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 <pierre.equoy@canonical.com>

---------

Co-authored-by: Pierre Equoy <pierre.equoy@canonical.com>

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 <nancy.chen@canonical.com>
+#
+# 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