COMP 3430 – Operating systems
File systems part 3
March 18th, 2022
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By the end of today’s lecture, you should be able to:
▶ Describe how a specific file system is implemented.
▶ Evaluate the data structures used by a file system implementation.
▶ Criticize a file system implementation.
The Rocket Book (Public Domain)
Let’s look at the course schedule.
FAT → File Allocation Table
▶ FAT (8 bit), FAT12, FAT16, and FAT32. ▶ Now exFAT.
exFAT spec ( ©Microsoft 2021)
exFAT is like FAT
FAT and exFAT are structurally very similar.
▶ Clusters,
▶ linked lists, ▶ FAT.
exFAT != FAT
FAT and exFAT are not backwards compatible; exFAT has
▶ Long file name support (up to 255 characters). ▶ Unicode support.
▶ Larger disk and file support.
▶ Allocation structures (bitmaps).
Let’s draw exFAT.
Evaluating the file system
Let’s look at our guiding questions again. On evaluating, compare to vsfs/ext2.
▶ vsfs/ext2 and FAT are both file systems.
▶ vsfs/ext2 and FAT solve similar problems very differently.
ext2 in the kernel
Let’s see if we can find where ext2 is implemented in the Linux kernel.
Tux! (CC0)
Everyone: Looking at the names of folders, which is likely to contain the implementation of ext2?
With your team: Find out where and how the super block is implemented. What kinds of metadata does the ext2 superblock track?
With your team: Find out where an inode is implemented.
▶ How are direct/indirect block pointers stored?
▶ What other metadata is kept in an inode in ext2?
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