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

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Thu, Oct 09, 2025 at 03:28:30PM -0400, Nabil S. Alramli wrote:
> 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.

Hi Nabil,

What stops you from loading a dummy XDP program to interface? This has
been an approach that we follow when we want to use anything that utilizes
XDP resources (XDP Tx queues).

> 
> 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
> 
>