a5ebd5de4b
The restorer can issue multiple calls to WriteAt in parallel. This can result in unexpected orderings of the Truncate and WriteAt calls and sometimes too short restored files.
116 lines
2.6 KiB
Go
116 lines
2.6 KiB
Go
package restorer
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import (
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"os"
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"sync"
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"github.com/cespare/xxhash/v2"
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"github.com/restic/restic/internal/debug"
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)
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// writes blobs to target files.
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// multiple files can be written to concurrently.
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// multiple blobs can be concurrently written to the same file.
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// TODO I am not 100% convinced this is necessary, i.e. it may be okay
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// to use multiple os.File to write to the same target file
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type filesWriter struct {
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buckets []filesWriterBucket
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}
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type filesWriterBucket struct {
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lock sync.Mutex
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files map[string]*partialFile
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}
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type partialFile struct {
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*os.File
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users int // Reference count.
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sparse bool
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}
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func newFilesWriter(count int) *filesWriter {
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buckets := make([]filesWriterBucket, count)
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for b := 0; b < count; b++ {
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buckets[b].files = make(map[string]*partialFile)
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}
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return &filesWriter{
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buckets: buckets,
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}
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}
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func (w *filesWriter) writeToFile(path string, blob []byte, offset int64, createSize int64, sparse bool) error {
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bucket := &w.buckets[uint(xxhash.Sum64String(path))%uint(len(w.buckets))]
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acquireWriter := func() (*partialFile, error) {
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bucket.lock.Lock()
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defer bucket.lock.Unlock()
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if wr, ok := bucket.files[path]; ok {
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bucket.files[path].users++
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return wr, nil
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}
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var flags int
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if createSize >= 0 {
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flags = os.O_CREATE | os.O_TRUNC | os.O_WRONLY
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} else {
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flags = os.O_WRONLY
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}
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f, err := os.OpenFile(path, flags, 0600)
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if err != nil {
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return nil, err
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}
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wr := &partialFile{File: f, users: 1, sparse: sparse}
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bucket.files[path] = wr
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if createSize >= 0 {
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if sparse {
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err = f.Truncate(createSize)
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if err != nil {
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return nil, err
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}
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} else {
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err := preallocateFile(wr.File, createSize)
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if err != nil {
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// Just log the preallocate error but don't let it cause the restore process to fail.
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// Preallocate might return an error if the filesystem (implementation) does not
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// support preallocation or our parameters combination to the preallocate call
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// This should yield a syscall.ENOTSUP error, but some other errors might also
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// show up.
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debug.Log("Failed to preallocate %v with size %v: %v", path, createSize, err)
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}
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}
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}
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return wr, nil
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}
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releaseWriter := func(wr *partialFile) error {
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bucket.lock.Lock()
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defer bucket.lock.Unlock()
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if bucket.files[path].users == 1 {
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delete(bucket.files, path)
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return wr.Close()
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}
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bucket.files[path].users--
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return nil
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}
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wr, err := acquireWriter()
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if err != nil {
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return err
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}
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_, err = wr.WriteAt(blob, offset)
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if err != nil {
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// ignore subsequent errors
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_ = releaseWriter(wr)
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return err
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}
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return releaseWriter(wr)
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}
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