需求： 使用 trace_marker 来跟踪程序

trace_marker 是一个文件节点，允许用户程序写入字符串，frace 会记录写入动作的时间戳

cd /sys/kernel/debug/tracing/

echo nop > current_tracer // 设置function 跟踪器是不能捕捉到示踪标志
echo 1 > tracing_on // 打开ftrace 才能捕捉到示踪标志

echo 0 > tracing_on // 关闭ftrace

 

一、程序编写

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/time.h>
#include <linux/unistd.h>
#include <stdarg.h>
#include <unistd.h>
#include <ctype.h>

static int mark_fd = -1;
static __thread char buff[BUFSIZ+1];

static void setup_ftrace_marker(void)
{
	struct stat st;
	char *files[] = {
		"/sys/kernel/debug/tracing/trace_marker",
		"/debug/tracing/trace_marker",
		"/debugfs/tracing/trace_marker",
	};
	int ret;
	int i;

	for (i = 0; i < (sizeof(files) / sizeof(char *)); i++) {
		ret = stat(files[i], &st);
		if (ret >= 0)
			goto found;
	}
	/* todo, check mounts system */
	printf("canot found the sys tracing\n");
	return;
found:
	mark_fd = open(files[i], O_WRONLY);
}

static void ftrace_write(const char *fmt, ...)
{
	va_list ap;
	int n;

	if (mark_fd < 0)
		return;

	va_start(ap, fmt);
	n = vsnprintf(buff, BUFSIZ, fmt, ap);
	va_end(ap);

	write(mark_fd, buff, n);
}

int main()
{
	int count = 0;
	setup_ftrace_marker();
	ftrace_write("rlk start program\n");
	while (1) {
		usleep(100*1000);
		count++;
		ftrace_write("rlk count=%d\n", count);
	}
}

编译: arm-linux-gnueabi-gcc trace_marker_test.c -o trace_marker_test --static

运行：

/sys/kernel/debug/tracing # /mnt/trace_marker_test 

... 等待几秒
Ctrl+c 终止程序

/sys/kernel/debug/tracing # cat trace
# tracer: nop
#
# entries-in-buffer/entries-written: 170/170   #P:4
#
#                              _-----=> irqs-off
#                             / _----=> need-resched
#                            | / _---=> hardirq/softirq
#                            || / _--=> preempt-depth
#                            ||| /     delay
#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
#              | |       |   ||||       |         |
           <...>-778   [000] ...1   124.054672: tracing_mark_write: rlk start program
           <...>-778   [000] ...1   124.180858: tracing_mark_write: rlk count=1
           <...>-778   [000] ...1   124.297803: tracing_mark_write: rlk count=2
           <...>-778   [000] ...1   124.408593: tracing_mark_write: rlk count=3
           <...>-778   [000] ...1   124.518589: tracing_mark_write: rlk count=4
           <...>-778   [000] ...1   124.628374: tracing_mark_write: rlk count=5
           <...>-778   [000] ...1   124.738971: tracing_mark_write: rlk count=6
           <...>-778   [000] ...1   124.849366: tracing_mark_write: rlk count=7
           <...>-778   [000] ...1   124.959502: tracing_mark_write: rlk count=8
           <...>-778   [000] ...1   125.071421: tracing_mark_write: rlk count=9
           <...>-778   [000] ...1   125.190520: tracing_mark_write: rlk count=10
           <...>-778   [000] ...1   125.300335: tracing_mark_write: rlk count=11
           <...>-778   [000] ...1   125.401471: tracing_mark_write: rlk count=12
           <...>-778   [000] ...1   125.511686: tracing_mark_write: rlk count=13
           <...>-778   [000] ...1   125.621551: tracing_mark_write: rlk count=14
           <...>-778   [000] ...1   125.732367: tracing_mark_write: rlk count=15
           <...>-778   [000] ...1   125.842521: tracing_mark_write: rlk count=16
           <...>-778   [000] ...1   125.952524: tracing_mark_write: rlk count=17
           <...>-778   [000] ...1   126.063389: tracing_mark_write: rlk count=18
           <...>-778   [000] ...1   126.173682: tracing_mark_write: rlk count=19