Module Qcow.Make

Parameters

• B : Qcow_s.RESIZABLE_BLOCK
• Time : Mirage_time.S

Signature

val create : B.t -> size:int64 -> ?⁠lazy_refcounts:bool -> ?⁠cluster_bits:int -> ?⁠config:Config.t -> unit -> (t, write_error) Stdlib.result Lwt.t

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 Lwt.t

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) Stdlib.result Lwt.t

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 = {

copied : int64;	number of sectors copied
refs_updated : int64;	number of cluster references updated
old_size : int64;	previous size in sectors
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) Stdlib.result Lwt.t

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) Stdlib.result Lwt.t

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) Stdlib.result Lwt.t

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) Stdlib.result Lwt.t

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) Stdlib.result Lwt.t

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

type check_result = {

free : int64;	unused sectors
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 ]) Stdlib.result Lwt.t

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) Stdlib.result Lwt.t

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