package mirage-block-ramdisk

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Basic operation
Resizing support
Querying sparseness information
Compatibility

mirage-block-ramdisk
- Ramdisk

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An in-memory BLOCK device also known as a Ramdisk

Basic operation

include Mirage_block.S

type nonrec error = private [>

| Mirage_block.error

]

The type for block errors.

val pp_error : error Fmt.t

pp_error is the pretty-printer for errors.

type nonrec write_error = private [>

| Mirage_block.write_error

]

The type for write errors.

val pp_write_error : write_error Fmt.t

pp_write_error is the pretty-printer for write errors.

type t

The type representing the internal state of the block device

val disconnect : t -> unit Lwt.t

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 Lwt.t

Query the characteristics of a specific block device

val read : t -> int64 -> Cstruct.t list -> (unit, error) result Lwt.t

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. Some implementations may further require that each element in buffers is exactly sector_size long.

val write : t -> int64 -> Cstruct.t list -> (unit, write_error) result Lwt.t

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: `Is_read_only: the device is read-only, no 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. Some implementations may further require that each element in buffers is exactly sector_size long.

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

val connect : name:string -> t Lwt.t

Connect to the named ramdisk.

val create : 
  name:string ->
  size_sectors:int64 ->
  sector_size:int ->
  (t, error) result Lwt.t

Create an in-memory block device (a "ramdisk") with a given name, total size in sectors and sector size. Two calls to connect with the same name will return the same block device

val destroy : name:string -> unit

Destroy removes an in-memory block device. Subsequent calls to connect will create a fresh empty device.

Resizing support

val resize : t -> int64 -> (unit, write_error) result Lwt.t

resize t new_size_sectors attempts to resize the connected device to have the given number of sectors. If successful, subsequent calls to get_info will reflect the new size.

Querying sparseness information

val seek_unmapped : t -> int64 -> (int64, error) result Lwt.t

seek_unmapped t start returns the offset of the next guaranteed zero-filled region (typically guaranteed because it is unmapped)

val seek_mapped : t -> int64 -> (int64, error) result Lwt.t

seek_mapped t start returns the offset of the next regoin of the device which may have data in it (typically this is the next mapped region)

Compatibility

val flush : t -> (unit, write_error) result Lwt.t

flush t is a no-op on a Ramdisk