fusefrontend: move hole padding check out of Write()

The details of the hole handling don't have to be in
Write, so move it away.

2 files changed, 29 insertions, 21 deletions

diff --git a/internal/fusefrontend/file.go b/internal/fusefrontend/file.go
index 9fb9f7e..ee48930 100644
--- a/internal/fusefrontend/file.go
+++ b/internal/fusefrontend/file.go
@@ -297,21 +297,11 @@ func (f *file) Write(data []byte, off int64) (uint32, fuse.Status) {
 	}
 	wlock.lock(f.ino)
 	defer wlock.unlock(f.ino)
-
 	tlog.Debug.Printf("ino%d: FUSE Write: offset=%d length=%d", f.ino, off, len(data))
-
-	fi, err := f.fd.Stat()
-	if err != nil {
-		tlog.Warn.Printf("Write: Fstat failed: %v", err)
-		return 0, fuse.ToStatus(err)
-	}
-	plainSize := f.contentEnc.CipherSizeToPlainSize(uint64(fi.Size()))
-	if f.createsCiphertextHole(plainSize, off) {
-		status := f.zeroPad(plainSize)
-		if status != fuse.OK {
-			tlog.Warn.Printf("zeroPad returned error %v", status)
-			return 0, status
-		}
+	// If the write creates a file hole, we have to zero-pad the last block.
+	status := f.writePadHole(off)
+	if !status.Ok() {
+		return 0, status
 	}
 	return f.doWrite(data, off)
 }
diff --git a/internal/fusefrontend/file_holes.go b/internal/fusefrontend/file_holes.go
index ff626d1..5b7a244 100644
--- a/internal/fusefrontend/file_holes.go
+++ b/internal/fusefrontend/file_holes.go
@@ -8,17 +8,35 @@ import (
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
-// Will a write to plaintext offset "off" create a file hole in the ciphertext?
-func (f *file) createsCiphertextHole(plainSize uint64, off int64) bool {
+// Will a write to plaintext offset "targetOff" create a file hole in the
+// ciphertext? If yes, zero-pad the last ciphertext block.
+func (f *file) writePadHole(targetOff int64) fuse.Status {
+	// Get the current file size.
+	fi, err := f.fd.Stat()
+	if err != nil {
+		tlog.Warn.Printf("checkAndPadHole: Fstat failed: %v", err)
+		return fuse.ToStatus(err)
+	}
+	plainSize := f.contentEnc.CipherSizeToPlainSize(uint64(fi.Size()))
 	// Appending a single byte to the file (equivalent to writing to
 	// offset=plainSize) would write to "nextBlock".
 	nextBlock := f.contentEnc.PlainOffToBlockNo(plainSize)
 	// targetBlock is the block the user wants to write to.
-	targetBlock := f.contentEnc.PlainOffToBlockNo(uint64(off))
-	// If the write goes past the next block, nextBlock will have
-	// to be zero-padded to the block boundary and at least nextBlock+1
-	// becomes a file hole in the ciphertext.
-	return targetBlock > nextBlock
+	targetBlock := f.contentEnc.PlainOffToBlockNo(uint64(targetOff))
+	// The write goes into an existing block or (if the last block was full)
+	// starts a new one directly after the last block. Nothing to do.
+	if targetBlock <= nextBlock {
+		return fuse.OK
+	}
+	// The write goes past the next block. nextBlock has
+	// to be zero-padded to the block boundary and (at least) nextBlock+1
+	// will become a file hole in the ciphertext.
+	status := f.zeroPad(plainSize)
+	if status != fuse.OK {
+		tlog.Warn.Printf("zeroPad returned error %v", status)
+		return status
+	}
+	return fuse.OK
 }
 
 // Zero-pad the file of size plainSize to the next block boundary