http://blog.csdn.net/qq_26768741/article/details/54348586

当把一个程序加载到内存当中，此时，这个时候就有了进程，关于进程，有一个相关的叫做进程控制块（PCB），这个是系统为了方便进行管理进程所设置的一个数据结构，通过PCB，就可以记录进程的特征以及一些信息。 
内核当中使用进程描述符task_struct。 
这个task_struct就是一个定义的一个结构体，通过这个结构体，可以对进程的所有的相关的信息进行维护，对进程进行管理。

接下来我们需要对task_struct结构体当中的成员进行一些分析。

1 task_struct

1.1 进程状态

volatile long state;
int exit_state;`

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表示进程的状态， 在进程执行的时候，它会有一个状态，这个状态对于进程来说是很重要的一个属性。进程主要有以下几个状态。

state可能的取值 

这些状态就不再一一说明了，后续进程篇会有专门的说明。

1.2 进程标识符（PID）

pid_t pid;
pid_t tgid;

每个进程都有进程标识符、用户标识符、组标识符，进程标识符对于每一个进程来说都是唯一的。内核通过进程标识符来对不同的进程进行识别，一般来说，行创建的进程都是在前一个进程的基础上PID加上1作为本进程的PID。为了linux平台兼容性，PID一般最大为32767。

1.3 进程内核栈

void *stack

stack用来维护分配给进程的内核栈，内核栈的意义在于，进程task_struct所占的内存是由内核动态分配的，确切的说就是内核根本不给task_struct分配内存，只给内核栈分配8KB内存，并且一部分会提供给task_struct使用。 
task_struct结构体大约占用的大小为1K左右，根据内核版本的不同，大小也会有差异。 
所以，也就可以知道内核栈最大也就是7KB，否则，内核栈会覆盖task_struct结构。

1.4 标记

unsigned int flags

用来反映一个进程的状态信息，但不是运行状态，用于内核识别进程当前的状态，flags的取值如下：

1.5 表示进程亲属关系的成员

struct task_struct *real_parent;
struct task_struct *parent;
struct list_head children;
struct list_head sibling;
struct task_struct *group_leader;

linux系统当中，考虑到进程的派生，所以进程之间会存在父进程和子进程这样的关系，当然，对于同一个父进程派生出来的进程，他们的关系当然是兄弟进程了。

1.6 ptrace系统调用

unsigned int ptrace;
struct list_head ptraced;
struct list_head ptrace_entry;

首先我们要清楚ptrace是什么东西，ptrace是一种提供父进程控制子进程运行，并且可以检查和改变它的核心image。当trace设置为0时不需要被跟踪。

1.7 性能诊断工具——Performance Event

#ifdef CONFIG_PERF_EVENTS
#ifndef __GENKSYMS__
    void * __reserved_perf__;
#else
    struct perf_event_context *perf_event_ctxp;
#endif
    struct mutex perf_event_mutex;
    struct list_head perf_event_list;
#endif

Performance Event是性能诊断工具，这些成员用来帮助它进行分析进程性能问题。

1.8 进程调度

    int prio, static_prio, normal_prio;
    unsigned int rt_priority;

调度进程利用这部分信息决定系统当中的那个进程最应该运行，并且结合进程的状态信息保证系统运作高效。

提到进程调度，当然还需要说明一下进程调度策略，我们来看下关于调度策略的成员：

    unsigned int policy;
    const struct sched_class *sched_class;
    struct sched_entity se;
    struct sched_rt_entity rt;

policy表示进程的调度策略，主要有以下五种：

说完了调度策略，我们再来看一下调度类。

它们的优先级顺序为Stop>rt>fair>idle

1.9进程的地址空间

    struct mm_struct *mm, *active_mm;

对于内核线程切记是没有地址空间的。

后续会有专门的博客来叙述

1.10 判断标志

    //用于进程判断标志
    int exit_state;
    int exit_code, exit_signal;
    int pdeath_signal;  /*  The signal sent when the parent dies  */
    /* ??? */
    unsigned int personality;
    unsigned did_exec:1;
    unsigned in_execve:1;   /* Tell the LSMs that the process is doing an
                 * execve */
    unsigned in_iowait:1;

    /* Revert to default priority/policy when forking */
    unsigned sched_reset_on_fork:1;

1.11 时间与定时器

    //描述CPU时间的内容
    cputime_t utime, stime, utimescaled, stimescaled;
    cputime_t gtime;
    cputime_t prev_utime, prev_stime;
    unsigned long nvcsw, nivcsw; /* context switch counts */
    struct timespec start_time;         /* monotonic time */
    struct timespec real_start_time;    /* boot based time */
    struct task_cputime cputime_expires;
    struct list_head cpu_timers[3];

然后接下来我们来看一下进程的定时器，一共是三种定时器。

进程总过有三种定时器，这三种定时器的特征有到期时间，定时间隔，和要触发的时间，

1.12 信号处理

    struct signal_struct *signal;
    struct sighand_struct *sighand;

    sigset_t blocked, real_blocked;
    sigset_t saved_sigmask; /* restored if set_restore_sigmask() was used */
    struct sigpending pending;

    unsigned long sas_ss_sp;
    size_t sas_ss_size;

关于信号处理：

1.13 文件系统信息

    //文件系统信息结构体
/* filesystem information */
    struct fs_struct *fs;

    //打开文件相关信息结构体
/* open file information */
    struct files_struct *files;

进程可以用来打开和关闭文件，文件属于系统资源，task_struct有两个来描述文件资源，他们会描述两个VFS索引节点，两个节点分别是root和pwd，分别指向根目录和当前的工作目录。

1.14 其他

struct task_struct {
    //进程状态（-1就绪态，0运行态，>0停止态）
    volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */

    //进程内核栈
    void *stack;

    //有几个进程只在使用此结构
    atomic_t usage;

    //标记
    unsigned int flags; /* per process flags, defined below */

    //ptrace系统调用，关于实现断点调试，跟踪进程运行。
    unsigned int ptrace;

    //锁的深度
    int lock_depth;     /* BKL lock depth */

    //SMP实现无加锁的进程切换
#ifdef CONFIG_SMP
#ifdef __ARCH_WANT_UNLOCKED_CTXSW
    int oncpu;
#endif
#endif

    //关于进程调度
    int prio, static_prio, normal_prio;

    //优先级
    unsigned int rt_priority;

    //关于进程
    const struct sched_class *sched_class;
    struct sched_entity se;
    struct sched_rt_entity rt;

    //preempt_notifier结构体链表
#ifdef CONFIG_PREEMPT_NOTIFIERS
    /* list of struct preempt_notifier: */
    struct hlist_head preempt_notifiers;
#endif

    /*
     * fpu_counter contains the number of consecutive context switches
     * that the FPU is used. If this is over a threshold, the lazy fpu
     * saving becomes unlazy to save the trap. This is an unsigned char
     * so that after 256 times the counter wraps and the behavior turns
     * lazy again; this to deal with bursty apps that only use FPU for
     * a short time
     */

     //FPU使用计数
    unsigned char fpu_counter;

    //块设备I/O层的跟踪工具
#ifdef CONFIG_BLK_DEV_IO_TRACE
    unsigned int btrace_seq;
#endif
    //进程调度策略相关的字段
    unsigned int policy;

    cpumask_t cpus_allowed;

    //RCU同步原语
#ifdef CONFIG_TREE_PREEMPT_RCU
    int rcu_read_lock_nesting;
    char rcu_read_unlock_special;
    struct rcu_node *rcu_blocked_node;
    struct list_head rcu_node_entry;
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */

//用于调度器统计进程运行信息
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
    struct sched_info sched_info;
#endif

//用于构架进程链表
    struct list_head tasks;
    struct plist_node pushable_tasks;

    //关于进程的地址空间，指向进程的地址空间。（链表和红黑树）
    struct mm_struct *mm, *active_mm;

/* task state */
    //进程状态参数
    int exit_state;

    //退出信号处理
    int exit_code, exit_signal;

    //接收父进程终止的时候会发送信号
    int pdeath_signal;  /*  The signal sent when the parent dies  */
    /* ??? */
    unsigned int personality;
    unsigned did_exec:1;
    unsigned in_execve:1;   /* Tell the LSMs that the process is doing an
                 * execve */
    unsigned in_iowait:1;

    /* Revert to default priority/policy when forking */
    unsigned sched_reset_on_fork:1;

    //进程pid，父进程ppid。
    pid_t pid;
    pid_t tgid;

    //防止内核堆栈溢出
#ifdef CONFIG_CC_STACKPROTECTOR
    /* Canary value for the -fstack-protector gcc feature */
    unsigned long stack_canary;
#endif

    /*
     * pointers to (original) parent process, youngest child, younger sibling,
     * older sibling, respectively.  (p->father can be replaced with
     * p->real_parent->pid)
     */

     //这部分是用来进行维护进程之间的亲属关系的。
     //初始化父进程
    struct task_struct *real_parent; /* real parent process */
    //接纳终止的进程
    struct task_struct *parent; /* recipient of SIGCHLD, wait4() reports */
    /*
     * children/sibling forms the list of my natural children
     */
     //维护子进程链表
    struct list_head children;  /* list of my children */
    //兄弟进程链表
    struct list_head sibling;   /* linkage in my parent‘s children list */
    //线程组组长
    struct task_struct *group_leader;   /* threadgroup leader */

    /*
     * ptraced is the list of tasks this task is using ptrace on.
     * This includes both natural children and PTRACE_ATTACH targets.
     * p->ptrace_entry is p‘s link on the p->parent->ptraced list.
     */

     //ptrace，系统调用，关于断点调试。
    struct list_head ptraced;
    struct list_head ptrace_entry;

    //PID与PID散列表的联系
    /* PID/PID hash table linkage. */
    struct pid_link pids[PIDTYPE_MAX];

    //维护一个链表，里面有该进程所有的线程
    struct list_head thread_group;

    //do_fork()函数
    struct completion *vfork_done;      /* for vfork() */
    int __user *set_child_tid;      /* CLONE_CHILD_SETTID */
    int __user *clear_child_tid;        /* CLONE_CHILD_CLEARTID */

    //描述CPU时间的内容
    //utime是用户态下的执行时间
    //stime是内核态下的执行时间
    cputime_t utime, stime, utimescaled, stimescaled;
    cputime_t gtime;
    cputime_t prev_utime, prev_stime;

    //上下文切换计数
    unsigned long nvcsw, nivcsw; /* context switch counts */
    struct timespec start_time;         /* monotonic time */
    struct timespec real_start_time;    /* boot based time */
/* mm fault and swap info: this can arguably be seen as either mm-specific or thread-specific */

    //缺页统计
    unsigned long min_flt, maj_flt;

    struct task_cputime cputime_expires;
    struct list_head cpu_timers[3];

/* process credentials */

//进程身份凭据
    const struct cred *real_cred;   /* objective and real subjective task
                     * credentials (COW) */
    const struct cred *cred;    /* effective (overridable) subjective task
                     * credentials (COW) */
    struct mutex cred_guard_mutex;  /* guard against foreign influences on
                     * credential calculations
                     * (notably. ptrace) */
    struct cred *replacement_session_keyring; /* for KEYCTL_SESSION_TO_PARENT */

    //去除路径以后的可执行文件名称，进程名
    char comm[TASK_COMM_LEN]; /* executable name excluding path
                     - access with [gs]et_task_comm (which lock
                       it with task_lock())
                     - initialized normally by setup_new_exec */
/* file system info */

    //文件系统信息
    int link_count, total_link_count;
#ifdef CONFIG_SYSVIPC
/* ipc stuff */
//进程通信
    struct sysv_sem sysvsem;
#endif
#ifdef CONFIG_DETECT_HUNG_TASK
/* hung task detection */
    unsigned long last_switch_count;
#endif

//该进程在特点CPU下的状态
/* CPU-specific state of this task */
    struct thread_struct thread;

    //文件系统信息结构体
/* filesystem information */
    struct fs_struct *fs;

    //打开文件相关信息结构体
/* open file information */
    struct files_struct *files;
/* namespaces */
//命名空间：
    struct nsproxy *nsproxy;
/* signal handlers */

    //关于进行信号处理
    struct signal_struct *signal;
    struct sighand_struct *sighand;

    sigset_t blocked, real_blocked;
    sigset_t saved_sigmask; /* restored if set_restore_sigmask() was used */
    struct sigpending pending;

    unsigned long sas_ss_sp;
    size_t sas_ss_size;
    int (*notifier)(void *priv);
    void *notifier_data;
    sigset_t *notifier_mask;

    //进程审计
    struct audit_context *audit_context;
#ifdef CONFIG_AUDITSYSCALL
    uid_t loginuid;
    unsigned int sessionid;
#endif
    seccomp_t seccomp;

#ifdef CONFIG_UTRACE
    struct utrace *utrace;
    unsigned long utrace_flags;
#endif

//线程跟踪组
/* Thread group tracking */
    u32 parent_exec_id;
    u32 self_exec_id;
/* Protection of (de-)allocation: mm, files, fs, tty, keyrings, mems_allowed,
 * mempolicy */
    spinlock_t alloc_lock;

    //中断
#ifdef CONFIG_GENERIC_HARDIRQS
    /* IRQ handler threads */
    struct irqaction *irqaction;
#endif

//task_rq_lock函数所使用的锁
    /* Protection of the PI data structures: */
    spinlock_t pi_lock;

    //基于PI协议的等待互斥锁
#ifdef CONFIG_RT_MUTEXES
    /* PI waiters blocked on a rt_mutex held by this task */
    struct plist_head pi_waiters;
    /* Deadlock detection and priority inheritance handling */
    struct rt_mutex_waiter *pi_blocked_on;
#endif

//死锁检测
#ifdef CONFIG_DEBUG_MUTEXES
    /* mutex deadlock detection */
    struct mutex_waiter *blocked_on;
#endif

//中断
#ifdef CONFIG_TRACE_IRQFLAGS
    unsigned int irq_events;
    int hardirqs_enabled;
    unsigned long hardirq_enable_ip;
    unsigned int hardirq_enable_event;
    unsigned long hardirq_disable_ip;
    unsigned int hardirq_disable_event;
    int softirqs_enabled;
    unsigned long softirq_disable_ip;
    unsigned int softirq_disable_event;
    unsigned long softirq_enable_ip;
    unsigned int softirq_enable_event;
    int hardirq_context;
    int softirq_context;
#endif

//lockdep
#ifdef CONFIG_LOCKDEP
# define MAX_LOCK_DEPTH 48UL
    u64 curr_chain_key;
    int lockdep_depth;
    unsigned int lockdep_recursion;
    struct held_lock held_locks[MAX_LOCK_DEPTH];
    gfp_t lockdep_reclaim_gfp;
#endif

//日志文件
/* journalling filesystem info */

    void *journal_info;

/* stacked block device info */
    //块设备链表
    struct bio *bio_list, **bio_tail;

/* VM state */
    //虚拟内存状态，内存回收
    struct reclaim_state *reclaim_state;

    //存放块设备I/O流量信息
    struct backing_dev_info *backing_dev_info;

    //I/O调度器所用信息
    struct io_context *io_context;

    unsigned long ptrace_message;
    siginfo_t *last_siginfo; /* For ptrace use.  */

    //记录进程I/O计数
    struct task_io_accounting ioac;
#if defined(CONFIG_TASK_XACCT)
    u64 acct_rss_mem1;  /* accumulated rss usage */
    u64 acct_vm_mem1;   /* accumulated virtual memory usage */
    cputime_t acct_timexpd; /* stime + utime since last update */
#endif

    //CPUSET功能
#ifdef CONFIG_CPUSETS
    nodemask_t mems_allowed;    /* Protected by alloc_lock */
#ifndef __GENKSYMS__
    /*
     * This does not change the size of the struct_task(2+2+4=4+4)
     * so the offsets of the remaining fields are unchanged and
     * therefore the kABI is preserved.  Only the kernel uses
     * cpuset_mem_spread_rotor and cpuset_slab_spread_rotor so
     * it is safe to change it to use shorts instead of ints.
     */
    unsigned short cpuset_mem_spread_rotor;
    unsigned short cpuset_slab_spread_rotor;
    int mems_allowed_change_disable;
#else
    int cpuset_mem_spread_rotor;
    int cpuset_slab_spread_rotor;
#endif
#endif

//Control Groups
#ifdef CONFIG_CGROUPS
    /* Control Group info protected by css_set_lock */
    struct css_set *cgroups;
    /* cg_list protected by css_set_lock and tsk->alloc_lock */
    struct list_head cg_list;
#endif

//futex同步机制
#ifdef CONFIG_FUTEX
    struct robust_list_head __user *robust_list;
#ifdef CONFIG_COMPAT
    struct compat_robust_list_head __user *compat_robust_list;
#endif
    struct list_head pi_state_list;
    struct futex_pi_state *pi_state_cache;
#endif

//关于内存检测工具Performance Event
#ifdef CONFIG_PERF_EVENTS
#ifndef __GENKSYMS__
    void * __reserved_perf__;
#else
    struct perf_event_context *perf_event_ctxp;
#endif
    struct mutex perf_event_mutex;
    struct list_head perf_event_list;
#endif

    //非一致内存访问
#ifdef CONFIG_NUMA
    struct mempolicy *mempolicy;    /* Protected by alloc_lock */
    short il_next;
#endif

    //文件系统互斥资源
    atomic_t fs_excl;   /* holding fs exclusive resources */

    //RCU链表
    struct rcu_head rcu;

    /*
     * cache last used pipe for splice
     */

     //管道
    struct pipe_inode_info *splice_pipe;

    //延迟计数
#ifdef  CONFIG_TASK_DELAY_ACCT
    struct task_delay_info *delays;
#endif
#ifdef CONFIG_FAULT_INJECTION
    int make_it_fail;
#endif
    struct prop_local_single dirties;
#ifdef CONFIG_LATENCYTOP
    int latency_record_count;
    struct latency_record latency_record[LT_SAVECOUNT];
#endif
    /*
     * time slack values; these are used to round up poll() and
     * select() etc timeout values. These are in nanoseconds.
     */

     //time slack values,常用于poll和select函数
    unsigned long timer_slack_ns;
    unsigned long default_timer_slack_ns;

    //socket控制消息
    struct list_head    *scm_work_list;
#ifdef CONFIG_FUNCTION_GRAPH_TRACER

    //ftrace跟踪器
    /* Index of current stored adress in ret_stack */
    int curr_ret_stack;
    /* Stack of return addresses for return function tracing */
    struct ftrace_ret_stack *ret_stack;
    /* time stamp for last schedule */
    unsigned long long ftrace_timestamp;
    /*
     * Number of functions that haven‘t been traced
     * because of depth overrun.
     */
    atomic_t trace_overrun;
    /* Pause for the tracing */
    atomic_t tracing_graph_pause;
#endif
#ifdef CONFIG_TRACING
    /* state flags for use by tracers */
    unsigned long trace;
    /* bitmask of trace recursion */
    unsigned long trace_recursion;
#endif /* CONFIG_TRACING */
    /* reserved for Red Hat */
    unsigned long rh_reserved[2];
#ifndef __GENKSYMS__
    struct perf_event_context *perf_event_ctxp[perf_nr_task_contexts];
#ifdef CONFIG_CGROUP_MEM_RES_CTLR /* memcg uses this to do batch job */
    struct memcg_batch_info {
        int do_batch;   /* incremented when batch uncharge started */
        struct mem_cgroup *memcg; /* target memcg of uncharge */
        unsigned long bytes;        /* uncharged usage */
        unsigned long memsw_bytes; /* uncharged mem+swap usage */
    } memcg_batch;
#endif
#endif
};

如果需要，可从github处取走注释源码：https://github.com/wsy081414/C_linux_practice/blob/master/task_struct.h