xen-netback: Add stat counters for zerocopy

These counters help determine how often the buffers had to be copied. Also
they help find out if packets are leaked, as if "sent != success + fail",
there are probably packets never freed up properly.

NOTE: if bisect brought you here, you should apply the series up until
"xen-netback: Timeout packets in RX path", otherwise Windows guests can't work
properly and malicious guests can block other guests by not releasing their sent
packets.

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 26 insertions, 1 deletions

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 49109afa2253..683d30160a7c 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -179,6 +179,9 @@ struct xenvif {
 
         /* Statistics */
         unsigned long rx_gso_checksum_fixup;
+        unsigned long tx_zerocopy_sent;
+        unsigned long tx_zerocopy_success;
+        unsigned long tx_zerocopy_fail;
 
         /* Miscellaneous private stuff. */
         struct net_device *dev;
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index 1fe9fe523cc8..44df8581b4d7 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -238,6 +238,21 @@ static const struct xenvif_stat {
                 "rx_gso_checksum_fixup",
                 offsetof(struct xenvif, rx_gso_checksum_fixup)
         },
+        /* If (sent != success + fail), there are probably packets never
+         * freed up properly!
+         */
+        {
+                "tx_zerocopy_sent",
+                offsetof(struct xenvif, tx_zerocopy_sent),
+        },
+        {
+                "tx_zerocopy_success",
+                offsetof(struct xenvif, tx_zerocopy_success),
+        },
+        {
+                "tx_zerocopy_fail",
+                offsetof(struct xenvif, tx_zerocopy_fail)
+        },
 };
 
 static int xenvif_get_sset_count(struct net_device *dev, int string_set)
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 46a75706cb78..3cb586357df7 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1323,8 +1323,10 @@ static int xenvif_tx_submit(struct xenvif *vif)
                  * do a skb_copy_ubufs while we are still in control of the
                  * skb. E.g. the __pskb_pull_tail earlier can do such thing.
                  */
-                if (skb_shinfo(skb)->destructor_arg)
+                if (skb_shinfo(skb)->destructor_arg) {
                         skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+                        vif->tx_zerocopy_sent++;
+                }
 
                 netif_receive_skb(skb);
         }
@@ -1364,6 +1366,11 @@ void xenvif_zerocopy_callback(struct ubuf_info *ubuf, bool zerocopy_success)
                 napi_schedule(&vif->napi);
                 local_bh_enable();
         }
+
+        if (likely(zerocopy_success))
+                vif->tx_zerocopy_success++;
+        else
+                vif->tx_zerocopy_fail++;
 }
 
 static inline void xenvif_tx_dealloc_action(struct xenvif *vif)