From 34aea784eb29c81e0b5929900cb6762f6738c4b3 Mon Sep 17 00:00:00 2001
From: Ivan Babrou <github@ivan.computer>
Date: Thu, 18 Apr 2024 14:24:35 -0700
Subject: [PATCH] Add sk_error_report span to sock-trace

---
 examples/sock-trace.bpf.c | 33 +++++++++++++++++++++++++++++++++
 examples/sock-trace.yaml  | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/examples/sock-trace.bpf.c b/examples/sock-trace.bpf.c
index da602e9b..efe8d105 100644
--- a/examples/sock-trace.bpf.c
+++ b/examples/sock-trace.bpf.c
@@ -3,6 +3,8 @@
 #include <bpf/usdt.bpf.h>
 #include "tracing.bpf.h"
 
+#define MAX_STACK_DEPTH 8
+
 // Skipping 3 frames off the top as they are just bpf trampoline
 #define SKIP_FRAMES (3 & BPF_F_SKIP_FIELD_MASK)
 
@@ -23,6 +25,12 @@ struct sk_span_t {
     u64 ksym;
 };
 
+struct sk_error_report_span_t {
+    struct span_base_t span_base;
+    u64 kstack[MAX_STACK_DEPTH];
+    u32 sk_err;
+};
+
 struct {
     __uint(type, BPF_MAP_TYPE_RINGBUF);
     __uint(max_entries, 256 * 1024);
@@ -38,6 +46,11 @@ struct {
     __uint(max_entries, 256 * 1024);
 } sk_spans SEC(".maps");
 
+struct {
+    __uint(type, BPF_MAP_TYPE_RINGBUF);
+    __uint(max_entries, 256 * 1024);
+} sk_error_report_spans SEC(".maps");
+
 struct {
     __uint(type, BPF_MAP_TYPE_LRU_HASH);
     __uint(max_entries, 1024 * 10);
@@ -150,4 +163,24 @@ int BPF_PROG(dev_hard_start_xmit, struct sk_buff *skb)
     return handle_skb((struct pt_regs *) ctx, skb);
 }
 
+// bpf_get_socket_cookie is not available in raw_tp:
+// * https://github.com/torvalds/linux/blob/v6.6/kernel/trace/bpf_trace.c#L1926-L1939
+SEC("fentry/sk_error_report")
+int BPF_PROG(sk_error_report, struct sock *sk)
+{
+    u64 socket_cookie = bpf_get_socket_cookie(sk);
+    struct span_parent_t *parent = bpf_map_lookup_elem(&traced_socket_cookies, &socket_cookie);
+
+    if (!parent) {
+        return 0;
+    }
+
+    submit_span(&sk_error_report_spans, struct sk_error_report_span_t, parent, {
+        bpf_get_stack(ctx, &span->kstack, sizeof(span->kstack), SKIP_FRAMES);
+        span->sk_err = sk->sk_err;
+    });
+
+    return 0;
+}
+
 char LICENSE[] SEC("license") = "GPL";
diff --git a/examples/sock-trace.yaml b/examples/sock-trace.yaml
index b1e3ba5a..83279e42 100644
--- a/examples/sock-trace.yaml
+++ b/examples/sock-trace.yaml
@@ -79,3 +79,36 @@ tracing:
           size: 8
           decoders:
             - name: ksym
+    - name: sk_error_report
+      ringbuf: sk_error_report_spans
+      service: kernel
+      labels:
+        - name: trace_id
+          size: 16
+          decoders:
+            - name: hex
+        - name: parent_span_id
+          size: 8
+          decoders:
+            - name: hex
+        - name: span_id
+          size: 8
+          decoders:
+            - name: hex
+        - name: span_monotonic_timestamp_ns
+          size: 8
+          decoders:
+            - name: uint
+        - name: span_duration_ns
+          size: 8
+          decoders:
+            - name: uint
+        - name: kstack
+          size: 64
+          decoders:
+            - name: kstack
+        - name: sk_err
+          size: 4
+          decoders:
+            - name: uint
+            - name: errno