[RFC ixgbe 1/2] ixgbe: Implement support for ndo_xdp_xmit in skb mode

["Nabil S. Alramli" <dev@nalramli.com>]

This commit adds support for `ndo_xdp_xmit` in skb mode in the ixgbe
ethernet driver, by allowing the call to continue to transmit the packets
using `dev_direct_xmit`.

Previously, the driver did not support the operation in skb mode. The
handler `ixgbe_xdp_xmit` had the following condition:

```
	ring = adapter->xdp_prog ? ixgbe_determine_xdp_ring(adapter) : NULL;
	if (unlikely(!ring))
		return -ENXIO;
```

That only works in native mode. In skb mode, `adapter->xdp_prog == NULL` so
the call returned an error, which prevented the ability to send packets
using `bpf_prog_test_run_opts` with the `BPF_F_TEST_XDP_LIVE_FRAMES` flag.

Signed-off-by: Nabil S. Alramli <dev@nalramli.com>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe.h      |  8 ++++
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 43 +++++++++++++++++--
 2 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe.h b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
index e6a380d4929b..26c378853755 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe.h
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
@@ -846,6 +846,14 @@ struct ixgbe_ring *ixgbe_determine_xdp_ring(struct ixgbe_adapter *adapter)
 	return adapter->xdp_ring[index];
 }
 
+static inline
+struct ixgbe_ring *ixgbe_determine_tx_ring(struct ixgbe_adapter *adapter)
+{
+	int index = ixgbe_determine_xdp_q_idx(smp_processor_id());
+
+	return adapter->tx_ring[index];
+}
+
 static inline u8 ixgbe_max_rss_indices(struct ixgbe_adapter *adapter)
 {
 	switch (adapter->hw.mac.type) {
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 467f81239e12..fed70cbdb1b2 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -10748,7 +10748,8 @@ static int ixgbe_xdp_xmit(struct net_device *dev, int n,
 	/* During program transitions its possible adapter->xdp_prog is assigned
 	 * but ring has not been configured yet. In this case simply abort xmit.
 	 */
-	ring = adapter->xdp_prog ? ixgbe_determine_xdp_ring(adapter) : NULL;
+	ring = adapter->xdp_prog ? ixgbe_determine_xdp_ring(adapter) :
+		ixgbe_determine_tx_ring(adapter);
 	if (unlikely(!ring))
 		return -ENXIO;
 
@@ -10762,9 +10763,43 @@ static int ixgbe_xdp_xmit(struct net_device *dev, int n,
 		struct xdp_frame *xdpf = frames[i];
 		int err;
 
-		err = ixgbe_xmit_xdp_ring(ring, xdpf);
-		if (err != IXGBE_XDP_TX)
-			break;
+		if (adapter->xdp_prog) {
+			err = ixgbe_xmit_xdp_ring(ring, xdpf);
+			if (err != IXGBE_XDP_TX)
+				break;
+		} else {
+			struct xdp_buff xdp = {0};
+			unsigned int metasize = 0;
+			unsigned int size = 0;
+			unsigned int truesize = 0;
+			struct sk_buff *skb = NULL;
+
+			xdp_convert_frame_to_buff(xdpf, &xdp);
+			size = xdp.data_end - xdp.data;
+			metasize = xdp.data - xdp.data_meta;
+			truesize = SKB_DATA_ALIGN(xdp.data_end - xdp.data_hard_start) +
+				   SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+
+			skb = napi_alloc_skb(&ring->q_vector->napi, truesize);
+			if (likely(skb)) {
+				skb_reserve(skb, xdp.data - xdp.data_hard_start);
+				skb_put_data(skb, xdp.data, size);
+				build_skb_around(skb, skb->data, truesize);
+				if (metasize)
+					skb_metadata_set(skb, metasize);
+				skb->dev = dev;
+				skb->queue_mapping = ring->queue_index;
+
+				err = dev_direct_xmit(skb, ring->queue_index);
+				if (!dev_xmit_complete(err))
+					break;
+			} else {
+				break;
+			}
+
+			xdp_return_frame_rx_napi(xdpf);
+		}
+
 		nxmit++;
 	}
 
-- 
2.43.0