Kernel Data Structure

What is Kernel?

The fundamental component that bridges the software programs and the underlying hardware is called the Kernel. It's in charge of operating processes, controlling system resources, and interacting with hardware. When a computer's operating system is loaded, the kernel loads immediately and stays in memory until the operating system is shut down. The Kernel communicates with hardware, allots memory, and responds to interruptions and requests from the computer's processes. It controls fundamental operations, including memory, task, and disc management.

A kernel must be rapid and efficient to process all requests and answers accurately. The Kernel makes extensive use of kernel-level memory to do this. This memory is separate from your computer's primary memory. This implies that the Kernel may use it to store information and code without harming other applications. A kernel may access various computer resources, including RAM, CPU, and I/O devices. Every program requires memory access to run. The Kernel decides each process' memory allocation, and if memory is not available, a response is provided. The system won't turn on entirely if the Kernel isn't functioning or can't load effectively. Service will be required to fix hardware issues or return the operating system's Kernel to a functional state.

Kernel Data Structures

The kernel data structures are crucial because they store details about the system's current state. A kernel data structure is also built when a new process is introduced to the system to hold the details of the process. These data structures are critical to the workings of the operating system and are designed to handle activities like process management, memory management, file systems, and device drivers effectively. Only the Kernel and its subsystems have access to the majority of the Kernel's data structures. In addition to data, they could also have references to other data structures. The Kernel's three main structural components are the process table, file table, and v node/i node information.

• Process table:

Information on every active process in the system is recorded in the process table. It acts as a central store for archiving and classifying data of processes, enabling the Kernel to monitor, plan, and manage activities effectively. A linked list, array, or other comparable data structure is frequently represented as the process table. A data structure called the Program Control Block holds details about a particular process, including its process ID (PID), status, program counter, register values, scheduling information, memory allocation information, open file descriptors, and other pertinent process-specific data. Using this PID, the Kernel may rapidly find and access the appropriate PCB in the process table. Fast process management procedures, including process creation, termination, scheduling, and context switching, are made possible by efficient indexing. Process tables provide information such as:

• User ID: The user ID specifies the privileges given to users for a certain process.
• Process state: The information defining whether a process is new, active, running, or terminated is stored in the process state.
• Process ID: When a new process is created, a Process ID is produced and used to identify the process.
• Timer: The most time-consuming resource is found using the timer
• Pointer: It serves as a pointer to the process Uarea and a pointer to a page table that facilitates memory management.

A PCB is allotted and filled with the relevant data when the Kernel establishes a new process. A new entry is subsequently made in the process table by inserting the freshly built PCB. Similarly, the Kernel releases the resources connected to a process when it terminates or quits by deleting the related PCB item from the process table. The operating system's method for scheduling processes has a strong relationship with the process table. It includes data that assists in scheduling decisions made by the Kernel. The process state, priority, status of the execution, and other scheduling variables are all included in this data. The process table enables the Kernel to monitor and control each process's state throughout the system. The process status recorded in the PCB indicates whether a process is currently running, still waiting, or terminated. Inter-process communication can also be facilitated by using the process table. This file may mention or point to shared memory regions, message queues, or other communication objects connected to each process. This enables the Kernel to manage and coordinate process communication efficiently.

• File Tables:

Operating systems employ file tables as a data structure for managing open files. It acts as a central database for details on the files opened by system processes. A file table is often called a control block or descriptor table.

A linked list or array of file table entries is typically used to implement the file table. Entries regarding the files in the system are found in the file table. Every entry is a single open file that is represented by and contains the necessary data for each entry. When many processes share a single file, the file descriptor number and file information are shared.

A file table entry's detailed contents consist of the following:

• File Status Flags: The Flags that describe the file and regulate its behavior are contained in the file status flags. In addition, to read and write flags, there are also append and non-blocking flags. These flags specify the allowed file operations and the read-and-write behavior the file should follow.
• File Descriptor: A file descriptor is a special label given to an open file that is frequently shown as a non-negative integer. In subsequent file-related activities, programs will use this descriptor to refer to the file.
• File position: The current read/write location within the file is indicated by the file's position. It specifies where the subsequent read or write operation will start. The location is updated by data that is read from or written to the file.
• File Mode: The file mode specifies the access rights and file type. It specifies whether various individuals or groups can read, write, or execute the file.
• File Reference Count: File Reference Count counts how many file descriptors are used to describe the same open file. This count ensures proper cleaning when a file is no longer in use while enabling different processes to share access.
• File Operations Table: The read, write, seek, close, and local operations and other activities that may be carried out on a file are defined in the file operations table, a table of function pointers. The file table contains entries that direct the user to the proper file operation functions.

Additionally, the file table has v-node and I-node pointers that refer to the virtual node and index node. The instructions for reading a file are located in these nodes.

• V-node and I-node tables:

The file's storage system and storage methods reference the V-node and I-node. They link the software and the hardware together.

The system's active instances of files or objects that resemble files are managed and represented by the V-node table, a data structure. It offers a layer of abstraction that enables the kernel to handle various file systems and device types uniformly. Arrays or hash tables are commonly used to implement the V-node table. Each element contains File System-Specific Information. This comprises information related to the file system on which the file is stored, such as disc block addresses, file size, and other metadata. File Operation Functions are pointers to the different file operation functions, including read, write, seek, and delete. These operations specify how a file or object that resembles a file is supposed to perform and relate to other system components. The V-node table may contain locks or other synchronization techniques that safeguard crucial parts of the entry to maintain thread safety and avoid race problems. The V-node table enables the kernel to preserve a constant representation of files and objects that resemble files across various file systems and media.

There is a specialized data structure called the I-node table for file systems that employ the I-node-based method of managing files. It represents individual I-nodes, data structures that keep track of information about files, including permissions, ownership, file size, and pointers to data blocks on the disc. Usually, a hash table or an array is used to implement the I-node table. The I-node table is necessary for file system operations because it enables the kernel to discover and handle files quickly. Each file operation normally entails searching for the proper I-node entry in the I-node table to obtain the required information and carry out the desired action, such as reading or writing data to the file. Each entry's File Metadata section includes a file's rights, ownership, size, timestamps, and pointers to the data blocks containing the file's contents. Locks or other synchronization techniques may be included in I-node entries to prevent concurrent access to the metadata.