Subject: Re: [PATCH bpf-next 1/5] libbpf: support XDP_SHARED_UMEM with external XDP program

From: William Tu <[email-masked]>
Date: Fri, 8 Nov 2019 10:03:14 -0800

Hi Magnus,

Thanks for the patch.

On Thu, Nov 07, 2019 at 06:47:36PM +0100, Magnus Karlsson wrote:
> Add support in libbpf to create multiple sockets that share a single
> umem. Note that an external XDP program need to be supplied that
> routes the incoming traffic to the desired sockets. So you need to
> supply the libbpf_flag XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD and load
> your own XDP program.
> 
> Signed-off-by: Magnus Karlsson <[email-masked]>
> ---
>  tools/lib/bpf/xsk.c | 27 +++++++++++++++++----------
>  1 file changed, 17 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> index 86c1b61..8ebd810 100644
> --- a/tools/lib/bpf/xsk.c
> +++ b/tools/lib/bpf/xsk.c
> @@ -586,15 +586,21 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
>  	if (!umem || !xsk_ptr || !rx || !tx)
>  		return -EFAULT;
>  
> -	if (umem->refcount) {
> -		pr_warn("Error: shared umems not supported by libbpf.\n");
> -		return -EBUSY;
> -	}
> -
>  	xsk = calloc(1, sizeof(*xsk));
>  	if (!xsk)
>  		return -ENOMEM;
>  
> +	err = xsk_set_xdp_socket_config(&xsk->config, usr_config);
> +	if (err)
> +		goto out_xsk_alloc;
> +
> +	if (umem->refcount &&
> +	    !(xsk->config.libbpf_flags & XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD)) {
> +		pr_warn("Error: shared umems not supported by libbpf supplied XDP program.\n");

Why can't we use the existing default one in libbpf?
If users don't want to redistribute packet to different queue,
then they can still use the libbpf default one.

William
> +		err = -EBUSY;
> +		goto out_xsk_alloc;
> +	}
> +
>  	if (umem->refcount++ > 0) {
>  		xsk->fd = socket(AF_XDP, SOCK_RAW, 0);
>  		if (xsk->fd < 0) {
> @@ -616,10 +622,6 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
>  	memcpy(xsk->ifname, ifname, IFNAMSIZ - 1);
>  	xsk->ifname[IFNAMSIZ - 1] = '\0';
>  
> -	err = xsk_set_xdp_socket_config(&xsk->config, usr_config);
> -	if (err)
> -		goto out_socket;
> -
>  	if (rx) {
>  		err = setsockopt(xsk->fd, SOL_XDP, XDP_RX_RING,
>  				 &xsk->config.rx_size,
> @@ -687,7 +689,12 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
>  	sxdp.sxdp_family = PF_XDP;
>  	sxdp.sxdp_ifindex = xsk->ifindex;
>  	sxdp.sxdp_queue_id = xsk->queue_id;
> -	sxdp.sxdp_flags = xsk->config.bind_flags;
> +	if (umem->refcount > 1) {
> +		sxdp.sxdp_flags = XDP_SHARED_UMEM;
> +		sxdp.sxdp_shared_umem_fd = umem->fd;
> +	} else {
> +		sxdp.sxdp_flags = xsk->config.bind_flags;
> +	}
>  
>  	err = bind(xsk->fd, (struct sockaddr *)&sxdp, sizeof(sxdp));
>  	if (err) {
> -- 
> 2.7.4
>