virtio: add virtqueue_alloc_element tracepoint

This tracepoint can help diagnosing failures due to memory
fragmentation in the guest.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 2 insertions, 0 deletions

diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
index 1f7a7c1..e24d8fa 100644
--- a/hw/virtio/trace-events
+++ b/hw/virtio/trace-events
@@ -1,6 +1,7 @@
 # See docs/tracing.txt for syntax documentation.
 
 # hw/virtio/virtio.c
+virtqueue_alloc_element(void *elem, size_t sz, unsigned in_num, unsigned out_num) "elem %p size %zd in_num %u out_num %u"
 virtqueue_fill(void *vq, const void *elem, unsigned int len, unsigned int idx) "vq %p elem %p len %u idx %u"
 virtqueue_flush(void *vq, unsigned int count) "vq %p count %u"
 virtqueue_pop(void *vq, void *elem, unsigned int in_num, unsigned int out_num) "vq %p elem %p in_num %u out_num %u"
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index f99d99f..464947f 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -815,6 +815,7 @@ static void *virtqueue_alloc_element(size_t sz, unsigned out_num, unsigned in_nu
 
     assert(sz >= sizeof(VirtQueueElement));
     elem = g_malloc(out_sg_end);
+    trace_virtqueue_alloc_element(elem, sz, in_num, out_num);
     elem->out_num = out_num;
     elem->in_num = in_num;
     elem->in_addr = (void *)elem + in_addr_ofs;