text: // SPDX-License-Identifier: GPL-2.0
  #include <stdio.h>
  #include <unistd.h>
  #include <stdlib.h>
  #include <signal.h>
  #include <linux/bpf.h>
  #include <string.h>
  #include <sys/resource.h>
  
  #include <bpf/bpf.h>
  #include "bpf_load.h"
  #include "bpf_util.h"
  
  #define MAX_INDEX	64
  #define MAX_STARS	38
  
  static void stars(char *str, long val, long max, int width)
  {
  	int i;
  
  	for (i = 0; i < (width * val / max) - 1 && i < width - 1; i++)
  		str[i] = '*';
  	if (val > max)
  		str[i - 1] = '+';
  	str[i] = '\0';
  }
  
  struct task {
  	char comm[16];
  	__u64 pid_tgid;
  	__u64 uid_gid;
  };
  
  struct hist_key {
  	struct task t;
  	__u32 index;
  };
  
  #define SIZE sizeof(struct task)
  
  static void print_hist_for_pid(int fd, void *task)
  {
  	unsigned int nr_cpus = bpf_num_possible_cpus();
  	struct hist_key key = {}, next_key;
  	long values[nr_cpus];
  	char starstr[MAX_STARS];
  	long value;
  	long data[MAX_INDEX] = {};
  	int max_ind = -1;
  	long max_value = 0;
  	int i, ind;
  
  	while (bpf_map_get_next_key(fd, &key, &next_key) == 0) {
  		if (memcmp(&next_key, task, SIZE)) {
  			key = next_key;
  			continue;
  		}
  		bpf_map_lookup_elem(fd, &next_key, values);
  		value = 0;
  		for (i = 0; i < nr_cpus; i++)
  			value += values[i];
  		ind = next_key.index;
  		data[ind] = value;
  		if (value && ind > max_ind)
  			max_ind = ind;
  		if (value > max_value)
  			max_value = value;
  		key = next_key;
  	}
  
  	printf("           syscall write() stats\n");
  	printf("     byte_size       : count     distribution\n");
  	for (i = 1; i <= max_ind + 1; i++) {
  		stars(starstr, data[i - 1], max_value, MAX_STARS);
  		printf("%8ld -> %-8ld : %-8ld |%-*s|\n",
  		       (1l << i) >> 1, (1l << i) - 1, data[i - 1],
  		       MAX_STARS, starstr);
  	}
  }
  
  static void print_hist(int fd)
  {
  	struct hist_key key = {}, next_key;
  	static struct task tasks[1024];
  	int task_cnt = 0;
  	int i;
  
  	while (bpf_map_get_next_key(fd, &key, &next_key) == 0) {
  		int found = 0;
  
  		for (i = 0; i < task_cnt; i++)
  			if (memcmp(&tasks[i], &next_key, SIZE) == 0)
  				found = 1;
  		if (!found)
  			memcpy(&tasks[task_cnt++], &next_key, SIZE);
  		key = next_key;
  	}
  
  	for (i = 0; i < task_cnt; i++) {
  		printf("\npid %d cmd %s uid %d\n",
  		       (__u32) tasks[i].pid_tgid,
  		       tasks[i].comm,
  		       (__u32) tasks[i].uid_gid);
  		print_hist_for_pid(fd, &tasks[i]);
  	}
  
  }
  
  static void int_exit(int sig)
  {
  	print_hist(map_fd[1]);
  	exit(0);
  }
  
  int main(int ac, char **argv)
  {
  	struct rlimit r = {1024*1024, RLIM_INFINITY};
  	char filename[256];
  	long key, next_key, value;
  	FILE *f;
  	int i;
  
  	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
  
  	if (setrlimit(RLIMIT_MEMLOCK, &r)) {
  		perror("setrlimit(RLIMIT_MEMLOCK)");
  		return 1;
  	}
  
  	signal(SIGINT, int_exit);
  	signal(SIGTERM, int_exit);
  
  	/* start 'ping' in the background to have some kfree_skb events */
  	f = popen("ping -4 -c5 localhost", "r");
  	(void) f;
  
  	/* start 'dd' in the background to have plenty of 'write' syscalls */
  	f = popen("dd if=/dev/zero of=/dev/null count=5000000", "r");
  	(void) f;
  
  	if (load_bpf_file(filename)) {
  		printf("%s", bpf_log_buf);
  		return 1;
  	}
  
  	for (i = 0; i < 5; i++) {
  		key = 0;
  		while (bpf_map_get_next_key(map_fd[0], &key, &next_key) == 0) {
  			bpf_map_lookup_elem(map_fd[0], &next_key, &value);
  			printf("location 0x%lx count %ld\n", next_key, value);
  			key = next_key;
  		}
  		if (key)
  			printf("\n");
  		sleep(1);
  	}
  	print_hist(map_fd[1]);
  
  	return 0;
  }
  