From 2003ca965d2905e240f2b2f1c596aa02f7786c77 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher <jakobunt@gmail.com>
Date: Sun, 4 Oct 2015 11:39:35 +0200
Subject: [PATCH] Zero-pad last block if a file hole is created on Write()

Fixes TestFileHoles test
---
 pathfs_frontend/file.go       | 16 +++++++++------
 pathfs_frontend/file_holes.go | 38 +++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 6 deletions(-)
 create mode 100644 pathfs_frontend/file_holes.go

diff --git a/pathfs_frontend/file.go b/pathfs_frontend/file.go
index 9c58557..2c2f1eb 100644
--- a/pathfs_frontend/file.go
+++ b/pathfs_frontend/file.go
@@ -113,7 +113,7 @@ func (f *file) doRead(off uint64, length uint64) ([]byte, fuse.Status) {
 
 // Read - FUSE call
 func (f *file) Read(buf []byte, off int64) (resultData fuse.ReadResult, code fuse.Status) {
-	cryptfs.Debug.Printf("ino%d: Read: offset=%d length=%d\n", f.ino, len(buf), off)
+	cryptfs.Debug.Printf("ino%d: FUSE Read: offset=%d length=%d\n", f.ino, len(buf), off)
 
 	if f.writeOnly {
 		cryptfs.Warn.Printf("ino%d: Tried to read from write-only file\n", f.ino)
@@ -133,10 +133,8 @@ func (f *file) Read(buf []byte, off int64) (resultData fuse.ReadResult, code fus
 	return fuse.ReadResultData(out), status
 }
 
-// Write - FUSE call
-func (f *file) Write(data []byte, off int64) (uint32, fuse.Status) {
-	cryptfs.Debug.Printf("ino%d: Write %s: offset=%d length=%d\n", f.ino, off, len(data))
-
+// Do the actual write
+func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
 	var written uint32
 	status := fuse.OK
 	dataBuf := bytes.NewBuffer(data)
@@ -177,10 +175,16 @@ func (f *file) Write(data []byte, off int64) (uint32, fuse.Status) {
 		}
 		written += uint32(b.Length)
 	}
-
 	return written, status
 }
 
+// Write - FUSE call
+func (f *file) Write(data []byte, off int64) (uint32, fuse.Status) {
+	cryptfs.Debug.Printf("ino%d: FUSE Write %s: offset=%d length=%d\n", f.ino, off, len(data))
+	f.conditionalZeroPad(off)
+	return f.doWrite(data, off)
+}
+
 // Release - FUSE call, forget file
 func (f *file) Release() {
 	f.lock.Lock()
diff --git a/pathfs_frontend/file_holes.go b/pathfs_frontend/file_holes.go
new file mode 100644
index 0000000..8c9c83f
--- /dev/null
+++ b/pathfs_frontend/file_holes.go
@@ -0,0 +1,38 @@
+package pathfs_frontend
+
+import (
+	"fmt"
+	"github.com/hanwen/go-fuse/fuse"
+	"github.com/rfjakob/gocryptfs/cryptfs"
+)
+
+// Will a write to offset "off" create a file hole?
+func (f *file) createsHole(cipherSize uint64, off int64) bool {
+	nextBlock := f.cfs.BlockNoCipherOff(cipherSize)
+	targetBlock := f.cfs.BlockNoPlainOff(uint64(off))
+	if targetBlock > nextBlock {
+		return true
+	}
+	return false
+}
+
+// Zero-pad the file if a write to "off" creates a file hole
+func (f *file) conditionalZeroPad(off int64) fuse.Status {
+	fi, err := f.fd.Stat()
+	if err != nil {
+		cryptfs.Warn.Printf("conditionalZeroPad: Stat: %v\n", err)
+		return fuse.ToStatus(err)
+	}
+	cipherSize := uint64(fi.Size())
+
+	if f.createsHole(cipherSize, off) == false {
+		return fuse.OK
+	}
+
+	plainSize := f.cfs.PlainSize(cipherSize)
+	lastBlockLen := plainSize % f.cfs.PlainBS()
+	missing := f.cfs.PlainBS() - lastBlockLen
+	pad := make([]byte, missing)
+	_, status := f.doWrite(pad, int64(plainSize))
+	return status
+}