virtio_balloon: transitional interface

[karo-tx-linux.git] / include / uapi / linux / virtio_balloon.h

diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
index 4b0488f20b2ef5bfa9c3c4e94c4dba112a9d0527..984169a819ee4c8f2163c6a5c12d24fbf273caec 100644 (file)
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -25,6 +25,7 @@
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE. */
+#include <linux/types.h>
 #include <linux/virtio_ids.h>
 #include <linux/virtio_config.h>
 
@@ -38,9 +39,9 @@
 
 struct virtio_balloon_config {
        /* Number of pages host wants Guest to give up. */
-       __le32 num_pages;
+       __u32 num_pages;
        /* Number of pages we've actually got in balloon. */
-       __le32 actual;
+       __u32 actual;
 };
 
 #define VIRTIO_BALLOON_S_SWAP_IN  0   /* Amount of memory swapped in */
@@ -51,9 +52,32 @@ struct virtio_balloon_config {
 #define VIRTIO_BALLOON_S_MEMTOT   5   /* Total amount of memory */
 #define VIRTIO_BALLOON_S_NR       6
 
+/*
+ * Memory statistics structure.
+ * Driver fills an array of these structures and passes to device.
+ *
+ * NOTE: fields are laid out in a way that would make compiler add padding
+ * between and after fields, so we have to use compiler-specific attributes to
+ * pack it, to disable this padding. This also often causes compiler to
+ * generate suboptimal code.
+ *
+ * We maintain this statistics structure format for backwards compatibility,
+ * but don't follow this example.
+ *
+ * If implementing a similar structure, do something like the below instead:
+ *     struct virtio_balloon_stat {
+ *         __virtio16 tag;
+ *         __u8 reserved[6];
+ *         __virtio64 val;
+ *     };
+ *
+ * In other words, add explicit reserved fields to align field and
+ * structure boundaries at field size, avoiding compiler padding
+ * without the packed attribute.
+ */
 struct virtio_balloon_stat {
-       __u16 tag;
-       __u64 val;
+       __virtio16 tag;
+       __virtio64 val;
 } __attribute__((packed));
 
 #endif /* _LINUX_VIRTIO_BALLOON_H */