/
erasure-decode.go
334 lines (300 loc) · 8.71 KB
/
erasure-decode.go
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// Copyright (c) 2015-2021 MinIO, Inc.
//
// This file is part of MinIO Object Storage stack
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package cmd
import (
"context"
"errors"
"fmt"
"io"
"sync"
"sync/atomic"
xioutil "github.com/minio/minio/internal/ioutil"
)
// Reads in parallel from readers.
type parallelReader struct {
readers []io.ReaderAt
orgReaders []io.ReaderAt
dataBlocks int
offset int64
shardSize int64
shardFileSize int64
buf [][]byte
readerToBuf []int
}
// newParallelReader returns parallelReader.
func newParallelReader(readers []io.ReaderAt, e Erasure, offset, totalLength int64) *parallelReader {
r2b := make([]int, len(readers))
for i := range r2b {
r2b[i] = i
}
return ¶llelReader{
readers: readers,
orgReaders: readers,
dataBlocks: e.dataBlocks,
offset: (offset / e.blockSize) * e.ShardSize(),
shardSize: e.ShardSize(),
shardFileSize: e.ShardFileSize(totalLength),
buf: make([][]byte, len(readers)),
readerToBuf: r2b,
}
}
// preferReaders can mark readers as preferred.
// These will be chosen before others.
func (p *parallelReader) preferReaders(prefer []bool) {
if len(prefer) != len(p.orgReaders) {
return
}
// Copy so we don't change our input.
tmp := make([]io.ReaderAt, len(p.orgReaders))
copy(tmp, p.orgReaders)
p.readers = tmp
// next is the next non-preferred index.
next := 0
for i, ok := range prefer {
if !ok || p.readers[i] == nil {
continue
}
if i == next {
next++
continue
}
// Move reader with index i to index next.
// Do this by swapping next and i
p.readers[next], p.readers[i] = p.readers[i], p.readers[next]
p.readerToBuf[next] = i
p.readerToBuf[i] = next
next++
}
}
// Returns if buf can be erasure decoded.
func (p *parallelReader) canDecode(buf [][]byte) bool {
bufCount := 0
for _, b := range buf {
if len(b) > 0 {
bufCount++
}
}
return bufCount >= p.dataBlocks
}
// Read reads from readers in parallel. Returns p.dataBlocks number of bufs.
func (p *parallelReader) Read(dst [][]byte) ([][]byte, error) {
newBuf := dst
if len(dst) != len(p.readers) {
newBuf = make([][]byte, len(p.readers))
} else {
for i := range newBuf {
newBuf[i] = newBuf[i][:0]
}
}
var newBufLK sync.RWMutex
if p.offset+p.shardSize > p.shardFileSize {
p.shardSize = p.shardFileSize - p.offset
}
if p.shardSize == 0 {
return newBuf, nil
}
readTriggerCh := make(chan bool, len(p.readers))
defer xioutil.SafeClose(readTriggerCh) // close the channel upon return
for i := 0; i < p.dataBlocks; i++ {
// Setup read triggers for p.dataBlocks number of reads so that it reads in parallel.
readTriggerCh <- true
}
disksNotFound := int32(0)
bitrotHeal := int32(0) // Atomic bool flag.
missingPartsHeal := int32(0) // Atomic bool flag.
readerIndex := 0
var wg sync.WaitGroup
// if readTrigger is true, it implies next disk.ReadAt() should be tried
// if readTrigger is false, it implies previous disk.ReadAt() was successful and there is no need
// to try reading the next disk.
for readTrigger := range readTriggerCh {
newBufLK.RLock()
canDecode := p.canDecode(newBuf)
newBufLK.RUnlock()
if canDecode {
break
}
if readerIndex == len(p.readers) {
break
}
if !readTrigger {
continue
}
wg.Add(1)
go func(i int) {
defer wg.Done()
rr := p.readers[i]
if rr == nil {
// Since reader is nil, trigger another read.
readTriggerCh <- true
return
}
bufIdx := p.readerToBuf[i]
if p.buf[bufIdx] == nil {
// Reading first time on this disk, hence the buffer needs to be allocated.
// Subsequent reads will reuse this buffer.
p.buf[bufIdx] = make([]byte, p.shardSize)
}
// For the last shard, the shardsize might be less than previous shard sizes.
// Hence the following statement ensures that the buffer size is reset to the right size.
p.buf[bufIdx] = p.buf[bufIdx][:p.shardSize]
n, err := rr.ReadAt(p.buf[bufIdx], p.offset)
if err != nil {
switch {
case errors.Is(err, errFileNotFound):
atomic.StoreInt32(&missingPartsHeal, 1)
case errors.Is(err, errFileCorrupt):
atomic.StoreInt32(&bitrotHeal, 1)
case errors.Is(err, errDiskNotFound):
atomic.AddInt32(&disksNotFound, 1)
}
// This will be communicated upstream.
p.orgReaders[bufIdx] = nil
p.readers[i] = nil
// Since ReadAt returned error, trigger another read.
readTriggerCh <- true
return
}
newBufLK.Lock()
newBuf[bufIdx] = p.buf[bufIdx][:n]
newBufLK.Unlock()
// Since ReadAt returned success, there is no need to trigger another read.
readTriggerCh <- false
}(readerIndex)
readerIndex++
}
wg.Wait()
if p.canDecode(newBuf) {
p.offset += p.shardSize
if missingPartsHeal == 1 {
return newBuf, errFileNotFound
} else if bitrotHeal == 1 {
return newBuf, errFileCorrupt
}
return newBuf, nil
}
// If we cannot decode, just return read quorum error.
return nil, fmt.Errorf("%w (offline-disks=%d/%d)", errErasureReadQuorum, disksNotFound, len(p.readers))
}
// Decode reads from readers, reconstructs data if needed and writes the data to the writer.
// A set of preferred drives can be supplied. In that case they will be used and the data reconstructed.
func (e Erasure) Decode(ctx context.Context, writer io.Writer, readers []io.ReaderAt, offset, length, totalLength int64, prefer []bool) (written int64, derr error) {
if offset < 0 || length < 0 {
return -1, errInvalidArgument
}
if offset+length > totalLength {
return -1, errInvalidArgument
}
if length == 0 {
return 0, nil
}
reader := newParallelReader(readers, e, offset, totalLength)
if len(prefer) == len(readers) {
reader.preferReaders(prefer)
}
startBlock := offset / e.blockSize
endBlock := (offset + length) / e.blockSize
var bytesWritten int64
var bufs [][]byte
for block := startBlock; block <= endBlock; block++ {
var blockOffset, blockLength int64
switch {
case startBlock == endBlock:
blockOffset = offset % e.blockSize
blockLength = length
case block == startBlock:
blockOffset = offset % e.blockSize
blockLength = e.blockSize - blockOffset
case block == endBlock:
blockOffset = 0
blockLength = (offset + length) % e.blockSize
default:
blockOffset = 0
blockLength = e.blockSize
}
if blockLength == 0 {
break
}
var err error
bufs, err = reader.Read(bufs)
if len(bufs) > 0 {
// Set only if there are be enough data for reconstruction.
// and only for expected errors, also set once.
if errors.Is(err, errFileNotFound) || errors.Is(err, errFileCorrupt) {
if derr == nil {
derr = err
}
}
} else if err != nil {
// For all errors that cannot be reconstructed fail the read operation.
return -1, err
}
if err = e.DecodeDataBlocks(bufs); err != nil {
return -1, err
}
n, err := writeDataBlocks(ctx, writer, bufs, e.dataBlocks, blockOffset, blockLength)
if err != nil {
return -1, err
}
bytesWritten += n
}
if bytesWritten != length {
return bytesWritten, errLessData
}
return bytesWritten, derr
}
// Heal reads from readers, reconstruct shards and writes the data to the writers.
func (e Erasure) Heal(ctx context.Context, writers []io.Writer, readers []io.ReaderAt, totalLength int64, prefer []bool) (derr error) {
if len(writers) != e.parityBlocks+e.dataBlocks {
return errInvalidArgument
}
reader := newParallelReader(readers, e, 0, totalLength)
if len(readers) == len(prefer) {
reader.preferReaders(prefer)
}
startBlock := int64(0)
endBlock := totalLength / e.blockSize
if totalLength%e.blockSize != 0 {
endBlock++
}
var bufs [][]byte
for block := startBlock; block < endBlock; block++ {
var err error
bufs, err = reader.Read(bufs)
if len(bufs) > 0 {
if errors.Is(err, errFileNotFound) || errors.Is(err, errFileCorrupt) {
if derr == nil {
derr = err
}
}
} else if err != nil {
return err
}
if err = e.DecodeDataAndParityBlocks(ctx, bufs); err != nil {
return err
}
w := parallelWriter{
writers: writers,
writeQuorum: 1,
errs: make([]error, len(writers)),
}
if err = w.Write(ctx, bufs); err != nil {
return err
}
}
return derr
}