RE: [RFC qemu 2/4] virtio-balloon: Add a new feature to balloon device

On Thu,  3 Mar 2016 18:44:26 +0800
Liang Li [off-list ref] wrote:

quoted

Extend the virtio balloon device to support a new feature, this new
feature can help to get guest's free pages information, which can be
used for live migration optimzation.

Do you have a spec for this, e.g. as a patch to the virtio spec?

Not yet.

quoted

Signed-off-by: Liang Li <redacted>
---
 balloon.c                                       | 30 ++++++++-
 hw/virtio/virtio-balloon.c                      | 81 ++++++++++++++++++++++++-
 include/hw/virtio/virtio-balloon.h              | 17 +++++-
 include/standard-headers/linux/virtio_balloon.h |  1 +
 include/sysemu/balloon.h                        | 10 ++-
 5 files changed, 134 insertions(+), 5 deletions(-)

quoted

+static int virtio_balloon_free_pages(void *opaque,
+                                     unsigned long *free_pages_bitmap,
+                                     unsigned long *free_pages_count)
+{
+    VirtIOBalloon *s = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+    VirtQueueElement *elem = s->free_pages_vq_elem;
+    int len;
+
+    if (!balloon_free_pages_supported(s)) {
+        return -1;
+    }
+
+    if (s->req_status == NOT_STARTED) {
+        s->free_pages_bitmap = free_pages_bitmap;
+        s->req_status = STARTED;
+        s->mem_layout.low_mem =
+ pc_get_lowmem(PC_MACHINE(current_machine));

Please don't leak pc-specific information into generic code.

I have already notice that and just leave it here in this  initial RFC version,  
the hard part of this solution is how to handle different architecture ...

Thanks!

Liang