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Collect MTU from skb->_skb_refdst #388

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merged 1 commit into from
Jul 7, 2024
Merged

Collect MTU from skb->_skb_refdst #388

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18 changes: 18 additions & 0 deletions bpf/kprobe_pwru.c
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,17 @@
#define ETH_P_IP 0x800
#define ETH_P_IPV6 0x86dd

#define RTAX_MTU 2
#define SKB_DST_NOREF 1UL
#define SKB_DST_PTRMASK ~(SKB_DST_NOREF)
#define __SKB_DST_PTR(X) \
((struct dst_entry *)((X) & SKB_DST_PTRMASK))

#define DST_METRICS_FLAGS 0x3UL
#define __DST_METRICS_PTR(X) \
((u32 *)((X) & ~DST_METRICS_FLAGS))


const static bool TRUE = true;

volatile const static __u64 BPF_PROG_ADDR = 0;
Expand Down Expand Up @@ -230,6 +241,13 @@ set_meta(struct sk_buff *skb, struct skb_meta *meta) {
meta->protocol = BPF_CORE_READ(skb, protocol);
meta->ifindex = BPF_CORE_READ(skb, dev, ifindex);
meta->mtu = BPF_CORE_READ(skb, dev, mtu);
struct dst_entry *dst = __SKB_DST_PTR(BPF_CORE_READ(skb, _skb_refdst));
if (dst) {
u32 *metrics = __DST_METRICS_PTR(BPF_CORE_READ(dst, _metrics));
bpf_probe_read_kernel(&meta->mtu, sizeof(meta->mtu), metrics + RTAX_MTU - 1);
if (!meta->mtu)
meta->mtu = BPF_CORE_READ(dst, dev, mtu);
}
}

static __always_inline void
Expand Down
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