File xenpaging.mem_event_check_ring-free_requests.patch of Package xen.import4929

Subject: xenpaging: print info when free request slots drop below 2

Add debugging aid to free request slots in the ring buffer.
It should not happen that the ring gets full, print info anyway if it happens. 

(xen-unstable changeset:   22439:3bbb3969236c)

Signed-off-by: Olaf Hering <olaf@aepfle.de>

---
 xen/arch/x86/mm/mem_event.c |    5 +++++
 1 file changed, 5 insertions(+)

Index: xen-4.0.2-testing/xen/arch/x86/mm/mem_event.c
===================================================================
--- xen-4.0.2-testing.orig/xen/arch/x86/mm/mem_event.c
+++ xen-4.0.2-testing/xen/arch/x86/mm/mem_event.c
@@ -152,6 +152,11 @@ int mem_event_check_ring(struct domain *
     mem_event_ring_lock(d);
 
     free_requests = RING_FREE_REQUESTS(&d->mem_event.front_ring);
+    if ( unlikely(free_requests < 2) )
+    {
+        gdprintk(XENLOG_INFO, "free request slots: %d\n", free_requests);
+        WARN_ON(free_requests == 0);
+    }
     ring_full = free_requests < MEM_EVENT_RING_THRESHOLD;
 
     if ( (curr->domain->domain_id == d->domain_id) && ring_full )