ftrace学习 —— user_events的用法
参考
https://docs.kernel.org/trace/user_events.html
测试程序
samples/user_events/example.c
tools/testing/selftests/user_events/ftrace_test.c
正文
通过user_event可以实现对应用程序的跟踪，类似linux内核中的tracepoint那样。相似的方法还有借助/sys/kernel/debug/tracing/trace_marker，不过，user_event提供的方法功能更加强大，可以配合perf等工具使用。
要使用user_event，大致要经过：注册、使能跟踪、写入跟踪信息、读取跟踪信息、关闭跟踪、反注册、删除。需要用到的文件节点主要是：/sys/kernel/tracing/user_events_data。
打开文件节点
data_fd = open(data_file, O_RDWR);
注册和反注册
注册阶段用到的结构体是user_reg：
struct user_reg {
/* Input：固定为sizeof(user_reg)*/
__u32 size;
/* Input: 使用下面的enable_addr的哪个bit来显示使能状态 */
__u8 enable_bit;
/* Input: 下面的enable_addr的字节长度，4或者8 */
__u8 enable_size;
/* Input: 目前还用不到，设置为0即可 */
__u16 flags;
/* Input: 应用通过这个地址来查看该user_event事件是否使能*/
__u64 enable_addr;
/* Input: 事件描述信息*/
__u64 name_args;
/* Output: 应用通过该事件索引向内核中写入事件内容 */
__u32 write_index;
} __attribute__((__packed__));
反注册用到的结构体是：
struct user_unreg {
/* Input: 固定为sizeof(user_unreg) */
__u32 size;
/* Input: Bit to unregister */
__u8 disable_bit;
/* Input: Reserved, set to 0 */
__u8 __reserved;
/* Input: Reserved, set to 0 */
__u16 __reserved2;
/* Input: Address to unregister */
__u64 disable_addr;
} __attribute__((__packed__));
比如以下面的代码为例：
// 这两个结构体必须初始化为0
struct user_reg reg = {0};
struct user_unreg unreg = {0};
u32 check;
reg.size = sizeof(reg);
reg.name_args = (__u64)"__test_event0 u32 id; u32 age; char type; char[32] name";
reg.enable_bit = 31; // 通过check的bit31来查看使能状态，不同的事件可以使用同一个变量
reg.enable_addr = (__u64)✓
reg.enable_size = sizeof(check);
ioctl(data_fd, DIAG_IOCSREG, ®); // 如果传入的reg的内容一样，那么返回的write_index也一样
event0_index = reg.write_index;
reg.size = sizeof(reg);
reg.name_args = (__u64)"__test_event1 u32 money";
reg.enable_bit = 30; // 通过check的bit30来查看使能状态
reg.enable_addr = (__u64)check;
reg.enable_size = sizeof(check);
ioctl(data_fd, DIAG_IOCSREG, ®); // 如果传入的reg的内容一样，那么返回的write_index也一样
event1_index = reg.write_index;
注册成功后，可以看到注册的事件：
- 在
/sys/kernel/debug/tracing/dynamic_events下面：
- 在
/sys/kernel/debug/tracing/events/user_events下面：
- 可以查看一下format的内容，跟注册时设置的
name_args是一致的
user_events/__test_event0：
user_events/__test_event1：
使能跟踪和关闭跟踪
/sys/kernel/debug/tracing/events/user_events/__test_event0/enable
或者
/sys/kernel/debug/tracing/events/user_events/__test_event1/enable
当改变上面的enable文件节点的值时，check变量的相应bit会随之改变。具体是：
向__test_event0/enable写入0，那么check变量的bit31是0，向__test_event0/enable写入1，那么check变量的bit31是1.
向__test_event1/enable写入0，那么check变量的bit30是0，向__test_event0/enable写入1，那么check变量的bit30是1.
写入事件
char name[20] = "I am event0";
io[0].iov_base = &event0_index;
io[0].iov_len = sizeof(event0_index);
io[1].iov_base = &id;
io[1].iov_len = sizeof(id);
io[2].iov_base = &age;
io[2].iov_len = sizeof(age);
io[3].iov_base = &type;
io[3].iov_len = sizeof(type);
io[4].iov_base = name;
io[4].iov_len = sizeof(name);
// 使能
system("echo 1 > /sys/kernel/debug/tracing/events/user_events/__test_event0/enable");
// 写入
writev(data_fd, (const struct iovec *)io, 5);
io[0].iov_base = &event1_index;
io[0].iov_len = sizeof(event1_index);
io[1].iov_base = &money;
io[1].iov_len = sizeof(money);
// 使能
system("echo 1 > /sys/kernel/debug/tracing/events/user_events/__test_event1/enable");
// 写入
writev(data_fd, (const struct iovec *)io, 2);
读取跟踪日志、设置过滤以及trigger
# perf trace -e user_events:__test_event0 -e user_events:__test_event1
或者
# cat /sys/kernel/debug/tracing/trace_pipe
可以看到如下日志：
此外，我们还可以利用这个event的filter和trigger节点控制跟踪的条件：
比如对__test_event0实现下面的两个控制：
- 当age大于10，小于15时，不记录跟踪日志
- 当age等于20时，记录调用栈
下面是实现这两个条件的命令：
# cd /sys/kernel/debug/tracing/events/user_events/__test_event0
# echo 'age <= 10 || age >= 15' > filter
# cat filter
age <= 10 || age >= 15
# echo 'stacktrace if age == 20' > trigger
# cat trigger
stacktrace:unlimited if age == 20
下面是跟踪日志：
... ...
user_events_dem-542 [003] ..... 1125.702619: __test_event0: name=I am event0 type='E'(69) age=0x6 (6) id=0x10 (16)
user_events_dem-542 [003] ..... 1125.702837: __test_event1: name=I am event1 money=0x6 (6)
user_events_dem-542 [003] ..... 1128.141755: __test_event0: name=I am event0 type='E'(69) age=0x7 (7) id=0x10 (16)
user_events_dem-542 [003] ..... 1128.141953: __test_event1: name=I am event1 money=0x7 (7)
user_events_dem-542 [003] ..... 1129.022463: __test_event0: name=I am event0 type='E'(69) age=0x8 (8) id=0x10 (16)
user_events_dem-542 [003] ..... 1129.022682: __test_event1: name=I am event1 money=0x8 (8)
user_events_dem-542 [003] ..... 1130.070759: __test_event0: name=I am event0 type='E'(69) age=0x9 (9) id=0x10 (16)
user_events_dem-542 [003] ..... 1130.070904: __test_event1: name=I am event1 money=0x9 (9)
user_events_dem-542 [003] ..... 1130.630082: __test_event0: name=I am event0 type='E'(69) age=0xa (10) id=0x10 (16)
user_events_dem-542 [003] ..... 1130.630428: __test_event1: name=I am event1 money=0xa (10)
user_events_dem-542 [003] ..... 1131.285824: __test_event1: name=I am event1 money=0xb (11)
user_events_dem-542 [003] ..... 1132.414520: __test_event1: name=I am event1 money=0xc (12)
user_events_dem-542 [003] ..... 1133.022232: __test_event1: name=I am event1 money=0xd (13)
user_events_dem-542 [003] ..... 1133.727074: __test_event1: name=I am event1 money=0xe (14)
user_events_dem-542 [003] ..... 1134.694207: __test_event0: name=I am event0 type='E'(69) age=0xf (15) id=0x10 (16)
user_events_dem-542 [003] ..... 1134.694394: __test_event1: name=I am event1 money=0xf (15)
user_events_dem-542 [003] ..... 1136.030015: __test_event0: name=I am event0 type='E'(69) age=0x10 (16) id=0x10 (16)
user_events_dem-542 [003] ..... 1136.030468: __test_event1: name=I am event1 money=0x10 (16)
user_events_dem-542 [003] ..... 1136.630760: __test_event0: name=I am event0 type='E'(69) age=0x11 (17) id=0x10 (16)
user_events_dem-542 [003] ..... 1136.630908: __test_event1: name=I am event1 money=0x11 (17)
user_events_dem-542 [000] ..... 1137.221809: __test_event0: name=I am event0 type='E'(69) age=0x12 (18) id=0x10 (16)
user_events_dem-542 [000] ..... 1137.221880: __test_event1: name=I am event1 money=0x12 (18)
user_events_dem-542 [000] ..... 1137.766662: __test_event0: name=I am event0 type='E'(69) age=0x13 (19) id=0x10 (16)
user_events_dem-542 [000] ..... 1137.766844: __test_event1: name=I am event1 money=0x13 (19)
user_events_dem-542 [000] ..... 1138.261930: __test_event0: name=I am event0 type='E'(69) age=0x14 (20) id=0x10 (16)
user_events_dem-542 [000] ...1. 1138.262064: <stack trace>
=> user_event_ftrace
=> user_events_write_core.isra.22
=> do_iter_readv_writev
=> do_iter_write
=> vfs_writev
=> do_writev
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe
user_events_dem-542 [000] ..... 1138.262076: __test_event1: name=I am event1 money=0x14 (20)
user_events_dem-542 [000] ..... 1138.925935: __test_event0: name=I am event0 type='E'(69) age=0x15 (21) id=0x10 (16)
user_events_dem-542 [000] ..... 1138.926231: __test_event1: name=I am event1 money=0x15 (21)
user_events_dem-542 [000] ..... 1139.350572: __test_event0: name=I am event0 type='E'(69) age=0x16 (22) id=0x10 (16)
user_events_dem-542 [000] ..... 1139.350825: __test_event1: name=I am event1 money=0x16 (22)
... ...
注意：
需要先把__test_event0的filter和trigger清空才能反注册和删除这个probe。
echo > filter
echo '!stacktrace' > trigger
反注册
unreg.size = sizeof(unreg);
unreg.disable_bit = 31;
unreg.disable_addr = (__u64)✓
ioctl(data_fd, DIAG_IOCSUNREG, &unreg);
unreg.size = sizeof(unreg);
unreg.disable_bit = 30;
unreg.disable_addr = (__u64)✓
ioctl(data_fd, DIAG_IOCSUNREG, &unreg);
删除
// 先关闭
close(data_fd);
data_fd = open(data_file, O_RDWR);
ioctl(data_fd, DIAG_IOCSDEL, "__test_event0");
ioctl(data_fd, DIAG_IOCSDEL, "__test_event1");
下面是完整的测试程序：
点击查看代码
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/uio.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <linux/user_events.h>
#include <stdlib.h>
#define BIT(n) (1ULL << (n))
const char *data_file = "/sys/kernel/tracing/user_events_data";
int enabled = 0;
int main(int argc, const char *argv[])
{
int data_fd;
struct user_reg reg = {0};
struct user_unreg unreg = {0};
struct iovec io[5];
__u32 check, event0_index, event1_index;
int id, age = 0, money = 0;
char type = 'E', ch;
data_fd = open(data_file, O_RDWR);
if (data_fd < 0) {
perror("Open failed\n");
return -1;
}
reg.size = sizeof(reg);
reg.name_args = (__u64)"__test_event0 u32 id; u32 age; char type; char[32] name";
reg.enable_bit = 31; // 通过check的bit31来查看使能状态，不同的事件可以使用同一个变量
reg.enable_addr = (__u64)✓
reg.enable_size = sizeof(check);
if (ioctl(data_fd, DIAG_IOCSREG, ®) < 0) {
printf("reg event0 failed\n");
goto out;
}
event0_index = reg.write_index;
printf("event0_index: %d\n", event0_index);
reg.name_args = (__u64)"__test_event1 u32 money; char[32] name";
reg.enable_bit = 30; // 通过check的bit30来查看使能状态
if (ioctl(data_fd, DIAG_IOCSREG, ®) < 0) {
printf("reg event1 failed\n");
goto out;
}
event1_index = reg.write_index;
printf("event1_index: %d\n", event1_index);
system("echo 1 > /sys/kernel/debug/tracing/events/user_events/__test_event0/enable");
system("echo 1 > /sys/kernel/debug/tracing/events/user_events/__test_event1/enable");
loop:
printf("Press enter to write trace data, enter q to exit ...");
ch = getchar();
if (ch == 'q') {
system("echo 0 > /sys/kernel/debug/tracing/events/user_events/__test_event0/enable");
system("echo 0 > /sys/kernel/debug/tracing/events/user_events/__test_event1/enable");
unreg.size = sizeof(unreg);
unreg.disable_bit = 31;
unreg.disable_addr = (__u64)✓
if (ioctl(data_fd, DIAG_IOCSUNREG, &unreg) < 0) {
printf("unreg event0 failed\n");
goto out;
}
printf("unreg event0 success\n");
unreg.disable_bit = 30;
if (ioctl(data_fd, DIAG_IOCSUNREG, &unreg) < 0) {
printf("unreg event1 failed\n");
goto out;
}
printf("unreg event1 success\n");
close(data_fd);
data_fd = open(data_file, O_RDWR);
if (ioctl(data_fd, DIAG_IOCSDEL, "__test_event0") < 0) {
printf("del event0 failed\n");
goto out;
}
printf("del event0 success\n");
if (ioctl(data_fd, DIAG_IOCSDEL, "__test_event1") < 0) {
printf("del event1 failed\n");
goto out;
}
printf("del event1 success\n");
close(data_fd);
return 0;
}
if (check & BIT(31)) {
char name[32] = "I am event0";
id = 0x10;
io[0].iov_base = &event0_index;
io[0].iov_len = sizeof(event0_index);
io[1].iov_base = &id;
io[1].iov_len = sizeof(id);
io[2].iov_base = &age;
io[2].iov_len = sizeof(age);
io[3].iov_base = &type;
io[3].iov_len = sizeof(type);
io[4].iov_base = name;
io[4].iov_len = sizeof(name);
printf("\t write event0\n");
writev(data_fd, (const struct iovec *)io, 5);
age++;
}
if (check & BIT(30)) {
char name[32] = "I am event1";
io[0].iov_base = &event1_index;
io[0].iov_len = sizeof(event1_index);
io[1].iov_base = &money;
io[1].iov_len = sizeof(money);
io[2].iov_base = &name;
io[2].iov_len = sizeof(name);
printf("\t write event1\n");
writev(data_fd, (const struct iovec *)io, 3);
money++;
}
goto loop;
out:
return 0;
}
完。
本文来自博客园，作者：摩斯电码，未经同意，禁止转载
