oem: ensure a single kernel gets installed

Before running curthooks, we now look in the target if there is an
installed kernel. If there is, we instruct curtin _not_ to install
another one.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

apt-deps.txt

@@ -1,6 +1,7 @@
 build-essential
 cloud-init
 curl
+dctrl-tools
 fuseiso
 gettext
 gir1.2-umockdev-1.0

snapcraft.yaml

@@ -110,6 +110,7 @@ parts:
       # This list includes the dependencies for curtin and probert as well,
       # there doesn't seem to be any real benefit to listing them separately.
       - cloud-init
+      - dctrl-tools
       - iso-codes
       - libpython3-stdlib
       - libpython3.10-minimal

subiquity/models/kernel.py

@@ -29,13 +29,23 @@ class KernelModel:
     # should be True.
     explicitly_requested: bool = False
 
-    def render(self):
+    # If set to True, we won't request curthooks to install the kernel.
+    # We can use this option if the kernel is already part of the source image
+    # of if a kernel got installed using ubuntu-drivers.
+    curthooks_no_install: bool = False
+
+    @property
+    def needed_kernel(self) -> Optional[str]:
         if self.metapkg_name_override is not None:
-            metapkg = self.metapkg_name_override
-        else:
-            metapkg = self.metapkg_name
+            return self.metapkg_name_override
+        return self.metapkg_name
+
+    def render(self):
+        if self.curthooks_no_install:
+            return {'kernel': None}
+
         return {
             'kernel': {
-                'package': metapkg,
+                'package': self.needed_kernel,
                 },
             }

subiquity/server/controllers/install.py

@@ -34,7 +34,7 @@ from subiquitycore.async_helpers import (
     )
 from subiquitycore.context import with_context
 from subiquitycore.file_util import write_file, generate_config_yaml
-from subiquitycore.utils import log_process_streams
+from subiquitycore.utils import arun_command, log_process_streams
 
 from subiquity.common.errorreport import ErrorReportKind
 from subiquity.common.types import (
@@ -51,6 +51,9 @@ from subiquity.server.curtin import (
     run_curtin_command,
     start_curtin_command,
     )
+from subiquity.server.kernel import (
+    list_installed_kernels,
+    )
 from subiquity.server.mounter import (
     Mounter,
     )
@@ -312,6 +315,17 @@ class InstallController(SubiquityController):
                 step_config=self.generic_config(),
                 source=source,
                 )
+            if self.app.opts.dry_run:
+                # In dry-run, extract does not do anything. Let's create what's
+                # needed manually. Ideally, we would not hardcode
+                # var/lib/dpkg/status because it is an implementation detail.
+                status = "var/lib/dpkg/status"
+                (root / status).parent.mkdir(parents=True, exist_ok=True)
+                await arun_command([
+                    "cp", "-aT", "--",
+                    str(Path("/") / status),
+                    str(root / status),
+                ])
             await self.setup_target(context=context)
 
             # For OEM, we basically mimic what ubuntu-drivers does:
@@ -343,6 +357,12 @@ class InstallController(SubiquityController):
                 for pkg in self.model.oem.metapkgs:
                     await self.install_package(package=pkg.name)
 
+            # If we already have a kernel installed, don't bother requesting
+            # curthooks to install it again or we might end up with two
+            # kernels.
+            if await list_installed_kernels(Path(self.tpath())):
+                self.model.kernel.curthooks_no_install = True
+
             await run_curtin_step(
                 name="curthooks", stages=["curthooks"],
                 step_config=self.generic_config(),

subiquity/server/kernel.py

@@ -13,7 +13,12 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import pathlib
+import subprocess
+from typing import List
+
 from subiquitycore.lsb_release import lsb_release
+from subiquitycore.utils import arun_command
 
 
 def flavor_to_pkgname(flavor: str, *, dry_run: bool) -> str:
@@ -27,3 +32,28 @@ def flavor_to_pkgname(flavor: str, *, dry_run: bool) -> str:
     # that's a bit tricky until we get cleverer about
     # the apt config in general.
     return f'linux-{flavor}-{release}'
+
+
+async def list_installed_kernels(rootfs: pathlib.Path) -> List[str]:
+    ''' Return the list of linux-image packages installed in rootfs. '''
+    # TODO use python-apt instead coupled with rootdir.
+    # Ideally, we should not hardcode var/lib/dpkg/status which is an
+    # implementation detail.
+    try:
+        cp = await arun_command([
+            'grep-status',
+            '--whole-pkg',
+            '-FProvides', 'linux-image', '--and', '-FStatus', 'installed',
+            '--show-field=Package',
+            '--no-field-names',
+            str(rootfs / pathlib.Path('var/lib/dpkg/status')),
+        ], check=True)
+    except subprocess.CalledProcessError as cpe:
+        # grep-status exits with status 1 when there is no match.
+        if cpe.returncode != 1:
+            raise
+        stdout = cpe.stdout
+    else:
+        stdout = cp.stdout
+
+    return [line for line in stdout.splitlines() if line]

subiquity/server/tests/test_kernel.py

@@ -13,9 +13,14 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import subprocess
 import unittest
+from unittest import mock
 
-from subiquity.server.kernel import flavor_to_pkgname
+from subiquity.server.kernel import (
+    flavor_to_pkgname,
+    list_installed_kernels,
+)
 
 
 class TestFlavorToPkgname(unittest.TestCase):
@@ -33,3 +38,36 @@ class TestFlavorToPkgname(unittest.TestCase):
 
         self.assertEqual('linux-generic-hwe-20.04',
                          flavor_to_pkgname('generic-hwe', dry_run=True))
+
+
+class TestListInstalledKernels(unittest.IsolatedAsyncioTestCase):
+    async def test_one_kernel(self):
+        rv = subprocess.CompletedProcess([], 0)
+        rv.stdout = 'linux-image-6.1.0-16-generic'
+        with mock.patch('subiquity.server.kernel.arun_command',
+                        return_value=rv) as mock_arun:
+            ret = await list_installed_kernels('/')
+            self.assertEqual(['linux-image-6.1.0-16-generic'], ret)
+        mock_arun.assert_called_once()
+
+    async def test_two_kernels(self):
+        rv = subprocess.CompletedProcess([], 0)
+        rv.stdout = '''\
+linux-image-6.1.0-16-generic
+linux-image-6.2.0-24-generic
+'''
+        with mock.patch('subiquity.server.kernel.arun_command',
+                        return_value=rv) as mock_arun:
+            ret = await list_installed_kernels('/')
+            self.assertEqual(['linux-image-6.1.0-16-generic',
+                              'linux-image-6.2.0-24-generic'], ret)
+        mock_arun.assert_called_once()
+
+    async def test_no_kernel(self):
+        rv = subprocess.CompletedProcess([], 0)
+        rv.stdout = '\n'
+        with mock.patch('subiquity.server.kernel.arun_command',
+                        return_value=rv) as mock_arun:
+            ret = await list_installed_kernels('/')
+            self.assertEqual([], ret)
+        mock_arun.assert_called_once()