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    SubjectRe: [PATCH 1/2] virito: introduce methods of fixing device features
    On Thu, 13 Nov 2014 13:52:53 +0800
    Jason Wang <jasowang@redhat.com> wrote:

    typo in subject-prefix: s/virito/virtio/

    > Buggy host may advertised buggy host features (a usual case is that host
    > advertise a feature whose dependencies were missed). In this case, driver
    > should detect and disable the buggy features by itself.
    >
    > This patch introduces driver specific fix_features() method which is called
    > just before features finalizing to detect and disable buggy features
    > advertised by host.

    So the basic problem this patch fixes is that an individual driver may
    only specify a static set of features but cannot specify any
    dependencies, right? Adding a sanitizer step makes sense, I guess.

    >
    > Virtio-net will be the first user.
    >
    > Cc: Rusty Russell <rusty@rustcorp.com.au>
    > Cc: Michael S. Tsirkin <mst@redhat.com>
    > Signed-off-by: Jason Wang <jasowang@redhat.com>
    > ---
    > drivers/virtio/virtio.c | 4 ++++
    > include/linux/virtio.h | 1 +
    > include/linux/virtio_config.h | 12 ++++++++++++
    > 3 files changed, 17 insertions(+)
    >
    > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
    > index df598dd..7001d6e 100644
    > --- a/drivers/virtio/virtio.c
    > +++ b/drivers/virtio/virtio.c
    > @@ -181,6 +181,10 @@ static int virtio_dev_probe(struct device *_d)
    > if (device_features & (1 << i))
    > set_bit(i, dev->features);
    >
    > + /* Fix buggy features advertised by host */
    > + if (drv->fix_features)
    > + drv->fix_features(dev);

    I'd probably call this "sanitize_features" instead.

    > +
    > dev->config->finalize_features(dev);
    >
    > err = drv->probe(dev);

    > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
    > index 7f4ef66..7bd89ea 100644
    > --- a/include/linux/virtio_config.h
    > +++ b/include/linux/virtio_config.h
    > @@ -96,6 +96,18 @@ static inline bool virtio_has_feature(const struct virtio_device *vdev,
    > return test_bit(fbit, vdev->features);
    > }
    >
    > +static inline void virtio_disable_feature(struct virtio_device *vdev,
    > + unsigned int fbit)
    > +{
    > + BUG_ON(fbit >= VIRTIO_TRANSPORT_F_START);
    > + BUG_ON(vdev->config->get_status(vdev) &
    > + ~(VIRTIO_CONFIG_S_ACKNOWLEDGE | VIRTIO_CONFIG_S_DRIVER));

    When we add virtio-1 support, we can add a check for FEATURES_OK here,
    so we're really on the safe side.

    > +
    > + virtio_check_driver_offered_feature(vdev, fbit);
    > +
    > + clear_bit(fbit, vdev->features);
    > +}
    > +
    > static inline
    > struct virtqueue *virtio_find_single_vq(struct virtio_device *vdev,
    > vq_callback_t *c, const char *n)

    The approach looks good to me.



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