[PATCH] Fix div by zero in xenvif if no queues.

[Martin Harvey <Martin.Harvey@xxxxxxxxxx>]

In some cases (live migration), the front/backend can be pending
reconnect at the same point as Tx tries to send packets.
Previously, this caused a div by zero. However, since this is
a transient error, the drivers should ditch the packet,
and carry on.

Signed-off-by: Martin Harvey <martin.harvey@xxxxxxxxxx>
---
 src/xenvif/frontend.c    | 19 ++++++++++++-------
 src/xenvif/frontend.h    |  5 +++--
 src/xenvif/transmitter.c |  8 +++++++-
 3 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/src/xenvif/frontend.c b/src/xenvif/frontend.c
index e38d2bf..fc4b78c 100644
--- a/src/xenvif/frontend.c
+++ b/src/xenvif/frontend.c
@@ -2174,34 +2174,39 @@ fail1:
     return status;
 }
 
-ULONG
+NTSTATUS
 FrontendGetQueue(
     IN  PXENVIF_FRONTEND                Frontend,
     IN  XENVIF_PACKET_HASH_ALGORITHM    Algorithm,
-    IN  ULONG                           Value
+    IN  ULONG                           Value,
+    OUT PULONG                          QueueIndex
     )
 {
-    ULONG                               Queue;
+    if (QueueIndex == NULL)
+        return STATUS_INVALID_PARAMETER;
 
     switch (Algorithm) {
     case XENVIF_PACKET_HASH_ALGORITHM_NONE:
     case XENVIF_PACKET_HASH_ALGORITHM_UNSPECIFIED:
-        Queue = Value % __FrontendGetNumQueues(Frontend);
+        *QueueIndex = (__FrontendGetNumQueues(Frontend) != 0) ?
+            Value % __FrontendGetNumQueues(Frontend) :
+            0;
         break;
 
     case XENVIF_PACKET_HASH_ALGORITHM_TOEPLITZ:
-        Queue = (Frontend->Hash.Size != 0) ?
+        *QueueIndex = (Frontend->Hash.Size != 0) ?
                 Frontend->Hash.Mapping[Value % Frontend->Hash.Size] :
                 0;
         break;
 
     default:
         ASSERT(FALSE);
-        Queue = 0;
+        *QueueIndex = 0;
         break;
     }
 
-    return Queue;
+    return ((*QueueIndex) < __FrontendGetNumQueues(Frontend)) ?
+        STATUS_SUCCESS : STATUS_INTERNAL_ERROR;
 }
 
 static NTSTATUS
diff --git a/src/xenvif/frontend.h b/src/xenvif/frontend.h
index 8e5552e..5004b0e 100644
--- a/src/xenvif/frontend.h
+++ b/src/xenvif/frontend.h
@@ -237,11 +237,12 @@ FrontendSetHashTypes(
     IN  ULONG               Types
     );
 
-extern ULONG
+extern NTSTATUS
 FrontendGetQueue(
     IN  PXENVIF_FRONTEND                Frontend,
     IN  XENVIF_PACKET_HASH_ALGORITHM    Algorithm,
-    IN  ULONG                           Index
+    IN  ULONG                           Value,
+    OUT PULONG                          QueueIndex
     );
 
 #endif  // _XENVIF_FRONTEND_H
diff --git a/src/xenvif/transmitter.c b/src/xenvif/transmitter.c
index ed89f60..d089301 100644
--- a/src/xenvif/transmitter.c
+++ b/src/xenvif/transmitter.c
@@ -5194,13 +5194,19 @@ TransmitterQueuePacket(
         break;
     }
 
-    Index = FrontendGetQueue(Frontend, Algorithm, Value);
+    status = FrontendGetQueue(Frontend, Algorithm, Value, &Index);
+    if (!NT_SUCCESS(status))
+        goto fail2;
+
     Ring = Transmitter->Ring[Index];
 
     __TransmitterRingQueuePacket(Ring, Packet, More);
 
     return STATUS_SUCCESS;
 
+fail2:
+    Error("fail2\n");
+
 fail1:
     Error("fail1 (%08x)\n", status);
 
-- 
2.25.0.windows.1