Compress system disk images

Since tarball rootfs images are compressed with gzip -1, we should do
the same for disk images.  This means they'll need decompressing before
they can be used as disk images, but it means we'll be shunting around
something closer to their true data size rather than the disk image size.

For example, a 2G development system image compresses down to around
380M which is a lot faster to transfer and doesn't risk de-sparseification.

1 files changed, 45 insertions, 29 deletions

diff --git a/morphlib/builder2.py b/morphlib/builder2.py
index 72165ce7..81ee5692 100644
--- a/morphlib/builder2.py
+++ b/morphlib/builder2.py
@@ -23,6 +23,8 @@ from collections import defaultdict
 import tarfile
 import traceback
 import subprocess
+import tempfile
+import gzip
 
 import cliapp
 
@@ -663,40 +665,54 @@ class DiskImageBuilder(SystemKindBuilder):  # pragma: no cover
             rootfs_artifact = self.new_artifact(
                 self.artifact.source.morphology['name'] + '-rootfs')
             handle = self.local_artifact_cache.put(rootfs_artifact)
-            image_name = handle.name
-
-            self._create_image(image_name)
-            self._partition_image(image_name)
-            self._install_mbr(arch, image_name)
-            partition = self._setup_device_mapping(image_name)
-
-            mount_point = None
+            (image_file_fd, image_name) = \
+                tempfile.mkstemp(dir=self.app.settings['tempdir'])
             try:
-                self._create_fs(partition)
-                mount_point = self.staging_area.destdir(self.artifact.source)
-                self._mount(partition, mount_point)
-                factory_path = os.path.join(mount_point, 'factory')
-                self._create_subvolume(factory_path)
-                self.unpack_strata(factory_path)
-                self.create_fstab(factory_path)
-                self._create_bootloader_config(factory_path)
-                self._create_subvolume_snapshot(
-                    mount_point, 'factory', 'factory-run')
-                factory_run_path = os.path.join(mount_point, 'factory-run')
-                self._install_boot_files(arch, factory_run_path, mount_point)
-                self._install_bootloader(mount_point)
-                self.copy_kernel_into_artifact_cache(factory_path)
-                self._unmount(mount_point)
-            except BaseException, e:
-                logging.error(traceback.format_exc())
-                self.app.status(msg='Error while building system',
-                                error=True)
-                self._unmount(mount_point)
+                self._create_image(image_name)
+                self._partition_image(image_name)
+                self._install_mbr(arch, image_name)
+                partition = self._setup_device_mapping(image_name)
+
+                mount_point = None
+                try:
+                    self._create_fs(partition)
+                    mount_point = self.staging_area.destdir(self.artifact.source)
+                    self._mount(partition, mount_point)
+                    factory_path = os.path.join(mount_point, 'factory')
+                    self._create_subvolume(factory_path)
+                    self.unpack_strata(factory_path)
+                    self.create_fstab(factory_path)
+                    self._create_bootloader_config(factory_path)
+                    self._create_subvolume_snapshot(
+                        mount_point, 'factory', 'factory-run')
+                    factory_run_path = os.path.join(mount_point, 'factory-run')
+                    self._install_boot_files(arch, factory_run_path, mount_point)
+                    self._install_bootloader(mount_point)
+                    self.copy_kernel_into_artifact_cache(factory_path)
+                    self._unmount(mount_point)
+                except BaseException, e:
+                    logging.error(traceback.format_exc())
+                    self.app.status(msg='Error while building system',
+                                    error=True)
+                    self._unmount(mount_point)
+                    self._undo_device_mapping(image_name)
+                    raise
+
                 self._undo_device_mapping(image_name)
+
+                self.app.status(msg='Compressing disk image',
+                                chatty=True)
+                with os.fdopen(image_file_fd, "rb") as ifh:
+                    with gzip.GzipFile(fileobj=handle, mode="wb",
+                                       compresslevel=1) as ofh:
+                        shutil.copyfileobj(ifh, ofh, 1024 * 1024)
+
+            except:
+                os.remove(image_name)
                 handle.abort()
                 raise
 
-            self._undo_device_mapping(image_name)
+            os.remove(image_name)
             handle.close()
 
         self.save_build_times()