Hi Michael, Jason,
> From: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Sent: Wednesday, February 24, 2021 12:40 PM
>
> On Wed, Feb 24, 2021 at 08:18:36AM +0200, Parav Pandit wrote:
> > To honor VIRTIO_F_VERSION_1 feature bit, during endianness detection,
> > consider the read only supported features bit instead of current
> > features bit which can be modified by the driver.
> >
> > This enables vdpa_sim_net driver to invoke cpu_to_vdpasim16() early
> > enough just after vdpasim device creation in subsequent patch.
> >
> > Signed-off-by: Parav Pandit <parav@xxxxxxxxxx>
> > Reviewed-by: Eli Cohen <elic@xxxxxxxxxx>
>
> Well that works for legacy and modern devices but not for transitional ones.
> Without transitional device support vendors are reluctant to add modern
> features since that will break old guests ... I suspect we need to either add a
> new ioctl enabling modern mode, or abuse SET_FEATURES and call it from
> qemu on first config space access.
>
>From mgmt tool kernel point of view,
(a) config space decoding depends on current feature version bit
(b) feature get/set and config read are not atomic callbacks
Mgmt. tool kernel code need to read them in single call from the vendor driver.
I need to add mgmt_dev->ops->get_features_config(struct virtio_features_config*) calllback that returns value of both atomically in structure like below.
struct virtio_features_config {
u64 features;
union {
struct virtio_net_config net;
struct virtio_block_config blk;
} u;
}
What do you think?
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