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As per my understanding kernel maintains 4 tables.

  1. Per process FD table.
  2. System wide open file table struct file
  3. Inode (in-memory) table struct vnode
  4. Inode (on-disk) table.

struct file have one field named struct file_operations f_ops; which contains FS specific operations like ext2_read(), ext2_write();

struct vnode also have one field struct vnodeops v_op; which contains FS specific operations too.

My question is why we have similar functionalities inside both? Or am I getting something wrong? Are things different in Unix and Linux? Because I did not find struct vnode inside Linux's fs.h

Reference: https://www.usna.edu/Users/cs/wcbrown/courses/IC221/classes/L09/Class.html

Diagram (from "Unix internals new frontiers" book)

enter image description here

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Okay, I have found the answer.

In previous versions of Unix like SVR4, struct file does not contain file_operations field and all operations e.g. read, write etc. contained by vnode->v_op.

However, in case of Linux struct file will contain file_operations field which will have functions like open, read, write etc. and struct inode (similar to vnode) will contain inode_operations field which will have operations like lookup, link, unlink, symlink, rmdir, mkdir, rename, etc.

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