mountlib: ensure we don't open files with read and write intent

cmd/mountlib/mounttest/file.go

@@ -28,6 +28,11 @@ func TestFileModTime(t *testing.T) {
 	run.rm(t, "file")
 }
 
+// os.Create without opening for write too
+func osCreate(name string) (*os.File, error) {
+	return os.OpenFile(name, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
+}
+
 // TestFileModTimeWithOpenWriters tests mod time on open files
 func TestFileModTimeWithOpenWriters(t *testing.T) {
 	run.skipIfNoFUSE(t)
@@ -35,7 +40,7 @@ func TestFileModTimeWithOpenWriters(t *testing.T) {
 	mtime := time.Date(2012, 11, 18, 17, 32, 31, 0, time.UTC)
 	filepath := run.path("cp-archive-test")
 
-	f, err := os.Create(filepath)
+	f, err := osCreate(filepath)
 	require.NoError(t, err)
 
 	_, err = f.Write([]byte{104, 105})

cmd/mountlib/mounttest/write.go

@@ -1,7 +1,6 @@
 package mounttest
 
 import (
-	"os"
 	"testing"
 	"time"
 
@@ -13,7 +12,7 @@ import (
 func TestWriteFileNoWrite(t *testing.T) {
 	run.skipIfNoFUSE(t)
 
-	fd, err := os.Create(run.path("testnowrite"))
+	fd, err := osCreate(run.path("testnowrite"))
 	assert.NoError(t, err)
 
 	err = fd.Close()
@@ -31,7 +30,7 @@ func TestWriteFileNoWrite(t *testing.T) {
 func FIXMETestWriteOpenFileInDirListing(t *testing.T) {
 	run.skipIfNoFUSE(t)
 
-	fd, err := os.Create(run.path("testnowrite"))
+	fd, err := osCreate(run.path("testnowrite"))
 	assert.NoError(t, err)
 
 	run.checkDir(t, "testnowrite 0")
@@ -70,7 +69,7 @@ func TestWriteFileOverwrite(t *testing.T) {
 // NB the code for this is in file.go rather than write.go
 func TestWriteFileFsync(t *testing.T) {
 	filepath := run.path("to be synced")
-	fd, err := os.Create(filepath)
+	fd, err := osCreate(filepath)
 	require.NoError(t, err)
 	_, err = fd.Write([]byte("hello"))
 	require.NoError(t, err)

cmd/mountlib/mounttest/write_unix.go

@@ -3,7 +3,6 @@
 package mounttest
 
 import (
-	"os"
 	"syscall"
 	"testing"
 
@@ -14,7 +13,7 @@ import (
 func TestWriteFileDoubleClose(t *testing.T) {
 	run.skipIfNoFUSE(t)
 
-	out, err := os.Create(run.path("testdoubleclose"))
+	out, err := osCreate(run.path("testdoubleclose"))
 	assert.NoError(t, err)
 	fd := out.Fd()