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d5ce2f6944
Remove option of providing Technique and handling errors based on that choose a matrix type automatically based on number of data blocks. INTEL recommends on using cauchy for consistent invertible matrices, while vandermonde is faster we should default to cauchy for large data blocks.
121 lines
4.0 KiB
Go
121 lines
4.0 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 "ec.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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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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