Correctly setup /boot partition if availible

Treat the prescence of a /boot partition as the partition where the
bootloader configuration should live.

By maintaining the baserock system layout, and installing the
bootloader configuration to /boot in this manner, we can allow boot
syslinux and u-boot systems to be upgraded

Additionally move the installation of the MBR for x86 systems to where
the partitioned system is created, since we only need to do it when
deploying a partitioned system

Change-Id: I39c90f73f22da209eefc1c408bd6d6c0ab6fd048

1 files changed, 45 insertions, 10 deletions

diff --git a/extensions/writeexts.py b/extensions/writeexts.py
index 647f3742..f60458ce 100644
--- a/extensions/writeexts.py
+++ b/extensions/writeexts.py
@@ -302,8 +302,7 @@ class WriteExtension(Extension):
     def create_system(self, temp_root, raw_disk):
         with self.mount(raw_disk) as mp:
             try:
-                self.create_btrfs_system_layout(
-                    mp, version_label='factory')
+                self.create_versioned_layout(mp, version_label='factory')
                 self.create_btrfs_system_rootfs(
                     temp_root, mp, version_label='factory',
                     rootfs_uuid=self.get_uuid(raw_disk))
@@ -436,8 +435,25 @@ class WriteExtension(Extension):
             subprocess.check_call(['umount', mount_point])
             os.rmdir(mount_point)
 
-    def create_btrfs_system_layout(self, mountpoint, version_label):
-        '''Create the btrfs folder layout required for baserock
+    def create_versioned_layout(self, mountpoint, version_label):
+        '''Create a versioned directory structure within a partition.
+
+        The Baserock project has defined a 'reference upgrade mechanism'. This
+        mandates a specific directory layout. It consists of a toplevel
+        '/systems' directory, containing subdirectories named with a 'version
+        label'. These subdirectories contain the actual OS content.
+
+        For the root file system, a Btrfs partition must be used. For each
+        version, two subvolumes are created: 'orig' and 'run'. This is handled
+        in create_btrfs_system_rootfs().
+
+        Other partitions (e.g. /boot) can also follow the same layout. In the
+        case of /boot, content goes directly in the version directory. That
+        means there are no 'orig' and 'run' subvolumes, which avoids the
+        need to use Btrfs.
+
+        The `system-version-manager` tool from tbdiff.git is responsible for
+        deploying live upgrades, and it understands this layout.
 
         '''
         version_root = os.path.join(mountpoint, 'systems', version_label)
@@ -492,8 +508,6 @@ class WriteExtension(Extension):
                 root_guid = device.get_partition_uuid(root_part)
                 self.generate_bootloader_config(mountpoint,
                                                 root_guid=root_guid)
-                if self.get_bootloader_install() == 'extlinux':
-                    self.install_syslinux_blob(device, system_dir)
             else:
                 # Unpartitioned and no initramfs - cannot boot with a UUID
                 self.generate_bootloader_config(mountpoint)
@@ -938,6 +952,7 @@ class WriteExtension(Extension):
 
         dev = partitioning.do_partitioning(location, disk_size,
                                            temp_root, part_spec)
+        boot_partition_available = dev.get_partition_by_mountpoint('/boot')
 
         for part in dev.partitionlist:
             if not hasattr(part, 'mountpoint'):
@@ -957,13 +972,23 @@ class WriteExtension(Extension):
                     # Install root filesystem
                     rfs_uuid = self.get_uuid(location, part.extent.start *
                                                 dev.sector_size)
-                    self.create_btrfs_system_layout(part_mount_dir, 'factory')
+                    self.create_versioned_layout(part_mount_dir, 'factory')
                     self.create_btrfs_system_rootfs(temp_root, part_mount_dir,
                                                    'factory', rfs_uuid, dev)
 
-                    if self.bootloader_config_is_wanted():
-                        self.create_bootloader_config(temp_root, part_mount_dir,
-                                                      'factory', rfs_uuid, dev)
+                    # If there's no /boot partition, but we do need to generate
+                    # a bootloader configuration file, then it needs to go in
+                    # the root partition.
+                    if (boot_partition_available is False
+                            and self.bootloader_config_is_wanted()):
+                        self.create_bootloader_config(
+                            temp_root, part_mount_dir, 'factory', rfs_uuid,
+                            dev)
+
+                    if self.get_bootloader_install() == 'extlinux':
+                        # The extlinux/syslinux MBR blob always needs to be
+                        # installed in the root partition.
+                        self.install_syslinux_blob(dev, temp_root)
                 else:
                     # Copy files to partition from unpacked rootfs
                     src_dir = os.path.join(temp_root,
@@ -972,6 +997,16 @@ class WriteExtension(Extension):
                                      part.mountpoint)
                     self.copy_dir_contents(src_dir, part_mount_dir)
 
+                if (part.mountpoint == '/boot' and
+                        self.bootloader_config_is_wanted()):
+                    # We need to mirror the layout of the root partition in the
+                    # /boot partition. Each kernel lives in its own
+                    # systems/$version_label/ directory within the /boot
+                    # partition.
+                    self.create_versioned_layout(part_mount_dir, 'factory')
+                    self.create_bootloader_config(temp_root, part_mount_dir,
+                        'factory', None, dev)
+
         # Write raw files to disk with dd
         partitioning.process_raw_files(dev, temp_root)