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virtio_balloon: transitional interface

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Virtio 1.0 doesn't include a modern balloon device.
But it's not a big change to support a transitional
balloon device: this has the advantage of supporting
existing drivers, transparently.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Michael S. Tsirkin 2015-04-15 10:17:43 +09:30 • committed by Rusty Russell
commit df81b29c7b
2 changed files with 43 additions and 10 deletions
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32
include/uapi/linux/virtio_balloon.h
View file

@ -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 */