FileSystem

Socket File Descriptors and Their Kernel Structures A socket is a special type of file descriptor (FD) in Linux, represented as socket:[inode]. Unlike regular file FDs, socket FDs point to in-memory kernel structures, not disk inodes. The /proc/<pid>/fd directory lists all FDs for a process, including sockets. The inode number of a socket can be used to inspect its details via tools like ss and /proc/net/tcp. Example: Checking Open FDs for Process 216 ls -l /proc/216/fd Output: ...

Overall Organization Of Data In Disks Assuming we have a 256KB disk. Disk Blocks: The basic units of storage on the disk, each 4 KB in size. The disk is divided into these blocks, numbered from 0 to N-1 (where N is the total number of blocks). Inode Bitmap (i): Block 1; a bitmap tracking which inodes are free (0) or in-use (1). Data Bitmap (d): Block 2; a bitmap tracking which data blocks are free (0) or allocated (1). Inode Table (I): Blocks 3-7; an array of inodes, where each inode (256 bytes) holds metadata about a file, like size, permissions, and pointers to data blocks. 5 blocks of 4KB will contain 80 256 byte inode strutures. Data Region (D): Blocks 8-63; the largest section, storing the actual contents of files and directories. Inode Every inode has a unique identifier called an inode number (or i-number). This number acts like a file’s address in the file system, allowing the operating system to quickly locate its inode. For example: ...

Files and directories File systems virtualize persistent storage (e.g., hard drives, SSDs) into user-friendly files and directories, adding a third pillar to OS abstractions (processes for CPU, address spaces for memory). File Paths and System Calls Files are organized in a tree-like directory structure, starting from the root (/). A file’s location is identified by its pathname (e.g., /home/user/file.txt). To interact with files, processes use system calls: open(path, flags): Opens a file and returns a file descriptor (fd). read(fd, buffer, size): Reads data from the file into a buffer using the fd. write(fd, buffer, size): Writes data to the file via the fd. close(fd): Closes the file, freeing the fd. File Descriptors A file descriptor is a small integer, unique to each process, that identifies an open file. When a process calls open(), the operating system assigns it the next available fd (e.g., 3, 4, etc.). Every process starts with three default fds: ...