minio/erasure-readfile.go
2016-06-23 00:34:47 +05:30

255 lines
7.0 KiB
Go

/*
* 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"
"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) {
min := func(a int64, b int64) int {
if a < b {
return int(a)
}
return int(b)
}
// 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)
// Data chunk size on each block.
chunkSize := getEncodedBlockLen(eInfo.BlockSize, eInfo.DataBlocks)
// Get block info for given offset, length and block size.
startBlock, bytesToSkip := getBlockInfo(offset, eInfo.BlockSize)
orderedDisks := make([]StorageAPI, len(disks))
for index := range disks {
blockIndex := eInfo.Distribution[index]
orderedDisks[blockIndex-1] = disks[index]
}
for block := startBlock; bytesWritten < length; block++ {
curChunkSize := chunkSize
if totalLength-offset+bytesWritten < curChunkSize {
curChunkSize = getEncodedBlockLen(totalLength-offset+bytesWritten, eInfo.DataBlocks)
}
// Allocate encoded blocks up to storage disks.
enBlocks := make([][]byte, len(disks))
// Figure out the number of disks that are needed for the read.
// If all the data disks are available then dataDiskCount = eInfo.DataBlocks
// Else dataDiskCount = eInfo.DataBlocks + 1
diskCount := 0
for _, disk := range orderedDisks[:eInfo.DataBlocks] {
if disk == nil {
continue
}
diskCount++
}
if diskCount < eInfo.DataBlocks {
diskCount = eInfo.DataBlocks + 1
}
wg := &sync.WaitGroup{}
index := 0
for _, disk := range orderedDisks {
if disk == nil {
index++
continue
}
wg.Add(1)
go func(index int, disk StorageAPI) {
defer wg.Done()
buf := make([]byte, curChunkSize)
n, err := disk.ReadFile(volume, path, block*curChunkSize, buf)
if err != nil {
orderedDisks[index] = nil
return
}
enBlocks[index] = buf[:n]
}(index, disk)
index++
diskCount--
if diskCount == 0 {
break
}
}
wg.Wait()
// Counter to keep success data blocks.
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 {
for ; index < len(orderedDisks); index++ {
if (successDataBlocksCount + successParityBlocksCount) == (eInfo.DataBlocks + 1) {
break
}
buf := make([]byte, curChunkSize)
n, err := orderedDisks[index].ReadFile(volume, path, block*curChunkSize, buf)
if err != nil {
orderedDisks[index] = nil
continue
}
successParityBlocksCount++
enBlocks[index] = buf[:n]
}
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, min(eInfo.BlockSize, totalLength-offset+bytesWritten))
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 = buf[bytesToSkip:]
}
if len(buf) > int(length-bytesWritten) {
buf = 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
}