3.2. Process Descriptor

To manage processes, the kernel must have a clear picture of what each process is doing. It must know, for instance, the process's priority（调度的优先级）, whether it is running on a CPU or blocked on an event, what address space has been assigned to it, which files it is allowed to address, and so on. This is the role of the process descriptor a task_struct type structure whose fields contain all the information related to a single process. [*] As the repository of so much information, the process descriptor is rather complex. In addition to a large number of fields containing process attributes, the process descriptor contains several pointers to other data structures that, in turn, contain pointers to other structures. Figure 3-1 describes the Linux process descriptor schematically（按照图式）.

[*] The kernel also defines the task_t data type to be equivalent to struct task_struct

NOTE : task_struct 的源代码参见：

• https://elixir.bootlin.com/linux/latest/ident/task_struct
• https://github.com/torvalds/linux/blob/master/include/linux/sched.h

关于task_struct和process，thread之间的对应关系，在Chapter 3. Processes中进行了细致的分析；此处不再赘述；

The six data structures on the right side of the figure refer to specific resources owned by the process. Most of these resources will be covered in future chapters. This chapter focuses on two types of fields that refer to the process state and to process parent/child relationships.

Figure 3-1. The Linux process descriptor

task_structure的成员变量

name	type	note
pid		lightweight process ID，私有	chapter 3.2.2. Identifying a Process
tgid		标准process id，共享	chapter 3.2.2. Identifying a Process
thread_info		私有
mm_struct		process address space，共享	9.2. The Memory Descriptor