• Rusty Russell's avatar
    virtio: explicit advertisement of driver features · c45a6816
    Rusty Russell authored
    A recent proposed feature addition to the virtio block driver revealed
    some flaws in the API: in particular, we assume that feature
    negotiation is complete once a driver's probe function returns.
    
    There is nothing in the API to require this, however, and even I
    didn't notice when it was violated.
    
    So instead, we require the driver to specify what features it supports
    in a table, we can then move the feature negotiation into the virtio
    core.  The intersection of device and driver features are presented in
    a new 'features' bitmap in the struct virtio_device.
    
    Note that this highlights the difference between Linux unsigned-long
    bitmaps where each unsigned long is in native endian, and a
    straight-forward little-endian array of bytes.
    
    Drivers can still remove feature bits in their probe routine if they
    really have to.
    
    API changes:
    - dev->config->feature() no longer gets and acks a feature.
    - drivers should advertise their features in the 'feature_table' field
    - use virtio_has_feature() for extra sanity when checking feature bits
    Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
    c45a6816
virtio.h 4.19 KB