netdev - Re: [PATCH bpf-next] xsk: include XDP meta data in AF

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Date:   Thu, 30 Aug 2018 14:37:46 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Björn Töpel <bjorn.topel@...il.com>,
        magnus.karlsson@...el.com, magnus.karlsson@...il.com,
        ast@...nel.org, netdev@...r.kernel.org
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        brouer@...hat.com
Subject: Re: [PATCH bpf-next] xsk: include XDP meta data in AF_XDP frames

On 08/30/2018 10:09 AM, Björn Töpel wrote:
> From: Björn Töpel <bjorn.topel@...el.com>
> 
> Previously, the AF_XDP (XDP_DRV/XDP_SKB copy-mode) ingress logic did
> not include XDP meta data in the data buffers copied out to the user
> application.
> 
> In this commit, we check if meta data is available, and if so, it is
> prepended to the frame.
> 
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> ---
>  net/xdp/xsk.c | 37 ++++++++++++++++++++++++++++---------
>  1 file changed, 28 insertions(+), 9 deletions(-)
> 
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 4e937cd7c17d..817e4cee1540 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -55,20 +55,30 @@ EXPORT_SYMBOL(xsk_umem_discard_addr);
>  
>  static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
>  {
> -	void *buffer;
> +	void *to_buf, *from_buf;
> +	u32 metalen;
>  	u64 addr;
>  	int err;
>  
>  	if (!xskq_peek_addr(xs->umem->fq, &addr) ||
> -	    len > xs->umem->chunk_size_nohr) {
> +	    len > xs->umem->chunk_size_nohr - XDP_PACKET_HEADROOM) {
>  		xs->rx_dropped++;
>  		return -ENOSPC;
>  	}
>  
>  	addr += xs->umem->headroom;
>  
> -	buffer = xdp_umem_get_data(xs->umem, addr);
> -	memcpy(buffer, xdp->data, len);
> +	if (xdp_data_meta_unsupported(xdp)) {

Nit: Probably makes sense to wrap with unlikely() since we expect all
drivers to implement this.

> +		from_buf = xdp->data;
> +		metalen = 0;
> +	} else {
> +		from_buf = xdp->data_meta;
> +		metalen = xdp->data - xdp->data_meta;
> +	}
> +
> +	to_buf = xdp_umem_get_data(xs->umem, addr);
> +	memcpy(to_buf, from_buf, len + metalen);
> +	addr += metalen;
>  	err = xskq_produce_batch_desc(xs->rx, addr, len);
>  	if (!err) {
>  		xskq_discard_addr(xs->umem->fq);
> @@ -111,8 +121,8 @@ void xsk_flush(struct xdp_sock *xs)
>  
>  int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
>  {
> -	u32 len = xdp->data_end - xdp->data;
> -	void *buffer;
> +	u32 metalen, len = xdp->data_end - xdp->data;
> +	void *to_buf, *from_buf;
>  	u64 addr;
>  	int err;
>  
> @@ -120,15 +130,24 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
>  		return -EINVAL;
>  
>  	if (!xskq_peek_addr(xs->umem->fq, &addr) ||
> -	    len > xs->umem->chunk_size_nohr) {
> +	    len > xs->umem->chunk_size_nohr - XDP_PACKET_HEADROOM) {
>  		xs->rx_dropped++;
>  		return -ENOSPC;
>  	}
>  
>  	addr += xs->umem->headroom;
>  
> -	buffer = xdp_umem_get_data(xs->umem, addr);
> -	memcpy(buffer, xdp->data, len);
> +	if (xdp_data_meta_unsupported(xdp)) {
> +		from_buf = xdp->data;
> +		metalen = 0;

Note that this condition should be dead code. netif_receive_generic_xdp()
sets xdp->data_meta to xdp->data, so all good here and above is never hit.

> +	} else {
> +		from_buf = xdp->data_meta;
> +		metalen = xdp->data - xdp->data_meta;
> +	}
> +
> +	to_buf = xdp_umem_get_data(xs->umem, addr);
> +	memcpy(to_buf, from_buf, len + metalen);
> +	addr += metalen;
>  	err = xskq_produce_batch_desc(xs->rx, addr, len);
>  	if (!err) {
>  		xskq_discard_addr(xs->umem->fq);
>