Chapter 5th Process Environment (1) _ Process structure (task_struct)

1. concept and process structure of the process

1.1 Process

(1) program: A collection of ordered instructions stored on disk, which is an executable file stored in a disk file . But without any notion of execution, it is static .

(2) Progress (process)

the execution instance of the ① program, known as a process , is a dynamic concept that is the process of program execution, including creation, scheduling, and extinction.

The ② process has separate permissions and responsibilities, and it does not affect the rest of the process if a process in the system crashes.

③ each process runs in its own virtual address space , and processes can communicate with each other through a mechanism controlled by the kernel.

(3) Process ID: Each linux process has a unique numeric identifier called the process ID, and the process ID is always a non-negative integer.

1.2 process structure in the kernel

(1) Task_struct structural body

① process Number (PID): Used to uniquely identify a process.

　the state of the ② process , which identifies whether the process is in a running state, a waiting state, a stop state, or a dead state

　　A. Running state: The process is either running at this time, or ready to run

B. Wait state: At this point the process waits for an event to occur or some kind of system resource

C. Stop state: The process is terminated at this time

D. Death state: This is a terminated process, but it also occupies a task_struct structure in the process vector array.

③ the priority and time slices of the process.

Different priority processes are scheduled to run differently, typically high-priority processes run first. Time slices identify when a process will be run by the processor

④ Virtual Memory

Most processes have some virtual memory (kernel threads and daemons are not), and Linux must track how memory is mapped to system physical memory.

⑤ processor-related contexts

A process can be thought of as the sum of the current state of the system. Whenever a process runs, it uses the processor's register, stack, and so on, which is the context of the process. Also, whenever a process is paused, all CPU-related contexts must be stored in the task_struct of the process . When the process is restarted by the scheduler, its context resumes from here.

(3) Two data structures associated with a file

　　①fs_struct: It contains the current working directory and root directory of this process, umask. Umask is the default mode in which new files are created, which can be changed by a system call.

　②files_struct: contains information about all the files that this process is using . The F_mode field describes what mode the file was created in: Read-only, read-write, or write-only. F_pos saves the location where the next read or write in the file will occur . F_inode describe the VFS index node of a file, whereas F_ops is a pointer to a routine vector, each representing a function that wants to be applied to the action of the file . The Linux process starts with 3 file descriptors opened , which are standard input devices, standard output devices, and standard error devices , and are typically inherited from the parent process that created the process. .

Chapter 5th Process Environment (1) _ Process structure (task_struct)