# block

Block device abstraction for OCaml 5 with Eio direct-style I/O and Bytesrw integration.

## Overview

This library provides a minimal block device interface inspired by MirageOS
[mirage-block](https://github.com/mirage/mirage-block) but using Eio's
effects-based concurrency instead of Lwt.

## Features

- Eio direct-style I/O (no monads)
- Bytesrw integration for streaming access
- Memory, file, and flow backends
- CRC32C integrity checking wrapper
- Sub-device views for partitioning
- Read-only wrapper

## Installation

```
opam install block
```

## Usage

```ocaml
Eio_main.run @@ fun env ->
Eio.Switch.run @@ fun sw ->

(* Create a file-backed block device *)
let blk = Block.of_file ~sw env#fs "disk.img" ~sector_size:512 ~create:1000L () in
let info = Block.info blk in
Printf.printf "Sectors: %Ld\n" info.sectors;

(* Write a sector *)
let data = String.make 512 'A' in
Block.write blk 0L data |> Result.get_ok;

(* Read it back *)
let read = Block.read blk 0L |> Result.get_ok in
assert (data = read);

(* Add CRC32C integrity checking *)
let safe_blk = Block.with_crc32c blk in
(* Now reads verify checksums, writes compute them *)
```

## API

### Core Operations

- `Block.info` - Get device info (sector size, count, read/write)
- `Block.read` - Read a single sector
- `Block.write` - Write a single sector
- `Block.read_many` - Read multiple consecutive sectors
- `Block.write_many` - Write multiple consecutive sectors
- `Block.sync` - Flush pending writes
- `Block.close` - Release resources

### Backends

- `Block.of_memory` - In-memory device (for testing)
- `Block.of_string` - Read-only device from string
- `Block.of_file` - File-backed device
- `Block.of_flow` - Eio flow-backed device
- `Block.of_bigarray` - Bigarray-backed device

### Wrappers

- `Block.read_only` - Read-only view
- `Block.sub` - Sub-device view (for partitions)
- `Block.with_crc32c` - CRC32C integrity checking

### Bytesrw Integration

- `Block.to_reader` - Create sequential reader from offset
- `Block.to_writer` - Create sequential writer from offset

## Related Work

- [mirage-block](https://github.com/mirage/mirage-block) - MirageOS block
  interface (Lwt-based)
- [mirage-block-unix](https://github.com/mirage/mirage-block-unix) - Unix
  backend for mirage-block

## Licence

ISC License. See [LICENSE.md](LICENSE.md) for details.