Safe block devices

Construct a safe wrapper around B where necessary buffer preconditions are checked on read and write, and useful error messages generated. Some concrete implementations generate confusing errors (e.g. Unix might say "EINVAL") which are harder to debug.

Parameters

module B : S

Signature

type error = private [>
  1. | Mirage_block.error
  2. | `Unsafe of string
]

The type for errors.

type write_error = private [>
  1. | Mirage_block.write_error
  2. | `Unsafe of string
]

The type for write errors.

include S with type t = B.t and type error := error and type write_error := write_error
type page_aligned_buffer = Cstruct.t

The type for page-aligned memory buffers.

val pp_error : error Fmt.t

pp_error is the pretty-printer for errors.

val pp_write_error : write_error Fmt.t

pp_write_error is the pretty-printer for write errors.

include Mirage_device.S with type 'a io = 'a Lwt.t with type t = B.t
type 'a io = 'a Lwt.t

The type for potentially blocking I/O operation

type t = B.t

The type representing the internal state of the device

val disconnect : t -> unit io

Disconnect from the device. While this might take some time to complete, it can never result in an error.

val get_info : t -> Mirage_block.info io

Query the characteristics of a specific block device

val read : t -> int64 -> page_aligned_buffer list -> (unit, error) Pervasives.result io

read device sector_start buffers reads data starting at sector_start from the block device into buffers. Ok () means the buffers have been filled. Error _ indicates an I/O error has happened and some of the buffers may not be filled. Each of elements in the list buffers must be a whole number of sectors in length. The list of buffers can be of any length.

val write : t -> int64 -> page_aligned_buffer list -> (unit, write_error) Pervasives.result io

write device sector_start buffers writes data from buffers onto the block device starting at sector_start. Ok () means the contents of the buffers have been written. Error _ indicates a partial failure in which some of the writes may not have happened.

Once submitted, it is not possible to cancel a request and there is no timeout.

The operation may fail with:

  • `Unimplemented: the operation has not been implemented, no data has been written.
  • `Is_read_only: the device is read-only, no data has been written.
  • `Disconnected: the device has been disconnected at application request, an unknown amount of data has been written.

Each of buffers must be a whole number of sectors in length. The list of buffers can be of any length.

The data will not be copied, so the supplied buffers must not be re-used until the IO operation completes.

val unsafe_read : t -> int64 -> page_aligned_buffer list -> (unit, B.error) Pervasives.result Lwt.t

unsafe_read is like read except it bypasses the necessary buffer precondition checks. Only use this if you want maximum performance and if you can prove the preconditions are respected.

val unsafe_write : t -> int64 -> page_aligned_buffer list -> (unit, B.write_error) Pervasives.result Lwt.t

unsafe_write is like write except it bypasses the necessary buffer precondition checks. Only use this if you want maximum performance and if you can prove the buffer preconditions are respected.