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-rw-r--r--samples/bpf/xdp2skb_meta_kern.c105
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diff --git a/samples/bpf/xdp2skb_meta_kern.c b/samples/bpf/xdp2skb_meta_kern.c
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+/* SPDX-License-Identifier: GPL-2.0
+ * Copyright (c) 2018 Jesper Dangaard Brouer, Red Hat Inc.
+ *
+ * Example howto transfer info from XDP to SKB, e.g. skb->mark
+ * -----------------------------------------------------------
+ * This uses the XDP data_meta infrastructure, and is a cooperation
+ * between two bpf-programs (1) XDP and (2) clsact at TC-ingress hook.
+ *
+ * Notice: This example does not use the BPF C-loader (bpf_load.c),
+ * but instead rely on the iproute2 TC tool for loading BPF-objects.
+ */
+#include <uapi/linux/bpf.h>
+#include <uapi/linux/pkt_cls.h>
+
+#include "bpf_helpers.h"
+
+/*
+ * This struct is stored in the XDP 'data_meta' area, which is located
+ * just in-front-of the raw packet payload data. The meaning is
+ * specific to these two BPF programs that use it as a communication
+ * channel. XDP adjust/increase the area via a bpf-helper, and TC use
+ * boundary checks to see if data have been provided.
+ *
+ * The struct must be 4 byte aligned, which here is enforced by the
+ * struct __attribute__((aligned(4))).
+ */
+struct meta_info {
+ __u32 mark;
+} __attribute__((aligned(4)));
+
+SEC("xdp_mark")
+int _xdp_mark(struct xdp_md *ctx)
+{
+ struct meta_info *meta;
+ void *data, *data_end;
+ int ret;
+
+ /* Reserve space in-front of data pointer for our meta info.
+ * (Notice drivers not supporting data_meta will fail here!)
+ */
+ ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(*meta));
+ if (ret < 0)
+ return XDP_ABORTED;
+
+ /* Notice: Kernel-side verifier requires that loading of
+ * ctx->data MUST happen _after_ helper bpf_xdp_adjust_meta(),
+ * as pkt-data pointers are invalidated. Helpers that require
+ * this are determined/marked by bpf_helper_changes_pkt_data()
+ */
+ data = (void *)(unsigned long)ctx->data;
+
+ /* Check data_meta have room for meta_info struct */
+ meta = (void *)(unsigned long)ctx->data_meta;
+ if (meta + 1 > data)
+ return XDP_ABORTED;
+
+ meta->mark = 42;
+
+ return XDP_PASS;
+}
+
+SEC("tc_mark")
+int _tc_mark(struct __sk_buff *ctx)
+{
+ void *data = (void *)(unsigned long)ctx->data;
+ void *data_end = (void *)(unsigned long)ctx->data_end;
+ void *data_meta = (void *)(unsigned long)ctx->data_meta;
+ struct meta_info *meta = data_meta;
+
+ /* Check XDP gave us some data_meta */
+ if (meta + 1 > data) {
+ ctx->mark = 41;
+ /* Skip "accept" if no data_meta is avail */
+ return TC_ACT_OK;
+ }
+
+ /* Hint: See func tc_cls_act_is_valid_access() for BPF_WRITE access */
+ ctx->mark = meta->mark; /* Transfer XDP-mark to SKB-mark */
+
+ return TC_ACT_OK;
+}
+
+/* Manually attaching these programs:
+export DEV=ixgbe2
+export FILE=xdp2skb_meta_kern.o
+
+# via TC command
+tc qdisc del dev $DEV clsact 2> /dev/null
+tc qdisc add dev $DEV clsact
+tc filter add dev $DEV ingress prio 1 handle 1 bpf da obj $FILE sec tc_mark
+tc filter show dev $DEV ingress
+
+# XDP via IP command:
+ip link set dev $DEV xdp off
+ip link set dev $DEV xdp obj $FILE sec xdp_mark
+
+# Use iptable to "see" if SKBs are marked
+iptables -I INPUT -p icmp -m mark --mark 41 # == 0x29
+iptables -I INPUT -p icmp -m mark --mark 42 # == 0x2a
+
+# Hint: catch XDP_ABORTED errors via
+perf record -e xdp:*
+perf script
+
+*/