added WriteOpCmpExtStep with malloc'd rval

internal/cutil/aliases.go

@@ -21,8 +21,14 @@ const (
 
 	// SizeTSize is the size of C.size_t
 	SizeTSize = C.sizeof_size_t
+
+	// IntSize is the size of C.int
+	IntSize = C.sizeof_int
 )
 
+// Compile-time assertion ensuring that Go's `int` is at least as large as C's.
+const _ = unsafe.Sizeof(int(0)) - unsafe.Sizeof(C.int(0))
+
 // SizeT wraps size_t from C.
 type SizeT C.size_t
 

rados/write_op_preview.go

@@ -4,13 +4,41 @@ package rados
 
 // #cgo LDFLAGS: -lrados
 // #include <rados/librados.h>
+// #include <stdlib.h>
 //
 import "C"
 
 import (
 	"unsafe"
+
+	"github.com/ceph/go-ceph/internal/cutil"
 )
 
+// WriteOpCmpExtStep holds result of the CmpExt write operation.
+// Result is valid only after Operate() was called.
+type WriteOpCmpExtStep struct {
+	prval *C.int
+
+	// Result of the CmpExt write operation.
+	Result int
+}
+
+func (s *WriteOpCmpExtStep) update() error {
+	s.Result = (int)(*s.prval)
+	return nil
+}
+
+func (s *WriteOpCmpExtStep) free() {
+	C.free(unsafe.Pointer(s.prval))
+	s.prval = nil
+}
+
+func newWriteOpCmpExtStep() *WriteOpCmpExtStep {
+	return &WriteOpCmpExtStep{
+		prval: (*C.int)(C.malloc(cutil.IntSize)),
+	}
+}
+
 // CmpExt ensures that given object range (extent) satisfies comparison (PREVIEW).
 //
 // Implements:
@@ -19,13 +47,16 @@ import (
 //                             size_t cmp_len,
 //                             uint64_t off,
 //                             int * prval);
-func (w *WriteOp) CmpExt(b []byte, offset uint64, prval *int32) {
+func (w *WriteOp) CmpExt(b []byte, offset uint64) *WriteOpCmpExtStep {
 	oe := newWriteStep(b, 0, offset)
-	w.steps = append(w.steps, oe)
+	cmpExtStep := newWriteOpCmpExtStep()
+	w.steps = append(w.steps, oe, cmpExtStep)
 	C.rados_write_op_cmpext(
 		w.op,
 		oe.cBuffer,
 		oe.cDataLen,
 		oe.cOffset,
-		(*C.int)(unsafe.Pointer(prval)))
+		cmpExtStep.prval)
+
+	return cmpExtStep
 }

rados/write_op_preview_test.go

@@ -12,7 +12,6 @@ func (suite *RadosTestSuite) TestWriteOpCmpExt() {
 
 	oid := "TestWriteOpCmpExt"
 	data := []byte("compare this")
-	var prval int32
 
 	// Create an object and populate it with data.
 	op1 := CreateWriteOp()
@@ -25,16 +24,16 @@ func (suite *RadosTestSuite) TestWriteOpCmpExt() {
 	// Compare contents of the object. Should succeed.
 	op2 := CreateWriteOp()
 	defer op2.Release()
-	op2.CmpExt(data, 0, &prval)
+	cmpExtRes1 := op2.CmpExt(data, 0)
 	err = op2.Operate(suite.ioctx, oid, OperationNoFlag)
 	ta.NoError(err)
-	ta.Equal(prval, int32(0))
+	ta.Equal(cmpExtRes1.Result, int(0))
 
 	// Compare contents of the object. Should fail.
 	op3 := CreateWriteOp()
 	defer op3.Release()
-	op3.CmpExt([]byte("xxx"), 0, &prval)
+	cmpExtRes2 := op3.CmpExt([]byte("xxx"), 0)
 	err = op3.Operate(suite.ioctx, oid, OperationNoFlag)
 	ta.Error(err)
-	ta.NotEqual(prval, int32(0))
+	ta.NotEqual(cmpExtRes2.Result, int(0))
 }