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b46aa22b66
The existing XDP metadata test works by creating a veth pair and attaching XDP & TC programs that drop the packet when the condition of the test isn't fulfilled. The test then pings through the veth pair and succeeds when the ping comes through. While this test works great for a veth pair, it is hard to replicate for tap devices to test the XDP metadata support of them. A similar test for the tun driver would either involve logic to reply to the ping request, or would have to capture the packet to check if it was dropped or not. To make the testing of other drivers easier while still maximizing code reuse, this commit refactors the existing xdp_context_functional test to use a test_result map. Instead of conditionally passing or dropping the packet, the TC program is changed to copy the received metadata into the value of that single-entry array map. Tests can then verify that the map value matches the expectation. This testing logic is easy to adapt to other network drivers as the only remaining requirement is that there is some way to send a custom Ethernet packet through it that triggers the XDP & TC programs. The Ethernet header of that custom packet is all-zero, because it is not required to be valid for the test to work. The zero ethertype also helps to filter out packets that are not related to the test and would otherwise interfere with it. The payload of the Ethernet packet is used as the test data that is expected to be passed as metadata from the XDP to the TC program and written to the map. It has a fixed size of 32 bytes which is a reasonable size that should be supported by both drivers. Additional packet headers are not necessary for the test and were therefore skipped to keep the testing code short. This new testing methodology no longer requires the veth interfaces to have IP addresses assigned, therefore these were removed. Signed-off-by: Marcus Wichelmann <marcus.wichelmann@hetzner-cloud.de> Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org> Reviewed-by: Willem de Bruijn <willemb@google.com> Link: https://patch.msgid.link/20250305213438.3863922-5-marcus.wichelmann@hetzner-cloud.de
76 lines
1.8 KiB
C
76 lines
1.8 KiB
C
#include <linux/bpf.h>
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#include <linux/if_ether.h>
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#include <linux/pkt_cls.h>
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#include <bpf/bpf_helpers.h>
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#define META_SIZE 32
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#define ctx_ptr(ctx, mem) (void *)(unsigned long)ctx->mem
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/* Demonstrates how metadata can be passed from an XDP program to a TC program
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* using bpf_xdp_adjust_meta.
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* For the sake of testing the metadata support in drivers, the XDP program uses
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* a fixed-size payload after the Ethernet header as metadata. The TC program
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* copies the metadata it receives into a map so it can be checked from
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* userspace.
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*/
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struct {
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__uint(type, BPF_MAP_TYPE_ARRAY);
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__uint(max_entries, 1);
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__type(key, __u32);
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__uint(value_size, META_SIZE);
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} test_result SEC(".maps");
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SEC("tc")
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int ing_cls(struct __sk_buff *ctx)
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{
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__u8 *data, *data_meta;
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__u32 key = 0;
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data_meta = ctx_ptr(ctx, data_meta);
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data = ctx_ptr(ctx, data);
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if (data_meta + META_SIZE > data)
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return TC_ACT_SHOT;
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bpf_map_update_elem(&test_result, &key, data_meta, BPF_ANY);
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return TC_ACT_SHOT;
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}
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SEC("xdp")
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int ing_xdp(struct xdp_md *ctx)
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{
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__u8 *data, *data_meta, *data_end, *payload;
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struct ethhdr *eth;
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int ret;
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ret = bpf_xdp_adjust_meta(ctx, -META_SIZE);
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if (ret < 0)
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return XDP_DROP;
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data_meta = ctx_ptr(ctx, data_meta);
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data_end = ctx_ptr(ctx, data_end);
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data = ctx_ptr(ctx, data);
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eth = (struct ethhdr *)data;
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payload = data + sizeof(struct ethhdr);
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if (payload + META_SIZE > data_end ||
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data_meta + META_SIZE > data)
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return XDP_DROP;
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/* The Linux networking stack may send other packets on the test
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* interface that interfere with the test. Just drop them.
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* The test packets can be recognized by their ethertype of zero.
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*/
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if (eth->h_proto != 0)
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return XDP_DROP;
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__builtin_memcpy(data_meta, payload, META_SIZE);
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return XDP_PASS;
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}
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char _license[] SEC("license") = "GPL";
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