feat(xo-server): add MBR to cloud-init drive (#6889)

CHANGELOG.unreleased.md

@@ -12,6 +12,7 @@
 - [Plugin/auth-iodc] OpenID Connect scopes are now configurable and `profile` is included by default
 - [Dashboard/Health] Button to copy UUID of an orphan VDI to the clipboard (PR [#6893](https://github.com/vatesfr/xen-orchestra/pull/6893))
 - [Kubernetes recipe] Add the possibility to choose the version for the cluster [#6842](https://github.com/vatesfr/xen-orchestra/issues/6842) (PR [#6880](https://github.com/vatesfr/xen-orchestra/pull/6880))
+- [New VM] cloud-init drives are now bootable in a Windows VM (PR [#6889](https://github.com/vatesfr/xen-orchestra/pull/6889))
 
 ### Bug fixes
 
@@ -49,7 +50,7 @@
 - @xen-orchestra/vmware-explorer patch
 - xen-api patch
 - xo-cli minor
-- xo-server patch
+- xo-server minor
 - xo-server-auth-oidc minor
 - xo-server-perf-alert patch
 - xo-web minor

packages/xo-server/src/fatfs-buffer.mjs

@@ -23,6 +23,29 @@ const SECTOR_SIZE = 512
 
 const TEN_MIB = 10 * 1024 * 1024
 
+// https://en.wikipedia.org/wiki/Master_boot_record
+// we'll add a classical generic mbr
+// with one FAT16 partition addressed by LBA
+
+export function addMbr(buf) {
+  const mbr = Buffer.alloc(SECTOR_SIZE, 0)
+  // 0 - 446 is bootstrap code , keep it empty
+
+  // entry
+  mbr[446] = 0x80 // entry is bootable
+  mbr[450] = 0x0e // FAT16 LBA
+  mbr.writeInt32LE(1, 454) // LBA address of first sector
+  assert.strictEqual(buf.length % SECTOR_SIZE, 0, 'buffer  length must be aligned to sector size')
+  mbr.writeInt32LE(buf.length / SECTOR_SIZE + 1, 458) // LBA address of last sector
+
+  // 3 more 16 bytes entry we don't need
+
+  // boot signature
+  mbr[510] = 0x55
+  mbr[511] = 0xaa
+  return Buffer.concat([mbr, buf])
+}
+
 // Creates a 10MB buffer and initializes it as a FAT 16 volume.
 export function init({ label = 'NO LABEL   ' } = {}) {
   assert.strictEqual(typeof label, 'string')

packages/xo-server/src/xapi/index.mjs

@@ -28,7 +28,7 @@ import { extractOpaqueRef, parseDateTime, Xapi as XapiBase } from '@xen-orchestr
 import { Ref } from 'xen-api'
 import { synchronized } from 'decorator-synchronized'
 
-import fatfsBuffer, { init as fatfsBufferInit } from '../fatfs-buffer.mjs'
+import fatfsBuffer, { addMbr, init as fatfsBufferInit } from '../fatfs-buffer.mjs'
 import { camelToSnakeCase, forEach, map, pDelay, promisifyAll } from '../utils.mjs'
 import { debounceWithKey } from '../_pDebounceWithKey.mjs'
 
@@ -1301,15 +1301,7 @@ export default class Xapi extends XapiBase {
     const sr = this.getObject(srId)
 
     // First, create a small VDI (10MB) which will become the ConfigDrive
-    const buffer = fatfsBufferInit({ label: 'cidata     ' })
-    const vdi = await this._getOrWaitObject(
-      await this.VDI_create({
-        name_label: 'XO CloudConfigDrive',
-        SR: sr.$ref,
-        virtual_size: buffer.length,
-      })
-    )
-    $defer.onFailure(() => vdi.$destroy())
+    let buffer = fatfsBufferInit({ label: 'cidata     ' })
 
     // Then, generate a FAT fs
     const { mkdir, writeFile } = promisifyAll(fatfs.createFileSystem(fatfsBuffer(buffer)))
@@ -1334,6 +1326,15 @@ export default class Xapi extends XapiBase {
         )
       ),
     ])
+    buffer = addMbr(buffer)
+    const vdi = await this._getOrWaitObject(
+      await this.VDI_create({
+        name_label: 'XO CloudConfigDrive',
+        SR: sr.$ref,
+        virtual_size: buffer.length,
+      })
+    )
+    $defer.onFailure(() => vdi.$destroy())
 
     // ignore errors, I (JFT) don't understand why they are emitted
     // because it works