Linux kernel, this often hear, but do not know exactly what it is, do not feel very mysterious?
The Linux kernel is invisible, and we often don’t know what to do with things like that. This article will take you into the Linux kernel to see what it looks like in plain English.
The kernel is the core component of the Linux operating system, connecting applications upwards and dealing directly with hardware downwards. Its code is mainly written in C language and a little assembly language, and it can be adapted to a variety of different hardware architecture.
The kernel runs a series of concurrent processes and manages various resources on the hardware. Specifically, because the system’s resources are limited, the kernel allocates resources such as CPU time, memory space, network connections, and so on to each process.
Linux operating system architecture
The following figure shows a typical Linux operating system architecture.
The Linux operating system is divided into two parts:
- The user space
- The kernel space
1. User space
All user applications run in user space, not directly accessing hardware resources such as memory, but indirectly through the kernel. The GNU C library (Glibc) provides a mechanism for switching from user space to kernel space.
2. Kernel space
The kernel directly manages the CPU, memory, I/O devices, network devices and other peripherals of the system. It is divided into different modules to manage different operations of the system, such as file management, memory management, process management and so on.
User-space applications can access hardware resources by calling kernel-provided apis. For example, for file operations, we can call open(), read(), write() and so on.
The kernel directly manages the hardware and is independent of the hardware. It can be simply configured and run on Intel, ARM, Atemel and other chip architectures.
Major subsystems of the Linux kernel
According to the core functions of the kernel, the Linux kernel puts forward five subsystems, namely: system call, process management, memory management, file system, and network management, as shown below:
1. System Call Interface
System call interface. The process scheduling subsystem opens up the interface that needs to be provided to user space through the system call interface, while masking details that do not need to be cared for by user space programs.
SCI is actually a very useful function call multiplexing and demultiplexing service. You can find implementations of SCI in./ Linux /kernel, and architecture-dependent sections in./ Linux /arch.
2. Process Management
With so many processes in user space, keeping them organized is exactly what process management is all about. Each process needs to use CPU resources (such as CPU and memory), but CPU resources are limited, so it is impossible for a process to monopolize the resources.
Therefore, process management acts as the role of the administrator, it schedules all processes, when the need to choose the next process to run, the scheduling algorithm will choose the most need to run the process. If a process is waiting for other hardware resources, it will be suspended.
Therefore, the kernel uses CPU resources as fairly as possible for each process through a series of scheduling algorithms.
3. Memory Management
Memory management mainly provides access control over memory resources so that processes can safely share the memory resources of the machine. It provides a mapping relationship between physical memory and virtual memory, so that different processes can use the same virtual memory, and these same virtual memory can be mapped to different physical memory. This mapping is primarily done by the MMU.
In addition, memory management provides a virtual memory mechanism that allows processes to use more memory than is available to the system. Unused memory is stored in external non-volatile memory through the file system and retrieved back into memory when needed.
4. Virtual File System
The kernel hides the details of peripheral devices with different functions, such as hard disks, I/O devices, display devices, and so on, abstracting them into a unified file operation interface (open, Close, Read, write, and so on), known as “everything files.”
With the development of computer technology, there have been many file systems in history, such as FAT, FAT32, NTFS, EXT2, EXT3 and so on. To accommodate these file systems, the kernel abstracts them into a unified representation, which is the concept of a virtual file system.
Virtual file systems can be divided into logical file systems and device drivers. Logical file system refers to the file system supported by Linux, such as ext2 and FAT. Device driver refers to the device driver module written for each hardware controller.
5. Network Stack
The network subsystem in Linux kernel is mainly responsible for the management of various network devices, and the realization of various network protocol stacks, and finally realize the function of connecting other systems through the network.
The network interface provides access to various network standard protocols and supports various network hardware. Network interface can be divided into two parts: network protocol and network driver. The network protocol section is responsible for implementing every possible network transport protocol, the network device driver is responsible for communicating with the hardware device, and each possible hardware device has a corresponding device driver.
summary
The above is the Linux kernel some very basic knowledge, for the learning of the kernel there are very much content, is by no means an article can be written. Therefore, for the study of the kernel, you need to read more books, watch more videos, and do it yourself to practice, to really master.
Yesterday is a good xu public number operation anniversary day, originally wanted to send welfare yesterday, but yesterday’s article was too long, afraid of friends can not turn the last, so change to today.
In response to the readers’ support and help, I would like to offer you two benefits: 1. Kernel books; 2. Cash red envelopes.
1. Book giveaways
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Have a harvest? Hope the old iron people come to a triple whammy, give more people to see this article
Recommended reading:
- Dry goods | programmers advanced architect necessary resources free of charge
- Artifact | support resource site search