rados: use rados_write_op_omap_rm_keys2()

WriteOp.RmOmapKeys now uses rados_write_op_omap_rm_keys2().

The entirety of removeOmapKeysStep struct was removed as it's not necessary for
it to own the various C-allocated values passed to
rados_write_op_omap_rm_keys2() as arguments. rados_write_op_omap_rm_keys2()
makes copies of all the string-based args [1], so it's sufficient for them to
be short lived.

[1] 2bd3dd512a/src/librados/librados_c.cc (L3888-L3902)

rados/omap.go

@@ -97,40 +97,6 @@ func (gos *GetOmapStep) More() bool {
 	return *gos.more != 0
 }
 
-// removeOmapKeysStep is a write operation step used to track state, especially
-// C memory, across the setup and use of a WriteOp.
-type removeOmapKeysStep struct {
-	withRefs
-	withoutUpdate
-
-	// arguments:
-	cKeys cutil.CPtrCSlice
-	cNum  C.size_t
-}
-
-func newRemoveOmapKeysStep(keys []string) *removeOmapKeysStep {
-	cKeys := cutil.NewCPtrCSlice(len(keys))
-	roks := &removeOmapKeysStep{
-		cKeys: cKeys,
-		cNum:  C.size_t(len(keys)),
-	}
-
-	i := 0
-	for _, key := range keys {
-		cKeys[i] = cutil.CPtr(C.CString(key))
-		roks.add(unsafe.Pointer(cKeys[i]))
-		i++
-	}
-
-	runtime.SetFinalizer(roks, opStepFinalizer)
-	return roks
-}
-
-func (roks *removeOmapKeysStep) free() {
-	roks.cKeys.Free()
-	roks.withRefs.free()
-}
-
 // SetOmap appends the map `pairs` to the omap `oid`
 func (ioctx *IOContext) SetOmap(oid string, pairs map[string][]byte) error {
 	op := CreateWriteOp()

rados/write_op.go

@@ -118,12 +118,14 @@ func (w *WriteOp) SetOmap(pairs map[string][]byte) {
 
 // RmOmapKeys removes the specified `keys` from the omap `oid`.
 func (w *WriteOp) RmOmapKeys(keys []string) {
-	roks := newRemoveOmapKeysStep(keys)
-	w.steps = append(w.steps, roks)
-	C.rados_write_op_omap_rm_keys(
+	cKeys := cutil.NewBufferGroupStrings(keys)
+	defer cKeys.Free()
+
+	C.rados_write_op_omap_rm_keys2(
 		w.op,
-		(**C.char)(roks.cKeys.Ptr()),
-		roks.cNum)
+		(**C.char)(cKeys.BuffersPtr()),
+		(*C.size_t)(cKeys.LengthsPtr()),
+		(C.size_t)(len(keys)))
 }
 
 // CleanOmap clears the omap `oid`.