package qcow

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package qcow
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include Mirage_block_lwt.S
type page_aligned_buffer = Cstruct.t

The type for page-aligned memory buffers.

type error = private [>
  1. | Mirage_device.error
]

The type for block errors.

val pp_error : error Fmt.t

pp_error is the pretty-printer for errors.

type write_error = private [>
  1. | Mirage_device.error
  2. | `Is_read_only
]

The type for write 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
type 'a io = 'a Lwt.t

The type for potentially blocking I/O operation

type 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.

module Config : sig ... end
module Stats : sig ... end
val create : B.t -> size:int64 -> ?lazy_refcounts:bool -> ?cluster_bits:int -> ?config:Config.t -> unit -> (t, write_error) Pervasives.result io

create block ~size ?lazy_refcounts ?cluster_bits ?config () initialises a qcow-formatted image on block with virtual size size in bytes.

By default the file will use lazy refcounts, but this can be overriden by supplying ~lazy_refcounts:false. By default the file will use 64KiB clusters (= 16 bits) but this can be overridden by supplying ?cluster_bits. Note the cluster size must be greater than the sector size on the underlying block device.

The ?config argument does not affect the on-disk format but rather the behaviour as seen from this client.

val connect : ?config:Config.t -> B.t -> t io

connect ?config block connects to an existing qcow-formatted image on block.

val resize : t -> new_size:int64 -> ?ignore_data_loss:bool -> unit -> (unit, write_error) Pervasives.result io

resize block new_size_bytes ?ignore_data_loss changes the size of the qcow-formatted image to new_size_bytes, rounded up to the next allocation unit. This function will fail with an error if the new size would be smaller than the old size as this would cause data loss, unless the argument ?ignore_data_loss is set to true.

type compact_result = {
  1. copied : int64;
    (*

    number of sectors copied

    *)
  2. refs_updated : int64;
    (*

    number of cluster references updated

    *)
  3. old_size : int64;
    (*

    previous size in sectors

    *)
  4. new_size : int64;
    (*

    new size in sectors

    *)
}

Summary of the compaction run

val compact : t -> ?progress_cb:(percent:int -> unit) -> unit -> (compact_result, write_error) Pervasives.result io

compact t () scans the disk for unused space and attempts to fill it and shrink the file. This is useful if the underlying block device doesn't support discard and we must emulate it.

val discard : t -> sector:int64 -> n:int64 -> unit -> (unit, write_error) Pervasives.result io

discard sector n signals that the n sectors starting at sector are no longer needed and the contents may be discarded. Note the contents may not actually be deleted: this is not a "secure erase".

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

seek_unmapped t start returns the offset of the next "hole": a region of the device which is guaranteed to be full of zeroes (typically guaranteed because it is unmapped)

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

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

val rebuild_refcount_table : t -> (unit, write_error) Pervasives.result io

rebuild_refcount_table t rebuilds the refcount table from scratch. Normally we won't update the refcount table live, for performance.

type check_result = {
  1. free : int64;
    (*

    unused sectors

    *)
  2. used : int64;
    (*

    used sectors

    *)
}
val check : B.t -> (check_result, [ Mirage_block.error | `Reference_outside_file of int64 * int64 | `Duplicate_reference of (int64 * int) * (int64 * int) * int64 | `Msg of string ]) Pervasives.result io

check t performs sanity checks of the file, looking for errors. The error `Reference_outside_file (src, dst) means that at offset src there is a reference to offset dst which is outside the file. The error `Duplicate_reference (ref1, ref2, target) means that references at both [ref1] and [ref2] both point to the same [target] offset.

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

flush t flushes any outstanding buffered writes

val header : t -> Header.t

Return a snapshot of the current header

val to_config : t -> Config.t

to_config t returns the configuration of a device

val get_stats : t -> Stats.t

get_stats t returns the runtime statistics of a device

module Debug : sig ... end