代码

当内核要根据我们的PID导出对应PCB的时候，遍历进程链表检查PCB中的PID太慢了，于是引入了哈希表，Linux OS中用了一个叫做pid_hashfn的宏，来实现把PID转换成表的索引的哈希函数。在这里献上一个内核模块，功能为遍历进程链表，打印pcb相关字段的内核模块，并配上详细注释：

# include <linux/kernel.h>
# include <linux/module.h>
# include <uapi/linux/sched.h>
# include <linux/init_task.h>
# include <linux/init.h>
# include <linux/fdtable.h>
# include <linux/fs_struct.h>
# include <linux/mm_types.h>
//内核模块初始化函数
static int __init traverse_pcb(void)
{struct task_struct *task, *p;//定义指向task_struct类型的指针struct list_head *pos;//定义双向链表指针int count=0;//定义统计系统进程个数的变量printk("Printf process'message begin:\n");//提示模块开始运行task = &init_task;//指向0号进程的PCBlist_for_each(pos,&task->tasks)//使用list_for_each宏来遍历进程链表{p = list_entry(pos,struct task_struct,tasks);//指向当前进程的task_struct结构count++;//统计系统进程个数printk("\n\n");//方便查看后续打印信息/*打印task_struct中的字段，其中pid：进程的pid号；state：进程的状态；prio:动态优先级；static_prio:静态优先级; parent'pid:父进程的pid号；count:文件系统信息，文件被使用的次数; umask:进程权限位的默认设置;使用atomic_read原子操作是为了(p->files)->count字段计数不被打断*/printk("pid:%d; state:%lx; prio:%d; static_prio:%d; parent'pid:%d; count:%d; umask:%d;",    \p->pid,p->state,p->prio,p->static_prio,(p->parent)->pid,                             \atomic_read((&(p->files)->count)),(p->fs)->umask);//打印进程地址空间的信息if((p->mm)!=NULL)printk("total_vm:%ld;",(p->mm)->total_vm);//total_vm：线性区总的页数}printk("进程的个数：%d\n",count);//打印进程个数return 0;
}//内核模块退出函数
static void __exit end_pcb(void)
{printk("traverse pcb is end.");
}
module_init(traverse_pcb);//入口
module_exit(end_pcb);//出口
MODULE_LICENSE("GPL");//许可证

makefile

#产生目标文件
obj-m:=traverse_pcb.o
#路径变量，指明当前路径
CURRENT_PATH:=$(shell pwd)
#指明内核版本号
LINUX_KERNEL:=$(shell uname -r)
#指明内核源码的绝对路径
LINUX_KERNEL_PATH:=/usr/src/linux-headers-$(LINUX_KERNEL)
#编译模块
all:make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) modules
#清理模块
clean:make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) clean

每个进程的pid号，进程的状态，动态优先级，静态优先级，父进程的pid号，文件系统信息（文件被使用的次数），进程权限位的默认设置，总进程数等。有些进程的total_vm是空的，说明他们是内核线程。

附上linux内核4.20.11源代码

sched.h include\linux 53922 2/20/2019 208

struct task_struct {
#ifdef CONFIG_THREAD_INFO_IN_TASK/** For reasons of header soup (see current_thread_info()), this* must be the first element of task_struct.*/struct thread_info        thread_info;
#endif/* -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_startvoid              *stack;atomic_t         usage;/* Per task flags (PF_*), defined further below: */unsigned int           flags;unsigned int          ptrace;#ifdef CONFIG_SMPstruct llist_node       wake_entry;int              on_cpu;
#ifdef CONFIG_THREAD_INFO_IN_TASK/* Current CPU: */unsigned int         cpu;
#endifunsigned int          wakee_flips;unsigned long           wakee_flip_decay_ts;struct task_struct      *last_wakee;/** recent_used_cpu is initially set as the last CPU used by a task* that wakes affine another task. Waker/wakee relationships can* push tasks around a CPU where each wakeup moves to the next one.* Tracking a recently used CPU allows a quick search for a recently* used CPU that may be idle.*/int                recent_used_cpu;int             wake_cpu;
#endifint               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;
#ifdef CONFIG_CGROUP_SCHEDstruct task_group     *sched_task_group;
#endifstruct sched_dl_entity        dl;#ifdef CONFIG_PREEMPT_NOTIFIERS/* List of struct preempt_notifier: */struct hlist_head       preempt_notifiers;
#endif#ifdef CONFIG_BLK_DEV_IO_TRACEunsigned int            btrace_seq;
#endifunsigned int          policy;int              nr_cpus_allowed;cpumask_t           cpus_allowed;#ifdef CONFIG_PREEMPT_RCUint               rcu_read_lock_nesting;union rcu_special     rcu_read_unlock_special;struct list_head        rcu_node_entry;struct rcu_node          *rcu_blocked_node;
#endif /* #ifdef CONFIG_PREEMPT_RCU */#ifdef CONFIG_TASKS_RCUunsigned long          rcu_tasks_nvcsw;u8              rcu_tasks_holdout;u8                rcu_tasks_idx;int               rcu_tasks_idle_cpu;struct list_head     rcu_tasks_holdout_list;
#endif /* #ifdef CONFIG_TASKS_RCU */struct sched_info       sched_info;struct list_head     tasks;
#ifdef CONFIG_SMPstruct plist_node      pushable_tasks;struct rb_node           pushable_dl_tasks;
#endifstruct mm_struct      *mm;struct mm_struct        *active_mm;/* Per-thread vma caching: */struct vmacache         vmacache;#ifdef SPLIT_RSS_COUNTINGstruct task_rss_stat      rss_stat;
#endifint               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;
#ifdef CONFIG_PSIunsigned           sched_psi_wake_requeue:1;
#endif/* 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;
#ifndef TIF_RESTORE_SIGMASKunsigned         restore_sigmask:1;
#endif
#ifdef CONFIG_MEMCGunsigned         in_user_fault:1;
#endif
#ifdef CONFIG_COMPAT_BRKunsigned            brk_randomized:1;
#endif
#ifdef CONFIG_CGROUPS/* disallow userland-initiated cgroup migration */unsigned         no_cgroup_migration:1;
#endif
#ifdef CONFIG_BLK_CGROUP/* to be used once the psi infrastructure lands upstream. */unsigned            use_memdelay:1;
#endif/** May usercopy functions fault on kernel addresses?* This is not just a single bit because this can potentially nest.*/unsigned int         kernel_uaccess_faults_ok;unsigned long          atomic_flags; /* Flags requiring atomic access. */struct restart_block      restart_block;pid_t             pid;pid_t               tgid;#ifdef CONFIG_STACKPROTECTOR/* Canary value for the -fstack-protector GCC feature: */unsigned long         stack_canary;
#endif/** Pointers to the (original) parent process, youngest child, younger sibling,* older sibling, respectively.  (p->father can be replaced with* p->real_parent->pid)*//* 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;
#ifdef CONFIG_ARCH_HAS_SCALED_CPUTIMEu64                utimescaled;u64             stimescaled;
#endifu64               gtime;struct prev_cputime       prev_cputime;
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GENstruct vtime           vtime;
#endif#ifdef CONFIG_NO_HZ_FULLatomic_t          tick_dep_mask;
#endif/* 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;#ifdef CONFIG_POSIX_TIMERSstruct task_cputime       cputime_expires;struct list_head        cpu_timers[3];
#endif/* 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;#ifdef CONFIG_SYSVIPCstruct sysv_sem         sysvsem;struct sysv_shm         sysvshm;
#endif
#ifdef CONFIG_DETECT_HUNG_TASKunsigned long         last_switch_count;unsigned long         last_switch_time;
#endif/* 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;
#ifdef CONFIG_AUDITSYSCALLkuid_t                loginuid;unsigned int           sessionid;
#endifstruct 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;#ifdef CONFIG_RT_MUTEXES/* PI waiters blocked on a rt_mutex held by this task: */struct rb_root_cached       pi_waiters;/* Updated under owner's pi_lock and rq lock */struct task_struct       *pi_top_task;/* Deadlock detection and priority inheritance handling: */struct rt_mutex_waiter      *pi_blocked_on;
#endif#ifdef CONFIG_DEBUG_MUTEXES/* Mutex deadlock detection: */struct mutex_waiter     *blocked_on;
#endif#ifdef CONFIG_TRACE_IRQFLAGSunsigned int          irq_events;unsigned long            hardirq_enable_ip;unsigned long         hardirq_disable_ip;unsigned int         hardirq_enable_event;unsigned int           hardirq_disable_event;int               hardirqs_enabled;int                hardirq_context;unsigned long           softirq_disable_ip;unsigned long            softirq_enable_ip;unsigned int          softirq_disable_event;unsigned int          softirq_enable_event;int                softirqs_enabled;int                softirq_context;
#endif#ifdef CONFIG_LOCKDEP
# define MAX_LOCK_DEPTH         48ULu64             curr_chain_key;int              lockdep_depth;unsigned int          lockdep_recursion;struct held_lock      held_locks[MAX_LOCK_DEPTH];
#endif#ifdef CONFIG_UBSANunsigned int           in_ubsan;
#endif/* Journalling filesystem info: */void                *journal_info;/* Stacked block device info: */struct bio_list           *bio_list;#ifdef CONFIG_BLOCK/* Stack plugging: */struct blk_plug           *plug;
#endif/* 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;kernel_siginfo_t     *last_siginfo;struct task_io_accounting ioac;
#ifdef CONFIG_PSI/* Pressure stall state */unsigned int         psi_flags;
#endif
#ifdef CONFIG_TASK_XACCT/* Accumulated RSS usage: */u64             acct_rss_mem1;/* Accumulated virtual memory usage: */u64                acct_vm_mem1;/* stime + utime since last update: */u64             acct_timexpd;
#endif
#ifdef CONFIG_CPUSETS/* Protected by ->alloc_lock: */nodemask_t          mems_allowed;/* Seqence number to catch updates: */seqcount_t           mems_allowed_seq;int                cpuset_mem_spread_rotor;int             cpuset_slab_spread_rotor;
#endif
#ifdef CONFIG_CGROUPS/* Control Group info protected by css_set_lock: */struct css_set __rcu        *cgroups;/* cg_list protected by css_set_lock and tsk->alloc_lock: */struct list_head        cg_list;
#endif
#ifdef CONFIG_INTEL_RDTu32              closid;u32              rmid;
#endif
#ifdef CONFIG_FUTEXstruct robust_list_head __user   *robust_list;
#ifdef CONFIG_COMPATstruct compat_robust_list_head __user *compat_robust_list;
#endifstruct list_head      pi_state_list;struct futex_pi_state     *pi_state_cache;
#endif
#ifdef CONFIG_PERF_EVENTSstruct perf_event_context  *perf_event_ctxp[perf_nr_task_contexts];struct mutex            perf_event_mutex;struct list_head       perf_event_list;
#endif
#ifdef CONFIG_DEBUG_PREEMPTunsigned long            preempt_disable_ip;
#endif
#ifdef CONFIG_NUMA/* Protected by alloc_lock: */struct mempolicy        *mempolicy;short                il_prev;short               pref_node_fork;
#endif
#ifdef CONFIG_NUMA_BALANCINGint             numa_scan_seq;unsigned int          numa_scan_period;unsigned int           numa_scan_period_max;int                numa_preferred_nid;unsigned long            numa_migrate_retry;/* Migration stamp: */u64                node_stamp;u64              last_task_numa_placement;u64                last_sum_exec_runtime;struct callback_head      numa_work;struct numa_group     *numa_group;/** numa_faults is an array split into four regions:* faults_memory, faults_cpu, faults_memory_buffer, faults_cpu_buffer* in this precise order.** faults_memory: Exponential decaying average of faults on a per-node* basis. Scheduling placement decisions are made based on these* counts. The values remain static for the duration of a PTE scan.* faults_cpu: Track the nodes the process was running on when a NUMA* hinting fault was incurred.* faults_memory_buffer and faults_cpu_buffer: Record faults per node* during the current scan window. When the scan completes, the counts* in faults_memory and faults_cpu decay and these values are copied.*/unsigned long            *numa_faults;unsigned long          total_numa_faults;/** numa_faults_locality tracks if faults recorded during the last* scan window were remote/local or failed to migrate. The task scan* period is adapted based on the locality of the faults with different* weights depending on whether they were shared or private faults*/unsigned long           numa_faults_locality[3];unsigned long           numa_pages_migrated;
#endif /* CONFIG_NUMA_BALANCING */#ifdef CONFIG_RSEQstruct rseq __user *rseq;u32 rseq_len;u32 rseq_sig;/** RmW on rseq_event_mask must be performed atomically* with respect to preemption.*/unsigned long rseq_event_mask;
#endifstruct 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_TASK_DELAY_ACCTstruct task_delay_info       *delays;
#endif#ifdef CONFIG_FAULT_INJECTIONint              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_LATENCYTOPint               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_KASANunsigned int          kasan_depth;
#endif#ifdef CONFIG_FUNCTION_GRAPH_TRACER/* Index of current stored address in ret_stack: */int             curr_ret_stack;int              curr_ret_depth;/* 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_MEMCGstruct 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_CGROUPstruct request_queue      *throttle_queue;
#endif#ifdef CONFIG_UPROBESstruct 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_SLEEPunsigned long           task_state_change;
#endifint               pagefault_disabled;
#ifdef CONFIG_MMUstruct task_struct     *oom_reaper_list;
#endif
#ifdef CONFIG_VMAP_STACKstruct 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_LIVEPATCHint patch_state;
#endif
#ifdef CONFIG_SECURITY/* Used by LSM modules for access restriction: */void             *security;
#endif#ifdef CONFIG_GCC_PLUGIN_STACKLEAKunsigned long           lowest_stack;unsigned long          prev_lowest_stack;
#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!*/
};

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代码

代码

makefile

附上linux内核4.20.11源代码

sched.h include\linux 53922 2/20/2019 208

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