vfs: keep track of number of open RWHandles

vfs/file.go

@@ -21,6 +21,7 @@ type File struct {
 	mu                sync.Mutex // protects the following
 	o                 fs.Object  // NB o may be nil if file is being written
 	leaf              string     // leaf name of the object
+	rwOpenCount       int        // number of open files on this handle
 	writers           []Handle   // writers for this file
 	readWriters       int        // how many RWFileHandle are open for writing
 	readWriterClosing bool       // is a RWFileHandle currently cosing?
@@ -138,6 +139,31 @@ func (f *File) delWriter(h Handle, modifiedCacheFile bool) (lastWriterAndModifie
 	return
 }
 
+// addRWOpen should be called by ReadWriteHandle when they have
+// actually opened the file for read or write.
+func (f *File) addRWOpen() {
+	f.mu.Lock()
+	f.rwOpenCount++
+	f.mu.Unlock()
+}
+
+// delRWOpen should be called by ReadWriteHandle when they have closed
+// an actually opene file for read or write.
+func (f *File) delRWOpen() {
+	f.mu.Lock()
+	f.rwOpenCount--
+	f.mu.Unlock()
+}
+
+// rwOpens returns how many active open ReadWriteHandles there are.
+// Note that file handles which are in pending open state aren't
+// counted.
+func (f *File) rwOpens() int {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return f.rwOpenCount
+}
+
 // finishWriterClose resets the readWriterClosing flag
 func (f *File) finishWriterClose() {
 	f.mu.Lock()

vfs/read_write.go

@@ -192,6 +192,7 @@ func (fh *RWFileHandle) openPending(truncate bool) (err error) {
 	}
 	fh.File = fd
 	fh.opened = true
+	fh.file.addRWOpen()
 	fh.d.addObject(fh.file) // make sure the directory has this object in it now
 	return nil
 }
@@ -246,7 +247,12 @@ func (fh *RWFileHandle) close() (err error) {
 		return ECLOSED
 	}
 	fh.closed = true
-	defer fh.d.vfs.cache.close(fh.remote)
+	defer func() {
+		if fh.opened {
+			fh.file.delRWOpen()
+		}
+		fh.d.vfs.cache.close(fh.remote)
+	}()
 	rdwrMode := fh.flags & accessModeMask
 	writer := rdwrMode != os.O_RDONLY
 

vfs/read_write_test.go

@@ -74,9 +74,15 @@ func TestRWFileHandleMethodsRead(t *testing.T) {
 	// Size
 	assert.Equal(t, int64(16), fh.Size())
 
+	// No opens yet
+	assert.Equal(t, 0, fh.file.rwOpens())
+
 	// Read 1
 	assert.Equal(t, "0", rwReadString(t, fh, 1))
 
+	// Open after the read
+	assert.Equal(t, 1, fh.file.rwOpens())
+
 	// Read remainder
 	assert.Equal(t, "123456789abcdef", rwReadString(t, fh, 256))
 
@@ -101,6 +107,9 @@ func TestRWFileHandleMethodsRead(t *testing.T) {
 	assert.Equal(t, nil, fh.Close())
 	assert.True(t, fh.closed)
 
+	// No opens again
+	assert.Equal(t, 0, fh.file.rwOpens())
+
 	// Close again
 	assert.Equal(t, ECLOSED, fh.Close())
 }
@@ -266,6 +275,10 @@ func TestRWFileHandleMethodsWrite(t *testing.T) {
 	vfs, fh := rwHandleCreateWriteOnly(t, r)
 	defer cleanup(t, r, vfs)
 
+	// 1 opens since we opened with O_CREATE and the file didn't
+	// exist in the cache
+	assert.Equal(t, 1, fh.file.rwOpens())
+
 	// String
 	assert.Equal(t, "file1 (rw)", fh.String())
 	assert.Equal(t, "<nil *RWFileHandle>", (*RWFileHandle)(nil).String())
@@ -293,6 +306,9 @@ func TestRWFileHandleMethodsWrite(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, 5, n)
 
+	// Open after the write
+	assert.Equal(t, 1, fh.file.rwOpens())
+
 	// Offset #2
 	assert.Equal(t, int64(5), offset())
 	assert.Equal(t, int64(5), node.Size())
@@ -323,6 +339,9 @@ func TestRWFileHandleMethodsWrite(t *testing.T) {
 	// Close
 	assert.NoError(t, fh.Close())
 
+	// No opens again
+	assert.Equal(t, 0, fh.file.rwOpens())
+
 	// Check double close
 	err = fh.Close()
 	assert.Equal(t, ECLOSED, err)