will be especially useful once we have multiple group types.
>
>An alternative is per-type VQs. This is possible but will
>require more per-transport work. Discovery through the vq
>helps keep things contained.
>
>Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

[...]


>+
>+The driver issues the command VIRTIO_ADMIN_CMD_LIST_QUERY to
>+query the list of commands valid for this group and before sending
>+any commands for any member of a group.
>+
>+The driver then enables use of some of the opcodes by sending to
>+the device the command VIRTIO_ADMIN_CMD_LIST_USE with a subset
>+of the list returned by VIRTIO_ADMIN_CMD_LIST_QUERY that is
>+both understood and used by the driver.

To my untrained ear, this sounds somewhat similar to the feature
negotiantion mechanism. Why the fact that device/driver supports some
command can't be covered by just another feature? Looks like unnecassary
complexicity to negotiate supported commands like this.