inode pointer structure

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Diagram of the inode pointer structure

The inode pointer structure is a structure adopted by the inode of a file of the Unix file system for listing the data blocks of a file. It has also been adopted by many related file systems, including ext3, which is popular with Linux users .

structure

In the past, the structure consisted of 11 or 13 pointers, but most modern file systems use 15. These pointers include (assuming 15):

  • Twelve pointers that refer directly to data blocks in the file (direct pointers)
  • An indirect pointer (a pointer that points to a block of pointers whose pointers point to the data)
  • A double indirect pointer (a pointer that points to a block of pointers whose pointer points to another block of pointers whose pointers point to the data in the file)
  • A triple indirect pointer (a pointer that points to a block of pointers that points to a block of pointers that points to a block of pointers whose pointers point to the data in the file)

Key functions

Fixed logical block size: The structure is partially shown in the diagram on the right. It allows inodes to write large files in the file system with a fixed logical block size. The central mechanism is that block addresses (also called indirect blocks) are only assigned dynamically, i.e. when required.

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