Understand the linux kernel-ch3-Process descriptor

Chapter 3. Processes
		a process is an instance of a program in execution
		From the kernel's point of view, the purpose of a process is to act
		as an entity to which system resources (CPU time, memory, etc.) are allocated
		lightweight processes to offer better support for multithreaded applications
	Process Descriptor
		task_struct
		Process State
			#define TASK_RUNNING		0
			#define TASK_INTERRUPTIBLE		1
			#define TASK_UNINTERRUPTIBLE		2
			#define TASK_STOPPED		4
			#define TASK_ZOMBIE		8
			#define TASK_DEAD		16
			EXIT_ZOMBIE
			EXIT_DEAD
			set_task_state
			set_current_state
		Identifying a Process
			PID
			tgid
		Process descriptors handling
								task
			movl $0xffffe000,%ecx /* or 0xfffff000 for 4KB stacks */				thread_info		task_struct
			andl %esp,%ecx
			movl %ecx,p				kernel stack
									esp
			current macro	//current.h
				static inline struct thread_info *current_thread_info(void)
				{
					struct thread_info *ti;
					__asm__("andl %%esp,%0; ":"=r" (ti) : "0" (~8191UL));
					return ti;
				}
				static inline struct task_struct * get_current(void)
				{
					return current_thread_info()->task;
				}
				#define current get_current()
		Doubly linked lists
			LIST_HEAD_INIT	//include/linux/list.h
			LIST_HEAD
			INIT_LIST_HEAD
			：
			HLIST_HEAD_INIT
			HLIST_HEAD
			：