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task_struct
前言
宏观上看，操作系统能够同时运行多个进程；微观上看，如果操作系统只有一个处理器，那么在同一时刻只能运行一个进程。
操作系统以很短的时间间隔不停地切换多个进程的执行，这种管理方式需要注意以下问题：- 进程不能彼此干扰。进程 A 的错误不能传播到进程 B。Linux 是一个多用户系统，所以也要确保进程不能读取或修改其它进程的内存，否则就很容易访问其它用户的私有数据。
- CPU 时间必须在各种应用程序之间尽可能公平地共享，其中一些程序可能比其它程序更重要。内核必须决定为各个进程分配多长时间，何时切换到下一个进程。这又引出了哪个进程是下一个地问题。
- 在内核从进程 A 切换到进程 B 时，必须确保进程 B 的执行环境与上一次撤销其处理器资源时完全相同。例如，处理器寄存器的内容和虚拟地址空间的结构必须与此前相同。
第 3 项工作与处理器极度相关，不能只用 C 语言实现，还需要汇编代码的帮助。
第 2、3 项工作是称之为调度器的内核子系统的职责。task_struct
内核在实现上述功能时，使用的最主要的一个数据结构就是 task_struct。
- tasks 字段，是一个双向链表，正是这个字段将所有进程连接到了一起，我们才能对进程进行遍历
- 调度相关使用 sched_info 成员，包括优先级、vruntime、调度策略等
- 上下文信息使用 thread_stack、task_info、stack 成员存储，不同架构的 CPU，这些成员的定义也不同。
- 内存管理使用 mm 成员，其中页全局目录使用 mm->pgd 存储
除此之外还包括
- pid，进程号
- __state，进程状态，如，0: TASK_RUNNING
- parent，父进程
- comm，进程名
- files，进程打开的文件
- cpu，进程所在的处理器
- nvcsw：自愿进行上下文切换的次数
- nivcsw：非自愿进行上下文切换的次数
- stime：进程在内核态所经过的节拍数
- utime：进程在用户态所经过的节拍数
等
打印各字段
task_struct 结构体比较复杂，盯着代码看各个成员有时也不容易理解，最直接的办法就是将各个成员打印出来，理论结合实际，这样可以更加深刻的理解各个字段的含义。
下面我们就写一个内核模块，打印当前系统中各个进程的 task_struct 成员信息task_struct.c
#include#include #include #include //task结构体 #include //files #include //fs #include //打印内存信息 #include #include #include #include void show(struct task_struct *p) { printk("pid: %3d, %16.16s, state: %4d, prior: %3d, static_pri: %3d, " "parent_pid: %3d, count: %3d, umask: %3d, stack:0x%x, \n\t\t" "cpu:%d, nvcsw:%ld, nivcsw:%ld, stime:%lld, utime:%lld, " "policy:%d, vruntime:%lld" "\n", p->pid, p->comm, p->__state, p->prio, p->static_prio, (p->parent)->pid, atomic_read(&(p->files)->count), (p->fs)->umask, p->stack, task_thread_info(p)->cpu, p->nvcsw, p->nivcsw, p->stime, p->utime, p->policy, p->se.vruntime); // linux中内核线程的 mm 是空的，要对它进行打印，就会出错，指针错误 if ((p->mm) != NULL) { // 线性区总的页数, 页全局目录 printk("Total_vm: %ld, pgd:0x%x, ", (p->mm)->total_vm, p->mm->pgd[0]); } if ((p->active_mm) != NULL) { printk("active_mm_pgd:0x%x", p->active_mm->pgd[0]); } } static int __init print_pcb(void) { struct task_struct *task, *p; struct list_head *pos; //双向链表 int count = 0; //统计当前系统一共有多少个进程 printk("begin...\n"); // 对链表遍历时，希望从第一个开始，指向 0 号进程 pcb task = &init_task; show(task); //遍历操作，使用pos指向，传入的参数task指向tasks字段.0号进程的tasks进行遍历。tasks将所有的进程连在一块。 list_for_each (pos, &task->tasks) { //找到一个节点，就可以用这个节点的 tasks 字段，找到这个结构体的地址.对应的字段 tasks //此时的p指针已经指向task_struct结构体的首部，后面就可以通过p指针进行操作 p = list_entry(pos, struct task_struct, tasks); show(p); count++; } printk("进程的个数:%d\n", count); return 0; } static void __exit exit_pcb(void) { printk("Exiting...\n"); } module_init(print_pcb); module_exit(exit_pcb); MODULE_LICENSE("GPL"); - 1
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Makefile
obj-m:=task_struct.o KDIR=/home/liyongjun/project/board/buildroot/Vexpress/build/linux-5.15.18 CROSS_COMPILE=/home/liyongjun/project/board/buildroot/Vexpress/build/linux-5.15.18/../../host/bin/arm-buildroot-linux-uclibcgnueabihf- all: make -C $(KDIR) M=$(PWD) ARCH=arm CROSS_COMPILE=$(CROSS_COMPILE) modules clean: make -C $(KDIR) M=$(PWD) ARCH=arm CROSS_COMPILE=$(CROSS_COMPILE) clean- 1
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运行，
使用 qemu 运行一个 4 核 arm 系统，然后安装我们编译的内核模块# tftp -gr task_struct.ko 192.168.31.223 # insmod task_struct.ko begin... pid: 0, swapper/0, state: 0, prior: 120, static_pri: 120, parent_pid: 0, count: 54, umask: 18, stack:0x80c00000, cpu:0, nvcsw:0, nivcsw:273299, stime:100260000000, utime:0, policy:0, vruntime:0 active_mm_pgd:0x81b70000 pid: 1, init, state: 1, prior: 120, static_pri: 120, parent_pid: 0, count: 1, umask: 18, stack:0x81096000, cpu:2, nvcsw:311, nivcsw:11, stime:650000000, utime:40000000, policy:0, vruntime:1271261734 Total_vm: 393, pgd:0x811b0000, active_mm_pgd:0x811b0000 pid: 2, kthreadd, state: 1, prior: 120, static_pri: 120, parent_pid: 0, count: 54, umask: 18, stack:0x81098000, cpu:2, nvcsw:59, nivcsw:0, stime:40000000, utime:0, policy:0, vruntime:2859880532 pid: 3, rcu_gp, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x8109a000, cpu:0, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:10781931 pid: 4, rcu_par_gp, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x8109c000, cpu:0, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:12672772 pid: 6, kworker/0:0H, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x810cc000, cpu:0, nvcsw:4, nivcsw:0, stime:0, utime:0, policy:0, vruntime:467744348 pid: 7, kworker/u8:0, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810ce000, cpu:3, nvcsw:8, nivcsw:1, stime:90000000, utime:0, policy:0, vruntime:194562752 pid: 8, mm_percpu_wq, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x810d0000, cpu:0, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:19554971 pid: 9, ksoftirqd/0, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810d2000, cpu:0, nvcsw:10009, nivcsw:1, stime:0, utime:0, policy:0, vruntime:84093189061 pid: 10, rcu_sched, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810d4000, cpu:2, nvcsw:526, nivcsw:0, stime:10000000, utime:0, policy:0, vruntime:3005160995 pid: 11, migration/0, state: 1, prior: 0, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810d6000, cpu:0, nvcsw:6, nivcsw:0, stime:20000000, utime:0, policy:1, vruntime:0 pid: 12, cpuhp/0, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810de000, cpu:0, nvcsw:9, nivcsw:0, stime:0, utime:0, policy:0, vruntime:439359833 pid: 13, cpuhp/1, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810e0000, cpu:1, nvcsw:8, nivcsw:0, stime:0, utime:0, policy:0, vruntime:259698436 pid: 14, migration/1, state: 1, prior: 0, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810e2000, cpu:1, nvcsw:6, nivcsw:0, stime:20000000, utime:0, policy:1, vruntime:0 pid: 15, ksoftirqd/1, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810e4000, cpu:1, nvcsw:1211, nivcsw:0, stime:0, utime:0, policy:0, vruntime:40372256279 pid: 17, kworker/1:0H, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x810e8000, cpu:1, nvcsw:5, nivcsw:0, stime:0, utime:0, policy:0, vruntime:109593599 pid: 18, cpuhp/2, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810ea000, cpu:2, nvcsw:8, nivcsw:0, stime:0, utime:0, policy:0, vruntime:59346256 pid: 19, migration/2, state: 1, prior: 0, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810ec000, cpu:2, nvcsw:7, nivcsw:0, stime:20000000, utime:0, policy:1, vruntime:0 pid: 20, ksoftirqd/2, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810ee000, cpu:2, nvcsw:686, nivcsw:0, stime:0, utime:0, policy:0, vruntime:2800704118 pid: 21, kworker/2:0, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810f0000, cpu:2, nvcsw:5, nivcsw:0, stime:10000000, utime:0, policy:0, vruntime:11475716 pid: 23, cpuhp/3, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x810f4000, cpu:3, nvcsw:8, nivcsw:0, stime:0, utime:0, policy:0, vruntime:99372461 pid: 24, migration/3, state: 1, prior: 0, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x81104000, cpu:3, nvcsw:7, nivcsw:0, stime:20000000, utime:0, policy:1, vruntime:0 pid: 25, ksoftirqd/3, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x81106000, cpu:3, nvcsw:563, nivcsw:0, stime:0, utime:0, policy:0, vruntime:15162602723 pid: 26, kworker/3:0, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x81118000, cpu:3, nvcsw:5, nivcsw:0, stime:0, utime:0, policy:0, vruntime:9468662 pid: 28, kdevtmpfs, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x8111c000, cpu:2, nvcsw:142, nivcsw:0, stime:10000000, utime:0, policy:0, vruntime:68424254 pid: 29, inet_frag_wq, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x81120000, cpu:1, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:8684611 pid: 30, kworker/0:1, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x81192000, cpu:0, nvcsw:14, nivcsw:0, stime:10000000, utime:0, policy:0, vruntime:82145485871 pid: 31, kworker/2:1, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x81194000, cpu:2, nvcsw:28, nivcsw:0, stime:0, utime:0, policy:0, vruntime:2960087740 pid: 32, kworker/1:1, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x81196000, cpu:1, nvcsw:116960, nivcsw:0, stime:4110000000, utime:0, policy:0, vruntime:40372906611 pid: 33, kworker/3:1, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x811aa000, cpu:3, nvcsw:364, nivcsw:0, stime:10000000, utime:0, policy:0, vruntime:15162450516 pid: 34, khungtaskd, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x81178000, cpu:2, nvcsw:321, nivcsw:0, stime:0, utime:0, policy:0, vruntime:2967078288 pid: 35, oom_reaper, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x8117a000, cpu:3, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:37961818 pid: 36, writeback, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x81198000, cpu:1, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:38309928 pid: 37, kcompactd0, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x8119a000, cpu:2, nvcsw:76806, nivcsw:0, stime:1090000000, utime:0, policy:0, vruntime:3011151327 pid: 38, kblockd, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x811ac000, cpu:1, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:47985364 pid: 39, ata_sff, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x811ae000, cpu:1, nvcsw:2, nivcsw:0, stime:10000000, utime:0, policy:0, vruntime:58046861 pid: 41, rpciod, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x81256000, cpu:3, nvcsw:2, nivcsw:0, stime:10000000, utime:0, policy:0, vruntime:57739139 pid: 42, kworker/u9:0, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x812cc000, cpu:3, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:67126213 pid: 43, xprtiod, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x812ce000, cpu:3, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:76917350 pid: 44, kworker/1:1H, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x812d0000, cpu:1, nvcsw:70, nivcsw:0, stime:30000000, utime:0, policy:0, vruntime:40370062181 pid: 45, kswapd0, state: 1, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x812d2000, cpu:0, nvcsw:3, nivcsw:0, stime:0, utime:0, policy:0, vruntime:433440459 pid: 46, nfsiod, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x812d4000, cpu:0, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:432884339 pid: 47, kworker/1:2, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x812d6000, cpu:1, nvcsw:49, nivcsw:0, stime:40000000, utime:0, policy:0, vruntime:359242846 pid: 48, kworker/u8:2, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x813cc000, cpu:3, nvcsw:149, nivcsw:7, stime:270000000, utime:0, policy:0, vruntime:15178519976 pid: 52, irq/33-mmci-pl1, state: 1, prior: 49, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x813d4000, cpu:0, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:1, vruntime:0 pid: 54, mmc_complete, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x81aa0000, cpu:0, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:476729289 pid: 55, kworker/0:1H, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x81aa2000, cpu:0, nvcsw:94, nivcsw:1, stime:130000000, utime:0, policy:0, vruntime:84079734629 pid: 56, kworker/0:2, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x81aa4000, cpu:0, nvcsw:257435, nivcsw:1, stime:7380000000, utime:0, policy:0, vruntime:84094426935 pid: 57, card0-crtc0, state: 1, prior: 49, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x81aa6000, cpu:3, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:1, vruntime:0 pid: 58, kworker/3:1H, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x81882000, cpu:3, nvcsw:74, nivcsw:0, stime:30000000, utime:0, policy:0, vruntime:15161848812 pid: 59, ext4-rsv-conver, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x81884000, cpu:0, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:764178885 pid: 61, kworker/3:2H, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x81a88000, cpu:3, nvcsw:3, nivcsw:0, stime:0, utime:0, policy:0, vruntime:279463688 pid: 62, kworker/2:1H, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x81a8a000, cpu:2, nvcsw:100, nivcsw:1, stime:80000000, utime:0, policy:0, vruntime:1121465971 pid: 63, kworker/2:2H, state: 1026, prior: 100, static_pri: 100, parent_pid: 2, count: 54, umask: 18, stack:0x81a8c000, cpu:2, nvcsw:5, nivcsw:0, stime:0, utime:0, policy:0, vruntime:185536371 pid: 80, syslogd, state: 1, prior: 120, static_pri: 120, parent_pid: 1, count: 1, umask: 18, stack:0x81bf8000, cpu:2, nvcsw:377, nivcsw:10, stime:190000000, utime:220000000, policy:0, vruntime:3021892453 Total_vm: 391, pgd:0x81c08000, active_mm_pgd:0x81c08000 pid: 84, klogd, state: 0, prior: 120, static_pri: 120, parent_pid: 1, count: 1, umask: 18, stack:0x81ba4000, cpu:3, nvcsw:15, nivcsw:42, stime:350000000, utime:300000000, policy:0, vruntime:15200845932 Total_vm: 390, pgd:0x81b8c000, active_mm_pgd:0x81b8c000 pid: 136, udhcpc, state: 1, prior: 120, static_pri: 120, parent_pid: 1, count: 1, umask: 18, stack:0x81ba6000, cpu:3, nvcsw:4, nivcsw:0, stime:0, utime:0, policy:0, vruntime:14252907400 Total_vm: 392, pgd:0x81cac000, active_mm_pgd:0x81cac000 pid: 138, sh, state: 1, prior: 120, static_pri: 120, parent_pid: 1, count: 1, umask: 18, stack:0x81bbc000, cpu:0, nvcsw:121, nivcsw:7, stime:200000000, utime:130000000, policy:0, vruntime:84105463853 Total_vm: 396, pgd:0x81b70000, active_mm_pgd:0x81b70000 pid: 155, kworker/0:0, state: 1026, prior: 120, static_pri: 120, parent_pid: 2, count: 54, umask: 18, stack:0x81bb2000, cpu:0, nvcsw:2, nivcsw:0, stime:0, utime:0, policy:0, vruntime:82150084578 pid: 158, insmod, state: 0, prior: 120, static_pri: 120, parent_pid: 138, count: 1, umask: 18, stack:0x8111a000, cpu:1, nvcsw:0, nivcsw:0, stime:70000000, utime:0, policy:0, vruntime:40458619481 Total_vm: 391, pgd:0x81b88000, active_mm_pgd:0x81b88000 进程的个数:59 #- 1
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- 104
- 105
- 106
- 107
- 108
- 109
- 110
- 111
- 112
- 113
- 114
- 115
- 116
- 117
- 118
- 119
- 120
- 121
- 122
- 123
- 124
- 125
- 126
- 127
- 128
- 129
- 130
- 131
- 132
- 133
- 134
- 135
- 136
- 137
- 138
- 139
简单分析：
一、
处于运行状态的进程有 3 个，分别是- 0 号进程 swapper/0，运行在 cpu0 上
- 84 号进程 klogd，运行在 cpu3 上
- 158 号进程 insmod，运行在 cpu1 上
二、
insmod 进程为单次运行，所以 nvcsw(自愿进行上下文切换的次数) 和 nivcsw(非自愿进行上下文切换的次数) 均为 0。
0 号进程为空闲进程，只有系统空闲时才会被调度，它的优先级最低，所以自愿进行上下文切换的次数为 0，全都是非自愿进行上下文切换，nvcsw:0, nivcsw:273299。三、
大部分进程的调度策略 policy 都为 0：SCHED_NORMAL，该策略使用 CFS(完全公平调度器) 实现。所以 CFS 是内核用的最多的调度算法。该算法使用 vruntime 这个参数，谁小，下一个就调度谁。关于 CFS 后面有机会再展开讲。
有几个进程的调度策略 policy 为 1：SCHED_FIFO，该策略使用 RT(实时调度器)实现。四、
实时进程的优先级是 0~99 这 100 个优先级
普通进程的优先级是 100~139 这 40 个优先级
对应第三点，prior 为 120 的是普通进程，使用 CFS 调度策略；prior 为 0、49 的是实时进程，使用 RT 调度策略。五、
每个进程（包括内核线程和用户空间进程）的栈地址都不同，说明每个进程都有自己独立的栈空间。六、
所有内核线程的 utime 都为 0，因为它只会在内核态运行。
用户空间进程的 utime 和 stime 都有值，因为它既可以运行在用户空间，也可以通过系统调用让内核帮自己完成某些工作，这个时候该进程就运行于内核空间。七、
kthreadd 是所有内核线程的父进程，它生于 0 号进程。
init 是所有用户进程的父进程，它也生于 0 号进程。八、
最繁忙的进程是如下几个- swapper/0
- init
- kworker/2:1
- kworker/0:2
- kworker/1:2
swapper/0 进程很好理解，系统空闲时就会执行它
init 会监控所有用户进程，必要时为其"收尸"，所以 CPU 占用较高
kworker 处理中断下半部，内存管理、进程调度也都有参与，所以 CPU 占用率较高 -
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- 原文地址：https://blog.csdn.net/lyndon_li/article/details/132909636
