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minio/erasure-readfile.go

220 lines
6.8 KiB

/*
* Minio Cloud Storage, (C) 2016 Minio, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package main
import (
"bytes"
"encoding/hex"
"errors"
"io"
"github.com/klauspost/reedsolomon"
)
// erasureReadFile - read bytes from erasure coded files and writes to given writer.
// Erasure coded files are read block by block as per given erasureInfo and data chunks
// are decoded into a data block. Data block is trimmed for given offset and length,
// then written to given writer. This function also supports bit-rot detection by
// verifying checksum of individual block's checksum.
func erasureReadFile(writer io.Writer, disks []StorageAPI, volume string, path string, partName string, eInfos []erasureInfo, offset int64, length int64) (int64, error) {
// Total bytes written to writer
bytesWritten := int64(0)
// Gather previously calculated block checksums.
blockCheckSums := metaPartBlockChecksums(disks, eInfos, partName)
// Pick one erasure info.
eInfo := pickValidErasureInfo(eInfos)
// Get block info for given offset, length and block size.
startBlock, bytesToSkip, endBlock := getBlockInfo(offset, length, eInfo.BlockSize)
for block := startBlock; block <= endBlock; block++ {
// Allocate encoded blocks up to storage disks.
enBlocks := make([][]byte, len(disks))
// Counter to keep success data blocks.
var successDataBlocksCount = 0
var noReconstruct bool // Set for no reconstruction.
// Keep how many bytes are read for this block.
// In most cases, last block in the file is shorter than eInfo.BlockSize.
lastReadSize := int64(0)
// Read from all the disks.
for index, disk := range disks {
blockIndex := eInfo.Distribution[index] - 1
if !isValidBlock(disks, volume, path, toDiskIndex(blockIndex, eInfo.Distribution), blockCheckSums) {
continue
}
if disk == nil {
continue
}
// Initialize chunk slice and fill the data from each parts.
enBlocks[blockIndex] = make([]byte, eInfo.BlockSize)
// Read the necessary blocks.
n, err := disk.ReadFile(volume, path, block*eInfo.BlockSize, enBlocks[blockIndex])
if err != nil {
enBlocks[blockIndex] = nil
} else if n < eInfo.BlockSize {
// As the data we got is smaller than eInfo.BlockSize, keep only required chunk slice
enBlocks[blockIndex] = append([]byte{}, enBlocks[blockIndex][:n]...)
}
// Remember bytes read at first time.
if lastReadSize == 0 {
lastReadSize = n
}
// If bytes read is not equal to bytes read lastly, treat it as corrupted chunk.
if n != lastReadSize {
return bytesWritten, errXLDataCorrupt
}
// Verify if we have successfully read all the data blocks.
if blockIndex < eInfo.DataBlocks && enBlocks[blockIndex] != nil {
successDataBlocksCount++
// Set when we have all the data blocks and no
// reconstruction is needed, so that we can avoid
// erasure reconstruction.
noReconstruct = successDataBlocksCount == eInfo.DataBlocks
if noReconstruct {
// Break out we have read all the data blocks.
break
}
}
}
// Verify if reconstruction is needed, proceed with reconstruction.
if !noReconstruct {
err := decodeData(enBlocks, eInfo.DataBlocks, eInfo.ParityBlocks)
if err != nil {
return bytesWritten, err
}
}
// Get data blocks from encoded blocks.
dataBlocks, err := getDataBlocks(enBlocks, eInfo.DataBlocks, int(lastReadSize)*eInfo.DataBlocks)
if err != nil {
return bytesWritten, err
}
// Keep required bytes into buf.
buf := dataBlocks
// If this is start block, skip unwanted bytes.
if block == startBlock {
buf = append([]byte{}, dataBlocks[bytesToSkip:]...)
}
// If this is end block, retain only required bytes.
if block == endBlock {
buf = append([]byte{}, buf[:length-bytesWritten]...)
}
// Copy data blocks.
var n int64
n, err = io.Copy(writer, bytes.NewReader(buf))
bytesWritten += int64(n)
if err != nil {
return bytesWritten, err
}
}
return bytesWritten, nil
}
// PartObjectChecksum - returns the checksum for the part name from the checksum slice.
func (e erasureInfo) PartObjectChecksum(partName string) checkSumInfo {
for _, checksum := range e.Checksum {
if checksum.Name == partName {
return checksum
}
}
return checkSumInfo{}
}
// xlMetaPartBlockChecksums - get block checksums for a given part.
func metaPartBlockChecksums(disks []StorageAPI, eInfos []erasureInfo, partName string) (blockCheckSums []checkSumInfo) {
for index := range disks {
if eInfos[index].IsValid() {
// Save the read checksums for a given part.
blockCheckSums = append(blockCheckSums, eInfos[index].PartObjectChecksum(partName))
} else {
blockCheckSums = append(blockCheckSums, checkSumInfo{})
}
}
return blockCheckSums
}
// Takes block index and block distribution to get the disk index.
func toDiskIndex(blockIdx int, distribution []int) int {
// Find out the right disk index for the input block index.
for index, blockIndex := range distribution {
if blockIndex-1 == blockIdx {
return index
}
}
return -1
}
// isValidBlock - calculates the checksum hash for the block and
// validates if its correct returns true for valid cases, false otherwise.
func isValidBlock(disks []StorageAPI, volume, path string, diskIndex int, blockCheckSums []checkSumInfo) (ok bool) {
ok = false
// Unknown block index requested, treat it as error.
if diskIndex == -1 {
return ok
}
// Disk is not present, treat entire block to be non existent.
if disks[diskIndex] == nil {
return ok
}
// Read everything for a given block and calculate hash.
hashWriter := newHash(blockCheckSums[diskIndex].Algorithm)
hashBytes, err := hashSum(disks[diskIndex], volume, path, hashWriter)
if err != nil {
return ok
}
ok = hex.EncodeToString(hashBytes) == blockCheckSums[diskIndex].Hash
return ok
}
// decodeData - decode encoded blocks.
func decodeData(enBlocks [][]byte, dataBlocks, parityBlocks int) error {
rs, err := reedsolomon.New(dataBlocks, parityBlocks)
if err != nil {
return err
}
err = rs.Reconstruct(enBlocks)
if err != nil {
return err
}
// Verify reconstructed blocks (parity).
ok, err := rs.Verify(enBlocks)
if err != nil {
return err
}
if !ok {
// Blocks cannot be reconstructed, corrupted data.
err = errors.New("Verification failed after reconstruction, data likely corrupted.")
return err
}
return nil
}