release: add optional fallback to /etc/initrd-release

release/export_test.go

@@ -20,20 +20,9 @@
 package release
 
 var (
-	ReadOSRelease = readOSRelease
+	ReadOSReleaseFromRoot = readOSReleaseFromRoot
 )
 
-func MockOSReleasePath(filename string) (restore func()) {
-	old := osReleasePath
-	oldFallback := fallbackOsReleasePath
-	osReleasePath = filename
-	fallbackOsReleasePath = filename
-	return func() {
-		osReleasePath = old
-		fallbackOsReleasePath = oldFallback
-	}
-}
-
 func MockFileExists(mockFileExists func(string) bool) (restorer func()) {
 	// Cannot use testutil.Backup due to import loop
 	old := fileExists

release/release.go

@@ -23,6 +23,7 @@ import (
 	"bufio"
 	"fmt"
 	"os"
+	"path/filepath"
 	"strings"
 	"unicode"
 
@@ -53,25 +54,42 @@ func DistroLike(distros ...string) bool {
 var (
 	osReleasePath         = "/etc/os-release"
 	fallbackOsReleasePath = "/usr/lib/os-release"
+	initrdReleasePath     = "/etc/initrd-release"
 )
 
 // readOSRelease returns the os-release information of the current system.
-func readOSRelease() OS {
+func readOSReleaseFromRoot(rootdir string) OS {
 	// TODO: separate this out into its own thing maybe (if made more general)
 	osRelease := OS{
 		// from os-release(5): If not set, defaults to "ID=linux".
 		ID: "linux",
 	}
 
-	f, err := os.Open(osReleasePath)
-	if err != nil {
+	var f *os.File
+	var err error
+	for _, candidate := range []string{
+		// is a default described in os-release(5) and should be valid for both
+		// booted system and an initrd
+		osReleasePath,
 		// this fallback is as per os-release(5)
-		f, err = os.Open(fallbackOsReleasePath)
-		if err != nil {
-			return osRelease
+		fallbackOsReleasePath,
+		// maybe we're in an initrd which is missing a symlink to
+		// /etc/initrd-release?
+		initrdReleasePath,
+	} {
+		f, err = os.Open(filepath.Join(rootdir, candidate))
+		if err == nil {
+			break
 		}
 	}
 
+	if f == nil {
+		// no os-release information source, return a default
+		return osRelease
+	}
+
+	defer f.Close()
+
 	scanner := bufio.NewScanner(f)
 	for scanner.Scan() {
 		ws := strings.SplitN(scanner.Text(), "=", 2)
@@ -199,7 +217,7 @@ var WSLVersion int
 var ReleaseInfo OS
 
 func init() {
-	ReleaseInfo = readOSRelease()
+	ReleaseInfo = readOSReleaseFromRoot("/")
 
 	OnClassic = (ReleaseInfo.ID != "ubuntu-core")
 

release/release_test.go

@@ -44,11 +44,7 @@ func (s *ReleaseTestSuite) TestSetup(c *C) {
 	c.Check(release.Series, Equals, "16")
 }
 
-func mockOSRelease(c *C) string {
-	// FIXME: use AddCleanup here once available so that we
-	//        can do release.SetLSBReleasePath() here directly
-	mockOSRelease := filepath.Join(c.MkDir(), "mock-os-release")
-	s := `
+const refMockOSRelease = `
 NAME="Ubuntu"
 VERSION="18.09 (Awesome Artichoke)"
 ID=ubuntu
@@ -59,10 +55,22 @@ HOME_URL="http://www.ubuntu.com/"
 SUPPORT_URL="http://help.ubuntu.com/"
 BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
 `
-	err := os.WriteFile(mockOSRelease, []byte(s), 0644)
-	c.Assert(err, IsNil)
 
-	return mockOSRelease
+const refMockUbuntuCoreInitrdRelease = `
+NAME="Ubuntu Core Initramfs"
+VERSION="1"
+ID=ubuntucoreinitramfs
+PRETTY_NAME="Ubuntu Core Initramfs Kelly's Eye - Number One"
+VERSION_ID="1"
+VERSION_CODENAME=keelyseye
+`
+
+func mockOSRelease(c *C, root string, filesWithContent [][]string) {
+	for _, e := range filesWithContent {
+		target := filepath.Join(root, e[0])
+		c.Assert(os.MkdirAll(filepath.Dir(target), 0o755), IsNil)
+		c.Assert(os.WriteFile(target, []byte(e[1]), 0o644), IsNil)
+	}
 }
 
 // MockFilesystemRootType changes relase.ProcMountsPath so that it points to a temp file
@@ -109,16 +117,67 @@ func mockWSLsetup(c *C, settings mockWsl) func() {
 }
 
 func (s *ReleaseTestSuite) TestReadOSRelease(c *C) {
-	reset := release.MockOSReleasePath(mockOSRelease(c))
-	defer reset()
+	root := c.MkDir()
+	mockOSRelease(c, root, [][]string{
+		{"/etc/os-release", refMockOSRelease},
+	})
 
-	os := release.ReadOSRelease()
+	os := release.ReadOSReleaseFromRoot(root)
 	c.Check(os.ID, Equals, "ubuntu")
 	c.Check(os.VersionID, Equals, "18.09")
 }
 
+func (s *ReleaseTestSuite) TestReadOSReleaseSymlink(c *C) {
+	root := c.MkDir()
+	mockOSRelease(c, root, [][]string{
+		{"/etc/mock-release", refMockOSRelease},
+	})
+
+	// now try again but with a symlink
+	c.Assert(os.Symlink("mock-release", filepath.Join(root, "/etc/os-release")), IsNil)
+
+	osRel := release.ReadOSReleaseFromRoot(root)
+	c.Check(osRel.ID, Equals, "ubuntu")
+	c.Check(osRel.VersionID, Equals, "18.09")
+}
+
+func (s *ReleaseTestSuite) TestReadOSReleaseFallback(c *C) {
+	root := c.MkDir()
+	mockOSRelease(c, root, [][]string{
+		{"/usr/lib/os-release", refMockOSRelease},
+	})
+
+	os := release.ReadOSReleaseFromRoot(root)
+	c.Check(os.ID, Equals, "ubuntu")
+	c.Check(os.VersionID, Equals, "18.09")
+}
+
+func (s *ReleaseTestSuite) TestReadOSReleaseInitrdDirect(c *C) {
+	root := c.MkDir()
+	mockOSRelease(c, root, [][]string{
+		{"/etc/initrd-release", refMockUbuntuCoreInitrdRelease},
+	})
+
+	os := release.ReadOSReleaseFromRoot(root)
+	c.Check(os.ID, Equals, "ubuntucoreinitramfs")
+	c.Check(os.VersionID, Equals, "1")
+}
+
+func (s *ReleaseTestSuite) TestReadOSReleaseInitrdSymlink(c *C) {
+	root := c.MkDir()
+	mockOSRelease(c, root, [][]string{
+		{"/etc/mock-initrd-release", refMockUbuntuCoreInitrdRelease},
+	})
+
+	// now try again but with a symlink
+	c.Assert(os.Symlink("mock-initrd-release", filepath.Join(root, "/etc/os-release")), IsNil)
+
+	osRel := release.ReadOSReleaseFromRoot(root)
+	c.Check(osRel.ID, Equals, "ubuntucoreinitramfs")
+	c.Check(osRel.VersionID, Equals, "1")
+}
+
 func (s *ReleaseTestSuite) TestReadWonkyOSRelease(c *C) {
-	mockOSRelease := filepath.Join(c.MkDir(), "mock-os-release")
 	dump := `NAME="elementary OS"
 VERSION="0.4 Loki"
 ID="elementary OS"
@@ -128,19 +187,18 @@ VERSION_ID="0.4"
 HOME_URL="http://elementary.io/"
 SUPPORT_URL="http://elementary.io/support/"
 BUG_REPORT_URL="https://bugs.launchpad.net/elementary/+filebug"`
-	err := os.WriteFile(mockOSRelease, []byte(dump), 0644)
-	c.Assert(err, IsNil)
 
-	reset := release.MockOSReleasePath(mockOSRelease)
-	defer reset()
+	root := c.MkDir()
+	mockOSRelease(c, root, [][]string{
+		{"/etc/os-release", dump},
+	})
 
-	os := release.ReadOSRelease()
+	os := release.ReadOSReleaseFromRoot(root)
 	c.Check(os.ID, Equals, "elementary")
 	c.Check(os.VersionID, Equals, "0.4")
 }
 
 func (s *ReleaseTestSuite) TestFamilyOSRelease(c *C) {
-	mockOSRelease := filepath.Join(c.MkDir(), "mock-os-release")
 	dump := `NAME="CentOS Stream"
 VERSION="9"
 ID="centos"
@@ -155,43 +213,40 @@ HOME_URL="https://centos.org/"
 BUG_REPORT_URL="https://issues.redhat.com/"
 REDHAT_SUPPORT_PRODUCT="Red Hat Enterprise Linux 9"
 REDHAT_SUPPORT_PRODUCT_VERSION="CentOS Stream"`
-	err := os.WriteFile(mockOSRelease, []byte(dump), 0644)
-	c.Assert(err, IsNil)
 
-	reset := release.MockOSReleasePath(mockOSRelease)
-	defer reset()
+	root := c.MkDir()
+	mockOSRelease(c, root, [][]string{
+		{"/etc/os-release", dump},
+	})
 
-	os := release.ReadOSRelease()
+	os := release.ReadOSReleaseFromRoot(root)
 	c.Check(os.ID, Equals, "centos")
 	c.Check(os.VersionID, Equals, "9")
 	c.Check(os.IDLike, DeepEquals, []string{"rhel", "fedora"})
 }
 
 func (s *ReleaseTestSuite) TestUbuntuCoreVariantRelease(c *C) {
-	mockOSRelease := filepath.Join(c.MkDir(), "mock-os-release")
 	dump := `NAME="Ubuntu Core Desktop"
 VERSION="22"
 ID="ubuntu-core"
 VARIANT_ID="desktop"
 VERSION_ID="22"
 "`
-	err := os.WriteFile(mockOSRelease, []byte(dump), 0644)
-	c.Assert(err, IsNil)
 
-	reset := release.MockOSReleasePath(mockOSRelease)
-	defer reset()
+	root := c.MkDir()
+	mockOSRelease(c, root, [][]string{
+		{"/etc/os-release", dump},
+	})
 
-	os := release.ReadOSRelease()
+	os := release.ReadOSReleaseFromRoot(root)
 	c.Check(os.ID, Equals, "ubuntu-core")
 	c.Check(os.VariantID, Equals, "desktop")
 	c.Check(os.VersionID, Equals, "22")
 }
 
 func (s *ReleaseTestSuite) TestReadOSReleaseNotFound(c *C) {
-	reset := release.MockOSReleasePath("not-there")
-	defer reset()
-
-	os := release.ReadOSRelease()
+	root := c.MkDir()
+	os := release.ReadOSReleaseFromRoot(root)
 	c.Assert(os, DeepEquals, release.OS{ID: "linux"})
 }