feat(disk_util): Switch from SYSLINUX's gptmbr.bin to mbr.bin

cgpt now supports generating hybrid MBRs and the classic style mbr.bin
from any version of SYSLINUX should work the same with the hybrid MBR.
The other code, gptmbr.bin, changes after SYSLINUX 3. Switching lets me
play with different versions of SYSLINUX without breaking everything.

With this change all images feature a hybrid MBR so the special case for
some VM platforms has been removed.

build_library/base_image_util.sh

@@ -7,12 +7,11 @@ create_base_image() {
   local disk_layout=$2
 
   local disk_img="${BUILD_DIR}/${image_name}"
-  local mbr_img="/usr/share/syslinux/gptmbr.bin"
   local root_fs_dir="${BUILD_DIR}/rootfs"
 
   info "Using image type ${disk_layout}"
   "${BUILD_LIBRARY_DIR}/disk_util" --disk_layout="${disk_layout}" \
-      format --mbr_boot_code="${mbr_img}" "${disk_img}"
+      format "${disk_img}"
 
   "${BUILD_LIBRARY_DIR}/disk_util" --disk_layout="${disk_layout}" \
       mount "${disk_img}" "${root_fs_dir}"

build_library/disk_util

@@ -15,6 +15,10 @@ import uuid
 # First sector we can use.
 GPT_RESERVED_SECTORS = 34
 
+# Default MBR boot code for hybrid MBRs
+DEFAULT_MBR_BOOT_CODE = '/usr/share/syslinux/mbr.bin'
+
+
 class ConfigNotFound(Exception):
   pass
 class PartitionNotFound(Exception):
@@ -23,6 +27,8 @@ class InvalidLayout(Exception):
   pass
 class InvalidAdjustment(Exception):
   pass
+class InvalidBootCode(Exception):
+  pass
 
 
 def LoadPartitionConfig(options):
@@ -254,7 +260,7 @@ def WritePartitionTable(options, config=None, partitions=None):
 
   Cgpt('create', '-c', '-s', config['metadata']['blocks'], options.disk_image)
 
-  esp_number = None
+  syslinux = None
   for partition in partitions.itervalues():
     if partition['type'] != 'blank':
       Cgpt('add', '-i', partition['num'],
@@ -265,17 +271,28 @@ def WritePartitionTable(options, config=None, partitions=None):
                   '-u', partition['uuid'],
                   options.disk_image)
 
-    if partition['type'] == 'efi':
+      features = partition.get('features', [])
-      esp_number = partition['num']
+      if not syslinux and 'syslinux' in features:
+        syslinux = partition['num']
 
-  if esp_number is None:
+  if syslinux and options.mbr_boot_code:
-    raise InvalidLayout('Table does not include an EFI partition.')
+    # Enable legacy boot flag and generate a hybrid MBR partition table
+    Cgpt('add', '-i', syslinux, '-B1', options.disk_image)
 
-  if options.mbr_boot_code:
+    try:
-    Cgpt('boot', '-p',
+      with open(options.mbr_boot_code, 'r') as mbr_fd:
-                 '-b', options.mbr_boot_code,
+        mbr_code = mbr_fd.read()
-                 '-i', esp_number,
+    except IOError, ex:
-                 options.disk_image)
+      raise InvalidBootCode("Failed to read %s: %s",
+                            options.mbr_boot_code, ex)
+
+    # The boot code must fit in the first 440 bytes of disk
+    if len(mbr_code) != 440:
+      raise InvalidBootCode("Invalid %s size %s, must be 440 bytes",
+                            options.mbr_boot_code, len(mbr_code))
+
+    with open(options.disk_image, 'r+') as image_fd:
+      image_fd.write(mbr_code)
 
   Cgpt('show', options.disk_image)
 
@@ -847,19 +864,19 @@ def main(argv):
           help='initialize new partition table')
   a.add_argument('--update', action='store_false', dest='create',
           help='update existing partition table')
-  a.add_argument('--mbr_boot_code',
+  a.add_argument('--mbr_boot_code', default=DEFAULT_MBR_BOOT_CODE,
           help='path to mbr boot block, such as syslinux/gptmbr.bin')
   a.add_argument('disk_image', help='path to disk image file')
   a.set_defaults(func=WritePartitionTable)
 
   a = actions.add_parser('format', help='write gpt and filesystems to image')
-  a.add_argument('--mbr_boot_code',
+  a.add_argument('--mbr_boot_code', default=DEFAULT_MBR_BOOT_CODE,
           help='path to mbr boot block, such as syslinux/gptmbr.bin')
   a.add_argument('disk_image', help='path to disk image file')
   a.set_defaults(func=Format, create=True)
 
   a = actions.add_parser('resize', help='write gpt and resize filesystems')
-  a.add_argument('--mbr_boot_code',
+  a.add_argument('--mbr_boot_code', default=DEFAULT_MBR_BOOT_CODE,
           help='path to mbr boot block, such as syslinux/gptmbr.bin')
   a.add_argument('disk_image', help='path to disk image file')
   a.set_defaults(func=Resize, create=False)

build_library/vm_image_util.sh

@@ -37,9 +37,6 @@ VM_UUID=
 VM_GENERATED_FILES=()
 
 ## DEFAULT
-# If set to 1 use a hybrid GPT/MBR format instead of plain GPT
-IMG_DEFAULT_HYBRID_MBR=0
-
 # If set to 0 then a partition skeleton won't be laid out on VM_TMP_IMG
 IMG_DEFAULT_PARTITIONED_IMG=1
 
@@ -68,8 +65,6 @@ IMG_qemu_DISK_LAYOUT=vm
 IMG_qemu_CONF_FORMAT=qemu
 
 ## xen
-# Hybrid is required by pvgrub (pygrub supports GPT but we support both)
-IMG_xen_HYBRID_MBR=1
 IMG_xen_BOOT_KERNEL=0
 IMG_xen_CONF_FORMAT=xl
 
@@ -102,7 +97,6 @@ IMG_vmware_insecure_CONF_FORMAT=vmware_zip
 IMG_vmware_insecure_OEM_PACKAGE=oem-vagrant
 
 ## ami
-IMG_ami_HYBRID_MBR=1
 IMG_ami_BOOT_KERNEL=0
 IMG_ami_OEM_PACKAGE=oem-ami
 
@@ -213,10 +207,8 @@ setup_disk_image() {
     cp --sparse=always "${VM_SRC_IMG}" "${VM_TMP_IMG}"
 
     if [[ $(_get_vm_opt PARTITIONED_IMG) -eq 1 ]]; then
-      # TODO(marineam): Fix this so --mbr_boot_code isn't required
-      local mbr_img="/usr/share/syslinux/gptmbr.bin"
       "${BUILD_LIBRARY_DIR}/disk_util" --disk_layout="${disk_layout}" \
-          resize --mbr_boot_code="${mbr_img}" "${VM_TMP_IMG}"
+          resize "${VM_TMP_IMG}"
     fi
 
     info "Mounting image to $(relpath "${VM_TMP_ROOT}")"
@@ -250,33 +242,12 @@ write_vm_disk() {
         cleanup_mounts "${VM_TMP_ROOT}"
     fi
 
-    if [[ $(_get_vm_opt HYBRID_MBR) -eq 1 ]]; then
-        info "Creating hybrid MBR"
-        _write_hybrid_mbr "${VM_TMP_IMG}"
-    fi
-
     local disk_format=$(_get_vm_opt DISK_FORMAT)
     info "Writing $disk_format image $(basename "${VM_DST_IMG}")"
     _write_${disk_format}_disk "${VM_TMP_IMG}" "${VM_DST_IMG}"
     VM_GENERATED_FILES+=( "${VM_DST_IMG}" )
 }
 
-_write_hybrid_mbr() {
-    # TODO(marineam): Switch to sgdisk
-    /usr/sbin/gdisk "$1" <<EOF
-r
-h
-1
-N
-c
-Y
-N
-w
-Y
-Y
-EOF
-}
-
 _write_raw_disk() {
     mv "$1" "$2"
 }