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minio/erasure-readfile.go

296 lines
9.8 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 (
"encoding/hex"
"errors"
"io"
"sync"
"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, totalLength int64) (int64, error) {
// Pick one erasure info.
eInfo := pickValidErasureInfo(eInfos)
// Gather previously calculated block checksums.
blockCheckSums := metaPartBlockChecksums(disks, eInfos, partName)
orderedBlockCheckSums := make([]checkSumInfo, len(disks))
// []orderedDisks will have first eInfo.DataBlocks disks as data disks and rest will be parity.
orderedDisks := make([]StorageAPI, len(disks))
for index := range disks {
blockIndex := eInfo.Distribution[index]
orderedDisks[blockIndex-1] = disks[index]
orderedBlockCheckSums[blockIndex-1] = blockCheckSums[index]
}
// bitrotVerify verifies if the file on a particular disk does not have bitrot by verifying the hash of
// the contents of the file.
bitrotVerify := func() func(diskIndex int) bool {
verified := make([]bool, len(orderedDisks))
// Return closure so that we have reference to []verified and not recalculate the hash on it
// everytime the function is called for the same disk.
return func(diskIndex int) bool {
if verified[diskIndex] {
return true
}
isValid := isValidBlock(orderedDisks[diskIndex], volume, path, orderedBlockCheckSums[diskIndex])
verified[diskIndex] = isValid
return isValid
}
}()
// Total bytes written to writer
bytesWritten := int64(0)
// chunkSize is roughly BlockSize/DataBlocks.
// chunkSize is calculated such that chunkSize*DataBlocks accommodates BlockSize bytes.
// So chunkSize*DataBlocks can be slightly larger than BlockSize if BlockSize is not divisible by
// DataBlocks. The extra space will have 0-padding.
chunkSize := getEncodedBlockLen(eInfo.BlockSize, eInfo.DataBlocks)
startBlock, endBlock, bytesToSkip := getBlockInfo(offset, totalLength, eInfo.BlockSize)
// For each block, read chunk from each disk. If we are able to read all the data disks then we don't
// need to read parity disks. If one of the data disk is missing we need to read DataBlocks+1 number
// of disks. Once read, we Reconstruct() missing data if needed and write it to the given writer.
for block := startBlock; bytesWritten < length; block++ {
// curChunkSize will be chunkSize except for the last block because the size of the last block
// can be less than BlockSize.
curChunkSize := chunkSize
if block == endBlock && (totalLength%eInfo.BlockSize != 0) {
// If this is the last block and size of the block is < BlockSize.
curChunkSize = getEncodedBlockLen(totalLength%eInfo.BlockSize, eInfo.DataBlocks)
}
// Each element of enBlocks holds curChunkSize'd amount of data read from its corresponding disk.
enBlocks := make([][]byte, len(disks))
// Figure out the number of disks that are needed for the read.
// We will need DataBlocks number of disks if all the data disks are up.
// We will need DataBlocks+1 number of disks even if one of the data disks is down.
diskCount := 0
// Count the number of data disks that are up.
for _, disk := range orderedDisks[:eInfo.DataBlocks] {
if disk == nil {
continue
}
diskCount++
}
if diskCount < eInfo.DataBlocks {
// Not enough data disks up, so we need DataBlocks+1 number of disks for reed-solomon Reconstruct()
diskCount = eInfo.DataBlocks + 1
}
wg := &sync.WaitGroup{}
// current disk index from which to read, this will be used later in case one of the parallel reads fails.
index := 0
// Read from the disks in parallel.
for _, disk := range orderedDisks {
if disk == nil {
index++
continue
}
wg.Add(1)
go func(index int, disk StorageAPI) {
defer wg.Done()
ok := bitrotVerify(index)
if !ok {
// So that we don't read from this disk for the next block.
orderedDisks[index] = nil
return
}
buf := make([]byte, curChunkSize)
// Note that for the offset calculation we have to use chunkSize and not
// curChunkSize. If we use curChunkSize for offset calculation then it
// can result in wrong offset for the last block.
n, err := disk.ReadFile(volume, path, block*chunkSize, buf)
if err != nil {
// So that we don't read from this disk for the next block.
orderedDisks[index] = nil
return
}
enBlocks[index] = buf[:n]
}(index, disk)
index++
diskCount--
if diskCount == 0 {
break
}
}
wg.Wait()
// Count number of data and parity blocks that were read.
var successDataBlocksCount = 0
var successParityBlocksCount = 0
for bufidx, buf := range enBlocks {
if buf == nil {
continue
}
if bufidx < eInfo.DataBlocks {
successDataBlocksCount++
continue
}
successParityBlocksCount++
}
if successDataBlocksCount < eInfo.DataBlocks {
// If we don't have DataBlocks number of data blocks we will have to read enough
// parity blocks such that we have DataBlocks+1 number for blocks for reedsolomon.Reconstruct()
for ; index < len(orderedDisks); index++ {
if (successDataBlocksCount + successParityBlocksCount) == (eInfo.DataBlocks + 1) {
// We have DataBlocks+1 blocks, enough for reedsolomon.Reconstruct()
break
}
ok := bitrotVerify(index)
if !ok {
// Mark nil so that we don't read from this disk for the next block.
orderedDisks[index] = nil
continue
}
buf := make([]byte, curChunkSize)
n, err := orderedDisks[index].ReadFile(volume, path, block*chunkSize, buf)
if err != nil {
// Mark nil so that we don't read from this disk for the next block.
orderedDisks[index] = nil
continue
}
successParityBlocksCount++
enBlocks[index] = buf[:n]
}
// Reconstruct the missing data blocks.
err := decodeData(enBlocks, eInfo.DataBlocks, eInfo.ParityBlocks)
if err != nil {
return bytesWritten, err
}
}
// enBlocks data can have 0-padding hence we need to figure the exact number
// of bytes we want to read from enBlocks.
blockSize := eInfo.BlockSize
if block == endBlock && totalLength%eInfo.BlockSize != 0 {
// For the last block, the block size can be less than BlockSize.
blockSize = totalLength % eInfo.BlockSize
}
data, err := getDataBlocks(enBlocks, eInfo.DataBlocks, int(blockSize))
if err != nil {
return bytesWritten, err
}
// If this is start block, skip unwanted bytes.
if block == startBlock {
data = data[bytesToSkip:]
}
if len(data) > int(length-bytesWritten) {
// We should not send more data than what was requested.
data = data[:length-bytesWritten]
}
_, err = writer.Write(data)
if err != nil {
return bytesWritten, err
}
bytesWritten += int64(len(data))
}
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(disk StorageAPI, volume, path string, blockCheckSum checkSumInfo) (ok bool) {
ok = false
if disk == nil {
return false
}
// Read everything for a given block and calculate hash.
hashWriter := newHash(blockCheckSum.Algorithm)
hashBytes, err := hashSum(disk, volume, path, hashWriter)
if err != nil {
return ok
}
ok = hex.EncodeToString(hashBytes) == blockCheckSum.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
}