virtio — archive

[PATCH v10 00/10] Introduce device group and device management

From: Michael S. Tsirkin <[email protected]>
To: [email protected]
Date: Fri, 31 Mar 2023 11:44:00 -0000

On Wed, Mar 08, 2023 at 01:41:37PM +0100, Jiri Pirko wrote: > Wed, Mar 08, 2023 at 12:54:52PM CET, [email protected] wrote: > >On Mon, Mar 06, 2023 at 01:22:30PM +0100, Jiri Pirko wrote: > >> Thu, Mar 02, 2023 at 02:05:22PM CET, [email protected] 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 <[email protected]> > >> >Signed-off-by: Michael S. Tsirkin <[email protected]> > >> > >> [...] > >> > >> > >> >+ > >> >+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. > > > >Absolutely, it is similar. The issue is that a single device can > >be an owner for multiple group types. > >For example, I think an SRIOV PF itself can have subfunctions with SIOV > >as well as virtual functions with SRIOV. > >And the set of supported commands might differ. > > > >We thus need a command that is kind of like features but per group type. > > I see. But that does not mean it can't be done using existing features: > > _F_SRIOV_CMD1 > _F_SRIOV_CMD2 > .. > _F_SIOV_CMD1 > _F_SIOV_CMD2 > ... True. But annoying if each command has to be duplicated. > > > >As a small bonus as we are building this from scratch, I added > >something which was requested for a long time from features > >which is blocking access to commands not allowed by features. > >With standard virtio features we trust the driver not to send > >commands before enabling a feature and this was considered > >a maintainance/security problem. > > I understand. Is it unfixable for features not to break buggy drivers? > I think it is, feature negotiation is hard to evolve since our compat strategy is built around feature negotiation. -- MST