Collect and output skb->cb when --filter-trace-tc#461
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Asphaltt
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LGTM, I’ve left two comments for further discussion.
bpf/kprobe_pwru.c
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| } | ||
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| if (cfg->output_cb) { | ||
| bpf_probe_read_kernel(&event->meta.cb, sizeof(event->meta.cb), (void *)&skb->cb[8]); |
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It's hard to understand skb->cb[8] here. It's better to convert skb->cb as struct qdisc_skb_cb *, and then read data from cb->data like:
struct qdisc_skb_cb *cb = (typeof(cb))(void *) skb->cb;
bpf_probe_read_kernel(&event->meta.cb, sizeof(event->meta.cb), (void *) &cb->data);
bpf/kprobe_pwru.c
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| u32 mtu; | ||
| u16 protocol; | ||
| u16 pad; | ||
| u8 cb[20]; |
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It's OK to define as u32 cb[5] like cb in struct __sk_buff, I think.
According to kernel verifier implementation[1], __sk_buff->cb will be mapped to ((struct qdisc_skb_cb*)&sk_buff->cb)->data, let's collect 20 bytes from there and output cb as u32[5] when --filter-trace-tc is turned on. [1] https://elixir.bootlin.com/linux/v6.8/source/net/core/filter.c#L9593 Signed-off-by: gray <[email protected]>
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According to kernel verifier implementation[1], __sk_buff->cb will be mapped to ((struct qdisc_skb_cb*)&sk_buff->cb)->data, let's collect 20 bytes from there and output cb as u32[5] when --filter-trace-tc is turned on.
[1] https://elixir.bootlin.com/linux/v6.8/source/net/core/filter.c#L9593
Fixes: #295