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124 lines
4.1 KiB
Go
124 lines
4.1 KiB
Go
/*
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* Minio Cloud Storage, (C) 2014 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package erasure
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// #cgo CFLAGS: -O0
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// #include <stdlib.h>
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// #include "isa-l.h"
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// #include "ec_minio_common.h"
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import "C"
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import (
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"errors"
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"fmt"
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"unsafe"
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)
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// Decode decodes erasure coded blocks of data into its original
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// form. Erasure coded data contains K data blocks and M parity
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// blocks. Decode can withstand data loss up to any M number of blocks.
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//
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// "encodedDataBlocks" is an array of K data blocks and M parity
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// blocks. Data blocks are position and order dependent. Missing blocks
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// are set to "nil". There must be at least "K" number of data|parity
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// blocks.
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//
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// "dataLen" is the length of original source data
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func (e *Erasure) Decode(encodedDataBlocks [][]byte, dataLen int) (decodedData []byte, err error) {
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e.mutex.Lock()
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defer e.mutex.Unlock()
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var source, target **C.uchar
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k := int(e.params.K)
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m := int(e.params.M)
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n := k + m
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// We need the data and parity blocks preserved in the same order. Missing blocks are set to nil.
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if len(encodedDataBlocks) != n {
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msg := fmt.Sprintf("Encoded data blocks slice must of length [%d]", n)
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return nil, errors.New(msg)
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}
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// Length of a single encoded block
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encodedBlockLen := GetEncodedBlockLen(dataLen, uint8(k))
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// Keep track of errors per block.
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missingEncodedBlocks := make([]int, n+1)
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var missingEncodedBlocksCount int
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// Check for the missing encoded blocks
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for i := range encodedDataBlocks {
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if encodedDataBlocks[i] == nil || len(encodedDataBlocks[i]) == 0 {
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missingEncodedBlocks[missingEncodedBlocksCount] = i
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missingEncodedBlocksCount++
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}
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}
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// Cannot reconstruct original data. Need at least M number of data or parity blocks.
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if missingEncodedBlocksCount > m {
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return nil, fmt.Errorf("Cannot reconstruct original data. Need at least [%d] data or parity blocks", m)
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}
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// Convert from Go int slice to C int array
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missingEncodedBlocksC := intSlice2CIntArray(missingEncodedBlocks[:missingEncodedBlocksCount])
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// Allocate buffer for the missing blocks
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for i := range encodedDataBlocks {
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if encodedDataBlocks[i] == nil || len(encodedDataBlocks[i]) == 0 {
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encodedDataBlocks[i] = make([]byte, encodedBlockLen)
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}
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}
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// If not already initialized, recompute and cache
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if e.decodeMatrix == nil || e.decodeTbls == nil || e.decodeIndex == nil {
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var decodeMatrix, decodeTbls *C.uchar
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var decodeIndex *C.uint32_t
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C.minio_init_decoder(missingEncodedBlocksC, C.int(k), C.int(n), C.int(missingEncodedBlocksCount),
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e.encodeMatrix, &decodeMatrix, &decodeTbls, &decodeIndex)
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// cache this for future needs
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e.decodeMatrix = decodeMatrix
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e.decodeTbls = decodeTbls
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e.decodeIndex = decodeIndex
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}
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// Make a slice of pointers to encoded blocks. Necessary to bridge to the C world.
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pointers := make([]*byte, n)
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for i := range encodedDataBlocks {
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pointers[i] = &encodedDataBlocks[i][0]
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}
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// Get pointers to source "data" and target "parity" blocks from the output byte array.
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ret := C.minio_get_source_target(C.int(missingEncodedBlocksCount), C.int(k), C.int(m), missingEncodedBlocksC,
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e.decodeIndex, (**C.uchar)(unsafe.Pointer(&pointers[0])), &source, &target)
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if int(ret) == -1 {
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return nil, errors.New("Unable to decode data")
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}
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// Decode data
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C.ec_encode_data(C.int(encodedBlockLen), C.int(k), C.int(missingEncodedBlocksCount), e.decodeTbls,
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source, target)
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// Allocate buffer to output buffer
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decodedData = make([]byte, 0, encodedBlockLen*int(k))
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for i := 0; i < int(k); i++ {
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decodedData = append(decodedData, encodedDataBlocks[i]...)
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}
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return decodedData[:dataLen], nil
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}
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