fuse: print tweaks for passthrough support

Change-Id: I513d6344ff0d22649c240bbf31ef901dca70f4e2

fuse/passthrough_linux.go

@@ -35,7 +35,9 @@ func (ms *Server) RegisterBackingFd(fd int, flags uint32) (int32, syscall.Errno)
 	ms.writeMu.Lock()
 	id, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(ms.mountFd), uintptr(_DEV_IOC_BACKING_OPEN), uintptr(unsafe.Pointer(&m)))
 	ms.writeMu.Unlock()
-
+	if ms.opts.Debug {
+		ms.opts.Logger.Printf("ioctl: BACKING_OPEN %d (flags %x): id %d (%v)", fd, flags, id, errno)
+	}
 	return int32(id), errno
 }
 
@@ -43,8 +45,11 @@ func (ms *Server) RegisterBackingFd(fd int, flags uint32) (int32, syscall.Errno)
 // should have been acquired before using RegisterBackingFd.
 func (ms *Server) UnregisterBackingFd(id int32) syscall.Errno {
 	ms.writeMu.Lock()
-	_, _, ep := syscall.Syscall(syscall.SYS_IOCTL, uintptr(ms.mountFd), uintptr(_DEV_IOC_BACKING_CLOSE), uintptr(unsafe.Pointer(&id)))
+	_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(ms.mountFd), uintptr(_DEV_IOC_BACKING_CLOSE), uintptr(unsafe.Pointer(&id)))
 	ms.writeMu.Unlock()
 
-	return ep
+	if ms.opts.Debug {
+		ms.opts.Logger.Printf("ioctl: BACKING_CLOSE id %d: %v", id, errno)
+	}
+	return errno
 }

fuse/print.go

@@ -215,7 +215,7 @@ func (in *OpenOut) string() string {
 	if in.BackingID != 0 {
 		backing = fmt.Sprintf("backing=%d ", in.BackingID)
 	}
-	return fmt.Sprintf("{Fh %d %s %s}", in.Fh, backing,
+	return fmt.Sprintf("{Fh %d %s%s}", in.Fh, backing,
 		flagString(fuseOpenFlagNames, int64(in.OpenFlags), ""))
 }