rbd: disable rbd_discard_on_zeroed_write_same for thick-allocation

Signed-off-by: Niels de Vos <ndevos@redhat.com>

internal/rbd/rbd_util.go

@@ -299,6 +299,15 @@ func (rv *rbdVolume) open() (*librbd.Image, error) {
 func (rv *rbdVolume) allocate(ctx context.Context) error {
 	util.DebugLog(ctx, "going to allocate %q with %d bytes, this may take time", rv.String(), rv.VolSize)
 
+	// We do not want to call discard, we really want to write zeros to get
+	// the allocation. This sets the option for the re-used connection, and
+	// all subsequent images that are opened. That is not a problem, as
+	// this is the only place images get written.
+	err := rv.conn.DisableDiscardOnZeroedWriteSame()
+	if err != nil {
+		return err
+	}
+
 	image, err := rv.open()
 	if err != nil {
 		return err

internal/util/connection.go

@@ -32,6 +32,8 @@ type ClusterConnection struct {
 	// FIXME: temporary reference for credentials. Remove this when go-ceph
 	// is used for operations.
 	Creds *Credentials
+
+	discardOnZeroedWriteSameDisabled bool
 }
 
 var (
@@ -92,3 +94,22 @@ func (cc *ClusterConnection) GetFSAdmin() (*ca.FSAdmin, error) {
 
 	return ca.NewFromConn(cc.conn), nil
 }
+
+// DisableDiscardOnZeroedWriteSame enables the
+// `rbd_discard_on_zeroed_write_same` option in the cluster connection, so that
+// writing zero blocks of data are actual writes on the OSDs (doing
+// allocations) and not discard calls. This makes writes much slower, but
+// enables the option to do thick-provisioning.
+func (cc *ClusterConnection) DisableDiscardOnZeroedWriteSame() error {
+	if cc.discardOnZeroedWriteSameDisabled {
+		return nil
+	}
+
+	err := cc.conn.SetConfigOption("rbd_discard_on_zeroed_write_same", "false")
+	if err != nil {
+		return err
+	}
+
+	cc.discardOnZeroedWriteSameDisabled = true
+	return nil
+}