virtio: add low-level APIs for feature bits

Add low level APIs to test/set/clear feature bits.
For use by transports, to make it easier to
write code independent of feature bit array format.

Note: APIs is prefixed with __ and has _bit suffix
to stress its low level nature.  It's for use by transports only:
drivers should use virtio_has_feature and never need to set/clear
features.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>

1 files changed, 50 insertions, 3 deletions

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 7f4ef66873ef..d8e28a2a5738 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -77,11 +77,47 @@ void virtio_check_driver_offered_feature(const struct virtio_device *vdev,
                                          unsigned int fbit);
 
 /**
- * virtio_has_feature - helper to determine if this device has this feature.
+ * __virtio_test_bit - helper to test feature bits. For use by transports.
+ *                     Devices should normally use virtio_has_feature,
+ *                     which includes more checks.
  * @vdev: the device
  * @fbit: the feature bit
  */
-static inline bool virtio_has_feature(const struct virtio_device *vdev,
+static inline bool __virtio_test_bit(const struct virtio_device *vdev,
+                                     unsigned int fbit)
+{
+        /* Did you forget to fix assumptions on max features? */
+        if (__builtin_constant_p(fbit))
+                BUILD_BUG_ON(fbit >= 32);
+        else
+                BUG_ON(fbit >= 32);
+
+        return test_bit(fbit, vdev->features);
+}
+
+/**
+ * __virtio_set_bit - helper to set feature bits. For use by transports.
+ * @vdev: the device
+ * @fbit: the feature bit
+ */
+static inline void __virtio_set_bit(struct virtio_device *vdev,
+                                    unsigned int fbit)
+{
+        /* Did you forget to fix assumptions on max features? */
+        if (__builtin_constant_p(fbit))
+                BUILD_BUG_ON(fbit >= 32);
+        else
+                BUG_ON(fbit >= 32);
+
+        set_bit(fbit, vdev->features);
+}
+
+/**
+ * __virtio_clear_bit - helper to clear feature bits. For use by transports.
+ * @vdev: the device
+ * @fbit: the feature bit
+ */
+static inline void __virtio_clear_bit(struct virtio_device *vdev,
                                       unsigned int fbit)
 {
         /* Did you forget to fix assumptions on max features? */
@@ -90,10 +126,21 @@ static inline bool virtio_has_feature(const struct virtio_device *vdev,
         else
                 BUG_ON(fbit >= 32);
 
+        clear_bit(fbit, vdev->features);
+}
+
+/**
+ * virtio_has_feature - helper to determine if this device has this feature.
+ * @vdev: the device
+ * @fbit: the feature bit
+ */
+static inline bool virtio_has_feature(const struct virtio_device *vdev,
+                                      unsigned int fbit)
+{
         if (fbit < VIRTIO_TRANSPORT_F_START)
                 virtio_check_driver_offered_feature(vdev, fbit);
 
-        return test_bit(fbit, vdev->features);
+        return __virtio_test_bit(vdev, fbit);
 }
 
 static inline