进程之task_struct

进程

可以把进程当成一组元素组成的实体，进程的两个基本元素程序代码和与代码相关的数据集。假设处理器开始执行这个程序代码，且我们把这个执行实体称为进程。那么，在程序执行时，任意给定一个时间，进程都可以唯一的被表征为以下元素：

1、标识符：跟这个进程相关的唯一标识符，用来区别其他进程

2、状态：进程此时的状态

3、优先级：相对于其他进程的优先级

4、程序计数器：程序中即将被执行的下一跳指令的地址

5、内存指针：包括程序代码和进程进程相关数据的指针，以及和其他进程共享内存块的指针

6、上下文数据：进程执行时处理器中寄存器中的数据

7、i/o口状态信息：

8、记账信息

进程控制块 PCB

PCB是一种数据结构，这个数据结构用来存放进程的控制和管理信息

linux中定义一个PCB类型的结构体task_struct存放进程的相关信息；

那么在task_struct中具体存放哪些信息呢？

再centos6.5中，在其内核中可找到此结构体：

其在的目录为：

打开sched.h就可找到task_struct结构体所包含的内容：

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};