thin-provisioning-tools/functional-tests/btree.scm
2017-08-08 19:28:59 +01:00

139 lines
3.8 KiB
Scheme

(library
(btree)
(export btree-open
btree-lookup
btree-each)
(import (block-io)
(chezscheme)
(binary-format)
(list-utils))
;;; Unlike the kernel or c++ versions, I'm going to leave it to the hiogher
;;; levels to handle multi level btrees.
(binary-format
(node-header pack-btree-node unpack-btree-node)
(csum le32)
(flags le32)
(blocknr le64)
(nr-entries le32)
(max-entries le32)
(value-size le32)
(padding le32))
(define-record-type value-type (fields size unpacker))
(define (max-entries vt)
(/ (- metadata-block-size node-header-size)
(+ (size-of 'le64)
(value-type-size vt))))
(define (key-offset index)
(+ node-header-size (* (size-of 'le64 index))))
(define (value-base vt)
(+ node-header-size
(* (max-entries vt)
(size-of 'le64))))
(define (value-offset vt index)
(+ (value-base vt)
(* (value-type-size vt) index)))
(define-record-type btree
(fields value-type dev root))
(define (btree-open vt dev root)
(make-btree value-type dev root))
(define le64-type
(make-value-type (size-of 'le64)
(lambda (bv offset)
(unpack-type bv offset le64))))
(define (internal-node? header)
(bitwise-bit-set? 0 (node-header-flags header)))
(define (leaf-node? header)
(bitwise-bit-set? 1 (node-header-flags header)))
(define (key-at node index)
(unpack-type node (key-offset index le64)))
(define (value-at node index vt)
((value-type-unpacker vt) node (value-offset vt index)))
;;; Performs a binary search looking for the key and returns the index of the
;;; lower bound.
(define (lower-bound node header key)
(let ((nr-entries (node-header-nr-entries header)))
(let loop ((lo 0) (hi nr-entries))
(if (= 1 (- hi lo))
lo
(let* ((mid (+ lo (/ (- hi lo) 2)))
(k (key-at mid)))
(cond
((= key k) mid)
((< k key) (loop mid hi))
(else (loop lo mid))))))))
;;;;----------------------------------------------
;;;; Lookup
;;;;----------------------------------------------
(define (btree-lookup tree key default)
(let ((dev (btree-dev tree))
(vt (btree-value-type tree)))
(define (lookup root fail-k)
(let loop ((root root))
(let* ((node (read-block dev root))
(header (unpack-node-header node 0))
(index (lower-bound node header key fail-k)))
(if (internal-node? header)
(loop (unpack-value node index le64-type))
(if (= key (key-at node index))
(value-at node index vt)
(fail-k default))))))
(call/cc
(lambda (fail-k)
(lookup (btree-root tree) fail-k)))))
;;;;----------------------------------------------
;;;; Walking the btree
;;;;----------------------------------------------
;;; Calls (fn key value) on every entry of the btree.
(define (btree-each tree fn)
(let ((vt (btree-value-type tree)))
(define (visit-leaf node header)
(let loop ((index 0))
(when (< index (node-header-nr-entries header))
(fn (key-at node index) (value-at node index vt))
(loop (+ 1 index)))))
(define (visit-internal node header)
(let loop ((index 0))
(when (< index (node-header-nr-entries header))
(visit-node (value-at node index le64-type))
(loop (+ 1 index)))))
(define (visit-node root)
(let* ((node (read-block root))
(header (unpack-node-header node 0)))
((if (internal-node? header) visit-internal visit-leaf) node header)))
(visit-node (btree-root tree)))
))