[PATCH net-next v2 2/2] FDDI: defza: Support capturing outgoing SMT traffic

["Maciej W. Rozycki" <macro@linux-mips.org>]

DEC FDDIcontroller 700 (DEFZA) uses a Tx/Rx queue pair to communicate 
SMT frames with adapter's firmware.  Any SMT frame received from the RMC 
via the Rx queue is queued back by the driver to the SMT Rx queue for 
the firmware to process.  Similarly the firmware uses the SMT Tx queue 
to supply the driver with SMT frames which are queued back to the Tx 
queue for the RMC to send to the ring.

When a network tap is attached to an FDDI interface handled by `defza' 
any incoming SMT frames captured are queued to our usual processing of 
network data received, which in turn delivers them to any listening 
taps.

However the outgoing SMT frames produced by the firmware bypass our 
network protocol stack and are therefore not delivered to taps.  This in 
turn means that taps are missing a part of network traffic sent by the 
adapter, which may make it more difficult to track down network problems 
or do general traffic analysis.

Call `dev_queue_xmit_nit' then in the SMT Tx path, having checked that
a network tap is attached, with a newly-created `dev_nit_active' helper
wrapping the usual condition used in the transmit path.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
---
New in v2.
---
 drivers/net/fddi/defza.c  |   33 +++++++++++++++++++++++++++++++--
 include/linux/netdevice.h |    1 +
 net/core/dev.c            |   13 ++++++++++++-
 3 files changed, 44 insertions(+), 3 deletions(-)

linux-defza-1.1.4-pcap.patch
Index: net-next-20181008-4maxp64/drivers/net/fddi/defza.c
===================================================================
--- net-next-20181008-4maxp64.orig/drivers/net/fddi/defza.c
+++ net-next-20181008-4maxp64/drivers/net/fddi/defza.c
@@ -797,11 +797,40 @@ static void fza_tx_smt(struct net_device
 		smt_tx_ptr = fp->mmio + readl_u(&fp->ring_smt_tx[i].buffer);
 		len = readl_u(&fp->ring_smt_tx[i].rmc) & FZA_RING_PBC_MASK;
 
-		/* Queue the frame to the RMC transmit ring. */
-		if (!netif_queue_stopped(dev))
+		if (!netif_queue_stopped(dev)) {
+			if (dev_nit_active(dev)) {
+				struct sk_buff *skb;
+
+				/* Length must be a multiple of 4 as only word
+				 * reads are permitted!
+				 */
+				skb = fza_alloc_skb_irq(dev, (len + 3) & ~3);
+				if (!skb)
+					goto err_no_skb;	/* Drop. */
+
+				skb_data_ptr = (struct fza_buffer_tx *)
+					       skb->data;
+
+				fza_reads(smt_tx_ptr, skb_data_ptr,
+					  (len + 3) & ~3);
+				skb->dev = dev;
+				skb_reserve(skb, 3);	/* Skip over PRH. */
+				skb_put(skb, len - 3);
+				skb_reset_network_header(skb);
+
+				dev_queue_xmit_nit(skb, dev);
+
+				dev_kfree_skb_irq(skb);
+
+err_no_skb:
+				;
+			}
+
+			/* Queue the frame to the RMC transmit ring. */
 			fza_do_xmit((union fza_buffer_txp)
 				    { .mmio_ptr = smt_tx_ptr },
 				    len, dev, 1);
+		}
 
 		writel_o(FZA_RING_OWN_FZA, &fp->ring_smt_tx[i].own);
 		fp->ring_smt_tx_index =
Index: net-next-20181008-4maxp64/include/linux/netdevice.h
===================================================================
--- net-next-20181008-4maxp64.orig/include/linux/netdevice.h
+++ net-next-20181008-4maxp64/include/linux/netdevice.h
@@ -3632,6 +3632,7 @@ static __always_inline int ____dev_forwa
 	return 0;
 }
 
+bool dev_nit_active(struct net_device *dev);
 void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev);
 
 extern int		netdev_budget;
Index: net-next-20181008-4maxp64/net/core/dev.c
===================================================================
--- net-next-20181008-4maxp64.orig/net/core/dev.c
+++ net-next-20181008-4maxp64/net/core/dev.c
@@ -1954,6 +1954,17 @@ static inline bool skb_loop_sk(struct pa
 	return false;
 }
 
+/**
+ * dev_nit_active - return true if any network interface taps are in use
+ *
+ * @dev: network device to check for the presence of taps
+ */
+bool dev_nit_active(struct net_device *dev)
+{
+	return !list_empty(&ptype_all) || !list_empty(&dev->ptype_all);
+}
+EXPORT_SYMBOL_GPL(dev_nit_active);
+
 /*
  *	Support routine. Sends outgoing frames to any network
  *	taps currently in use.
@@ -3211,7 +3222,7 @@ static int xmit_one(struct sk_buff *skb,
 	unsigned int len;
 	int rc;
 
-	if (!list_empty(&ptype_all) || !list_empty(&dev->ptype_all))
+	if (dev_nit_active(dev))
 		dev_queue_xmit_nit(skb, dev);
 
 	len = skb->len;