kernel_os_test.go

// -*- Mode: Go; indent-tabs-mode: t -*-

/*
 * Copyright (C) 2014-2019 Canonical Ltd
 *
 * 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/>.
 *
 */

package boot_test

import (
	"errors"
	"io/ioutil"
	"os"
	"path/filepath"

	. "gopkg.in/check.v1"

	"github.com/snapcore/snapd/boot"
	"github.com/snapcore/snapd/boot/boottest"
	"github.com/snapcore/snapd/bootloader"
	"github.com/snapcore/snapd/dirs"
	"github.com/snapcore/snapd/osutil"
	"github.com/snapcore/snapd/snap"
	"github.com/snapcore/snapd/snap/snapfile"
	"github.com/snapcore/snapd/snap/snaptest"
	"github.com/snapcore/snapd/testutil"
)

const packageKernel = `
name: ubuntu-kernel
version: 4.0-1
type: kernel
vendor: Someone
`

func (s *bootenvSuite) TestExtractKernelAssetsError(c *C) {
	bootloader.ForceError(errors.New("brkn"))
	err := boot.NewCoreKernel(&snap.Info{}, boottest.MockDevice("")).ExtractKernelAssets(nil)
	c.Check(err, ErrorMatches, `cannot extract kernel assets: brkn`)
}

func (s *bootenvSuite) TestRemoveKernelAssetsError(c *C) {
	bootloader.ForceError(errors.New("brkn"))
	err := boot.NewCoreKernel(&snap.Info{}, boottest.MockDevice("")).RemoveKernelAssets()
	c.Check(err, ErrorMatches, `cannot remove kernel assets: brkn`)
}

func (s *bootenvSuite) TestSetNextBootError(c *C) {
	coreDev := boottest.MockDevice("some-snap")

	s.bootloader.GetErr = errors.New("zap")
	_, err := boot.NewCoreBootParticipant(&snap.Info{}, snap.TypeKernel, coreDev).SetNextBoot()
	c.Check(err, ErrorMatches, `cannot set next boot: zap`)

	bootloader.ForceError(errors.New("brkn"))
	_, err = boot.NewCoreBootParticipant(&snap.Info{}, snap.TypeKernel, coreDev).SetNextBoot()
	c.Check(err, ErrorMatches, `cannot set next boot: brkn`)
}

func (s *bootenvSuite) TestSetNextBootForCore(c *C) {
	coreDev := boottest.MockDevice("core")

	info := &snap.Info{}
	info.SnapType = snap.TypeOS
	info.RealName = "core"
	info.Revision = snap.R(100)

	bs := boot.NewCoreBootParticipant(info, info.Type(), coreDev)
	reboot, err := bs.SetNextBoot()
	c.Assert(err, IsNil)

	v, err := s.bootloader.GetBootVars("snap_try_core", "snap_mode")
	c.Assert(err, IsNil)
	c.Assert(v, DeepEquals, map[string]string{
		"snap_try_core": "core_100.snap",
		"snap_mode":     boot.TryStatus,
	})

	c.Check(reboot, Equals, true)
}

func (s *bootenvSuite) TestSetNextBootWithBaseForCore(c *C) {
	coreDev := boottest.MockDevice("core18")

	info := &snap.Info{}
	info.SnapType = snap.TypeBase
	info.RealName = "core18"
	info.Revision = snap.R(1818)

	bs := boot.NewCoreBootParticipant(info, info.Type(), coreDev)
	reboot, err := bs.SetNextBoot()
	c.Assert(err, IsNil)

	v, err := s.bootloader.GetBootVars("snap_try_core", "snap_mode")
	c.Assert(err, IsNil)
	c.Assert(v, DeepEquals, map[string]string{
		"snap_try_core": "core18_1818.snap",
		"snap_mode":     boot.TryStatus,
	})

	c.Check(reboot, Equals, true)
}

func (s *bootenvSuite) TestSetNextBootForKernel(c *C) {
	coreDev := boottest.MockDevice("krnl")

	info := &snap.Info{}
	info.SnapType = snap.TypeKernel
	info.RealName = "krnl"
	info.Revision = snap.R(42)

	bp := boot.NewCoreBootParticipant(info, snap.TypeKernel, coreDev)
	reboot, err := bp.SetNextBoot()
	c.Assert(err, IsNil)

	v, err := s.bootloader.GetBootVars("snap_try_kernel", "snap_mode")
	c.Assert(err, IsNil)
	c.Assert(v, DeepEquals, map[string]string{
		"snap_try_kernel": "krnl_42.snap",
		"snap_mode":       boot.TryStatus,
	})

	bootVars := map[string]string{
		"snap_kernel":     "krnl_40.snap",
		"snap_try_kernel": "krnl_42.snap"}
	s.bootloader.SetBootVars(bootVars)
	c.Check(reboot, Equals, true)

	// simulate good boot
	bootVars = map[string]string{"snap_kernel": "krnl_42.snap"}
	s.bootloader.SetBootVars(bootVars)

	reboot, err = bp.SetNextBoot()
	c.Assert(err, IsNil)
	c.Check(reboot, Equals, false)
}

func (s *bootenv20Suite) TestSetNextBoot20ForKernel(c *C) {
	coreDev := boottest.MockUC20Device("", nil)
	c.Assert(coreDev.HasModeenv(), Equals, true)

	r := setupUC20Bootenv(
		c,
		s.bootloader,
		s.normalDefaultState,
	)
	defer r()

	bs := boot.NewCoreBootParticipant(s.kern2, snap.TypeKernel, coreDev)
	c.Assert(bs.IsTrivial(), Equals, false)
	reboot, err := bs.SetNextBoot()
	c.Assert(err, IsNil)

	// check that kernel_status is now try
	v, err := s.bootloader.GetBootVars("kernel_status")
	c.Assert(err, IsNil)
	c.Assert(v, DeepEquals, map[string]string{
		"kernel_status": boot.TryStatus,
	})

	c.Check(reboot, Equals, true)

	// check that SetNextBoot enabled kernel2 as a TryKernel
	actual, _ := s.bootloader.GetRunKernelImageFunctionSnapCalls("EnableTryKernel")
	c.Assert(actual, DeepEquals, []snap.PlaceInfo{s.kern2})

	// also didn't move any try kernels to trusted kernels
	actual, _ = s.bootloader.GetRunKernelImageFunctionSnapCalls("EnableKernel")
	c.Assert(actual, DeepEquals, []snap.PlaceInfo(nil))

	// check that SetNextBoot asked the bootloader for a kernel
	_, nKernelCalls := s.bootloader.GetRunKernelImageFunctionSnapCalls("Kernel")
	c.Assert(nKernelCalls, Equals, 1)

	// and that the modeenv now has this kernel listed
	m2, err := boot.ReadModeenv("")
	c.Assert(err, IsNil)
	c.Assert(m2.CurrentKernels, DeepEquals, []string{s.kern1.Filename(), s.kern2.Filename()})
}

func (s *bootenv20EnvRefKernelSuite) TestSetNextBoot20ForKernel(c *C) {
	coreDev := boottest.MockUC20Device("", nil)
	c.Assert(coreDev.HasModeenv(), Equals, true)

	r := setupUC20Bootenv(
		c,
		s.bootloader,
		s.normalDefaultState,
	)
	defer r()

	bs := boot.NewCoreBootParticipant(s.kern2, snap.TypeKernel, coreDev)
	c.Assert(bs.IsTrivial(), Equals, false)
	reboot, err := bs.SetNextBoot()
	c.Assert(err, IsNil)

	m := s.bootloader.BootVars
	c.Assert(m, DeepEquals, map[string]string{
		"kernel_status":   boot.TryStatus,
		"snap_try_kernel": s.kern2.Filename(),
		"snap_kernel":     s.kern1.Filename(),
	})

	c.Check(reboot, Equals, true)

	// and that the modeenv now has this kernel listed
	m2, err := boot.ReadModeenv("")
	c.Assert(err, IsNil)
	c.Assert(m2.CurrentKernels, DeepEquals, []string{s.kern1.Filename(), s.kern2.Filename()})
}

func (s *bootenvSuite) TestSetNextBootForKernelForTheSameKernel(c *C) {
	coreDev := boottest.MockDevice("krnl")

	info := &snap.Info{}
	info.SnapType = snap.TypeKernel
	info.RealName = "krnl"
	info.Revision = snap.R(40)

	bootVars := map[string]string{"snap_kernel": "krnl_40.snap"}
	s.bootloader.SetBootVars(bootVars)

	reboot, err := boot.NewCoreBootParticipant(info, snap.TypeKernel, coreDev).SetNextBoot()
	c.Assert(err, IsNil)

	v, err := s.bootloader.GetBootVars("snap_kernel")
	c.Assert(err, IsNil)
	c.Assert(v, DeepEquals, map[string]string{
		"snap_kernel": "krnl_40.snap",
	})

	c.Check(reboot, Equals, false)
}

func (s *bootenv20Suite) TestSetNextBoot20ForKernelForTheSameKernel(c *C) {
	coreDev := boottest.MockUC20Device("", nil)
	c.Assert(coreDev.HasModeenv(), Equals, true)

	r := setupUC20Bootenv(
		c,
		s.bootloader,
		s.normalDefaultState,
	)
	defer r()

	bs := boot.NewCoreBootParticipant(s.kern1, snap.TypeKernel, coreDev)
	c.Assert(bs.IsTrivial(), Equals, false)
	reboot, err := bs.SetNextBoot()
	c.Assert(err, IsNil)

	// check that kernel_status is cleared
	v, err := s.bootloader.GetBootVars("kernel_status")
	c.Assert(err, IsNil)
	c.Assert(v, DeepEquals, map[string]string{
		"kernel_status": boot.DefaultStatus,
	})

	c.Check(reboot, Equals, false)

	// check that SetNextBoot didn't try to enable any try kernels
	actual, _ := s.bootloader.GetRunKernelImageFunctionSnapCalls("EnableTryKernel")
	c.Assert(actual, HasLen, 0)

	// also didn't move any try kernels to trusted kernels
	actual, _ = s.bootloader.GetRunKernelImageFunctionSnapCalls("EnableKernel")
	c.Assert(actual, HasLen, 0)

	// check that SetNextBoot asked the bootloader for a kernel
	_, nKernelCalls := s.bootloader.GetRunKernelImageFunctionSnapCalls("Kernel")
	c.Assert(nKernelCalls, Equals, 1)

	// and that the modeenv now has this kernel listed
	m2, err := boot.ReadModeenv("")
	c.Assert(err, IsNil)
	c.Assert(m2.CurrentKernels, DeepEquals, []string{s.kern1.Filename()})
}

func (s *bootenv20EnvRefKernelSuite) TestSetNextBoot20ForKernelForTheSameKernel(c *C) {
	coreDev := boottest.MockUC20Device("", nil)
	c.Assert(coreDev.HasModeenv(), Equals, true)

	r := setupUC20Bootenv(
		c,
		s.bootloader,
		s.normalDefaultState,
	)
	defer r()

	bs := boot.NewCoreBootParticipant(s.kern1, snap.TypeKernel, coreDev)
	c.Assert(bs.IsTrivial(), Equals, false)
	reboot, err := bs.SetNextBoot()
	c.Assert(err, IsNil)

	// check that kernel_status is cleared
	m := s.bootloader.BootVars
	c.Assert(m, DeepEquals, map[string]string{
		"kernel_status":   boot.DefaultStatus,
		"snap_kernel":     s.kern1.Filename(),
		"snap_try_kernel": "",
	})

	c.Check(reboot, Equals, false)

	// and that the modeenv now has this kernel listed
	m2, err := boot.ReadModeenv("")
	c.Assert(err, IsNil)
	c.Assert(m2.CurrentKernels, DeepEquals, []string{s.kern1.Filename()})
}

func (s *bootenvSuite) TestSetNextBootForKernelForTheSameKernelTryMode(c *C) {
	coreDev := boottest.MockDevice("krnl")

	info := &snap.Info{}
	info.SnapType = snap.TypeKernel
	info.RealName = "krnl"
	info.Revision = snap.R(40)

	bootVars := map[string]string{
		"snap_kernel":     "krnl_40.snap",
		"snap_try_kernel": "krnl_99.snap",
		"snap_mode":       boot.TryStatus}
	s.bootloader.SetBootVars(bootVars)

	reboot, err := boot.NewCoreBootParticipant(info, snap.TypeKernel, coreDev).SetNextBoot()
	c.Assert(err, IsNil)

	v, err := s.bootloader.GetBootVars("snap_kernel", "snap_try_kernel", "snap_mode")
	c.Assert(err, IsNil)
	c.Assert(v, DeepEquals, map[string]string{
		"snap_kernel":     "krnl_40.snap",
		"snap_try_kernel": "",
		"snap_mode":       boot.DefaultStatus,
	})

	c.Check(reboot, Equals, false)
}

func (s *bootenv20Suite) TestSetNextBoot20ForKernelForTheSameKernelTryMode(c *C) {
	coreDev := boottest.MockUC20Device("", nil)
	c.Assert(coreDev.HasModeenv(), Equals, true)

	// set all the same vars as if we were doing trying, except don't set a try
	// kernel
	r := setupUC20Bootenv(
		c,
		s.bootloader,
		&bootenv20Setup{
			modeenv: &boot.Modeenv{
				Mode:           "run",
				Base:           s.base1.Filename(),
				CurrentKernels: []string{s.kern1.Filename()},
			},
			kern: s.kern1,
			// no try-kernel
			kernStatus: boot.TryStatus,
		},
	)
	defer r()

	bs := boot.NewCoreBootParticipant(s.kern1, snap.TypeKernel, coreDev)
	c.Assert(bs.IsTrivial(), Equals, false)
	reboot, err := bs.SetNextBoot()
	c.Assert(err, IsNil)

	// check that kernel_status is cleared
	v, err := s.bootloader.GetBootVars("kernel_status")
	c.Assert(err, IsNil)
	c.Assert(v, DeepEquals, map[string]string{
		"kernel_status": boot.DefaultStatus,
	})

	c.Check(reboot, Equals, false)

	// check that SetNextBoot didn't try to enable any try kernels
	actual, _ := s.bootloader.GetRunKernelImageFunctionSnapCalls("EnableTryKernel")
	c.Assert(actual, HasLen, 0)

	// also didn't move any try kernels to trusted kernels
	actual, _ = s.bootloader.GetRunKernelImageFunctionSnapCalls("EnableKernel")
	c.Assert(actual, HasLen, 0)

	// check that SetNextBoot asked the bootloader for a kernel
	_, nKernelCalls := s.bootloader.GetRunKernelImageFunctionSnapCalls("Kernel")
	c.Assert(nKernelCalls, Equals, 1)

	// and that the modeenv didn't change
	m2, err := boot.ReadModeenv("")
	c.Assert(err, IsNil)
	c.Assert(m2.CurrentKernels, DeepEquals, []string{s.kern1.Filename()})
}

func (s *bootenv20EnvRefKernelSuite) TestSetNextBoot20ForKernelForTheSameKernelTryMode(c *C) {
	coreDev := boottest.MockUC20Device("", nil)
	c.Assert(coreDev.HasModeenv(), Equals, true)

	// set all the same vars as if we were doing trying, except don't set a try
	// kernel
	r := setupUC20Bootenv(
		c,
		s.bootloader,
		&bootenv20Setup{
			modeenv: &boot.Modeenv{
				Mode:           "run",
				Base:           s.base1.Filename(),
				CurrentKernels: []string{s.kern1.Filename()},
			},
			kern: s.kern1,
			// no try-kernel
			kernStatus: boot.TryStatus,
		},
	)
	defer r()

	bs := boot.NewCoreBootParticipant(s.kern1, snap.TypeKernel, coreDev)
	c.Assert(bs.IsTrivial(), Equals, false)
	reboot, err := bs.SetNextBoot()
	c.Assert(err, IsNil)

	// check that kernel_status is cleared
	m := s.bootloader.BootVars
	c.Assert(m, DeepEquals, map[string]string{
		"kernel_status":   boot.DefaultStatus,
		"snap_kernel":     s.kern1.Filename(),
		"snap_try_kernel": "",
	})

	c.Check(reboot, Equals, false)

	// and that the modeenv didn't change
	m2, err := boot.ReadModeenv("")
	c.Assert(err, IsNil)
	c.Assert(m2.CurrentKernels, DeepEquals, []string{s.kern1.Filename()})
}

type ubootSuite struct {
	baseBootenvSuite
}

var _ = Suite(&ubootSuite{})

// forceUbootBootloader sets up a uboot bootloader, in the uc16/uc18 style
// where all env is stored in a single uboot.env
func (s *ubootSuite) forceUbootBootloader(c *C) {
	bootloader.Force(nil)

	mockGadgetDir := c.MkDir()
	// this is testing the uc16/uc18 style uboot bootloader layout, the file
	// must be non-empty for uc16/uc18 gadget config install behavior
	err := ioutil.WriteFile(filepath.Join(mockGadgetDir, "uboot.conf"), []byte{1}, 0644)
	c.Assert(err, IsNil)
	err = bootloader.InstallBootConfig(mockGadgetDir, dirs.GlobalRootDir, nil)
	c.Assert(err, IsNil)

	bloader, err := bootloader.Find("", nil)
	c.Assert(err, IsNil)
	c.Check(bloader, NotNil)
	s.forceBootloader(bloader)

	fn := filepath.Join(s.bootdir, "/uboot/uboot.env")
	c.Assert(osutil.FileExists(fn), Equals, true)
}

// forceUbootBootloader sets up a uboot bootloader, in the uc20 style where we
// have a separate boot.sel file for snapd specific bootloader env
func (s *ubootSuite) forceUC20UbootBootloader(c *C) {
	bootloader.Force(nil)

	// for the uboot bootloader InstallBootConfig we pass in
	// NoSlashBoot because that's where the gadget assets get
	// installed to
	installOpts := &bootloader.Options{
		Role:        bootloader.RoleRunMode,
		NoSlashBoot: true,
	}

	mockGadgetDir := c.MkDir()
	// this must be empty for uc20 behavior
	// TODO:UC20: update this test for the new behavior when that is implemented
	err := ioutil.WriteFile(filepath.Join(mockGadgetDir, "uboot.conf"), nil, 0644)
	c.Assert(err, IsNil)
	err = bootloader.InstallBootConfig(mockGadgetDir, dirs.GlobalRootDir, installOpts)
	c.Assert(err, IsNil)

	// in reality for uc20, we will bind mount <ubuntu-boot>/uboot/ubuntu/ onto
	// /boot/uboot, so to emulate this at runtime for the tests, just put files
	// into "/uboot" under bootdir for the test to see things that on disk are
	// at "/uboot/ubuntu" as "/boot/uboot/"

	fn := filepath.Join(dirs.GlobalRootDir, "/uboot/ubuntu/boot.sel")
	c.Assert(osutil.FileExists(fn), Equals, true)

	targetFile := filepath.Join(s.bootdir, "uboot", "boot.sel")
	err = os.MkdirAll(filepath.Dir(targetFile), 0755)
	c.Assert(err, IsNil)
	err = os.Rename(fn, targetFile)
	c.Assert(err, IsNil)

	// find the run mode bootloader under /boot
	runtimeOpts := &bootloader.Options{
		Role: bootloader.RoleRunMode,
	}

	bloader, err := bootloader.Find("", runtimeOpts)
	c.Assert(err, IsNil)
	c.Check(bloader, NotNil)
	s.forceBootloader(bloader)
	c.Assert(bloader.Name(), Equals, "uboot")
}

func (s *ubootSuite) TestExtractKernelAssetsAndRemoveOnUboot(c *C) {

	// test for both uc16/uc18 style uboot bootloader and for uc20 style bootloader
	bloaderSetups := []func(){
		func() { s.forceUbootBootloader(c) },
		func() { s.forceUC20UbootBootloader(c) },
	}

	for _, setup := range bloaderSetups {
		setup()

		files := [][]string{
			{"kernel.img", "I'm a kernel"},
			{"initrd.img", "...and I'm an initrd"},
			{"dtbs/foo.dtb", "g'day, I'm foo.dtb"},
			{"dtbs/bar.dtb", "hello, I'm bar.dtb"},
			// must be last
			{"meta/kernel.yaml", "version: 4.2"},
		}

		si := &snap.SideInfo{
			RealName: "ubuntu-kernel",
			Revision: snap.R(42),
		}
		fn := snaptest.MakeTestSnapWithFiles(c, packageKernel, files)
		snapf, err := snapfile.Open(fn)
		c.Assert(err, IsNil)

		info, err := snap.ReadInfoFromSnapFile(snapf, si)
		c.Assert(err, IsNil)

		bp := boot.NewCoreKernel(info, boottest.MockDevice(""))
		err = bp.ExtractKernelAssets(snapf)
		c.Assert(err, IsNil)

		// this is where the kernel/initrd is unpacked
		kernelAssetsDir := filepath.Join(s.bootdir, "/uboot/ubuntu-kernel_42.snap")
		for _, def := range files {
			if def[0] == "meta/kernel.yaml" {
				break
			}

			fullFn := filepath.Join(kernelAssetsDir, def[0])
			c.Check(fullFn, testutil.FileEquals, def[1])
		}

		// it's idempotent
		err = bp.ExtractKernelAssets(snapf)
		c.Assert(err, IsNil)

		// remove
		err = bp.RemoveKernelAssets()
		c.Assert(err, IsNil)
		c.Check(osutil.FileExists(kernelAssetsDir), Equals, false)

		// it's idempotent
		err = bp.RemoveKernelAssets()
		c.Assert(err, IsNil)

	}

}

type grubSuite struct {
	baseBootenvSuite
}

var _ = Suite(&grubSuite{})

func (s *grubSuite) SetUpTest(c *C) {
	s.baseBootenvSuite.SetUpTest(c)
	s.forceGrubBootloader(c)
}

func (s *grubSuite) forceGrubBootloader(c *C) bootloader.Bootloader {
	bootloader.Force(nil)

	// make mock grub bootenv dir
	mockGadgetDir := c.MkDir()
	err := ioutil.WriteFile(filepath.Join(mockGadgetDir, "grub.conf"), nil, 0644)
	c.Assert(err, IsNil)
	err = bootloader.InstallBootConfig(mockGadgetDir, dirs.GlobalRootDir, nil)
	c.Assert(err, IsNil)

	bloader, err := bootloader.Find("", nil)
	c.Assert(err, IsNil)
	c.Check(bloader, NotNil)
	bloader.SetBootVars(map[string]string{
		"snap_kernel": "kernel_41.snap",
		"snap_core":   "core_21.snap",
	})
	s.forceBootloader(bloader)

	fn := filepath.Join(s.bootdir, "/grub/grub.cfg")
	c.Assert(osutil.FileExists(fn), Equals, true)
	return bloader
}

func (s *grubSuite) TestExtractKernelAssetsNoUnpacksKernelForGrub(c *C) {
	files := [][]string{
		{"kernel.img", "I'm a kernel"},
		{"initrd.img", "...and I'm an initrd"},
		{"meta/kernel.yaml", "version: 4.2"},
	}
	si := &snap.SideInfo{
		RealName: "ubuntu-kernel",
		Revision: snap.R(42),
	}
	fn := snaptest.MakeTestSnapWithFiles(c, packageKernel, files)
	snapf, err := snapfile.Open(fn)
	c.Assert(err, IsNil)

	info, err := snap.ReadInfoFromSnapFile(snapf, si)
	c.Assert(err, IsNil)

	bp := boot.NewCoreKernel(info, boottest.MockDevice(""))
	err = bp.ExtractKernelAssets(snapf)
	c.Assert(err, IsNil)

	// kernel is *not* here
	kernimg := filepath.Join(s.bootdir, "grub", "ubuntu-kernel_42.snap", "kernel.img")
	c.Assert(osutil.FileExists(kernimg), Equals, false)

	// it's idempotent
	err = bp.ExtractKernelAssets(snapf)
	c.Assert(err, IsNil)
}

func (s *grubSuite) TestExtractKernelForceWorks(c *C) {
	files := [][]string{
		{"kernel.img", "I'm a kernel"},
		{"initrd.img", "...and I'm an initrd"},
		{"meta/force-kernel-extraction", ""},
		{"meta/kernel.yaml", "version: 4.2"},
	}
	si := &snap.SideInfo{
		RealName: "ubuntu-kernel",
		Revision: snap.R(42),
	}
	fn := snaptest.MakeTestSnapWithFiles(c, packageKernel, files)
	snapf, err := snapfile.Open(fn)
	c.Assert(err, IsNil)

	info, err := snap.ReadInfoFromSnapFile(snapf, si)
	c.Assert(err, IsNil)

	bp := boot.NewCoreKernel(info, boottest.MockDevice(""))
	err = bp.ExtractKernelAssets(snapf)
	c.Assert(err, IsNil)

	// kernel is extracted
	kernimg := filepath.Join(s.bootdir, "/grub/ubuntu-kernel_42.snap/kernel.img")
	c.Assert(osutil.FileExists(kernimg), Equals, true)
	// initrd
	initrdimg := filepath.Join(s.bootdir, "/grub/ubuntu-kernel_42.snap/initrd.img")
	c.Assert(osutil.FileExists(initrdimg), Equals, true)

	// it's idempotent
	err = bp.ExtractKernelAssets(snapf)
	c.Assert(err, IsNil)

	// ensure that removal of assets also works
	err = bp.RemoveKernelAssets()
	c.Assert(err, IsNil)
	exists, _, err := osutil.DirExists(filepath.Dir(kernimg))
	c.Assert(err, IsNil)
	c.Check(exists, Equals, false)

	// it's idempotent
	err = bp.RemoveKernelAssets()
	c.Assert(err, IsNil)
}