Module slice 

Slice adapters — view a byte sub-range of any BlockRead as its own device. Useful any time you want to feed a fragment of a larger device to a consumer that expects a whole block source — partition probes, image-file extents, mmap-style views, fuzzer harnesses.

Three variants:

• SliceReader borrows the parent, lifetime-tied. Cheaper when the parent outlives the slice and you can express that statically.
• OwnedSlice holds an Arc to the parent. Use when the parent’s lifetime can’t be expressed in a borrow (FFI handles, slice handed across thread boundaries, etc.).
• OwnedRwSlice holds an Arc<dyn BlockDevice> and propagates writes to the parent.

The first two are strictly read-only: the default Err(ReadOnly) write path from BlockDevice applies.

Which error an out-of-range request gets

All three share one range check — SliceGeometry::rebase — and it answers in two different currencies depending on the direction of the request:

request outside [0, length)	error
read	Error::ShortRead with got: 0
write	Error::OutOfBounds

The asymmetry is deliberate. A slice exists to be substitutable for a real device of size length, and a real device — FileDevice — answers a read that begins at or past its end with exactly ShortRead { offset, want, got: 0 }. A slice that answered OutOfBounds would be distinguishable from the thing it stands in for, and every caller that already handles end-of-device would need a second arm to cope with slices. Writes have no partial-write variant to stay consistent with, and a caller that overran a write needs the device size in order to clamp and retry — which is what Error::OutOfBounds carries and Error::ShortRead does not.

The match is on the variant, not on got. A slice refuses an out-of-range read before it touches the parent, so it reports got: 0 and leaves the buffer untouched — including for a read that begins inside the slice and runs off its end, where FileDevice would have copied the readable prefix and reported its length. got counts bytes actually delivered, and a slice delivers none.

This governs the slice’s own range only. A request that is inside [0, length) is forwarded to the parent, and whatever the parent says about it — including Error::OutOfBounds from a container reader that knows its virtual size — comes back unchanged.

Structs

OwnedRwSlice

Owned, read-WRITE slice over an Arc<dyn BlockDevice>. Use when the parent is writable and the slice should propagate writes (e.g. an individual partition handed to a filesystem driver).

OwnedSlice

Owned slice over an Arc<dyn BlockRead>. Use when the parent’s lifetime can’t be expressed in a borrow — e.g. when the slice is handed across an FFI boundary or stored in a long-lived struct.

SliceReader

Borrowed slice of a parent BlockRead.