text: // SPDX-License-Identifier: GPL-2.0
  // Copyright (c) 2018 Facebook
  
  #include <linux/bpf.h>
  #include <bpf/bpf_helpers.h>
  
  #ifndef PERF_MAX_STACK_DEPTH
  #define PERF_MAX_STACK_DEPTH         127
  #endif
  
  struct {
  	__uint(type, BPF_MAP_TYPE_ARRAY);
  	__uint(max_entries, 1);
  	__type(key, __u32);
  	__type(value, __u32);
  } control_map SEC(".maps");
  
  struct {
  	__uint(type, BPF_MAP_TYPE_HASH);
  	__uint(max_entries, 16384);
  	__type(key, __u32);
  	__type(value, __u32);
  } stackid_hmap SEC(".maps");
  
  typedef __u64 stack_trace_t[PERF_MAX_STACK_DEPTH];
  
  struct {
  	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
  	__uint(max_entries, 16384);
  	__type(key, __u32);
  	__type(value, stack_trace_t);
  } stackmap SEC(".maps");
  
  struct {
  	__uint(type, BPF_MAP_TYPE_ARRAY);
  	__uint(max_entries, 16384);
  	__type(key, __u32);
  	__type(value, stack_trace_t);
  } stack_amap SEC(".maps");
  
  /* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
  struct sched_switch_args {
  	unsigned long long pad;
  	char prev_comm[16];
  	int prev_pid;
  	int prev_prio;
  	long long prev_state;
  	char next_comm[16];
  	int next_pid;
  	int next_prio;
  };
  
  SEC("tracepoint/sched/sched_switch")
  int oncpu(struct sched_switch_args *ctx)
  {
  	__u32 max_len = PERF_MAX_STACK_DEPTH * sizeof(__u64);
  	__u32 key = 0, val = 0, *value_p;
  	void *stack_p;
  
  	value_p = bpf_map_lookup_elem(&control_map, &key);
  	if (value_p && *value_p)
  		return 0; /* skip if non-zero *value_p */
  
  	/* The size of stackmap and stackid_hmap should be the same */
  	key = bpf_get_stackid(ctx, &stackmap, 0);
  	if ((int)key >= 0) {
  		bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
  		stack_p = bpf_map_lookup_elem(&stack_amap, &key);
  		if (stack_p)
  			bpf_get_stack(ctx, stack_p, max_len, 0);
  	}
  
  	return 0;
  }
  
  char _license[] SEC("license") = "GPL";
  