[PATCH 6 of 6] xen-balloon: define a section_ops

[Jeremy Fitzhardinge <jeremy@goop.org>]

Define a xen_balloon_section_ops to control how xen balloon pages are onlined.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
 drivers/xen/balloon.c |   17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -139,6 +139,21 @@
 	}
 }
 
+/* Only online a page if there's some memory backing it */
+static bool xen_online_page(struct page *page)
+{
+    unsigned long pfn = page_to_pfn(page);
+
+    if (get_phys_to_machine(pfn) == INVALID_P2M_ENTRY)
+	return false;
+
+    return online_page(page);
+}
+
+static const struct section_ops xen_balloon_section_ops = {
+    .online_page = xen_online_page
+};
+
 /* hotplug some memory we can add pages to */
 static void balloon_expand(unsigned pages)
 {
@@ -165,7 +180,7 @@
 	start_pfn = res->start >> PAGE_SHIFT;
 	end_pfn = (res->end + 1) >> PAGE_SHIFT;
 
-	ret = add_memory_resource(0, res, &default_section_ops);
+	ret = add_memory_resource(0, res, &xen_balloon_section_ops);
 	if (ret)
 		goto release_res;