Create disk images without root

`mke2fs` has a `-d` option that allows to populate the newly created filesystem without needing to temporarily mount it. That allows to use `parted` and `mkfs.ext3` on regular files without needing root access.

Author: eduardosm

lib/generator.py

@@ -59,26 +59,16 @@ def prepare(self, target, using_kernel=False, kernel_bootstrap=False, target_siz
         # argument matrix ... or we could just use ext3 instead which
         # is effectively universally the same
         if kernel_bootstrap:
-            init_path = os.path.join(self.target_dir, 'init')
+            self.target_dir = os.path.join(self.target_dir, 'init')
+            os.mkdir(self.target_dir)
 
-            os.mkdir(init_path)
-            self.target_dir = init_path
-
-            if self.repo_path or self.external_sources:
-                target.add_disk("external", filesystem="ext3")
-                target.mount_disk("external", "external")
-            else:
+            if not self.repo_path and not self.external_sources:
                 self.external_dir = os.path.join(self.target_dir, 'external')
         elif using_kernel:
             self.target_dir = os.path.join(self.target_dir, 'disk')
-            target.add_disk("disk",
-                            filesystem="ext3",
-                            size=(str(target_size) + "M") if target_size else "16G",
-                            bootable=True)
-            target.mount_disk("disk", "disk")
             self.external_dir = os.path.join(self.target_dir, 'external')
 
-        os.makedirs(self.external_dir, exist_ok=True)
+        os.makedirs(self.external_dir)
 
         if self.early_preseed:
             # Extract tar containing preseed
@@ -103,10 +93,16 @@ def prepare(self, target, using_kernel=False, kernel_bootstrap=False, target_siz
         if kernel_bootstrap:
             self.create_builder_hex0_disk_image(self.target_dir + '.img', target_size)
 
-        if kernel_bootstrap and (self.external_sources or self.repo_path):
-            target.umount_disk('external')
+            if self.repo_path or self.external_sources:
+                mkfs_args = ['-d', os.path.join(target.path, 'external')]
+                target.add_disk("external", filesystem="ext3", mkfs_args=mkfs_args)
         elif using_kernel:
-            target.umount_disk('disk')
+            mkfs_args = ['-d', os.path.join(target.path, 'disk')]
+            target.add_disk("disk",
+                            filesystem="ext3",
+                            size=(str(target_size) + "M") if target_size else "16G",
+                            bootable=True,
+                            mkfs_args=mkfs_args)
 
     def steps(self):
         """Copy in steps."""

lib/target.py

@@ -8,10 +8,9 @@
 """
 
 import enum
-import getpass
 import os
 
-from lib.utils import mount, umount, create_disk, run_as_root
+from lib.utils import mount, create_disk
 
 class TargetType(enum.Enum):
     """Different types of target dirs we can have"""
@@ -24,7 +23,6 @@ class Target:
     """
 
     _disks = {}
-    _disk_filesystems = {}
     _mountpoints = {}
 
     def __init__(self, path="target"):
@@ -34,15 +32,6 @@ def __init__(self, path="target"):
         if not os.path.exists(self.path):
             os.mkdir(self.path)
 
-    def __del__(self):
-        for path in self._mountpoints:
-            print(f"Unmounting {path}")
-            umount(path)
-
-        for disk in self._disks.values():
-            print(f"Detaching {disk}")
-            run_as_root("losetup", "-d", disk)
-
     def tmpfs(self, size="8G"):
         """Mount a tmpfs"""
         print(f"Mounting tmpfs on {self.path}")
@@ -59,32 +48,13 @@ def add_disk(self,
                  mkfs_args=None):
         """Add a disk"""
         disk_path = os.path.join(self.path, f"{name}.img")
-        self._disks[name] = create_disk(disk_path,
-                                        tabletype,
-                                        filesystem,
-                                        size,
-                                        bootable,
-                                        mkfs_args)
-        self._disk_filesystems[name] = filesystem
-        # Allow executing user to access it
-        run_as_root("chown", getpass.getuser(), self._disks[name])
-
-    def mount_disk(self, name, mountpoint=None):
-        """Mount the disk"""
-        if mountpoint is None:
-            mountpoint = f"{name}_mnt"
-        mountpoint = os.path.join(self.path, mountpoint)
-        os.mkdir(mountpoint)
-        mount(self._disks[name] + "p1", mountpoint, self._disk_filesystems[name])
-        # Allow executing user to access it
-        run_as_root("chown", getpass.getuser(), mountpoint)
-        self._mountpoints[name] = mountpoint
-        return mountpoint
-
-    def umount_disk(self, name):
-        """Unmount a disk"""
-        umount(self._mountpoints[name])
-        del self._mountpoints[name]
+        create_disk(disk_path,
+                    tabletype,
+                    filesystem,
+                    size,
+                    bootable,
+                    mkfs_args)
+        self._disks[name] = disk_path
 
     def get_disk(self, name):
         """Get the path to a device of a disk"""

lib/utils.py

@@ -37,16 +37,13 @@ def create_disk(image, disk_type, fs_type, size, bootable=False, mkfs_args=None)
     if mkfs_args is None:
         mkfs_args = []
     run('truncate', '-s', size, image)
-    # First find the device we will use, then actually use it
-    loop_dev = run_as_root('losetup', '-f', capture_output=True).stdout.decode().strip()
-    run_as_root('losetup', '-P', loop_dev, image)
     # Create the partition
     if disk_type != "none":
-        run_as_root('parted', '--script', image, 'mklabel', disk_type, 'mkpart',
-                'primary', fs_type, '1GiB' if bootable else '1MiB', '100%')
-        run_as_root('partprobe', loop_dev)
-        run_as_root('mkfs.' + fs_type, loop_dev + "p1", *mkfs_args)
-    return loop_dev
+        # 1 GiB if bootable, 1 MiB otherwise
+        offset = str(1024 * 1024 * (1024 if bootable else 1))
+        run('parted', '--script', image, 'mklabel', disk_type, 'mkpart',
+            'primary', fs_type, offset + 'B', '100%')
+        run('mkfs.' + fs_type, image, '-E', 'offset=' + offset, *mkfs_args)
 
 def mount(source, target, fs_type, options='', **kwargs):
     """Mount filesystem"""