main, fusefrontend: add "-noprealloc" option

Preallocation is very slow on hdds that run btrfs. Give the
user the option to disable it. This greatly speeds up small file
operations but reduces the robustness against out-of-space errors.

Also add the option to the man page.

More info: https://github.com/rfjakob/gocryptfs/issues/63

1 files changed, 19 insertions, 11 deletions

diff --git a/internal/fusefrontend/file.go b/internal/fusefrontend/file.go
index d637528..5fe866b 100644
--- a/internal/fusefrontend/file.go
+++ b/internal/fusefrontend/file.go
@@ -49,10 +49,12 @@ type file struct {
 	// The opCount is used to judge whether "lastWrittenOffset" is still
 	// guaranteed to be correct.
 	lastOpCount uint64
+	// Parent filesystem
+	fs *FS
 }
 
 // NewFile returns a new go-fuse File instance.
-func NewFile(fd *os.File, writeOnly bool, contentEnc *contentenc.ContentEnc) (nodefs.File, fuse.Status) {
+func NewFile(fd *os.File, writeOnly bool, fs *FS) (nodefs.File, fuse.Status) {
 	var st syscall.Stat_t
 	err := syscall.Fstat(int(fd.Fd()), &st)
 	if err != nil {
@@ -65,10 +67,11 @@ func NewFile(fd *os.File, writeOnly bool, contentEnc *contentenc.ContentEnc) (no
 	return &file{
 		fd:             fd,
 		writeOnly:      writeOnly,
-		contentEnc:     contentEnc,
+		contentEnc:     fs.contentEnc,
 		devIno:         di,
 		fileTableEntry: t,
 		loopbackFile:   nodefs.NewLoopbackFile(fd),
+		fs:             fs,
 	}, fuse.OK
 }
 
@@ -107,10 +110,12 @@ func (f *file) createHeader() (fileID []byte, err error) {
 	h := contentenc.RandomHeader()
 	buf := h.Pack()
 	// Prevent partially written (=corrupt) header by preallocating the space beforehand
-	err = syscallcompat.EnospcPrealloc(int(f.fd.Fd()), 0, contentenc.HeaderLen)
-	if err != nil {
-		tlog.Warn.Printf("ino%d: createHeader: prealloc failed: %s\n", f.devIno.ino, err.Error())
-		return nil, err
+	if !f.fs.args.NoPrealloc {
+		err = syscallcompat.EnospcPrealloc(int(f.fd.Fd()), 0, contentenc.HeaderLen)
+		if err != nil {
+			tlog.Warn.Printf("ino%d: createHeader: prealloc failed: %s\n", f.devIno.ino, err.Error())
+			return nil, err
+		}
 	}
 	// Actually write header
 	_, err = f.fd.WriteAt(buf, 0)
@@ -285,7 +290,7 @@ func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
 		writeChain[i] = blockData
 		numOutBytes += len(blockData)
 	}
-	// Concatenenate all elements in the writeChain into one contigous buffer
+	// Concatenenate all elements in the writeChain into one contiguous buffer
 	tmp := make([]byte, numOutBytes)
 	writeBuf := bytes.NewBuffer(tmp[:0])
 	for _, w := range writeChain {
@@ -293,11 +298,14 @@ func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
 	}
 	// Preallocate so we cannot run out of space in the middle of the write.
 	// This prevents partially written (=corrupt) blocks.
+	var err error
 	cOff := blocks[0].BlockCipherOff()
-	err := syscallcompat.EnospcPrealloc(int(f.fd.Fd()), int64(cOff), int64(writeBuf.Len()))
-	if err != nil {
-		tlog.Warn.Printf("ino%d fh%d: doWrite: prealloc failed: %s", f.devIno.ino, f.intFd(), err.Error())
-		return 0, fuse.ToStatus(err)
+	if !f.fs.args.NoPrealloc {
+		err = syscallcompat.EnospcPrealloc(int(f.fd.Fd()), int64(cOff), int64(writeBuf.Len()))
+		if err != nil {
+			tlog.Warn.Printf("ino%d fh%d: doWrite: prealloc failed: %s", f.devIno.ino, f.intFd(), err.Error())
+			return 0, fuse.ToStatus(err)
+		}
 	}
 	// Write
 	_, err = f.fd.WriteAt(writeBuf.Bytes(), int64(cOff))