setup: deal with btrfs subvolumes when checking mapped storage

When the container storage is checked it may come from a btrfs
subvolume. In /proc/self/mountinfo this looks like:
```
1364 1345 0:33 /root/var/lib/containers/storage /var/lib/containers/storage rw,relatime - btrfs /dev/mapper/luks-1356123c-c7b9-1bd7-a8bf-e13d4cbb5500 rw,seclabel,compress=zstd:1,ssd,discard=async,space_cache,subvolid=257,subvol=/root
```
as a quick fix just compare the suffix of the root instead of the
full path.

Thanks for Ondrej!

bib/internal/setup/export_test.go

@@ -0,0 +1,13 @@
+package setup
+
+var (
+	ValidateHasContainerStorageMountedFromReader = validateHasContainerStorageMountedFromReader
+)
+
+func MockInsideContainer(f func() (bool, error)) (restore func()) {
+	saved := insideContainer
+	insideContainer = f
+	return func() {
+		insideContainer = saved
+	}
+}

bib/internal/setup/setup.go

@@ -2,9 +2,11 @@ package setup
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
 
 	"github.com/moby/sys/mountinfo"
 	"golang.org/x/sys/unix"
@@ -100,23 +102,43 @@ func Validate() error {
 	return nil
 }
 
-// ValidateHasContainerStorageMounted checks that the container storage
-// is mounted inside the container
-func ValidateHasContainerStorageMounted() error {
+var insideContainer = func() (bool, error) {
 	if err := exec.Command("systemd-detect-virt", "-c").Run(); err != nil {
 		if exitErr, ok := err.(*exec.ExitError); ok {
 			// not running in a container, just exit
 			if exitErr.ExitCode() == 1 {
-				return nil
+				return true, nil
 			}
 		}
+		return false, err
+	}
+	return false, nil
+}
+
+// ValidateHasContainerStorageMounted checks that the container storage
+// is mounted inside the container
+func ValidateHasContainerStorageMounted() error {
+	inside, err := insideContainer()
+	if err != nil {
+		return err
+	}
+	if inside {
+		return nil
+	}
+
+	f, err := os.Open("/proc/self/mountinfo")
+	if err != nil {
 		return err
 	}
+	defer f.Close()
+	return validateHasContainerStorageMountedFromReader(f)
+}
 
+func validateHasContainerStorageMountedFromReader(r io.Reader) error {
 	containersStorage := "/var/lib/containers/storage"
 	containerStorageMountFound := false
 
-	mnts, err := mountinfo.GetMounts(nil)
+	mnts, err := mountinfo.GetMountsFromReader(r, nil)
 	if err != nil {
 		return err
 	}
@@ -125,8 +147,10 @@ func ValidateHasContainerStorageMounted() error {
 			continue
 		}
 		containerStorageMountFound = true
-		if mnt.Root != containersStorage {
-			return fmt.Errorf("not the host /var/lib/storage/containers but %q", mnt.Root)
+		// on btrfs the containers storage might be on a subvolume
+		// so we just compare the final part of the path
+		if !strings.HasSuffix(mnt.Root, containersStorage) {
+			return fmt.Errorf("cannot find suffix %q in mounted %q", containersStorage, mnt.Root)
 		}
 	}
 	if !containerStorageMountFound {

bib/internal/setup/setup_test.go

@@ -0,0 +1,79 @@
+package setup_test
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/osbuild/bootc-image-builder/bib/internal/setup"
+)
+
+var (
+	procSelfMountinfoBtrfs = `1345 1307 0:92 / / rw,relatime - overlay overlay rw,context="system_u:object_r:container_file_t:s0:c98,c684",lowerdir=/var/lib/containers/storage/overlay/l/T4G5ED56VRUEC2ID7JMJSGW3QT:/var/lib/containers/storage/overlay/l/KZGLWVLLUSCKZYWV57JF6WSK2I:/var/lib/containers/storage/overlay/l/HXWMTP6IYXVK4KUZ2UCSNJXOIW:/var/lib/containers/storage/overlay/l/YLBHA4OHH25PNVUIUV7LKJA67Q:/var/lib/containers/storage/overlay/l/7IH6AODKJYPJSHYY3KTKRAGDZO:/var/lib/containers/storage/overlay/l/EELW6SDH3FRQMJJEGMTWJ223DL:/var/lib/containers/storage/overlay/l/GNKPUG6OGVJANN4MB447IM4JK7,upperdir=/var/lib/containers/storage/overlay/f2d065994b6e5d208732fc71a7421f882a6b2f73809bcc210a00d4c49309c10f/diff,workdir=/var/lib/containers/storage/overlay/f2d065994b6e5d208732fc71a7421f882a6b2f73809bcc210a00d4c49309c10f/work,redirect_dir=on,uuid=on,metacopy=on,volatile
+1346 1345 0:96 / /sys rw,nosuid,nodev,noexec,relatime - sysfs sysfs rw,seclabel
+1348 1345 0:97 / /proc rw,nosuid,nodev,noexec,relatime - proc proc rw
+1349 1345 0:99 / /dev rw,nosuid - tmpfs tmpfs rw,context="system_u:object_r:container_file_t:s0:c98,c684",size=65536k,mode=755,inode64
+1352 1349 0:100 / /dev/pts rw,nosuid,noexec,relatime - devpts devpts rw,context="system_u:object_r:container_file_t:s0:c98,c684",gid=5,mode=620,ptmxmode=666
+1361 1349 0:85 / /dev/shm rw,nosuid,nodev,noexec,relatime - tmpfs shm rw,context="system_u:object_r:container_file_t:s0:c98,c684",size=64000k,inode64
+1363 1346 0:27 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - cgroup2 cgroup2 rw,seclabel,nsdelegate,memory_recursiveprot
+1364 1345 0:33 /root/var/lib/containers/storage /var/lib/containers/storage rw,relatime - btrfs /dev/mapper/luks-12345678-1234-1234-1234-123456789012 rw,seclabel,compress=zstd:1,ssd,discard=async,space_cache,subvolid=257,subvol=/root
+1365 1364 0:33 /root/var/lib/containers/storage/overlay /var/lib/containers/storage/overlay rw,relatime - btrfs /dev/mapper/luks-12345678-1234-1234-1234-123456789012 rw,seclabel,compress=zstd:1,ssd,discard=async,space_cache,subvolid=257,subvol=/root
+`
+	procSelfMountinfoWithVolume = `735 665 0:83 / / rw,relatime - overlay overlay rw,lowerdir=/var/lib/containers/storage/overlay/l/2BFF257G6Q5T5OWGW4JVUDTM3R:/var/lib/containers/storage/overlay/l/AEC37A7HVU4SH5Q4GWQLB7KCZU:/var/lib/containers/storage/overlay/l/JFOUQY5ZWN3DIZQP22SYYLXEV7,upperdir=/var/lib/containers/storage/overlay/d545c8ca670b6820eae79e43836175558d71f9f927fb68feffa608a2b3020f09/diff,workdir=/var/lib/containers/storage/overlay/d545c8ca670b6820eae79e43836175558d71f9f927fb68feffa608a2b3020f09/work,uuid=on,volatile
+736 735 259:2 /var/lib/containers/storage/volumes/e14ef96e3db8bdc3dcdbd340208995e6770cd7873f78788e737c8b7b5d17fdaa/_data /output rw,nosuid,nodev,relatime - ext4 /dev/nvme0n1p2 rw,errors=remount-ro
+737 735 0:86 / /proc rw,nosuid,nodev,noexec,relatime - proc proc rw
+738 735 0:87 / /dev rw,nosuid - tmpfs tmpfs rw,size=65536k,mode=755,inode64
+741 735 0:88 / /sys rw,nosuid,nodev,noexec,relatime - sysfs sysfs rw
+742 738 0:89 / /dev/pts rw,nosuid,noexec,relatime - devpts devpts rw,gid=5,mode=620,ptmxmode=666
+743 738 0:85 / /dev/mqueue rw,nosuid,nodev,noexec,relatime - mqueue mqueue rw
+744 735 0:24 /containers/storage/overlay-containers/5e5914d9351994648b28b8b58ba3c67ce06a48ccdd3a52679b82ae4dc693fa53/userdata/.containerenv /run/.containerenv rw,relatime - tmpfs tmpfs rw,size=3262508k,mode=755,inode64
+745 735 0:24 /containers/storage/overlay-containers/5e5914d9351994648b28b8b58ba3c67ce06a48ccdd3a52679b82ae4dc693fa53/userdata/hostname /etc/hostname rw,relatime - tmpfs tmpfs rw,size=3262508k,mode=755,inode64
+746 735 0:24 /containers/storage/overlay-containers/5e5914d9351994648b28b8b58ba3c67ce06a48ccdd3a52679b82ae4dc693fa53/userdata/resolv.conf /etc/resolv.conf rw,relatime - tmpfs tmpfs rw,size=3262508k,mode=755,inode64
+747 735 0:24 /containers/storage/overlay-containers/5e5914d9351994648b28b8b58ba3c67ce06a48ccdd3a52679b82ae4dc693fa53/userdata/hosts /etc/hosts rw,relatime - tmpfs tmpfs rw,size=3262508k,mode=755,inode64
+748 738 0:82 / /dev/shm rw,nosuid,nodev,noexec,relatime - tmpfs shm rw,size=64000k,inode64
+749 741 0:28 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - cgroup2 cgroup2 rw,nsdelegate,memory_recursiveprot
+750 735 259:2 /var/lib/containers/storage /var/lib/containers/storage rw,relatime - ext4 /dev/nvme0n1p2 rw,errors=remount-ro
+751 750 259:2 /var/lib/containers/storage/overlay /var/lib/containers/storage/overlay rw,relatime - ext4 /dev/nvme0n1p2 rw,errors=remount-ro
+`
+
+	procSelfMountinfoNoVolume = `736 735 259:2 /var/lib/containers/storage/volumes/5c45612492556520d9549b3ee24d6a11ac3a0e9266c0900bf427a3bdaafadeb8/_data /rpmmd rw,nosuid,nodev,relatime - ext4 /dev/nvme0n1p2 rw,errors=remount-ro
+737 735 259:2 /var/lib/containers/storage/volumes/e17849f054757adebabc844a1fd510308a1c22b6668526e84511a8dfd617aec8/_data /output rw,nosuid,nodev,relatime - ext4 /dev/nvme0n1p2 rw,errors=remount-ro
+738 735 0:86 / /proc rw,nosuid,nodev,noexec,relatime - proc proc rw
+739 735 259:2 /var/lib/containers/storage/volumes/8b15ab68602eaee4923cfddd7c0cbb19d7d33190c9d2f97adeea357370f5ba3b/_data /store rw,nosuid,nodev,relatime - ext4 /dev/nvme0n1p2 rw,errors=remount-ro
+740 735 0:87 / /sys rw,nosuid,nodev,noexec,relatime - sysfs sysfs rw
+741 735 0:88 / /dev rw,nosuid - tmpfs tmpfs rw,size=65536k,mode=755,inode64
+742 741 0:85 / /dev/mqueue rw,nosuid,nodev,noexec,relatime - mqueue mqueue rw
+743 741 0:89 / /dev/pts rw,nosuid,noexec,relatime - devpts devpts rw,gid=5,mode=620,ptmxmode=666
+745 741 0:82 / /dev/shm rw,nosuid,nodev,noexec,relatime - tmpfs shm rw,size=64000k,inode64
+750 735 259:2 /var/lib/containers/storage/volumes/8612bf74115e4610cf4a57da8a0209fa07d1782584752bf4a1991d773f9c608f/_data /var/lib/containers/storage rw,nosuid,nodev,relatime - ext4 /dev/nvme0n1p2 rw,errors=remount-ro
+666 741 0:89 /0 /dev/console rw,relatime - devpts devpts rw,gid=5,mode=620,ptmxmode=666
+`
+)
+
+func TestValidateHasContainerStorageMountedBtrfs(t *testing.T) {
+	restore := setup.MockInsideContainer(func() (bool, error) {
+		return true, nil
+	})
+	defer restore()
+
+	for _, tc := range []struct {
+		fakeMountinfo string
+		expectedErr   string
+	}{
+		// good
+		{procSelfMountinfoBtrfs, ""},
+		{procSelfMountinfoWithVolume, ""},
+		// bad
+		{procSelfMountinfoNoVolume, `cannot find suffix "/var/lib/containers/storage" in mounted "/var/lib/containers/storage/volumes/8612bf74115e4610cf4a57da8a0209fa07d1782584752bf4a1991d773f9c608f/_data"`},
+	} {
+		buf := bytes.NewBufferString(tc.fakeMountinfo)
+		err := setup.ValidateHasContainerStorageMountedFromReader(buf)
+		if tc.expectedErr == "" {
+			assert.NoError(t, err)
+		} else {
+			assert.Error(t, err)
+			assert.Equal(t, tc.expectedErr, err.Error())
+		}
+	}
+}