How does the inode map to data block of a file?

Answer Posted / sangu

When a file system is created, data structures that contain
Information about files are created. Each file is
represented by a structure, called an inode and is
identified by an inode number. Each inode contains the
description of the file: file type, access rights, owners,
timestamps, size, pointers to data blocks. The addresses of
data blocks allocated to a file are stored in its inode.When
a user requests an I/O operation on the file, the kernel
code converts the current offset to a block number, uses
this number as an index in the block addresses table and
reads or writes the physical block. The inode structure uses
fifteen pointers. These pointers consist of:
• Twelve pointers that directly point to blocks of the
file's data (direct pointers)
• One singly indirect pointer (a pointer that points to a
block of pointers that then point to blocks of the file's data)
• One doubly indirect pointer (a pointer that points to a
block of pointers that point to other blocks of pointers
that then point to blocks of the file's data)
• One triply indirect pointer (a pointer that points to a
block of pointers that point to other blocks of pointers
that point to other blocks of pointers that then point to
blocks of the file's data)

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