1 files changed, 38 insertions, 0 deletions
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
+}