Fix snap boot kernel path (Bugfix) (#884)

As describe in this snap doc[1], to access to host’s snap-related files, it's now have to access via /var/lib/snapd/hostfs. This system-backup interface gives privileged read-only access to system data. The change can be traced back to snapd 2.36.

[1] https://snapcraft.io/docs/the-system-backup-interface

* fix snap boot kernel path

* add comment for reference

* add unit test for boot_mode_test_snappy.py

* amend for flake8 check

* remove unnecessary test data

Co-authored-by: Pierre Equoy <[email protected]>

---------

Co-authored-by: Pierre Equoy <[email protected]>

providers/base/bin/boot_mode_test_snappy.py

@@ -61,18 +61,8 @@ def fitdumpimage(filename):
     return objects
 
 
-def main():
-    if len(sys.argv) != 3:
-        raise SystemExit('ERROR: please supply gadget & kernel name')
-    gadget = sys.argv[1]
-    kernel = sys.argv[2]
-
-    gadget_yaml = os.path.join('/snap', gadget, 'current/meta/gadget.yaml')
-
-    if not os.path.exists(gadget_yaml):
-        raise SystemExit(
-            'ERROR: failed to find gadget.yaml at {}'.format(gadget_yaml))
-
+def get_bootloader(gadget_yaml):
+    """Parse gadget.yaml to get bootloader"""
     with open(gadget_yaml) as f:
         data = yaml.load(f, Loader=yaml.SafeLoader)
         for k in data['volumes'].keys():
@@ -84,16 +74,42 @@ def main():
 
     if bootloader not in ('u-boot', 'grub', 'lk'):
         raise SystemExit(
-            'ERROR: Unexpected bootloader name {}'.format(bootloader))
+            'ERROR: Unexpected bootloader name {}'.format(bootloader)
+        )
     print('Bootloader is {}\n'.format(bootloader))
+    return bootloader
+
+
+def get_uboot_kernel(kernel):
+    """Get u-boot kernel path"""
+    kernel_rev = os.path.basename(
+        os.path.realpath('/snap/{}/current'.format(kernel))
+    )
+    # update boot kernel path according to
+    # https://snapcraft.io/docs/the-system-backup-interface
+    return '/var/lib/snapd/hostfs/boot/uboot/{}_{}.snap/kernel.img'.format(
+        kernel, kernel_rev
+    )
+
+
+def main():
+    if len(sys.argv) != 3:
+        raise SystemExit('ERROR: please supply gadget & kernel name')
+    gadget = sys.argv[1]
+    kernel = sys.argv[2]
+
+    gadget_yaml = os.path.join('/snap', gadget, 'current/meta/gadget.yaml')
+
+    if not os.path.exists(gadget_yaml):
+        raise SystemExit(
+            'ERROR: failed to find gadget.yaml at {}'.format(gadget_yaml))
+
+    bootloader = get_bootloader(gadget_yaml)
 
     if bootloader == 'u-boot':
         print('Parsing FIT image information...\n')
 
-        kernel_rev = os.path.basename(
-            os.path.realpath('/snap/{}/current'.format(kernel)))
-        boot_kernel = '/boot/uboot/{}_{}.snap/kernel.img'.format(
-            kernel, kernel_rev)
+        boot_kernel = get_uboot_kernel(kernel)
         boot_objects = fitdumpimage(boot_kernel)
 
         for obj, attrs in boot_objects.items():

providers/base/tests/test_boot_mode_test_snappy.py

@@ -0,0 +1,39 @@
+#!/usr/bin/env python3
+# Copyright 2023 Canonical Ltd.
+# Written by:
+#   Nancy Chen <[email protected]>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 3,
+# as published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import unittest
+import os
+from boot_mode_test_snappy import get_bootloader, get_uboot_kernel
+
+
+class TestBootModeTestSnappy(unittest.TestCase):
+    def test_get_bootloader(self):
+        """Test for get_bootloader function"""
+        kdrp_kdrp_k4500_gadget_yaml = os.path.join(
+            os.path.dirname(os.path.abspath(__file__)),
+            "test_data/kdrp-kdrp-k4500-gadget.yaml",
+        )
+        self.assertEqual("u-boot", get_bootloader(kdrp_kdrp_k4500_gadget_yaml))
+
+    def test_get_uboot_kernel(self):
+        """
+        Test if system-backup interface is included in kernel.img file path
+        https://snapcraft.io/docs/the-system-backup-interface
+        """
+        self.assertIn(
+            "/var/lib/snapd/hostfs/boot/uboot/", get_uboot_kernel("kernel")
+        )

providers/base/tests/test_data/kdrp-kdrp-k4500-gadget.yaml

@@ -0,0 +1,40 @@
+volumes:
+  kdrp-k4500:
+    schema: mbr
+    bootloader: u-boot
+    structure:
+      - name: ubuntu-seed
+        role: system-seed
+        filesystem: vfat
+        type: 0C
+        size: 2400M
+        content:
+          - source: $kernel:boot-assets/boot-assets/
+            target: /
+          - source: $kernel:dtbs/dtbs/bcm2710-rpi-custom-keurig.dtb
+            target: /
+          - source: $kernel:dtbs/dtbs/dt-blob-keurig.dtb
+            target: /dt-blob.bin
+          - source: $kernel:dtbs/dtbs/overlays/
+            target: /overlays
+      - name: ubuntu-boot
+        role: system-boot
+        filesystem: vfat
+        type: 0C
+        # whats the appropriate size?
+        size: 750M
+        content:
+          # TODO:UC20: install the boot.sel via snapd instead of via the gadget
+          - source: boot.sel
+            target: uboot/ubuntu/boot.sel
+      - name: ubuntu-save
+        role: system-save
+        filesystem: ext4
+        type: 83,0FC63DAF-8483-4772-8E79-3D69D8477DE4
+        size: 16M
+      - name: ubuntu-data
+        role: system-data
+        filesystem: ext4
+        type: 83,0FC63DAF-8483-4772-8E79-3D69D8477DE4
+        # XXX: make auto-grow to partition
+        size: 2500M