Linux系統中無論是進程還是線程都統一叫任務，有一個統一的結構task_struct進行管理。
linnux中關於task_struct的定義如下
Struct task_struct{
/* -1 unrunnable, 0 runnable, >0 stopped: */
volatile long state;
/*
* This begins the randomizable portion of task_struct. Only
* scheduling-critical items should be added above here.
*/
randomized_struct_fields_start
void *stack;
atomic_t usage;
/* Per task flags (PF_*), defined further below: */
unsigned int flags;
unsigned int ptrace;
int on_rq;
int prio;
int static_prio;
int normal_prio;
unsigned int rt_priority;
const struct sched_class *sched_class;
struct sched_entity se;
struct sched_rt_entity rt;
struct sched_dl_entity dl;
unsigned int policy;
int nr_cpus_allowed;
cpumask_t cpus_allowed;
struct sched_info sched_info;
struct list_head tasks;
struct mm_struct *mm;
struct mm_struct *active_mm;
/* Per-thread vma caching: */
struct vmacache vmacache;
int exit_state;
int exit_code;
int exit_signal;
/* The signal sent when the parent dies: */
int pdeath_signal;
/* JOBCTL_*, siglock protected: */
unsigned long jobctl;
/* Used for emulating ABI behavior of previous Linux versions: */
unsigned int personality;
/* Scheduler bits, serialized by scheduler locks: */
unsigned sched_reset_on_fork:1;
unsigned sched_contributes_to_load:1;
unsigned sched_migrated:1;
unsigned sched_remote_wakeup:1;
/* Force alignment to the next boundary: */
unsigned :0;
/* Unserialized, strictly 'current' */
/* Bit to tell LSMs we're in execve(): */
unsigned in_execve:1;
unsigned in_iowait:1;
unsigned long atomic_flags; /* Flags requiring atomic access. */
struct restart_block restart_block;
pid_t pid;
pid_t tgid;
/* Real parent process: */
struct task_struct __rcu *real_parent;
/* Recipient of SIGCHLD, wait4() reports: */
struct task_struct __rcu *parent;
/*
* Children/sibling form the list of natural children:
*/
struct list_head children;
struct list_head sibling;
struct task_struct *group_leader;
/*
* 'ptraced' is the list of tasks this task is using ptrace() on.
*
* This includes both natural children and PTRACE_ATTACH targets.
* 'ptrace_entry' is this task's link on the p->parent->ptraced list.
*/
struct list_head ptraced;
struct list_head ptrace_entry;
/* PID/PID hash table linkage. */
struct pid *thread_pid;
struct hlist_node pid_links[PIDTYPE_MAX];
struct list_head thread_group;
struct list_head thread_node;
struct completion *vfork_done;
/* CLONE_CHILD_SETTID: */
int __user *set_child_tid;
/* CLONE_CHILD_CLEARTID: */
int __user *clear_child_tid;
u64 utime;
u64 stime;
u64 gtime;
struct prev_cputime prev_cputime;
/* Context switch counts: */
unsigned long nvcsw;
unsigned long nivcsw;
/* Monotonic time in nsecs: */
u64 start_time;
/* Boot based time in nsecs: */
u64 real_start_time;
/* MM fault and swap info: this can arguably be seen as either mm-specific or thread-specific: */
unsigned long min_flt;
unsigned long maj_flt;
/* Process credentials: */
/* Tracer's credentials at attach: */
const struct cred __rcu *ptracer_cred;
/* Objective and real subjective task credentials (COW): */
const struct cred __rcu *real_cred;
/* Effective (overridable) subjective task credentials (COW): */
const struct cred __rcu *cred;
/*
* executable name, excluding path.
*
* - normally initialized setup_new_exec()
* - access it with [gs]et_task_comm()
* - lock it with task_lock()
*/
char comm[TASK_COMM_LEN];
struct nameidata *nameidata;
/* Filesystem information: */
struct fs_struct *fs;
/* Open file information: */
struct files_struct *files;
/* Namespaces: */
struct nsproxy *nsproxy;
/* Signal handlers: */
struct signal_struct *signal;
struct sighand_struct *sighand;
sigset_t blocked;
sigset_t real_blocked;
/* Restored if set_restore_sigmask() was used: */
sigset_t saved_sigmask;
struct sigpending pending;
unsigned long sas_ss_sp;
size_t sas_ss_size;
unsigned int sas_ss_flags;
struct callback_head *task_works;
struct audit_context *audit_context;
struct seccomp seccomp;
/* Thread group tracking: */
u32 parent_exec_id;
u32 self_exec_id;
/* Protection against (de-)allocation: mm, files, fs, tty, keyrings, mems_allowed, mempolicy: */
spinlock_t alloc_lock;
/* Protection of the PI data structures: */
raw_spinlock_t pi_lock;
struct wake_q_node wake_q;
/* Journalling filesystem info: */
void *journal_info;
/* Stacked block device info: */
struct bio_list *bio_list;
/* VM state: */
struct reclaim_state *reclaim_state;
struct backing_dev_info *backing_dev_info;
struct io_context *io_context;
/* Ptrace state: */
unsigned long ptrace_message;
siginfo_t *last_siginfo;
struct task_io_accounting ioac;
struct tlbflush_unmap_batch tlb_ubc;
struct rcu_head rcu;
/* Cache last used pipe for splice(): */
struct pipe_inode_info *splice_pipe;
struct page_frag task_frag;
#ifdef CONFIG_FAULT_INJECTION
int make_it_fail;
unsigned int fail_nth;
#endif
/*
* When (nr_dirtied >= nr_dirtied_pause), it's time to call
* balance_dirty_pages() for a dirty throttling pause:
*/
int nr_dirtied;
int nr_dirtied_pause;
/* Start of a write-and-pause period: */
unsigned long dirty_paused_when;
#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.
*/
u64 timer_slack_ns;
u64 default_timer_slack_ns;
#ifdef CONFIG_KASAN
unsigned int kasan_depth;
#endif
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/* Index of current stored address in ret_stack: */
int curr_ret_stack;
/* Stack of return addresses for return function tracing: */
struct ftrace_ret_stack *ret_stack;
/* Timestamp 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 tracing: */
atomic_t tracing_graph_pause;
#endif
#ifdef CONFIG_TRACING
/* State flags for use by tracers: */
unsigned long trace;
/* Bitmask and counter of trace recursion: */
unsigned long trace_recursion;
#endif /* CONFIG_TRACING */
#ifdef CONFIG_KCOV
/* Coverage collection mode enabled for this task (0 if disabled): */
unsigned int kcov_mode;
/* Size of the kcov_area: */
unsigned int kcov_size;
/* Buffer for coverage collection: */
void *kcov_area;
/* KCOV descriptor wired with this task or NULL: */
struct kcov *kcov;
#endif
#ifdef CONFIG_MEMCG
struct mem_cgroup *memcg_in_oom;
gfp_t memcg_oom_gfp_mask;
int memcg_oom_order;
/* Number of pages to reclaim on returning to userland: */
unsigned int memcg_nr_pages_over_high;
/* Used by memcontrol for targeted memcg charge: */
struct mem_cgroup *active_memcg;
#endif
#ifdef CONFIG_BLK_CGROUP
struct request_queue *throttle_queue;
#endif
#ifdef CONFIG_UPROBES
struct uprobe_task *utask;
#endif
#if defined(CONFIG_BCACHE) || defined(CONFIG_BCACHE_MODULE)
unsigned int sequential_io;
unsigned int sequential_io_avg;
#endif
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
unsigned long task_state_change;
#endif
int pagefault_disabled;
#ifdef CONFIG_MMU
struct task_struct *oom_reaper_list;
#endif
#ifdef CONFIG_VMAP_STACK
struct vm_struct *stack_vm_area;
#endif
#ifdef CONFIG_THREAD_INFO_IN_TASK
/* A live task holds one reference: */
atomic_t stack_refcount;
#endif
#ifdef CONFIG_LIVEPATCH
int patch_state;
#endif
#ifdef CONFIG_SECURITY
/* Used by LSM modules for access restriction: */
void *security;
#endif
/*
* New fields for task_struct should be added above here, so that
* they are included in the randomized portion of task_struct.
*/
randomized_struct_fields_end
/* CPU-specific state of this task: */
struct thread_struct thread;
/*
* WARNING: on x86, 'thread_struct' contains a variable-sized
* structure. It *MUST* be at the end of 'task_struct'.
*
* Do not put anything below here!
*/
}
下面將逐個介紹重要的成員變量
任務鏈表
struct list_head tasks;//進程鏈表，將所有的進程串起來
進程ID
task_struct中涉及ID 的有下面幾個
pid_t pid;//process id
pid_t tgid;//thread group id
struct task_struct *group_leader;
信號處理
關於信號處理的字段如下:
/* Signal handlers: */
struct signal_struct *signal;
struct sighand_struct *sighand;//正通過信號處理函數進行處理的信號
sigset_t blocked;//被阻塞不處理的信號
sigset_t real_blocked;
/* Restored if set_restore_sigmask() was used: */
sigset_t saved_sigmask;
struct sigpending pending;//尚等待處理的信號
unsigned long sas_ss_sp;
size_t sas_ss_size;
unsigned int sas_ss_flags;
進程狀態
在task_struct中涉及任務狀態的是下面幾個變量
/* -1 unrunnable, 0 runnable, >0 stopped: */
volatile long state;
unsigned int flags;
int exit_state;
其中其中state的可以取值定義在/include/linux/sched.h頭文件中
/* Used in tsk->state: */
#define TASK_RUNNING 0x0000
#define TASK_INTERRUPTIBLE 0x0001
#define TASK_UNINTERRUPTIBLE 0x0002
#define __TASK_STOPPED 0x0004
#define __TASK_TRACED 0x0008
/* Used in tsk->exit_state: */
#define EXIT_DEAD 0x0010
#define EXIT_ZOMBIE 0x0020
#define EXIT_TRACE (EXIT_ZOMBIE | EXIT_DEAD)
/* Used in tsk->state again: */
#define TASK_PARKED 0x0040
#define TASK_DEAD 0x0080
#define TASK_WAKEKILL 0x0100
#define TASK_WAKING 0x0200
#define TASK_NOLOAD 0x0400
#define TASK_NEW 0x0800
#define TASK_STATE_MAX 0x1000
#define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
#define TASK_STOPPED (TASK_WAKEKILL | __TASK_STOPPED)
#define TASK_TRACED (TASK_WAKEKILL | __TASK_TRACED)
#define TASK_IDLE (TASK_UNINTERRUPTIBLE | TASK_NOLOAD)
/* Convenience macros for the sake of wake_up(): */
#define TASK_NORMAL (TASK_INTERRUPTIBLE | TASK_UNINTERRUPTIBLE)
其中
TASK_RUNNING： 並不是說進程正在運行，而是表示進程時刻準備運行的狀態。
TASK_INTERRUPTIBLE：表示可以中斷的睡眠狀態，這是一種淺睡眠狀態，儘管是在睡眠當等待的時間沒有到來這時候又有信號來的時候進程還是會被喚醒，喚醒後不是繼續原來的動作而是響應信號處理。
TASK_UNINTERRUPTIBLE： 是不可中斷的睡眠狀態，深度睡眠狀態不樂可以被信號喚醒，只能死等要等待的事件到來，linux系統中應儘量避免這種狀態的出現。
TASK_KILLABLE：則是可以終止的睡眠狀態
TASK_STOPPED：是進程收到SIGSTOP、SIGTTIN、SIGTSTP或者SIGTTOU信號之後進入該狀態
TASK_TRACED：表示進程被debugger等進程監視，進程執行被調試程序所停止的狀態。
進程調度
進程調度相關的字段主要如下
int on_rq;//是否在運行隊列上
//優先級相關
int prio;
int static_prio;
int normal_prio;
unsigned int rt_priority;
//調度器類
const struct sched_class *sched_class;
//調度實體
struct sched_entity se;
struct sched_rt_entity rt;
struct sched_dl_entity dl;
//調度策略
unsigned int policy;
//可以使用那些CPU
int nr_cpus_allowed;
cpumask_t cpus_allowed;
struct sched_info sched_info;
運行統計信息
進程的運行需要一些統計量，這些信息包括了進程在用戶態和內核態消耗的時間，上下文切換的次數等，具體信息如下：
u64 utime;//用戶態消耗的CPU時間
u64 stime;//內核態消耗的CPU時間
/* Context switch counts: */
unsigned long nvcsw;//自願上下文切換的次數
unsigned long nivcsw;//非自願上下文切換的次數
/* Monotonic time in nsecs: */
u64 start_time;//進程啓動時間，不包含睡眠時間
/* Boot based time in nsecs: */
u64 real_start_time;//進程啓動時間包含了睡眠時間
進程親緣關係
每一個進程都有一個父進程，同樣也會有兄弟進程。進程親緣關係變量如下：
/* Real parent process: */
struct task_struct __rcu *real_parent;
/* Recipient of SIGCHLD, wait4() reports: */
struct task_struct __rcu *parent;
/*
* Children/sibling form the list of natural children:
*/
struct list_head children;
struct list_head sibling;
parent指向其父進程，當它終止時，必須向父進程發送信息
children表示鏈表的頭部，鏈表中所有的元素都是該進程的子進程
sibling用於把當前進程插入到兄弟鏈表中
通常情況下real_parent和parent是一樣的。
進程親緣關係可以用下圖來表示
進程權限
在linux中，對於進程權限的定義如下：
/* Process credentials: */
/* Tracer's credentials at attach: */
const struct cred __rcu *ptracer_cred;
/* Objective and real subjective task credentials (COW): */
const struct cred __rcu *real_cred;
/* Effective (overridable) subjective task credentials (COW): */
const struct cred __rcu *cred;
上面的註釋信息中Objective表示誰能操作我，real_cred就是說明誰能操作我這個進程；
cred就是說明我這個進程能操作誰。該結構體的詳細定義如下：
Struct crud{
atomic_t usage;
kuid_t uid; /* real UID of the task */
kgid_t gid; /* real GID of the task */
kuid_t suid; /* saved UID of the task */
kgid_t sgid; /* saved GID of the task */
kuid_t euid; /* effective UID of the task */
kgid_t egid; /* effective GID of the task */
kuid_t fsuid; /* UID for VFS ops */
kgid_t fsgid; /* GID for VFS ops */
unsigned securebits; /* SUID-less security management */
kernel_cap_t cap_inheritable; /* caps our children can inherit */
kernel_cap_t cap_permitted; /* caps we're permitted */
kernel_cap_t cap_effective; /* caps we can actually use */
kernel_cap_t cap_bset; /* capability bounding set */
kernel_cap_t cap_ambient; /* Ambient capability set */
struct user_struct *user; /* real user ID subscription */
struct user_namespace *user_ns; /* user_ns the caps and keyrings are relative to. */
struct group_info *group_info; /* supplementary groups for euid/fsgid */
struct rcu_head rcu; /* RCU deletion hook */
}
該結構體大部分是關於用戶和用於所屬的用戶組的信息。
內存管理
每個進程都有自己獨立的虛擬內存空間，這需要一個數據結構來表示，這個結構就是mm_struct。
struct mm_struct *mm;
struct mm_struct *active_mm;
文件與文件系統
每個進程都一個文件系統的數據結構，還有一個打開文件的數據結構，具體如下
/* Filesystem information: */
struct fs_struct *fs;
/* Open file information: */
struct files_struct *files;
總結
進程數據結構比較複雜 下面的結構圖清晰的描述了進程數據結構各個主要字段的意義
