進程之task_struct

進程

可以把進程當成一組元素組成的實體，進程的兩個基本元素程序代碼和與代碼相關的數據集。假設處理器開始執行這個程序代碼，且我們把這個執行實體稱爲進程。那麼，在程序執行時，任意給定一個時間，進程都可以唯一的被表徵爲以下元素：

1、標識符：跟這個進程相關的唯一標識符，用來區別其他進程

2、狀態：進程此時的狀態

3、優先級：相對於其他進程的優先級

4、程序計數器：程序中即將被執行的下一跳指令的地址

5、內存指針：包括程序代碼和進程進程相關數據的指針，以及和其他進程共享內存塊的指針

6、上下文數據：進程執行時處理器中寄存器中的數據

7、i/o口狀態信息：

8、記賬信息

進程控制塊 PCB

PCB是一種數據結構，這個數據結構用來存放進程的控制和管理信息

linux中定義一個PCB類型的結構體task_struct存放進程的相關信息；

那麼在task_struct中具體存放哪些信息呢？

再centos6.5中，在其內核中可找到此結構體：

其在的目錄爲：

打開sched.h就可找到task_struct結構體所包含的內容：

struct task_struct {
    //進程狀態（-1就緒態，0運行態，>0停止態）
    volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */

    //進程內核棧
    void *stack;

    //有幾個進程只在使用此結構
    atomic_t usage;

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

    //ptrace系統調用，關於實現斷點調試，跟蹤進程運行。
    unsigned int ptrace;

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

    //SMP實現無加鎖的進程切換
#ifdef CONFIG_SMP
#ifdef __ARCH_WANT_UNLOCKED_CTXSW
    int oncpu;
#endif
#endif

    //關於進程調度
    int prio, static_prio, normal_prio;

    //優先級
    unsigned int rt_priority;

    //關於進程
    const struct sched_class *sched_class;
    struct sched_entity se;
    struct sched_rt_entity rt;

    //preempt_notifier結構體鏈表
#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使用計數
    unsigned char fpu_counter;

    //塊設備I/O層的跟蹤工具
#ifdef CONFIG_BLK_DEV_IO_TRACE
    unsigned int btrace_seq;
#endif
    //進程調度策略相關的字段
    unsigned int policy;

    cpumask_t cpus_allowed;

    //RCU同步原語
#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 */

//用於調度器統計進程運行信息
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
    struct sched_info sched_info;
#endif

//用於構架進程鏈表
    struct list_head tasks;
    struct plist_node pushable_tasks;

    //關於進程的地址空間，指向進程的地址空間。（鏈表和紅黑樹）
    struct mm_struct *mm, *active_mm;

/* task state */
    //進程狀態參數
    int exit_state;

    //退出信號處理
    int exit_code, exit_signal;

    //接收父進程終止的時候會發送信號
    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;

    //進程pid，父進程ppid。
    pid_t pid;
    pid_t tgid;

    //防止內核堆棧溢出
#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)
     */

     //這部分是用來進行維護進程之間的親屬關係的。
     //初始化父進程
    struct task_struct *real_parent; /* real parent process */
    //接納終止的進程
    struct task_struct *parent; /* recipient of SIGCHLD, wait4() reports */
    /*
     * children/sibling forms the list of my natural children
     */
     //維護子進程鏈表
    struct list_head children;  /* list of my children */
    //兄弟進程鏈表
    struct list_head sibling;   /* linkage in my parent's children list */
    //線程組組長
    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，系統調用，關於斷點調試。
    struct list_head ptraced;
    struct list_head ptrace_entry;

    //PID與PID散列表的聯繫
    /* PID/PID hash table linkage. */
    struct pid_link pids[PIDTYPE_MAX];

    //維護一個鏈表，裏面有該進程所有的線程
    struct list_head thread_group;

    //do_fork()函數
    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時間的內容
    //utime是用戶態下的執行時間
    //stime是內核態下的執行時間
    cputime_t utime, stime, utimescaled, stimescaled;
    cputime_t gtime;
    cputime_t prev_utime, prev_stime;

    //上下文切換計數
    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 */

    //缺頁統計
    unsigned long min_flt, maj_flt;

    struct task_cputime cputime_expires;
    struct list_head cpu_timers[3];

/* process credentials */

//進程身份憑據
    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 */

    //去除路徑以後的可執行文件名稱，進程名
    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 */

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

//該進程在特點CPU下的狀態
/* CPU-specific state of this task */
    struct thread_struct thread;

    //文件系統信息結構體
/* filesystem information */
    struct fs_struct *fs;

    //打開文件相關信息結構體
/* open file information */
    struct files_struct *files;
/* namespaces */
//命名空間：
    struct nsproxy *nsproxy;
/* signal handlers */

    //關於進行信號處理
    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;

    //進程審計
    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

//線程跟蹤組
/* 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;

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

//task_rq_lock函數所使用的鎖
    /* Protection of the PI data structures: */
    spinlock_t pi_lock;

    //基於PI協議的等待互斥鎖
#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

//死鎖檢測
#ifdef CONFIG_DEBUG_MUTEXES
    /* mutex deadlock detection */
    struct mutex_waiter *blocked_on;
#endif

//中斷
#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

//日誌文件
/* journalling filesystem info */

    void *journal_info;

/* stacked block device info */
    //塊設備鏈表
    struct bio *bio_list, **bio_tail;

/* VM state */
    //虛擬內存狀態，內存回收
    struct reclaim_state *reclaim_state;

    //存放塊設備I/O流量信息
    struct backing_dev_info *backing_dev_info;

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

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

    //記錄進程I/O計數
    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同步機制
#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

//關於內存檢測工具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

    //非一致內存訪問
#ifdef CONFIG_NUMA
    struct mempolicy *mempolicy;    /* Protected by alloc_lock */
    short il_next;
#endif

    //文件系統互斥資源
    atomic_t fs_excl;   /* holding fs exclusive resources */

    //RCU鏈表
    struct rcu_head rcu;

    /*
     * cache last used pipe for splice
     */

     //管道
    struct pipe_inode_info *splice_pipe;

    //延遲計數
#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,常用於poll和select函數
    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跟蹤器
    /* 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
};