Add a ReadOnlyFile wrapper type, and use it in UnionFs when applicable.

fuse/files.go

@@ -116,3 +116,30 @@ func (me *LoopbackFile) GetAttr() (*os.FileInfo, Status) {
 	}
 	return fi, OK
 }
+
+////////////////////////////////////////////////////////////////
+
+// ReadOnlyFile is a wrapper that denies writable operations
+type ReadOnlyFile struct {
+	File
+}
+
+func (me *ReadOnlyFile) Write(input *WriteIn, data []byte) (uint32, Status) {
+	return 0, EPERM
+}
+
+func (me *ReadOnlyFile) Fsync(*FsyncIn) (code Status) {
+	return OK
+}
+
+func (me *ReadOnlyFile) Truncate(size uint64) Status {
+	return EPERM
+}
+
+func (me *ReadOnlyFile) Chmod(mode uint32) Status {
+	return EPERM
+}
+
+func (me *ReadOnlyFile) Chown(uid uint32, gid uint32) Status {
+	return EPERM
+}

fuse/readonlyfs.go

@@ -61,8 +61,8 @@ func (me *ReadonlyFileSystem) Open(name string, flags uint32, context *Context)
 	if flags&O_ANYWRITE != 0 {
 		return nil, EPERM
 	}
-	// TODO - wrap the File object inside a R/O wrapper too?
-	return me.FileSystem.Open(name, flags, context)
+	file, code = me.FileSystem.Open(name, flags, context)
+	return &ReadOnlyFile{file}, code
 }
 
 func (me *ReadonlyFileSystem) OpenDir(name string, context *Context) (stream chan DirEntry, status Status) {

unionfs/unionfs.go

@@ -917,6 +917,9 @@ func (me *UnionFs) Open(name string, flags uint32, context *fuse.Context) (fuseF
 	if fuseFile != nil {
 		fuseFile = &UnionFsFile{fuseFile, r.branch}
 	}
+	if r.branch > 0 && fuseFile != nil {
+		fuseFile = &fuse.ReadOnlyFile{fuseFile}
+	}
 	return fuseFile, status
 }