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    SubjectRe: [PATCH v2 4/7] virtio: VIRTIO_DEVICE_F_MASK for all per-device features
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    On 2/2/2023 9:29 AM, Michael S. Tsirkin wrote:
    > On Tue, Jan 31, 2023 at 03:22:22PM -0800, Si-Wei Liu wrote:
    >> Introduce VIRTIO_DEVICE_F_MASK bitmask used for identification
    >> of per-device features. Feature bits VIRTIO_TRANSPORT_F_START
    >> through VIRTIO_TRANSPORT_F_END are reserved for transport
    >> features hence are not counted as per-device features against
    >> the 64bit feature space.
    >>
    >> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
    >> ---
    >> include/uapi/linux/virtio_config.h | 8 ++++++++
    >> 1 file changed, 8 insertions(+)
    > Pls don't add this in uapi, people tend to depend on this and then
    > things fail when we extend virtio. For example this won't work with >64
    > feature bits.
    Good point. Then keep this macro private to vdpa.c for now?

    -Siwei
    >
    >> diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
    >> index 3c05162..3bdc7ed 100644
    >> --- a/include/uapi/linux/virtio_config.h
    >> +++ b/include/uapi/linux/virtio_config.h
    >> @@ -54,6 +54,14 @@
    >> #define VIRTIO_TRANSPORT_F_START 28
    >> #define VIRTIO_TRANSPORT_F_END 41
    >>
    >> +/*
    >> + * Bitmask for all per-device features: feature bits VIRTIO_TRANSPORT_F_START
    >> + * through VIRTIO_TRANSPORT_F_END are unset, i.e. 0xfffffc000fffffff for
    >> + * all 64bit features
    >> + */
    >> +#define VIRTIO_DEVICE_F_MASK (~0ULL << (VIRTIO_TRANSPORT_F_END + 1) | \
    >> + ((1ULL << VIRTIO_TRANSPORT_F_START) - 1))
    >> +
    >> #ifndef VIRTIO_CONFIG_NO_LEGACY
    >> /* Do we get callbacks when the ring is completely used, even if we've
    >> * suppressed them? */
    >> --
    >> 1.8.3.1

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