minio/cmd/erasure-readfile.go

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2016-03-28 00:52:38 -04:00
/*
* 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 cmd
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import (
"io"
"github.com/minio/minio/pkg/errors"
)
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type errIdx struct {
idx int
err error
}
func (s ErasureStorage) readConcurrent(volume, path string, offset, length int64,
verifiers []*BitrotVerifier) (buffers [][]byte, needsReconstruction bool,
err error) {
errChan := make(chan errIdx)
stageBuffers := make([][]byte, len(s.disks))
buffers = make([][]byte, len(s.disks))
readDisk := func(i int) {
stageBuffers[i] = make([]byte, length)
disk := s.disks[i]
if disk == OfflineDisk {
errChan <- errIdx{i, errors.Trace(errDiskNotFound)}
return
}
_, rerr := disk.ReadFile(volume, path, offset, stageBuffers[i], verifiers[i])
errChan <- errIdx{i, rerr}
}
var finishedCount, successCount, launchIndex int
for ; launchIndex < s.dataBlocks; launchIndex++ {
go readDisk(launchIndex)
}
for finishedCount < launchIndex {
select {
case errVal := <-errChan:
finishedCount++
if errVal.err != nil {
// TODO: meaningfully log the disk read error
// A disk failed to return data, so we
// request an additional disk if possible
if launchIndex < s.dataBlocks+s.parityBlocks {
needsReconstruction = true
// requiredBlocks++
go readDisk(launchIndex)
launchIndex++
}
} else {
successCount++
buffers[errVal.idx] = stageBuffers[errVal.idx]
stageBuffers[errVal.idx] = nil
}
}
}
if successCount != s.dataBlocks {
// Not enough disks returns data.
err = errors.Trace(errXLReadQuorum)
}
return
}
// ReadFile reads as much data as requested from the file under the
// given volume and path and writes the data to the provided writer.
// The algorithm and the keys/checksums are used to verify the
// integrity of the given file. ReadFile will read data from the given
// offset up to the given length. If parts of the file are corrupted
// ReadFile tries to reconstruct the data.
func (s ErasureStorage) ReadFile(writer io.Writer, volume, path string, offset,
length, totalLength int64, checksums [][]byte, algorithm BitrotAlgorithm,
blocksize int64) (f ErasureFileInfo, err error) {
if offset < 0 || length < 0 {
return f, errors.Trace(errUnexpected)
}
if offset+length > totalLength {
return f, errors.Trace(errUnexpected)
}
if !algorithm.Available() {
return f, errors.Trace(errBitrotHashAlgoInvalid)
}
f.Checksums = make([][]byte, len(s.disks))
verifiers := make([]*BitrotVerifier, len(s.disks))
for i, disk := range s.disks {
if disk == OfflineDisk {
continue
}
verifiers[i] = NewBitrotVerifier(algorithm, checksums[i])
}
chunksize := ceilFrac(blocksize, int64(s.dataBlocks))
// We read all whole-blocks of erasure coded data containing
// the requested data range.
//
// The start index of the erasure coded block containing the
// `offset` byte of data is:
partDataStartIndex := (offset / blocksize) * chunksize
// The start index of the erasure coded block containing the
// (last) byte of data at the index `offset + length - 1` is:
blockStartIndex := ((offset + length - 1) / blocksize) * chunksize
// However, we need the end index of the e.c. block containing
// the last byte - we need to check if that block is the last
// block in the part (in that case, it may be have a different
// chunk size)
isLastBlock := (totalLength-1)/blocksize == (offset+length-1)/blocksize
var partDataEndIndex int64
if isLastBlock {
lastBlockChunkSize := chunksize
if totalLength%blocksize != 0 {
lastBlockChunkSize = ceilFrac(totalLength%blocksize, int64(s.dataBlocks))
}
partDataEndIndex = blockStartIndex + lastBlockChunkSize - 1
} else {
partDataEndIndex = blockStartIndex + chunksize - 1
}
// Thus, the length of data to be read from the part file(s) is:
partDataLength := partDataEndIndex - partDataStartIndex + 1
// The calculation above does not apply when length == 0:
if length == 0 {
partDataLength = 0
}
var buffers [][]byte
var needsReconstruction bool
buffers, needsReconstruction, err = s.readConcurrent(volume, path,
partDataStartIndex, partDataLength, verifiers)
if err != nil {
// Could not read enough disks.
return
}
numChunks := ceilFrac(partDataLength, chunksize)
blocks := make([][]byte, len(s.disks))
if needsReconstruction && numChunks > 1 {
// Allocate once for all the equal length blocks. The
// last block may have a different length - allocation
// for this happens inside the for loop below.
for i := range blocks {
if len(buffers[i]) == 0 {
blocks[i] = make([]byte, chunksize)
}
}
}
var buffOffset int64
for chunkNumber := int64(0); chunkNumber < numChunks; chunkNumber++ {
if chunkNumber == numChunks-1 && partDataLength%chunksize != 0 {
chunksize = partDataLength % chunksize
// We allocate again as the last chunk has a
// different size.
for i := range blocks {
if len(buffers[i]) == 0 {
blocks[i] = make([]byte, chunksize)
}
}
}
for i := range blocks {
if len(buffers[i]) == 0 {
blocks[i] = blocks[i][0:0]
}
}
for i := range blocks {
if len(buffers[i]) != 0 {
blocks[i] = buffers[i][buffOffset : buffOffset+chunksize]
}
}
buffOffset += chunksize
if needsReconstruction {
if err = s.ErasureDecodeDataBlocks(blocks); err != nil {
return f, errors.Trace(err)
}
}
var writeStart int64
if chunkNumber == 0 {
writeStart = offset % blocksize
}
writeLength := blocksize - writeStart
if chunkNumber == numChunks-1 {
lastBlockLength := (offset + length) % blocksize
if lastBlockLength != 0 {
writeLength = lastBlockLength - writeStart
}
}
n, err := writeDataBlocks(writer, blocks, s.dataBlocks, writeStart, writeLength)
if err != nil {
return f, err
}
f.Size += n
}
f.Algorithm = algorithm
for i, disk := range s.disks {
if disk == OfflineDisk || buffers[i] == nil {
continue
}
f.Checksums[i] = verifiers[i].Sum(nil)
}
return f, nil
}