virtio_balloon: add array of stat names

Jason Wang points out that it's very hard for users to build an array of
stat names. The naive thing is to use VIRTIO_BALLOON_S_NR but that
breaks if we add more stats - as done e.g. recently by commit 6c64fe7f2
("virtio_balloon: export hugetlb page allocation counts").

Let's add an array of reasonably readable names.

Fixes: 6c64fe7f2 ("virtio_balloon: export hugetlb page allocation counts")
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Jonathan Helman <jonathan.helman@oracle.com>

include/uapi/linux/virtio_balloon.h

@@ -57,6 +57,21 @@ struct virtio_balloon_config {
 #define VIRTIO_BALLOON_S_HTLB_PGFAIL   9  /* Hugetlb page allocation failures */
 #define VIRTIO_BALLOON_S_NR       10
 
+#define VIRTIO_BALLOON_S_NAMES_WITH_PREFIX(VIRTIO_BALLOON_S_NAMES_prefix) { \
+	VIRTIO_BALLOON_S_NAMES_prefix "swap-in", \
+	VIRTIO_BALLOON_S_NAMES_prefix "swap-out", \
+	VIRTIO_BALLOON_S_NAMES_prefix "major-faults", \
+	VIRTIO_BALLOON_S_NAMES_prefix "minor-faults", \
+	VIRTIO_BALLOON_S_NAMES_prefix "free-memory", \
+	VIRTIO_BALLOON_S_NAMES_prefix "total-memory", \
+	VIRTIO_BALLOON_S_NAMES_prefix "available-memory", \
+	VIRTIO_BALLOON_S_NAMES_prefix "disk-caches", \
+	VIRTIO_BALLOON_S_NAMES_prefix "hugetlb-allocations", \
+	VIRTIO_BALLOON_S_NAMES_prefix "hugetlb-failures" \
+}
+
+#define VIRTIO_BALLOON_S_NAMES VIRTIO_BALLOON_S_NAMES_WITH_PREFIX("")
+
 /*
  * Memory statistics structure.
  * Driver fills an array of these structures and passes to device.