Struct CachedDevice 

pub struct CachedDevice { /* private fields */ }

LRU-cached BlockDevice. Pass-through for is_writable + size_bytes; caches block-aligned reads, invalidates on writes.

Implementations

impl CachedDevice

pub fn new( inner: Arc<dyn BlockDevice>, block_size: u32, capacity: usize, ) -> Self

Wrap inner with an LRU of capacity blocks. Pick capacity based on workload: 64 blocks (256 KiB at 4 KiB) is a reasonable default for general use; bigger directory walks benefit from 256+.

pub fn stats(&self) -> (u64, u64)

Snapshot (hits, misses) — useful for benchmarks and tests.

pub fn pinned_blocks(&self) -> usize

How many blocks are pinned: held whatever the capacity, because their bytes are not yet at their final location on the device.

Trait Implementations

impl BlockDevice for CachedDevice

fn read_at(&self, offset: u64, buf: &mut [u8]) -> Result<()>

Read exactly buf.len() bytes starting at offset (bytes from start of device).

fn size_bytes(&self) -> u64

Total device size in bytes (for bounds-checking).

fn write_at(&self, offset: u64, buf: &[u8]) -> Result<()>

Write exactly buf.len() bytes at offset. Default: returns an error for read-only devices. Writable devices override this.

fn flush(&self) -> Result<()>

Flush any pending writes to stable storage. Default: no-op for read-only devices; writable devices should implement fsync semantics.

fn is_writable(&self) -> bool

Reports whether write_at is likely to succeed. Used by the mount path to decide whether journal replay is possible.

fn populate_cache(&self, block: u64, bytes: Vec<u8>)

Buffer-cache hook: stash bytes for block so a subsequent read_at returns those bytes instead of reading from physical storage. Used by a read-only mount’s journal replay to make committed metadata visible to readers without writing it back to the data area on disk.

fn unpin_all(&self)

Buffer-cache hook: tell the device the journal has been checkpointed, so any blocks pinned via populate_cache are now consistent with disk and can be evicted under normal LRU pressure. No-op for un-cached devices.

fn invalidate_cache(&self) -> Result<()>

Discard clean read-cache entries. Pinned journal metadata must be checkpointed and unpinned first; cached implementations reject otherwise. This does not flush writes and requires exclusive filesystem ownership.