butane/util: use yaml instead of json for unmarhal

butane/config/config_test.go

@@ -0,0 +1,51 @@
+// Copyright 2020 Red Hat, Inc
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package config
+
+import (
+	"testing"
+
+	"github.com/coreos/ignition/v2/butane/config/common"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// Ensures that large sizeMiB values are rendered as normal integers in
+// the generated MachineConfig YAML, rather than being formatted with
+// scientific notation (e.g. "1e+06" instead of "1000000").
+// See: https://github.com/coreos/ignition/issues/2309
+func TestOpenShiftSizeMiBFormatting(t *testing.T) {
+	input := []byte(`
+variant: openshift
+version: 4.19.0
+metadata:
+  name: test
+  labels:
+    machineconfiguration.openshift.io/role: worker
+storage:
+  disks:
+    - device: /dev/sda
+      partitions:
+        - number: 1
+          size_mib: 17179869184
+`)
+	out, r, err := TranslateBytes(input, common.TranslateBytesOptions{})
+	assert.NoError(t, err)
+	assert.False(t, r.IsFatal())
+
+	strOut := string(out)
+	assert.Contains(t, strOut, "sizeMiB: 17179869184")
+	assert.NotContains(t, strOut, "e+")
+}

butane/config/util/util.go

@@ -156,7 +156,7 @@ func TranslateBytesYAML(input []byte, container interface{}, translateMethod str
 	}
 
 	var ifaceCfg interface{}
-	if err := json.Unmarshal(jsonCfg, &ifaceCfg); err != nil {
+	if err := yaml.Unmarshal(jsonCfg, &ifaceCfg); err != nil {
 		return []byte{}, r, err
 	}
 

docs/release-notes.md

@@ -15,6 +15,8 @@ nav_order: 9
 ### Bug fixes
 
 - Resolve intermediate symlinks in relabel paths, fixing SELinux relabeling failures for users with `home_dir` on OSTree platforms after policycoreutils 3.11 ([#2316](https://github.com/coreos/ignition/pull/2316))
+- Fix Butane rendering large `sizeMiB`/`startMiB` values in scientific
+  notation when generating OpenShift MachineConfig YAML ([#2310](https://github.com/coreos/ignition/pull/2310))
 
 ## Ignition 2.27.0 (2026-08-26)