Re: [PATCH v2 bpf-next] bpf: devmap: move drop error path to devmap for XDP_REDIRECT

[Shay Agroskin]

Lorenzo Bianconi <lore...@kernel.org> writes:

...
diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c 
b/drivers/net/ethernet/amazon/ena/ena_netdev.c
index 102f2c91fdb8..7ad0557dedbd 100644
--- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
+++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
...

@@ -339,8 +337,8 @@ static int ena_xdp_xmit(struct net_device 
*dev, int n,
                        struct xdp_frame **frames, u32 flags)
 {
        struct ena_adapter *adapter = netdev_priv(dev);
-       int qid, i, err, drops = 0;
        struct ena_ring *xdp_ring;
+       int qid, i, nxmit = 0;
 
 	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK))
                return -EINVAL;
@@ -360,12 +358,12 @@ static int ena_xdp_xmit(struct net_device 
*dev, int n,
        spin_lock(&xdp_ring->xdp_tx_lock);
 
 	for (i = 0; i < n; i++) {
-		err = ena_xdp_xmit_frame(xdp_ring, dev, frames[i], 
0);
 		/* The descriptor is freed by ena_xdp_xmit_frame 
 in case
                 * of an error.
                 */

Thanks a lot for the patch. It's a good idea. Do you mind removing 
the comment here as well ? ena_xdp_xmit_frame() no longer frees 
the frame in case of an error after this patch.

-               if (err)
-                       drops++;
+		if (ena_xdp_xmit_frame(xdp_ring, dev, frames[i], 
0))
+                       break;
+               nxmit++;
        }
 
 	/* Ring doorbell to make device aware of the packets */
@@ -378,7 +376,7 @@ static int ena_xdp_xmit(struct net_device 
*dev, int n,
        spin_unlock(&xdp_ring->xdp_tx_lock);
 
 	/* Return number of packets sent */
-       return n - drops;
+       return nxmit;
 }
...
diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 85d9d1b72a33..9f158b3862df 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -344,29 +344,26 @@ static void bq_xmit_all(struct 
xdp_dev_bulk_queue *bq, u32 flags)
 
 	sent = dev->netdev_ops->ndo_xdp_xmit(dev, bq->count, 
 bq->q, flags);
        if (sent < 0) {
+		/* If ndo_xdp_xmit fails with an errno, no frames 
have
+                * been xmit'ed.
+                */
                err = sent;
                sent = 0;
-               goto error;
        }
+
        drops = bq->count - sent;
-out:
-       bq->count = 0;
+       if (unlikely(drops > 0)) {
+		/* If not all frames have been transmitted, it is 
our
+                * responsibility to free them
+                */
+               for (i = sent; i < bq->count; i++)
+                       xdp_return_frame_rx_napi(bq->q[i]);
+       }

Wouldn't the logic above be the same even w/o the 'if' condition ?

 
+	bq->count = 0;
        trace_xdp_devmap_xmit(bq->dev_rx, dev, sent, drops, err);
        bq->dev_rx = NULL;
        __list_del_clearprev(&bq->flush_node);
-       return;
-error:
-	/* If ndo_xdp_xmit fails with an errno, no frames have 
been
-        * xmit'ed and it's our responsibility to them free all.
-        */
-       for (i = 0; i < bq->count; i++) {
-               struct xdp_frame *xdpf = bq->q[i];
-
-               xdp_return_frame_rx_napi(xdpf);
-               drops++;
-       }
-       goto out;
 }
 
 /* __dev_flush is called from xdp_do_flush() which _must_ be 
 signaled

Thanks, Shay