Filesystems · Cluster
Filesystem Implementation
On-disk formats and kernel interfaces.
- 01 The Superblock: Magic Number, Geometry, and Feature Flags How a filesystem announces its own layout at a fixed disk offset, why its feature bits are split into three classes with different contracts, and what a driver does when it meets a bit it does not understand.
- 02 Block Groups and the Cost of Metadata Locality Why a filesystem carves itself into groups with their own bitmaps and inode tables, what the descriptor table records, and how allocation policy turns locality into seek distance.
- 03 Inode Tables and the Arithmetic of Inode Numbers How a fixed-size inode record is found from its number with one division, why the table is preallocated rather than grown, and what happens when the number of inodes runs out before the space does.
- 04 Extent Trees and the Replacement of Indirect Block Maps What an extent record actually encodes, why the inode-sized root makes small files free of external metadata, and how the tree splits when a file fragments.
- 05 Directory Hash Trees: Indexing Names Without Breaking Enumeration How a hashed b-tree stores directory entries in blocks while preserving the linear order readdir requires, and how a fake dirent hides the interior nodes from a reader that does not know about them.
- 06 VFS Objects and the Operation Vector The four in-kernel objects every filesystem must supply, the function table each one carries, and how a single open() call ends up in a filesystem-specific method.
- 07 The Page Cache and the Writeback Path Where a written byte actually lives before it reaches the device, how dirty pages are tracked and flushed, and why write() returning does not mean the data is on disk.
- 08 Delayed Allocation and the Reservation Window Why holding back the block-allocation decision until writeback makes layout better and failure later, and how a per-file reservation prevents the space from being promised twice.
- 09 Mounting: From Device Node to a Live Superblock The sequence a filesystem driver follows when it is handed a block device, the checks that must pass before the volume becomes writable, and what a failed mount must unwind.
- 10 fsck and the Ordering of Repairs Why the consistency passes run in a fixed order, how each pass builds the data the next one needs, and why some findings can only be resolved by discarding data.