vfs: move writeback of dirty data out of close() method into its own method (FlushWrites) and remove close() call from Flush()

If a file handle is duplicated with dup() and the duplicate handle is
flushed, rclone will go ahead and close the file, making the original
file handle stale. This change removes the close() call from Flush() and
replaces it with FlushWrites() so that the file only gets closed when
Release() is called. The new FlushWrites method takes care of actually
writing the file back to the underlying storage.

Fixes #3381

cmd/mountlib/mounttest/fs.go

@@ -77,6 +77,7 @@ func RunTests(t *testing.T, fn MountFn) {
 			t.Run("TestWriteFileOverwrite", TestWriteFileOverwrite)
 			t.Run("TestWriteFileDoubleClose", TestWriteFileDoubleClose)
 			t.Run("TestWriteFileFsync", TestWriteFileFsync)
+			t.Run("TestWriteFileDup", TestWriteFileDup)
 		})
 		log.Printf("Finished test run with cache mode %v (ok=%v)", cacheMode, ok)
 		if !ok {

cmd/mountlib/mounttest/write.go

@@ -1,10 +1,13 @@
 package mounttest
 
 import (
+	"os"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"github.com/rclone/rclone/vfs"
 )
 
 // TestWriteFileNoWrite tests writing a file with no write()'s to it
@@ -82,3 +85,48 @@ func TestWriteFileFsync(t *testing.T) {
 	run.waitForWriters()
 	run.rm(t, "to be synced")
 }
+
+// TestWriteFileDup tests behavior of mmap() in Python by using dup() on a file handle
+func TestWriteFileDup(t *testing.T) {
+	run.skipIfNoFUSE(t)
+
+	if run.vfs.Opt.CacheMode < vfs.CacheModeWrites {
+		t.Skip("not supported on vfs-cache-mode < writes")
+		return
+	}
+
+	filepath := run.path("to be synced")
+	fh, err := osCreate(filepath)
+	require.NoError(t, err)
+
+	testData := []byte("0123456789")
+
+	err = fh.Truncate(int64(len(testData) + 2))
+	require.NoError(t, err)
+
+	err = fh.Sync()
+	require.NoError(t, err)
+
+	var dupFd uintptr
+	dupFd, err = writeTestDup(fh.Fd())
+	require.NoError(t, err)
+
+	dupFile := os.NewFile(dupFd, fh.Name())
+	_, err = dupFile.Write(testData)
+	require.NoError(t, err)
+
+	err = dupFile.Close()
+	require.NoError(t, err)
+
+	_, err = fh.Seek(int64(len(testData)), 0)
+	require.NoError(t, err)
+
+	_, err = fh.Write([]byte("10"))
+	require.NoError(t, err)
+
+	err = fh.Close()
+	require.NoError(t, err)
+
+	run.waitForWriters()
+	run.rm(t, "to be synced")
+}

cmd/mountlib/mounttest/write_non_unix.go

@@ -5,9 +5,21 @@ package mounttest
 import (
 	"runtime"
 	"testing"
+
+	"golang.org/x/sys/windows"
 )
 
 // TestWriteFileDoubleClose tests double close on write
 func TestWriteFileDoubleClose(t *testing.T) {
 	t.Skip("not supported on " + runtime.GOOS)
 }
+
+// writeTestDup performs the platform-specific implementation of the dup() syscall
+func writeTestDup(oldfd uintptr) (uintptr, error) {
+	p, err := windows.GetCurrentProcess()
+	if err != nil {
+		return 0, err
+	}
+	var h windows.Handle
+	return uintptr(h), windows.DuplicateHandle(p, windows.Handle(oldfd), p, &h, 0, true, windows.DUPLICATE_SAME_ACCESS)
+}

cmd/mountlib/mounttest/write_unix.go

@@ -4,10 +4,12 @@ package mounttest
 
 import (
 	"runtime"
-	"syscall"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"golang.org/x/sys/unix"
+
+	"github.com/rclone/rclone/vfs"
 )
 
 // TestWriteFileDoubleClose tests double close on write
@@ -21,14 +23,14 @@ func TestWriteFileDoubleClose(t *testing.T) {
 	assert.NoError(t, err)
 	fd := out.Fd()
 
-	fd1, err := syscall.Dup(int(fd))
+	fd1, err := unix.Dup(int(fd))
 	assert.NoError(t, err)
 
-	fd2, err := syscall.Dup(int(fd))
+	fd2, err := unix.Dup(int(fd))
 	assert.NoError(t, err)
 
 	// close one of the dups - should produce no error
-	err = syscall.Close(fd1)
+	err = unix.Close(fd1)
 	assert.NoError(t, err)
 
 	// write to the file
@@ -41,14 +43,26 @@ func TestWriteFileDoubleClose(t *testing.T) {
 	err = out.Close()
 	assert.NoError(t, err)
 
-	// write to the other dup - should produce an error
-	_, err = syscall.Write(fd2, buf)
+	// write to the other dup
+	_, err = unix.Write(fd2, buf)
+	if run.vfs.Opt.CacheMode < vfs.CacheModeWrites {
+		// produces an error if cache mode < writes
 		assert.Error(t, err, "input/output error")
+	} else {
+		// otherwise does not produce an error
+		assert.NoError(t, err)
+	}
 
 	// close the dup - should not produce an error
-	err = syscall.Close(fd2)
+	err = unix.Close(fd2)
 	assert.NoError(t, err)
 
 	run.waitForWriters()
 	run.rm(t, "testdoubleclose")
 }
+
+// writeTestDup performs the platform-specific implementation of the dup() unix
+func writeTestDup(oldfd uintptr) (uintptr, error) {
+	newfd, err := unix.Dup(int(oldfd))
+	return uintptr(newfd), err
+}

vfs/read_write.go

@@ -230,28 +230,14 @@ func (fh *RWFileHandle) modified() bool {
 	return true
 }
 
-// close the file handle returning EBADF if it has been
-// closed already.
+// flushWrites flushes any pending writes to cloud storage
 //
-// Must be called with fh.mu held
-//
-// Note that we leave the file around in the cache on error conditions
-// to give the user a chance to recover it.
-func (fh *RWFileHandle) close() (err error) {
-	defer log.Trace(fh.logPrefix(), "")("err=%v", &err)
-	fh.file.muRW.Lock()
-	defer fh.file.muRW.Unlock()
+// Must be called with fh.muRW held
+func (fh *RWFileHandle) flushWrites(closeFile bool) error {
+	if fh.closed && !closeFile {
+		return nil
+	}
 
-	if fh.closed {
-		return ECLOSED
-	}
-	fh.closed = true
-	defer func() {
-		if fh.opened {
-			fh.file.delRWOpen()
-		}
-		fh.d.vfs.cache.close(fh.remote)
-	}()
 	rdwrMode := fh.flags & accessModeMask
 	writer := rdwrMode != os.O_RDONLY
 
@@ -284,8 +270,8 @@ func (fh *RWFileHandle) close() (err error) {
 	}
 
 	// Close the underlying file
-	if fh.opened {
-		err = fh.File.Close()
+	if fh.opened && closeFile {
+		err := fh.File.Close()
 		if err != nil {
 			err = errors.Wrap(err, "failed to close cache file")
 			return err
@@ -314,6 +300,32 @@ func (fh *RWFileHandle) close() (err error) {
 	return nil
 }
 
+// close the file handle returning EBADF if it has been
+// closed already.
+//
+// Must be called with fh.mu held
+//
+// Note that we leave the file around in the cache on error conditions
+// to give the user a chance to recover it.
+func (fh *RWFileHandle) close() (err error) {
+	defer log.Trace(fh.logPrefix(), "")("err=%v", &err)
+	fh.file.muRW.Lock()
+	defer fh.file.muRW.Unlock()
+
+	if fh.closed {
+		return ECLOSED
+	}
+	fh.closed = true
+	defer func() {
+		if fh.opened {
+			fh.file.delRWOpen()
+		}
+		fh.d.vfs.cache.close(fh.remote)
+	}()
+
+	return fh.flushWrites(true)
+}
+
 // Close closes the file
 func (fh *RWFileHandle) Close() error {
 	fh.mu.Lock()
@@ -346,7 +358,11 @@ func (fh *RWFileHandle) Flush() error {
 		fs.Debugf(fh.logPrefix(), "RWFileHandle.Flush ignoring flush on unwritten handle")
 		return nil
 	}
-	err := fh.close()
+
+	fh.file.muRW.Lock()
+	defer fh.file.muRW.Unlock()
+	err := fh.flushWrites(false)
+
 	if err != nil {
 		fs.Errorf(fh.logPrefix(), "RWFileHandle.Flush error: %v", err)
 	} else {

vfs/read_write_test.go

@@ -457,14 +457,19 @@ func TestRWFileHandleFlushWrite(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, 5, n)
 
-	// Check Flush closes file if write called
+	// Check Flush does not close file if write called
 	err = fh.Flush()
 	assert.NoError(t, err)
-	assert.True(t, fh.closed)
+	assert.False(t, fh.closed)
 
 	// Check flush does nothing if called again
 	err = fh.Flush()
 	assert.NoError(t, err)
+	assert.False(t, fh.closed)
+
+	// Check that Close closes the file
+	err = fh.Close()
+	assert.NoError(t, err)
 	assert.True(t, fh.closed)
 }
 

vfs/vfs.go

@@ -254,7 +254,7 @@ func (vfs *VFS) Fs() fs.Fs {
 func (vfs *VFS) SetCacheMode(cacheMode CacheMode) {
 	vfs.Shutdown()
 	vfs.cache = nil
-	if vfs.Opt.CacheMode > CacheModeOff {
+	if cacheMode > CacheModeOff {
 		ctx, cancel := context.WithCancel(context.Background())
 		cache, err := newCache(ctx, vfs.f, &vfs.Opt) // FIXME pass on context or get from Opt?
 		if err != nil {
@@ -263,6 +263,7 @@ func (vfs *VFS) SetCacheMode(cacheMode CacheMode) {
 			cancel()
 			return
 		}
+		vfs.Opt.CacheMode = cacheMode
 		vfs.cancel = cancel
 		vfs.cache = cache
 	}