samples/bpf: sample application and documentation for AF_XDP sockets

This is a sample application for AF_XDP sockets. The application
supports three different modes of operation: rxdrop, txonly and l2fwd.

To show-case a simple round-robin load-balancing between a set of
sockets in an xskmap, set the RR_LB compile time define option to 1 in
"xdpsock.h".

v2: The entries variable was calculated twice in {umem,xq}_nb_avail.

Co-authored-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/samples/bpf/xdpsock_kern.c b/samples/bpf/xdpsock_kern.c
new file mode 100644
index 000000000000..d8806c41362e
--- /dev/null
+++ b/samples/bpf/xdpsock_kern.c
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+#define KBUILD_MODNAME "foo"
+#include <uapi/linux/bpf.h>
+#include "bpf_helpers.h"
+
+#include "xdpsock.h"
+
+struct bpf_map_def SEC("maps") qidconf_map = {
+	.type		= BPF_MAP_TYPE_ARRAY,
+	.key_size	= sizeof(int),
+	.value_size	= sizeof(int),
+	.max_entries	= 1,
+};
+
+struct bpf_map_def SEC("maps") xsks_map = {
+	.type = BPF_MAP_TYPE_XSKMAP,
+	.key_size = sizeof(int),
+	.value_size = sizeof(int),
+	.max_entries = 4,
+};
+
+struct bpf_map_def SEC("maps") rr_map = {
+	.type = BPF_MAP_TYPE_PERCPU_ARRAY,
+	.key_size = sizeof(int),
+	.value_size = sizeof(unsigned int),
+	.max_entries = 1,
+};
+
+SEC("xdp_sock")
+int xdp_sock_prog(struct xdp_md *ctx)
+{
+	int *qidconf, key = 0, idx;
+	unsigned int *rr;
+
+	qidconf = bpf_map_lookup_elem(&qidconf_map, &key);
+	if (!qidconf)
+		return XDP_ABORTED;
+
+	if (*qidconf != ctx->rx_queue_index)
+		return XDP_PASS;
+
+#if RR_LB /* NB! RR_LB is configured in xdpsock.h */
+	rr = bpf_map_lookup_elem(&rr_map, &key);
+	if (!rr)
+		return XDP_ABORTED;
+
+	*rr = (*rr + 1) & (MAX_SOCKS - 1);
+	idx = *rr;
+#else
+	idx = 0;
+#endif
+
+	return bpf_redirect_map(&xsks_map, idx, 0);
+}
+
+char _license[] SEC("license") = "GPL";