343 lines
14 KiB
OCaml
343 lines
14 KiB
OCaml
type bigstring =
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(char, Bigarray.int8_unsigned_elt, Bigarray.c_layout) Bigarray.Array1.t
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val memcpy :
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bigstring -> src_off:int -> bigstring -> dst_off:int -> len:int -> unit
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val memmove :
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bigstring -> src_off:int -> bigstring -> dst_off:int -> len:int -> unit
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module Bstr : sig
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(** A read-only bigstring. *)
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type t = private bigstring
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val empty : t
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(** [empty] is an empty bigstring. *)
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val of_bigstring : bigstring -> t
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val length : t -> int
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(** [length bstr] is the number of bytes in [bstr]. *)
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val get : t -> int -> char
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(** [get bstr i] is the byte of [bstr]' at index [i]. This is
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equivalent to the [bstr.{i}] notation.
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@raise Invalid_argument if [i] is not an index of [bstr]. *)
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val get_int8 : t -> int -> int
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(** [get_int8 bstr i] is [bstr]'s signed 8-bit integer starting at byte index
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[i]. *)
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val get_uint8 : t -> int -> int
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(** [get_uint8 bstr i] is [bstr]'s unsigned 8-bit integer starting at byte
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index [i]. *)
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val get_uint16_ne : t -> int -> int
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(** [get_int16_ne bstr i] is [bstr]'s native-endian unsigned 16-bit integer
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starting at byte index [i]. *)
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val get_uint16_le : t -> int -> int
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(** [get_int16_le bstr i] is [bstr]'s little-endian unsigned 16-bit integer
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starting at byte index [i]. *)
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val get_uint16_be : t -> int -> int
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(** [get_int16_be bstr i] is [bstr]'s big-endian unsigned 16-bit integer
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starting at byte index [i]. *)
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val get_int16_ne : t -> int -> int
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(** [get_int16_ne bstr i] is [bstr]'s native-endian signed 16-bit integer
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starting at byte index [i]. *)
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val get_int16_le : t -> int -> int
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(** [get_int16_le bstr i] is [bstr]'s little-endian signed 16-bit integer
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starting at byte index [i]. *)
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val get_int16_be : t -> int -> int
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(** [get_int16_be bstr i] is [bstr]'s big-endian signed 16-bit integer
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starting at byte index [i]. *)
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val get_int32_ne : t -> int -> int32
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(** [get_int32_ne bstr i] is [bstr]'s native-endian 32-bit integer starting
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at byte index [i]. *)
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val get_int32_le : t -> int -> int32
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(** [get_int32_le bstr i] is [bstr]'s little-endian 32-bit integer starting
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at byte index [i]. *)
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val get_int32_be : t -> int -> int32
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(** [get_int32_be bstr i] is [bstr]'s big-endian 32-bit integer starting at
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byte index [i]. *)
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val get_int64_ne : t -> int -> int64
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(** [get_int64_ne bstr i] is [bstr]'s native-endian 64-bit integer starting
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at byte index [i]. *)
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val get_int64_le : t -> int -> int64
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(** [get_int64_le bstr i] is [bstr]'s little-endian 64-bit integer starting
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at byte index [i]. *)
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val get_int64_be : t -> int -> int64
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(** [get_int64_be bstr i] is [bstr]'s big-endian 64-bit integer starting at
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byte index [i]. *)
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val sub : t -> off:int -> len:int -> t
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(** [sub bstr ~off ~len] does not allocate a bigstring, but instead returns a
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new
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view into [bstr] starting at [off], and with length [len].
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{b Note} that this does not allocate a new buffer, but instead shares the
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buffer of [bstr] with the newly-returned bigstring. *)
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val sub_string : t -> off:int -> len:int -> string
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(** [sub_string bstr ~off ~len] returns a string of length [len] containing
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the bytes of [t] starting at [off]. *)
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val to_string : t -> string
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(** [to_string bstr] is equivalent to [sub_string bstr ~off:0 ~len:(length
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bstr)]. *)
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val blit_to_bytes :
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t -> src_off:int -> bytes -> dst_off:int -> len:int -> unit
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(** [blit_to_bytes src ~src_off dst ~dst_off ~len] copies [len] bytes from
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[src], starting at index [src_off], to byte sequence [dst], starting at
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index [dst_off].
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@raise Invalid_argument if [src_off] and [len] do not designate a valid
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range of [src], or if [dst_off] and [len] do not designate a valid range
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of [dst]. *)
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val is_empty : t -> bool
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(** [is_empty bstr] is [length bstr = 0]. *)
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val is_prefix : affix:string -> t -> bool
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(** [is_prefix ~affix bstr] is [true] iff [affix.[idx] = bstr.{idx}] for all
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indices [idx] of [affix]. *)
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val is_infix : affix:string -> t -> bool
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(** [is_infix ~affix bstr] is [true] iff there exists an index [j] in [bstr]
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such that for all indices [i] of [affix] we have [affix.[i] = bstr.{j +
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i}]. *)
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val is_suffix : affix:string -> t -> bool
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(** [is_suffix ~affix bstr] is [true] iff [affix.[n - idx] = bstr.{m - idx}]
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for all indices [idx] of [affix] with [n = String.length affix - 1] and
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[m = length bstr - 1]. *)
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val for_all : (char -> bool) -> t -> bool
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(** [for_all p bstr] is [true] iff for all indices [idx] of [bstr], [p
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bstr.{idx} = true]. *)
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val exists : (char -> bool) -> t -> bool
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(** [exists p bstr] is [true] iff there exists an index [idx] of [bstr] with
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[p bstr.{idx} = true]. *)
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val equal : t -> t -> bool
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(** [equal a b] is [a = b]. *)
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val with_range : ?first:int -> ?len:int -> t -> t
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(** [with_range ~first ~len bstr] are the consecutive bytes of [bstr] whose
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indices exist in the range \[[first];[first + len - 1]\].
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[first] defaults to [0] and [len] to [max_int]. Note that [first] can be
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any integer and [len] any positive integer. *)
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val with_index_range : ?first:int -> ?last:int -> t -> t
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(** [with_index_range ~first ~last bstr] are the consecutive bytes of [bstr]
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whose indices exists in the range \[[first];[last]\].
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[first] defaults to [0] and [last] to [length bstr - 1].
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Note that both [first] and [last] can be any integer. If [first > last]
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the interval is empty and the empty bigstring is returned. *)
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val trim : ?drop:(char -> bool) -> t -> t
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(** [trim ~drop bstr] is [bstr] with prefix and suffix bytes satisfying
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[drop] in [bstr] removed. [drop] defaults to [fun chr -> chr = ' ']. *)
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val span :
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?rev:bool -> ?min:int -> ?max:int -> ?sat:(char -> bool) -> t -> t * t
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(** [span ~rev ~min ~max ~sat bstr] is [(l, r)] where:
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{ul
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{- if [rev] is [false] (default), [l] is at least [min] and at most [max]
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consecutive [sat] satisfying initial bytes of [bstr] or {!empty} if
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there are no such bytes. [r] are the remaining bytes of [bstr].}
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{- if [rev] is [true], [r] is at least [min] and at most [max]
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consecutive [sat] satisfying final bytes of [bstr] or {!empty} if there
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are no such bytes. [l] are the remaining bytes of [bstr].}}
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If [max] is unspecified the span is unlimited. If [min] is unspecified it
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defaults to [0]. If [min > max] the condition can't be satisfied and the
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left or right span, depending on [rev], is always empty. [sat] defaults to
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[Fun.const true].
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@raise Invalid_argument if [max] or [min] is negative. *)
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val take : ?rev:bool -> ?min:int -> ?max:int -> ?sat:(char -> bool) -> t -> t
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val drop : ?rev:bool -> ?min:int -> ?max:int -> ?sat:(char -> bool) -> t -> t
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end
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type slice = private { offset: int; length: int; payload: Bstr.t }
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(** A slice is an aligned segment of bytes (according to the [pagesize]
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specified by the cache, see {!val:make}) with its absolute position into the
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underlying {i block-device} and size. *)
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val pp_slice : Format.formatter -> slice -> unit
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val bstr_of_slice : ?logical_address:int -> slice -> Bstr.t
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type 'fd map = 'fd -> pos:int -> int -> bigstring
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(** A value [map : 'fd map] when applied [map fd ~pos len] reads a
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{!type:bigstring} at [pos]. [map] must return as much data as is available,
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though never more than [len] bytes. [map] never fails. Instead, an empty
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[bigstring] must be returned if e.g. the position is out of range.
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Depending on how the cache is configured (see {!val:make}), [map] never
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read more than [pagesize] bytes. *)
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(** {2 Note about schedulers and [Cachet].}
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[Cachet] assumes that {!type:map} is {b atomic}, in other words: {!type:map}
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is a unit of work that is indivisible and guaranteed to be executed as a
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single, coherent, and uninterrupted operation.
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In this way, the [map] function is considered as a "direct" computation that
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does {b not} interact with a scheduler. However, reading a page can take
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time. It may therefore be necessary to add a cooperation point after
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{!val:load} or the {{!user_friendly} user-friendly functions}.
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These functions can read one or more pages. {!val:load} reads one page at
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most.
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{2 Note about large file and [Cachet].}
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For performance reasons, Cachet has chosen to use an [int] rather than an
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[int64] for the offset (the logical address). On a 64-bit architecture,
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addressing in the block device should not be a problem and Cachet is able
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to manage large block devices. However, on a 32-bit architecture, Cachet
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should only be able to handle ~2 GB files.
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We consider that it is up to the developer to check this:
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{[
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let _max_int31 = 2147483647L (* (1 lsl 31) - 1 *)
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let () =
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let fd = Unix.openfile "disk.img" Unix.[ O_RDONLY ] 0o644 in
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let stat = Unix.LargeFile.fstat fd in
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if Sys.word_size = 32 && stat.Unix.LargeFile.st_size > _max_int31
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then failwith "Too big block-device";
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...
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]}
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So that, as soon as possible, the user can find out whether or not the
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program can handle large block-devices. *)
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type 'fd t
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val fd : 'fd t -> 'fd
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val cache_hit : 'fd t -> int
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(** [cache_hit t] is the number of times a load hit the cache. *)
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val cache_miss : 'fd t -> int
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(** [cache_miss t] is the number of times a load didn't hit the cache. *)
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val copy : 'fd t -> 'fd t
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(** [copy t] creates a new, empty cache using the same [map] function. *)
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val make : ?cachesize:int -> ?pagesize:int -> map:'fd map -> 'fd -> 'fd t
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(** [make ~cachesize ~pagesize ~map fd] creates a new, empty cache using [map]
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and [fd] for reading [pagesize] bytes. The size of the cache is [cachesize].
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@raise Invalid_argument if either [cachesize] or [pagesize] is not a power
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of two. *)
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val load : 'fd t -> ?len:int -> int -> slice option
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(** [load t ~len logical_address] loads a page at the given [logical_address]
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and returns a {!type:slice}. [len] (defaults to [1]) is the expected
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minimum number of bytes returned.
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If the slice does not contains, at least, [len] bytes, [load] returns [None].
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[load t ~len:0 logical_address] always returns an empty slice. *)
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val invalidate : 'fd t -> off:int -> len:int -> unit
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(** [invalidate t ~off ~len] invalidates the cache on [len] bytes from [off]. *)
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(** {2:user_friendly User friendly functions.} *)
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(** {3 Binary decoding of integers.}
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The functions in this section binary decode integers from byte sequences.
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All following functions raise [Invalid_argument] if the space needed at
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index [i] to decode the integer is not available.
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Little-endian (resp. big-endian) encoding means that least (resp. most)
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significant bytes are stored first. Big-endian is also known as network byte
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order. Native-endian encoding is either little-endian or big-endian
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depending on {!Sys.big_endian}.
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32-bit and 64-bit integers are represented by the [int] type, which has more
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bits than the binary encoding. Functions that decode signed (resp. unsigned)
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8-bit or 16-bit integers represented by [int] values sign-extend (resp.
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zero-extend) their result. *)
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exception Out_of_bounds of int
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(** If Cachet tries to retrieve a byte outside the block device, this exception is raised. *)
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val get_int8 : 'fd t -> int -> int
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(** [get_int8 t logical_address] is [t]'s signed 8-bit integer starting at byte
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index [logical_address].
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@raise Out_of_bounds if [logical_address] is not accessible. *)
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val get_uint8 : 'fd t -> int -> int
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(** [get_uint8 t logical_address] is [t]'s unsigned 8-bit integer starting at
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byte index [logical_address].
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@raise Out_of_bounds if [logical_address] is not accessible. *)
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val get_uint16_ne : 'fd t -> int -> int
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val get_uint16_le : 'fd t -> int -> int
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val get_uint16_be : 'fd t -> int -> int
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val get_int16_ne : 'fd t -> int -> int
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val get_int16_le : 'fd t -> int -> int
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val get_int16_be : 'fd t -> int -> int
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val get_int32_ne : 'fd t -> int -> int32
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val get_int32_le : 'fd t -> int -> int32
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val get_int32_be : 'fd t -> int -> int32
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val get_int64_ne : 'fd t -> int -> int64
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val get_int64_le : 'fd t -> int -> int64
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val get_int64_be : 'fd t -> int -> int64
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val get_string : 'fd t -> len:int -> int -> string
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(** [get_string t ~len logical_address] loads the various pages needed from the
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cache or using [map] to copy [len] bytes available at [off].
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You can use {!val:syscalls} to find out how many times [get_string] can
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call [map] at most.
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@raise Out_of_bounds if [logical_address] and [len] byte(s) are not
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accessible. *)
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val get_seq : 'fd t -> int -> string Seq.t
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val next : 'fd t -> slice -> slice option
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val iter : 'fd t -> ?len:int -> fn:(int -> unit) -> int -> unit
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val blit_to_bytes :
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'fd t -> src_off:int -> bytes -> dst_off:int -> len:int -> unit
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(** [blit_to_bytes t ~src_off dst ~dst_off ~len] copies [len] bytes from
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the cached {i block-device} represented by [t], starting at index [src_off]
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as the logical address, to byte sequence [dst], starting at index
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[dst_off].
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This function can read several pages depending on the size of the [dst]
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buffer.
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@raise Invalid_argument if [src_off] and [len] do not designate a valid
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range of the {i block-device}, or if [dst_off] and [len] do not designate a
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valid range of [dst]. *)
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val syscalls : 'fd t -> logical_address:int -> len:int -> int
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(** [syscalls t ~logicial_address ~len] returns the maximum number (if the cache
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is empty) of calls to [map] to load a segment of the block-device according
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to the [logical_address] and the size [len] (in bytes) of the segment. *)
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