Build /usr/share/truenas/sysext-extensions/functioning-dpkg.raw (#768)

(cherry picked from commit b5fa484)
(cherry picked from commit 37cb425)

Co-authored-by: themylogin <[email protected]>

scale_build/image/update.py

@@ -5,6 +5,7 @@
 import textwrap
 import shutil
 import stat
+import tempfile
 
 from scale_build.config import SIGNING_KEY, SIGNING_PASSWORD
 from scale_build.utils.manifest import get_manifest
@@ -174,13 +175,33 @@ def custom_rootfs_setup():
     shutil.rmtree(tmp_systemd)
     run_in_chroot(['depmod'], check=False)
 
-    # /usr will be readonly and so we want the ca-certificates directory to
+    # /usr will be readonly, and so we want the ca-certificates directory to
     # symlink to writeable location in /var/local
     local_cacerts = os.path.join(CHROOT_BASEDIR, "usr/local/share/ca-certificates")
     os.makedirs(os.path.join(CHROOT_BASEDIR, "usr/local/share"), exist_ok=True)
     shutil.rmtree(local_cacerts, ignore_errors=True)
     os.symlink("/var/local/ca-certificates", local_cacerts)
 
+    # Build a systemd-sysext extension that, upon loading, will make `/usr/bin/dpkg` working.
+    # It is necessary for `update-initramfs` to function properly.
+    sysext_extensions_dir = os.path.join(CHROOT_BASEDIR, "usr/share/truenas/sysext-extensions")
+    os.makedirs(sysext_extensions_dir, exist_ok=True)
+    with tempfile.TemporaryDirectory() as td:
+        os.makedirs(f"{td}/usr/bin")
+        shutil.copy2(f"{CHROOT_BASEDIR}/usr/bin/dpkg", f"{td}/usr/bin/dpkg")
+
+        os.makedirs(f"{td}/usr/local/bin")
+        with open(f"{td}/usr/local/bin/dpkg", "w") as f:
+            f.write("#!/bin/bash\n")
+            f.write("exec /usr/bin/dpkg \"$@\"")
+        os.chmod(f"{td}/usr/local/bin/dpkg", 0o755)
+
+        os.makedirs(f"{td}/usr/lib/extension-release.d")
+        with open(f"{td}/usr/lib/extension-release.d/extension-release.functioning-dpkg", "w") as f:
+            f.write("ID=_any\n")
+
+        run(["mksquashfs", td, f"{sysext_extensions_dir}/functioning-dpkg.raw"])
+
 
 def clean_rootfs():
     to_remove = get_manifest()['base-prune']