Struct CallbackDevice 

pub struct CallbackDevice {
    pub size: u64,
    pub read: ReadCb,
    pub write: Option<WriteCb>,
    pub flush: Option<FlushCb>,
}

Callback-backed device — used when the host process owns the fd (e.g. FSBlockDeviceResource via the C bridge). Optional write callback; set to None for read-only.

Fields

size: u64

read: ReadCb

write: Option<WriteCb>

flush: Option<FlushCb>

Trait Implementations

impl BlockDevice for CallbackDevice

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.

impl BlockDevice for CallbackDevice

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

Write exactly buf.len() bytes at offset. Default: returns Error::ReadOnly.

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

Flush pending writes to stable storage. No-op by default.

fn is_writable(&self) -> bool

Whether write_at is likely to succeed. Mount paths use this to decide whether to attempt journal replay or stay strict-read-only.

fn set_len(&self, _new_len: u64) -> Result<(), Error>

Set the device’s length to new_len. Default: returns Error::ReadOnly.

fn can_grow(&self) -> bool

Whether set_len is likely to succeed. Default: false.

impl BlockRead for CallbackDevice

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

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

fn size_bytes(&self) -> u64

Total device size in bytes. Used for bounds checks.