[Qemu-devel] [PATCH for-2.7] hw/net/spapr_llan: Provide counter with dropped rx frames to the guest

[Thomas Huth <thuth@redhat.com>]

The last 8 bytes of the receive buffer list page (that has been supplied
by the guest with the H_REGISTER_LOGICAL_LAN call) contain a counter
for frames that have been dropped because there was no suitable receive
buffer available. This patch introduces code to use this field to
provide the information about dropped rx packets to the guest.
There it can be queried with "ethtool -S eth0 | grep rx_no_buffer".

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 Note: The patch has to be applied on top of the "Delay flushing of the
 RX queue while adding new RX buffers" patch that I sent last week
 (otherwise there will be context conflicts with the "return" statements).

 hw/net/spapr_llan.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/hw/net/spapr_llan.c b/hw/net/spapr_llan.c
index d604d55..719ad29 100644
--- a/hw/net/spapr_llan.c
+++ b/hw/net/spapr_llan.c
@@ -122,6 +122,21 @@ static int spapr_vlan_can_receive(NetClientState *nc)
 }
 
 /**
+ * The last 8 bytes of the receive buffer list page (that has been
+ * supplied by the guest with the H_REGISTER_LOGICAL_LAN call) contain
+ * a counter for frames that have been dropped because there was no
+ * suitable receive buffer available. This function is used to increase
+ * this counter by one.
+ */
+static void spapr_vlan_record_dropped_rx_frame(VIOsPAPRVLANDevice *dev)
+{
+    uint64_t cnt;
+
+    cnt = vio_ldq(&dev->sdev, dev->buf_list + 4096 - 8);
+    vio_stq(&dev->sdev, dev->buf_list + 4096 - 8, cnt + 1);
+}
+
+/**
  * Get buffer descriptor from one of our receive buffer pools
  */
 static vlan_bd_t spapr_vlan_get_rx_bd_from_pool(VIOsPAPRVLANDevice *dev,
@@ -206,6 +221,7 @@ static ssize_t spapr_vlan_receive(NetClientState *nc, const uint8_t *buf,
     }
 
     if (!dev->rx_bufs) {
+        spapr_vlan_record_dropped_rx_frame(dev);
         return 0;
     }
 
@@ -215,6 +231,7 @@ static ssize_t spapr_vlan_receive(NetClientState *nc, const uint8_t *buf,
         bd = spapr_vlan_get_rx_bd_from_page(dev, size);
     }
     if (!bd) {
+        spapr_vlan_record_dropped_rx_frame(dev);
         return 0;
     }
 
-- 
1.8.3.1