resolv.conf is not correctly restored after add-autoinstall-config

[imolein]

Today I used this script to add a package and an autoinstall config to the installer. During the installation I noticed that the name resolution was not working and looking into /etc showed me an incorrectly static resolv.conf and a resolv.conf.tmp symlink.

I looked into the source code and tracked it down to the setup_rootfs() function. This function calls the context method add_sys_mounts() which adds a _pre_repack callback, to restore the original resolv.conf. After this setup_rootfs() addes a _pre_repack callback too, which creates the custom squashfs. Since pre_repack hooks are later called in reverse by the repack() method, the custom squashfs is build before the original resolv.conf is restored.
For myself I fixed it by adding the pre_repack hook from setup_rootfs to the front of the list. I don't know if there are any side effects doing it this way if a more complicated action.yaml is used, because mine is very simple:

- name: add-debs-to-pool
  debs:
    - helper/subiquity-speed-up_1_all.deb

- name: add-autoinstall-config
  autoinstall_config: user-data

[imolein]

Adding it to the start of the whole list brought some other problems with it, so I added the _pre_repack hook from setup_rootfs before the one from add_sys_mounts. These are my two patches to archive this:

diff --git a/livefs_edit/actions.py b/livefs_edit/actions.py
index 106cf64..2b45711 100644
--- a/livefs_edit/actions.py
+++ b/livefs_edit/actions.py
@@ -143,7 +143,7 @@ def setup_rootfs(ctxt, target='rootfs'):
                 fp.write(
                     f"LAYERFS_PATH={new_squash_name}.squashfs\n")
 
-    ctxt.add_pre_repack_hook(_pre_repack)
+    ctxt.add_pre_repack_hook(_pre_repack, -1)
 
     return target
 
diff --git a/livefs_edit/context.py b/livefs_edit/context.py
index b689bd4..48df2d7 100644
--- a/livefs_edit/context.py
+++ b/livefs_edit/context.py
@@ -185,8 +185,10 @@ class EditContext:
                 'overlay', 'overlay', mountpoint, options=options).p(),
             upperdir=upperdir)
 
-    def add_pre_repack_hook(self, hook):
-        self._pre_repack_hooks.append(hook)
+    def add_pre_repack_hook(self, hook, place=None):
+        if place is None:
+            place = len(self._pre_repack_hooks) + 1
+        self._pre_repack_hooks.insert(place, hook)
 
     def mount_squash(self, name):
         target = self.p('old/' + name)

Since I don't know if this has some unknown effect on other actions, I leave this here instead of creating a PR.