《linux 内核分析》第6周进程创建及描述

王一+ 《Linux内核分析》MOOC课程http://mooc.study.163.com/course/USTC-1000029000

一、task_struct

操作系统的三大核心功能：1、进程管理 2、内存管理 3、文件系统

摘抄task_struct，并注释

//进程状态

1236 volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */

//进程的内核堆栈
1237 void *stack;
1238 atomic_t usage;

//每个进程的状态
1239   unsigned int flags;   /* per process flags, defined below */
1240   unsigned int ptrace;
1241

1251   int on_rq;
1252 //进程调度相关代码
1253   int prio, static_prio, normal_prio;
1254   unsigned int rt_priority;
1255   const struct sched_class *sched_class;
1256   struct sched_entity se;
1257   struct sched_rt_entity rt;
1258#ifdef CONFIG_CGROUP_SCHED
1259   struct task_group *sched_task_group;
1260#endif
1261   struct sched_dl_entity dl;
1262
1263#ifdef CONFIG_PREEMPT_NOTIFIERS
1264   /* list of struct preempt_notifier: */
1265   struct hlist_head preempt_notifiers;
1266#endif

1290
1291#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
1292   struct sched_info sched_info;
1293#endif
1294 //进程的链表
1295   struct list_head tasks;

1300//进程虚拟内存地址相关代码
1301   struct mm_struct *mm, *active_mm;
1302#ifdef CONFIG_COMPAT_BRK
1303   unsigned brk_randomized:1;
1304#endif
1305   /* per-thread vma caching */
1306   u32 vmacache_seqnum;
1307   struct vm_area_struct *vmacache[VMACACHE_SIZE];
1308#if defined(SPLIT_RSS_COUNTING)
1309   struct task_rss_stat   rss_stat;
1310#endif
1311 //任务状态及信号相关状态
1312   int exit_state;
1313   int exit_code, exit_signal;
1314   int pdeath_signal; /* The signal sent when the parent dies */
1315   unsigned int jobctl;   /* JOBCTL_*, siglock protected */
1316
1317   /* Used for emulating ABI behavior of previous Linux versions */
1318   unsigned int personality;
1319
1320   unsigned in_execve:1;   /* Tell the LSMs that the process is doing an
1321               * execve */
1322   unsigned in_iowait:1;
1323
1324   /* Revert to default priority/policy when forking */
1325   unsigned sched_reset_on_fork:1;
1326   unsigned sched_contributes_to_load:1;
1327
1328   unsigned long atomic_flags; /* Flags needing atomic access. */
1329// 进程标示符
1330   pid_t pid;
1331   pid_t tgid;
1332

1337   /*
1338   * pointers to (original) parent process, youngest child, younger sibling,
1339   * older sibling, respectively. (p->father can be replaced with
1340   * p->real_parent->pid)
1341   */
1342   struct task_struct __rcu *real_parent; /* real parent process */
1343   struct task_struct __rcu *parent; /* recipient of SIGCHLD, wait4() reports */
     //进程树有关
1344   /*
1345   * children/sibling forms the list of my natural children
1346   */
1347   struct list_head children;   /* list of my children */
1348   struct list_head sibling;   /* linkage in my parent's children list */
1349   struct task_struct *group_leader;   /* threadgroup leader */
1350
1351   /*
1352   * ptraced is the list of tasks this task is using ptrace on.
1353   * This includes both natural children and PTRACE_ATTACH targets.
1354   * p->ptrace_entry is p's link on the p->parent->ptraced list.
1355   */
1356   struct list_head ptraced;
1357   struct list_head ptrace_entry;
1358
1359   /* PID/PID hash table linkage. */
1360   struct pid_link pids[PIDTYPE_MAX];
1361   struct list_head thread_group;
1362   struct list_head thread_node;
1363
1364   struct completion *vfork_done;       /* for vfork() */
1365   int __user *set_child_tid;       /* CLONE_CHILD_SETTID */
1366   int __user *clear_child_tid;       /* CLONE_CHILD_CLEARTID
1411 //这个任务的cpu相关的数据
1412   struct thread_struct thread;
1413/* filesystem information */
1414   struct fs_struct *fs;
1415/* open file information */
1416   struct files_struct *files;
1417/* namespaces */
1418   struct nsproxy *nsproxy;
1419/* signal handlers */
1420   struct signal_struct *signal;
1421   struct sighand_struct *sighand;
1487/* journalling filesystem info */
1488   void *journal_info;
1489//块设备信息链表
1490/* stacked block device info */
1491   struct bio_list *bio_list;
1492
1493#ifdef CONFIG_BLOCK
1494/* stack plugging */
1495   struct blk_plug *plug;
1496#endif

进程的状态切换过程：

进程树和相互的关系：

进程的内核堆栈和thread_info的关系：

进程堆栈和thread_info使用一个空间，通过使用union的方式来定义，他们的地址开始于2^13的地址，分两个page(8k)；

这样就可以通过esp来获取thread_info的地址：

__asm__("andl %%esp,%0; ":"=r" (ti) : "0" (~(THREAD_SIZE - 1)));//通过屏蔽esp低13位,返回ti

二、进程的创建

进程的创建

1、创建线程需要调用通过调用fork系统调用，实现创建子进程，子进程在内核态创建之后，在内核态运行，而父线程返回到主线程运行。

子线程是在ret_from_fork之后执行。

2、、fork创建的过程分析

1）、在此系统中系统调用fork实际上是调用sys_clone,它和其他的两个系统调用都是调用的do_fork();

2）、在do_fork中调用copy_process（）来进行进程的复制和修改；

p = copy_process(clone_flags, stack_start, stack_size,
child_tidptr, NULL, trace);

3）、在copy_process（）中调用dup_task_struct()来实现创建task_struct空间，thread_info和内核堆栈的空间，并且复制task_struct和thread_infgo;

arch_dup_task_struct(tsk, orig)；//复制task_struct;

setup_thread_stack(tsk, orig);//复制thread_info;

4)、在copy_process 中对子线程的task_struct进行设置，然后将复制进程信息。在copy_thread 中将sp和ip指向内核堆栈中的sp和ip,

struct pt_regs *childregs = task_pt_regs(p);

struct pt_regs {
   unsigned long bx;
   unsigned long cx;
   unsigned long dx;
   unsigned long si;
   unsigned long di;
   unsigned long bp;
   unsigned long ax;// 系统调用号和参数
   unsigned long ds;
   unsigned long es;
   unsigned long fs;
   unsigned long gs;
   unsigned long orig_ax; //原来的系统的寄存器保存
   unsigned long ip;
   unsigned long cs;
   unsigned long flags; //本部分为系统自动存储的信息
   unsigned long sp;
   unsigned long ss;
};