From 794667fecd1a885e0c31b468947fc7a6110acfbf Mon Sep 17 00:00:00 2001
From: Michael Hudson-Doyle <michael.hudson@canonical.com>
Date: Mon, 6 Dec 2021 11:32:25 +1300
Subject: [PATCH 1/7] move setting up installation source to SourceController

---
 subiquity/server/controllers/install.py | 14 +++-----------
 subiquity/server/controllers/source.py  | 16 ++++++++++++++++
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/subiquity/server/controllers/install.py b/subiquity/server/controllers/install.py
index 21b292e1..594eb8a1 100644
--- a/subiquity/server/controllers/install.py
+++ b/subiquity/server/controllers/install.py
@@ -19,12 +19,11 @@ import os
 import re
 import shutil
 
-from curtin.commands.extract import get_handler_for_source
 from curtin.commands.install import (
     ERROR_TARFILE,
     INSTALL_LOG,
     )
-from curtin.util import sanitize_source, write_file
+from curtin.util import write_file
 
 import yaml
 
@@ -157,15 +156,8 @@ class InstallController(SubiquityController):
 
             self.app.update_state(ApplicationState.RUNNING)
 
-            handler = get_handler_for_source(
-                sanitize_source(self.model.source.get_source()))
-
-            if self.app.opts.dry_run:
-                path = '/'
-            else:
-                path = handler.setup()
-
-            self.apt_configurer = get_apt_configurer(self.app, path)
+            self.apt_configurer = get_apt_configurer(
+                self.app, self.app.controllers.Source.source_path)
 
             for_install_path = await self.configure_apt(context=context)
 
diff --git a/subiquity/server/controllers/source.py b/subiquity/server/controllers/source.py
index fe9d211b..c76f61ca 100644
--- a/subiquity/server/controllers/source.py
+++ b/subiquity/server/controllers/source.py
@@ -15,6 +15,9 @@
 
 import os
 
+from curtin.commands.extract import get_handler_for_source
+from curtin.util import sanitize_source
+
 from subiquity.common.apidef import API
 from subiquity.common.types import (
     SourceSelection,
@@ -48,6 +51,11 @@ class SourceController(SubiquityController):
 
     endpoint = API.source
 
+    def __init__(self, app):
+        super().__init__(app)
+        self._handler = None
+        self.source_path = None
+
     def start(self):
         path = '/cdrom/casper/install-sources.yaml'
         if self.app.opts.source_catalog is not None:
@@ -80,6 +88,14 @@ class SourceController(SubiquityController):
             self.model.current.id)
 
     async def configured(self):
+        if self._handler is not None:
+            self._handler.cleanup()
+        self._handler = get_handler_for_source(
+            sanitize_source(self.model.get_source()))
+        if self.app.opts.dry_run:
+            self.source_path = '/'
+        else:
+            self.source_path = self._handler.setup()
         await super().configured()
         self.app.base_model.set_source_variant(self.model.current.variant)
 

From 2de2ef7381a0048e2c2aafd6aba81e7f05b26e29 Mon Sep 17 00:00:00 2001
From: Michael Hudson-Doyle <michael.hudson@canonical.com>
Date: Mon, 6 Dec 2021 12:09:50 +1300
Subject: [PATCH 2/7] move apt_configurer to MirrorController

---
 subiquity/server/apt.py                 | 12 ++++++++----
 subiquity/server/controllers/install.py | 11 ++++-------
 subiquity/server/controllers/mirror.py  | 20 ++++++++++++++++++++
 3 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/subiquity/server/apt.py b/subiquity/server/apt.py
index 4d8eb221..5d01eb4b 100644
--- a/subiquity/server/apt.py
+++ b/subiquity/server/apt.py
@@ -150,6 +150,12 @@ class AptConfigurer:
 
         return for_install
 
+    async def cleanup(self):
+        for m in reversed(self._mounts):
+            await self.unmount(m)
+        for d in self._tdirs:
+            shutil.rmtree(d)
+
     async def deconfigure(self, context, target):
         await self.unmount(f'{target}/cdrom')
         os.rmdir(f'{target}/cdrom')
@@ -168,10 +174,8 @@ class AptConfigurer:
                 self.app, context, "in-target", "-t", target,
                 "--", "apt-get", "update")
 
-        for m in reversed(self._mounts):
-            await self.unmount(m)
-        for d in self._tdirs:
-            shutil.rmtree(d)
+        await self.cleanup()
+
         if self.app.base_model.network.has_network:
             await run_curtin_command(
                 self.app, context, "in-target", "-t", target,
diff --git a/subiquity/server/controllers/install.py b/subiquity/server/controllers/install.py
index 594eb8a1..cec84ca0 100644
--- a/subiquity/server/controllers/install.py
+++ b/subiquity/server/controllers/install.py
@@ -39,7 +39,6 @@ from subiquity.common.types import (
 from subiquity.journald import (
     journald_listen,
     )
-from subiquity.server.apt import get_apt_configurer
 from subiquity.server.controller import (
     SubiquityController,
     )
@@ -79,7 +78,6 @@ class InstallController(SubiquityController):
         self.unattended_upgrades_cmd = None
         self.unattended_upgrades_ctx = None
         self.tb_extractor = TracebackExtractor()
-        self.apt_configurer = None
 
     def interactive(self):
         return True
@@ -128,7 +126,8 @@ class InstallController(SubiquityController):
     @with_context(
         description="configuring apt", level="INFO", childlevel="DEBUG")
     async def configure_apt(self, *, context):
-        return await self.apt_configurer.configure(context)
+        configurer = self.app.controllers.Mirror.apt_configurer
+        return await configurer.configure(context)
 
     @with_context(
         description="installing system", level="INFO", childlevel="DEBUG")
@@ -156,9 +155,6 @@ class InstallController(SubiquityController):
 
             self.app.update_state(ApplicationState.RUNNING)
 
-            self.apt_configurer = get_apt_configurer(
-                self.app, self.app.controllers.Source.source_path)
-
             for_install_path = await self.configure_apt(context=context)
 
             if os.path.exists(self.model.target):
@@ -223,7 +219,8 @@ class InstallController(SubiquityController):
 
     @with_context(description="restoring apt configuration")
     async def restore_apt_config(self, context):
-        await self.apt_configurer.deconfigure(context, self.tpath())
+        configurer = self.app.controllers.Mirror.apt_configurer
+        await configurer.deconfigure(context, self.tpath())
 
     @with_context(description="downloading and installing {policy} updates")
     async def run_unattended_upgrades(self, context, policy):
diff --git a/subiquity/server/controllers/mirror.py b/subiquity/server/controllers/mirror.py
index e623ba4c..ff6a4e37 100644
--- a/subiquity/server/controllers/mirror.py
+++ b/subiquity/server/controllers/mirror.py
@@ -23,6 +23,7 @@ from curtin.config import merge_config
 from subiquitycore.context import with_context
 
 from subiquity.common.apidef import API
+from subiquity.server.apt import get_apt_configurer
 from subiquity.server.controller import SubiquityController
 from subiquity.server.types import InstallerChannels
 
@@ -57,7 +58,11 @@ class MirrorController(SubiquityController):
         super().__init__(app)
         self.geoip_enabled = True
         self.app.hub.subscribe(InstallerChannels.GEOIP, self.on_geoip)
+        self.app.hub.subscribe(
+            (InstallerChannels.CONFIGURED, 'source'), self.on_source)
         self.cc_event = asyncio.Event()
+        self.configured_once = True
+        self.apt_configurer = None
 
     def load_autoinstall_data(self, data):
         if data is None:
@@ -81,6 +86,10 @@ class MirrorController(SubiquityController):
             self.model.set_country(self.app.geoip.countrycode)
         self.cc_event.set()
 
+    def on_source(self):
+        if self.configured_once:
+            self.make_apt_configurer()
+
     def serialize(self):
         return self.model.get_mirror()
 
@@ -92,6 +101,17 @@ class MirrorController(SubiquityController):
         r['geoip'] = self.geoip_enabled
         return r
 
+    async def configured(self):
+        await super().configured()
+        self.configured_once = True
+        self.make_apt_configurer()
+
+    def make_apt_configurer(self):
+        if self.apt_configurer is not None:
+            self.apt_configurer.cleanup()
+        self.apt_configurer = get_apt_configurer(
+            self.app, self.app.controllers.Source.source_path)
+
     async def GET(self) -> str:
         return self.model.get_mirror()
 

From 75d9f38dd138afe1acc0f6bdd85547ea0bfce4fd Mon Sep 17 00:00:00 2001
From: Michael Hudson-Doyle <michael.hudson@canonical.com>
Date: Mon, 6 Dec 2021 12:53:21 +1300
Subject: [PATCH 3/7] refactor apt configuration a bit

using some stuff I originally wrote for livefs-editor
---
 subiquity/server/apt.py | 128 ++++++++++++++++++++++++++++------------
 1 file changed, 89 insertions(+), 39 deletions(-)

diff --git a/subiquity/server/apt.py b/subiquity/server/apt.py
index 5d01eb4b..c122f60b 100644
--- a/subiquity/server/apt.py
+++ b/subiquity/server/apt.py
@@ -29,12 +29,38 @@ from subiquitycore.utils import arun_command
 from subiquity.server.curtin import run_curtin_command
 
 
+class _MountBase:
+
+    def p(self, *args):
+        for a in args:
+            if a.startswith('/'):
+                raise Exception('no absolute paths here please')
+        return os.path.join(self.mountpoint, *args)
+
+    def write(self, path, content):
+        with open(self.p(path), 'w') as fp:
+            fp.write(content)
+
+
+class Mountpoint(_MountBase):
+    def __init__(self, *, mountpoint):
+        self.mountpoint = mountpoint
+
+
+class OverlayMountpoint(_MountBase):
+    def __init__(self, *, lowers, upperdir, mountpoint):
+        self.lowers = lowers
+        self.upperdir = upperdir
+        self.mountpoint = mountpoint
+
+
 class AptConfigurer:
 
     def __init__(self, app, source):
         self.app = app
         self.source = source
-        self.configured = None
+        self.configured_tree = None
+        self.install_mount = None
         self._mounts = []
         self._tdirs = []
 
@@ -51,21 +77,42 @@ class AptConfigurer:
             opts.extend(['-t', type])
         await self.app.command_runner.run(
             ['mount'] + opts + [device, mountpoint])
-        self._mounts.append(mountpoint)
+        m = Mountpoint(mountpoint=mountpoint)
+        self._mounts.append(m)
+        return m
 
     async def unmount(self, mountpoint):
         await self.app.command_runner.run(['umount', mountpoint])
 
-    async def setup_overlay(self, source, target):
+    async def setup_overlay(self, lowers):
         tdir = self.tdir()
-        w = f'{tdir}/work'
-        u = f'{tdir}/upper'
-        for d in w, u:
+        target = f'{tdir}/mount'
+        workdir = f'{tdir}/work'
+        upperdir = f'{tdir}/upper'
+        for d in target, workdir, upperdir:
             os.mkdir(d)
-        await self.mount(
-            'overlay', target, type='overlay',
-            options=f'lowerdir={source},upperdir={u},workdir={w}')
-        return u
+
+        def lowerdir_for(lower):
+            if isinstance(lower, str):
+                return lower
+            if isinstance(lower, Mountpoint):
+                return lower.p()
+            if isinstance(lower, OverlayMountpoint):
+                return lowerdir_for(lower.lowers)
+            if isinstance(lower, list):
+                return ':'.join(reversed([lowerdir_for(ll) for ll in lower]))
+            raise Exception(f'lowerdir_for({lower!r})')
+
+        lowerdir = lowerdir_for(lowers)
+        options = f'lowerdir={lowerdir},upperdir={upperdir},workdir={workdir}'
+
+        mount = await self.mount(
+            'overlay', target, options=options, type='overlay')
+
+        return OverlayMountpoint(
+            lowers=lowers,
+            mountpoint=mount.p(),
+            upperdir=upperdir)
 
     def apt_config(self):
         cfg = {}
@@ -77,11 +124,11 @@ class AptConfigurer:
         # Configure apt so that installs from the pool on the cdrom are
         # preferred during installation but not in the installed system.
         #
-        # First we create an overlay ('configured') over the installation
+        # First we create an overlay ('configured_tree') over the installation
         # source and configure that overlay as we want the target system to
         # end up by running curtin's apt-config subcommand.
         #
-        # Then we create a fresh overlay ('for_install') over the first one
+        # Then we create a fresh overlay ('install_tree') over the first one
         # and configure it for the installation. This means:
         #
         # 1. Bind-mounting /cdrom into this new overlay.
@@ -106,9 +153,7 @@ class AptConfigurer:
         #    system, or if it is not, just copy /var/lib/apt/lists from the
         #    'configured' overlay.
 
-        self.configured = self.tdir()
-
-        config_upper = await self.setup_overlay(self.source, self.configured)
+        self.configured_tree = await self.setup_overlay(self.source)
 
         config_location = os.path.join(
             self.app.root, 'var/log/installer/subiquity-curtin-apt.conf')
@@ -120,75 +165,77 @@ class AptConfigurer:
         self.app.note_data_for_apport("CurtinAptConfig", config_location)
 
         await run_curtin_command(
-            self.app, context, 'apt-config', '-t', self.configured,
+            self.app, context, 'apt-config', '-t', self.configured_tree.p(),
             config=config_location)
 
-        for_install = self.tdir()
-        await self.setup_overlay(config_upper + ':' + self.source, for_install)
+        self.install_tree = await self.setup_overlay(self.configured_tree)
 
-        os.mkdir(f'{for_install}/cdrom')
-        await self.mount('/cdrom', f'{for_install}/cdrom', options='bind')
+        os.mkdir(self.install_tree.p('cdrom'))
+        await self.mount(
+            '/cdrom', self.install_tree.p('cdrom'), options='bind')
 
         if self.app.base_model.network.has_network:
             os.rename(
-                f'{for_install}/etc/apt/sources.list',
-                f'{for_install}/etc/apt/sources.list.d/original.list')
+                self.install_tree.p('etc/apt/sources.list'),
+                self.install_tree.p('etc/apt/sources.list.d/original.list'))
         else:
-            proxy_path = f'{for_install}/etc/apt/apt.conf.d/90curtin-aptproxy'
+            proxy_path = self.install_tree.p(
+                'etc/apt/apt.conf.d/90curtin-aptproxy')
             if os.path.exists(proxy_path):
                 os.unlink(proxy_path)
 
         codename = lsb_release()['codename']
 
         write_file(
-            f'{for_install}/etc/apt/sources.list',
+            self.install_tree.p('etc/apt/sources.list'),
             f'deb [check-date=no] file:///cdrom {codename} main restricted\n')
 
         await run_curtin_command(
-            self.app, context, "in-target", "-t", for_install,
+            self.app, context, "in-target", "-t", self.install_tree.p(),
             "--", "apt-get", "update")
 
-        return for_install
+        return self.install_tree.p()
 
     async def cleanup(self):
         for m in reversed(self._mounts):
-            await self.unmount(m)
+            await self.unmount(m.mountpoint)
         for d in self._tdirs:
             shutil.rmtree(d)
 
     async def deconfigure(self, context, target):
-        await self.unmount(f'{target}/cdrom')
-        os.rmdir(f'{target}/cdrom')
+        target = Mountpoint(mountpoint=target)
+
+        await self.unmount(target.p('cdrom'))
+        os.rmdir(target.p('cdrom'))
 
         restore_dirs = ['etc/apt']
         if not self.app.base_model.network.has_network:
             restore_dirs.append('var/lib/apt/lists')
         for dir in restore_dirs:
-            shutil.rmtree(f'{target}/{dir}')
+            shutil.rmtree(target.p(dir))
             await self.app.command_runner.run([
-                'cp', '-aT', f'{self.configured}/{dir}', f'{target}/{dir}',
+                'cp', '-aT', self.configured_tree.p(dir), target.p(dir),
                 ])
 
         if self.app.base_model.network.has_network:
             await run_curtin_command(
-                self.app, context, "in-target", "-t", target,
+                self.app, context, "in-target", "-t", target.p(),
                 "--", "apt-get", "update")
 
         await self.cleanup()
 
         if self.app.base_model.network.has_network:
             await run_curtin_command(
-                self.app, context, "in-target", "-t", target,
+                self.app, context, "in-target", "-t", target.p(),
                 "--", "apt-get", "update")
 
 
 class DryRunAptConfigurer(AptConfigurer):
 
-    async def setup_overlay(self, source, target):
-        if source.startswith('u+'):
-            # Please excuse the obscure way the path is transmitted
-            # from the first invocation of this method to the second :/
-            source = source.split(':')[0][2:]
+    async def setup_overlay(self, source):
+        if isinstance(source, OverlayMountpoint):
+            source = source.lowers[0]
+        target = self.tdir()
         os.mkdir(f'{target}/etc')
         await arun_command([
             'cp', '-aT', f'{source}/etc/apt', f'{target}/etc/apt',
@@ -196,7 +243,10 @@ class DryRunAptConfigurer(AptConfigurer):
         if os.path.isdir(f'{target}/etc/apt/sources.list.d'):
             shutil.rmtree(f'{target}/etc/apt/sources.list.d')
         os.mkdir(f'{target}/etc/apt/sources.list.d')
-        return 'u+' + target
+        return OverlayMountpoint(
+            lowers=[source],
+            mountpoint=target,
+            upperdir=None)
 
     async def deconfigure(self, context, target):
         return

From 93432ccbb1f804458b1ed4b6e8968f5b6c60d69b Mon Sep 17 00:00:00 2001
From: Michael Hudson-Doyle <michael.hudson@canonical.com>
Date: Mon, 6 Dec 2021 13:26:11 +1300
Subject: [PATCH 4/7] split apt configuration into two methods

---
 subiquity/server/apt.py | 87 ++++++++++++++++++++++-------------------
 1 file changed, 47 insertions(+), 40 deletions(-)

diff --git a/subiquity/server/apt.py b/subiquity/server/apt.py
index c122f60b..81745fa2 100644
--- a/subiquity/server/apt.py
+++ b/subiquity/server/apt.py
@@ -120,6 +120,51 @@ class AptConfigurer:
         merge_config(cfg, self.app.base_model.proxy.get_apt_config())
         return {'apt': cfg}
 
+    async def apply_apt_config(self, context):
+        self.configured_tree = await self.setup_overlay(self.source)
+
+        config_location = os.path.join(
+            self.app.root, 'var/log/installer/subiquity-curtin-apt.conf')
+
+        datestr = '# Autogenerated by Subiquity: {} UTC\n'.format(
+            str(datetime.datetime.utcnow()))
+        write_file(config_location, datestr + yaml.dump(self.apt_config()))
+
+        self.app.note_data_for_apport("CurtinAptConfig", config_location)
+
+        await run_curtin_command(
+            self.app, context, 'apt-config', '-t', self.configured_tree.p(),
+            config=config_location)
+
+    async def configure_for_install(self, context):
+        assert self.configured_tree is not None
+
+        self.install_tree = await self.setup_overlay(self.configured_tree)
+
+        os.mkdir(self.install_tree.p('cdrom'))
+        await self.mount(
+            '/cdrom', self.install_tree.p('cdrom'), options='bind')
+
+        if self.app.base_model.network.has_network:
+            os.rename(
+                self.install_tree.p('etc/apt/sources.list'),
+                self.install_tree.p('etc/apt/sources.list.d/original.list'))
+        else:
+            proxy_path = self.install_tree.p(
+                'etc/apt/apt.conf.d/90curtin-aptproxy')
+            if os.path.exists(proxy_path):
+                os.unlink(proxy_path)
+
+        codename = lsb_release()['codename']
+
+        write_file(
+            self.install_tree.p('etc/apt/sources.list'),
+            f'deb [check-date=no] file:///cdrom {codename} main restricted\n')
+
+        await run_curtin_command(
+            self.app, context, "in-target", "-t", self.install_tree.p(),
+            "--", "apt-get", "update")
+
     async def configure(self, context):
         # Configure apt so that installs from the pool on the cdrom are
         # preferred during installation but not in the installed system.
@@ -153,46 +198,8 @@ class AptConfigurer:
         #    system, or if it is not, just copy /var/lib/apt/lists from the
         #    'configured' overlay.
 
-        self.configured_tree = await self.setup_overlay(self.source)
-
-        config_location = os.path.join(
-            self.app.root, 'var/log/installer/subiquity-curtin-apt.conf')
-
-        datestr = '# Autogenerated by Subiquity: {} UTC\n'.format(
-            str(datetime.datetime.utcnow()))
-        write_file(config_location, datestr + yaml.dump(self.apt_config()))
-
-        self.app.note_data_for_apport("CurtinAptConfig", config_location)
-
-        await run_curtin_command(
-            self.app, context, 'apt-config', '-t', self.configured_tree.p(),
-            config=config_location)
-
-        self.install_tree = await self.setup_overlay(self.configured_tree)
-
-        os.mkdir(self.install_tree.p('cdrom'))
-        await self.mount(
-            '/cdrom', self.install_tree.p('cdrom'), options='bind')
-
-        if self.app.base_model.network.has_network:
-            os.rename(
-                self.install_tree.p('etc/apt/sources.list'),
-                self.install_tree.p('etc/apt/sources.list.d/original.list'))
-        else:
-            proxy_path = self.install_tree.p(
-                'etc/apt/apt.conf.d/90curtin-aptproxy')
-            if os.path.exists(proxy_path):
-                os.unlink(proxy_path)
-
-        codename = lsb_release()['codename']
-
-        write_file(
-            self.install_tree.p('etc/apt/sources.list'),
-            f'deb [check-date=no] file:///cdrom {codename} main restricted\n')
-
-        await run_curtin_command(
-            self.app, context, "in-target", "-t", self.install_tree.p(),
-            "--", "apt-get", "update")
+        await self.apply_apt_config(context)
+        await self.configure_for_install(context)
 
         return self.install_tree.p()
 

From 06d42129a48adba6e445c397071ffd96a28b951d Mon Sep 17 00:00:00 2001
From: Michael Hudson-Doyle <michael.hudson@canonical.com>
Date: Mon, 6 Dec 2021 14:02:08 +1300
Subject: [PATCH 5/7] do the apt config application asap

---
 subiquity/server/apt.py                 | 70 ++++++++++++-------------
 subiquity/server/controllers/install.py |  5 +-
 subiquity/server/controllers/mirror.py  | 15 ++++--
 3 files changed, 49 insertions(+), 41 deletions(-)

diff --git a/subiquity/server/apt.py b/subiquity/server/apt.py
index 81745fa2..8bf70a7d 100644
--- a/subiquity/server/apt.py
+++ b/subiquity/server/apt.py
@@ -55,6 +55,40 @@ class OverlayMountpoint(_MountBase):
 
 
 class AptConfigurer:
+    # We configure apt during installation so that installs from the pool on
+    # the cdrom are preferred during installation but remove this again in the
+    # installed system.
+    #
+    # First we create an overlay ('configured_tree') over the installation
+    # source and configure that overlay as we want the target system to end up
+    # by running curtin's apt-config subcommand. This is done in the
+    # apply_apt_config method.
+    #
+    # Then in configure_for_install we create a fresh overlay ('install_tree')
+    # over the first one and configure it for the installation. This means:
+    #
+    # 1. Bind-mounting /cdrom into this new overlay.
+    #
+    # 2. When the network is expected to be working, copying the original
+    #    /etc/apt/sources.list to /etc/apt/sources.list.d/original.list.
+    #
+    # 3. writing "deb file:///cdrom $(lsb_release -sc) main restricted"
+    #    to /etc/apt/sources.list.
+    #
+    # 4. running "apt-get update" in the new overlay.
+    #
+    # When the install is done the deconfigure method makes the installed
+    # system's apt state look as if the pool had never been configured. So
+    # this means:
+    #
+    # 1. Removing /cdrom from the installed system.
+    #
+    # 2. Copying /etc/apt from the 'configured' overlay to the installed
+    #    system.
+    #
+    # 3. If the network is working, run apt-get update in the installed
+    #    system, or if it is not, just copy /var/lib/apt/lists from the
+    #    'configured_tree' overlay.
 
     def __init__(self, app, source):
         self.app = app
@@ -165,42 +199,6 @@ class AptConfigurer:
             self.app, context, "in-target", "-t", self.install_tree.p(),
             "--", "apt-get", "update")
 
-    async def configure(self, context):
-        # Configure apt so that installs from the pool on the cdrom are
-        # preferred during installation but not in the installed system.
-        #
-        # First we create an overlay ('configured_tree') over the installation
-        # source and configure that overlay as we want the target system to
-        # end up by running curtin's apt-config subcommand.
-        #
-        # Then we create a fresh overlay ('install_tree') over the first one
-        # and configure it for the installation. This means:
-        #
-        # 1. Bind-mounting /cdrom into this new overlay.
-        #
-        # 2. When the network is expected to be working, copying the original
-        #    /etc/apt/sources.list to /etc/apt/sources.list.d/original.list.
-        #
-        # 3. writing "deb file:///cdrom $(lsb_release -sc) main restricted"
-        #    to /etc/apt/sources.list.
-        #
-        # 4. running "apt-get update" in the new overlay.
-        #
-        # When the install is done we try to make the installed system's apt
-        # state look as if the pool had never been configured. So this means:
-        #
-        # 1. Removing /cdrom from the installed system.
-        #
-        # 2. Copying /etc/apt from the 'configured' overlay to the installed
-        #    system.
-        #
-        # 3. If the network is working, run apt-get update in the installed
-        #    system, or if it is not, just copy /var/lib/apt/lists from the
-        #    'configured' overlay.
-
-        await self.apply_apt_config(context)
-        await self.configure_for_install(context)
-
         return self.install_tree.p()
 
     async def cleanup(self):
diff --git a/subiquity/server/controllers/install.py b/subiquity/server/controllers/install.py
index cec84ca0..6e17728c 100644
--- a/subiquity/server/controllers/install.py
+++ b/subiquity/server/controllers/install.py
@@ -126,8 +126,9 @@ class InstallController(SubiquityController):
     @with_context(
         description="configuring apt", level="INFO", childlevel="DEBUG")
     async def configure_apt(self, *, context):
-        configurer = self.app.controllers.Mirror.apt_configurer
-        return await configurer.configure(context)
+        mirror = self.app.controllers.Mirror
+        configurer = await mirror.wait_config()
+        return await configurer.configure_for_install(context)
 
     @with_context(
         description="installing system", level="INFO", childlevel="DEBUG")
diff --git a/subiquity/server/controllers/mirror.py b/subiquity/server/controllers/mirror.py
index ff6a4e37..9524a7a1 100644
--- a/subiquity/server/controllers/mirror.py
+++ b/subiquity/server/controllers/mirror.py
@@ -20,6 +20,7 @@ from typing import List
 
 from curtin.config import merge_config
 
+from subiquitycore.async_helpers import SingleInstanceTask
 from subiquitycore.context import with_context
 
 from subiquity.common.apidef import API
@@ -62,6 +63,9 @@ class MirrorController(SubiquityController):
             (InstallerChannels.CONFIGURED, 'source'), self.on_source)
         self.cc_event = asyncio.Event()
         self.configured_once = True
+        self._apt_config_key = None
+        self._apply_apt_config_task = SingleInstanceTask(
+            self._apply_apt_config)
         self.apt_configurer = None
 
     def load_autoinstall_data(self, data):
@@ -88,7 +92,7 @@ class MirrorController(SubiquityController):
 
     def on_source(self):
         if self.configured_once:
-            self.make_apt_configurer()
+            self._apply_apt_config_task.start_sync()
 
     def serialize(self):
         return self.model.get_mirror()
@@ -104,13 +108,18 @@ class MirrorController(SubiquityController):
     async def configured(self):
         await super().configured()
         self.configured_once = True
-        self.make_apt_configurer()
+        self._apply_apt_config_task.start_sync()
 
-    def make_apt_configurer(self):
+    async def _apply_apt_config(self):
         if self.apt_configurer is not None:
             self.apt_configurer.cleanup()
         self.apt_configurer = get_apt_configurer(
             self.app, self.app.controllers.Source.source_path)
+        await self.apt_configurer.apply_apt_config(self.context)
+
+    async def wait_config(self):
+        await self._apply_apt_config_task.wait()
+        return self.apt_configurer
 
     async def GET(self) -> str:
         return self.model.get_mirror()

From 45ef2338cd4de4fbd5a5a8f980d4b122e67f82b4 Mon Sep 17 00:00:00 2001
From: Michael Hudson-Doyle <michael.hudson@canonical.com>
Date: Mon, 6 Dec 2021 14:27:35 +1300
Subject: [PATCH 6/7] another small refactor

---
 subiquity/server/apt.py | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/subiquity/server/apt.py b/subiquity/server/apt.py
index 8bf70a7d..92939880 100644
--- a/subiquity/server/apt.py
+++ b/subiquity/server/apt.py
@@ -210,22 +210,23 @@ class AptConfigurer:
     async def deconfigure(self, context, target):
         target = Mountpoint(mountpoint=target)
 
-        await self.unmount(target.p('cdrom'))
-        os.rmdir(target.p('cdrom'))
-
-        restore_dirs = ['etc/apt']
-        if not self.app.base_model.network.has_network:
-            restore_dirs.append('var/lib/apt/lists')
-        for dir in restore_dirs:
+        async def _restore_dir(dir):
             shutil.rmtree(target.p(dir))
             await self.app.command_runner.run([
                 'cp', '-aT', self.configured_tree.p(dir), target.p(dir),
                 ])
 
+        await self.unmount(target.p('cdrom'))
+        os.rmdir(target.p('cdrom'))
+
+        await _restore_dir('etc/apt')
+
         if self.app.base_model.network.has_network:
             await run_curtin_command(
                 self.app, context, "in-target", "-t", target.p(),
                 "--", "apt-get", "update")
+        else:
+            await _restore_dir('var/lib/apt/lists')
 
         await self.cleanup()
 

From 447b5730ec029359aaedc3b527a8d1a3366448e9 Mon Sep 17 00:00:00 2001
From: Michael Hudson-Doyle <michael.hudson@canonical.com>
Date: Wed, 8 Dec 2021 13:56:04 +1300
Subject: [PATCH 7/7] refactor the lowerdir_for calculation and fix a bug

---
 subiquity/server/apt.py | 44 +++++++++++++++++++++++++++++------------
 1 file changed, 31 insertions(+), 13 deletions(-)

diff --git a/subiquity/server/apt.py b/subiquity/server/apt.py
index 92939880..c6bfc563 100644
--- a/subiquity/server/apt.py
+++ b/subiquity/server/apt.py
@@ -14,6 +14,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import datetime
+import functools
 import os
 import shutil
 import tempfile
@@ -54,6 +55,34 @@ class OverlayMountpoint(_MountBase):
         self.mountpoint = mountpoint
 
 
+@functools.singledispatch
+def lowerdir_for(x):
+    """Return value suitable for passing to the lowerdir= overlayfs option."""
+    raise NotImplementedError(x)
+
+
+@lowerdir_for.register(str)
+def _lowerdir_for_str(path):
+    return path
+
+
+@lowerdir_for.register(Mountpoint)
+def _lowerdir_for_mnt(mnt):
+    return mnt.mountpoint
+
+
+@lowerdir_for.register(OverlayMountpoint)
+def _lowerdir_for_ovmnt(ovmnt):
+    # One cannot indefinitely stack overlayfses so construct an
+    # explicit list of the layers of the overlayfs.
+    return lowerdir_for(ovmnt.lowers + [ovmnt.upperdir])
+
+
+@lowerdir_for.register(list)
+def _lowerdir_for_lst(lst):
+    return ':'.join(reversed([lowerdir_for(item) for item in lst]))
+
+
 class AptConfigurer:
     # We configure apt during installation so that installs from the pool on
     # the cdrom are preferred during installation but remove this again in the
@@ -121,23 +150,12 @@ class AptConfigurer:
     async def setup_overlay(self, lowers):
         tdir = self.tdir()
         target = f'{tdir}/mount'
-        workdir = f'{tdir}/work'
+        lowerdir = lowerdir_for(lowers)
         upperdir = f'{tdir}/upper'
+        workdir = f'{tdir}/work'
         for d in target, workdir, upperdir:
             os.mkdir(d)
 
-        def lowerdir_for(lower):
-            if isinstance(lower, str):
-                return lower
-            if isinstance(lower, Mountpoint):
-                return lower.p()
-            if isinstance(lower, OverlayMountpoint):
-                return lowerdir_for(lower.lowers)
-            if isinstance(lower, list):
-                return ':'.join(reversed([lowerdir_for(ll) for ll in lower]))
-            raise Exception(f'lowerdir_for({lower!r})')
-
-        lowerdir = lowerdir_for(lowers)
         options = f'lowerdir={lowerdir},upperdir={upperdir},workdir={workdir}'
 
         mount = await self.mount(