rados: use ptrguard for writeStep buffer

Signed-off-by: Sven Anderson <[email protected]>

rados/write_step.go

@@ -5,15 +5,16 @@ import "C"
 
 import (
 	"unsafe"
+
+	"github.com/ceph/go-ceph/internal/cutil"
 )
 
 type writeStep struct {
 	withoutUpdate
-	withoutFree
-	// the c pointer utilizes the Go byteslice data and no free is needed
 
 	// inputs:
-	b []byte
+	b  []byte
+	pg *cutil.PtrGuard
 
 	// arguments:
 	cBuffer   *C.char
@@ -23,11 +24,17 @@ type writeStep struct {
 }
 
 func newWriteStep(b []byte, writeLen, offset uint64) *writeStep {
+	bufPtr := unsafe.Pointer(&b[0])
 	return &writeStep{
 		b:         b,
-		cBuffer:   (*C.char)(unsafe.Pointer(&b[0])),
+		pg:        cutil.NewPtrGuard(bufPtr),
+		cBuffer:   (*C.char)(bufPtr),
 		cDataLen:  C.size_t(len(b)),
 		cWriteLen: C.size_t(writeLen),
 		cOffset:   C.uint64_t(offset),
 	}
 }
+
+func (v *writeStep) free() {
+	v.pg.Release()
+}