Quadlet: add -list-images

Add a new `-list-images` string flag Quadlet which will write a list of
images mentioned in `.image` Quadlets to specified file.

In order to avoid disk bloat, many bootable containers do not embed
application-container images.  Hence, those must be pulled in _some_
use-case dependent way.  Quadlet is perfectly capable of pulling the
images on boot or on demand but that does not satisfy all use cases as
it slows down boot or initialization of the workloads.  In those cases,
we want a `bootc upgrade` to first pull down the bootable container
image and then analyze its root FS to extract all referenced images in
(rootful) `.image` Quadlets.  This change is a first step in this
direction.

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

cmd/quadlet/main.go

@@ -27,11 +27,12 @@ import (
 // for more details.
 
 var (
-	verboseFlag bool // True if -v passed
-	noKmsgFlag  bool
-	isUserFlag  bool // True if run as quadlet-user-generator executable
-	dryRunFlag  bool // True if -dryrun is used
-	versionFlag bool // True if -version is used
+	verboseFlag    bool // True if -v passed
+	noKmsgFlag     bool
+	isUserFlag     bool   // True if run as quadlet-user-generator executable
+	dryRunFlag     bool   // True if -dryrun is used
+	versionFlag    bool   // True if -version is used
+	listImagesFlag string // Set if -list-images is used
 )
 
 const (
@@ -549,7 +550,7 @@ func process() error {
 		prevError = err
 	}
 
-	if !dryRunFlag && flag.NArg() < 1 {
+	if !dryRunFlag && flag.NArg() < 1 && len(listImagesFlag) == 0 {
 		reportError(errors.New("missing output directory argument"))
 		return prevError
 	}
@@ -586,6 +587,31 @@ func process() error {
 		}
 	}
 
+	if len(listImagesFlag) > 0 {
+		fd, err := os.OpenFile(listImagesFlag, os.O_WRONLY, 0644)
+		if err != nil {
+			return err
+		}
+		for _, unit := range units {
+			if !strings.HasSuffix(unit.Filename, ".image") {
+				continue
+			}
+			imageName, err := quadlet.ListImage(unit)
+			if err != nil {
+				reportError(err)
+			}
+			if !isUnambiguousName(imageName) {
+				Logf("Warning: %s specifies the image \"%s\" which not a fully qualified image name and is hence being ignored.", unit.Filename, imageName)
+				continue
+			}
+			fmt.Fprintf(fd, "%s\n", imageName)
+		}
+		if err := fd.Close(); err != nil {
+			reportError(err)
+		}
+		return prevError
+	}
+
 	if !dryRunFlag {
 		err := os.MkdirAll(outputPath, os.ModePerm)
 		if err != nil {
@@ -681,4 +707,5 @@ func init() {
 	flag.BoolVar(&isUserFlag, "user", false, "Run as systemd user")
 	flag.BoolVar(&dryRunFlag, "dryrun", false, "Run in dryrun mode printing debug information")
 	flag.BoolVar(&versionFlag, "version", false, "Print version information and exit")
+	flag.StringVar(&listImagesFlag, "list-images", "", "Write a list of all images being references in .image Quadlets to specified file")
 }

pkg/systemd/quadlet/quadlet.go

@@ -1223,6 +1223,21 @@ func ConvertKube(kube *parser.UnitFile, names map[string]string, isUser bool) (*
 	return service, nil
 }
 
+func ListImage(image *parser.UnitFile) (string, error) {
+	// Even if we're only interested in the Image= of the unit, it should
+	// still be valid.
+	if err := checkForUnknownKeys(image, ImageGroup, supportedImageKeys); err != nil {
+		return "", err
+	}
+
+	imageName, ok := image.Lookup(ImageGroup, KeyImage)
+	if !ok || len(imageName) == 0 {
+		return "", fmt.Errorf("no Image key specified")
+	}
+
+	return imageName, nil
+}
+
 func ConvertImage(image *parser.UnitFile) (*parser.UnitFile, string, error) {
 	service := image.Dup()
 	service.Filename = replaceExtension(image.Filename, ".service", "", "-image")

test/system/252-quadlet.bats

@@ -1027,6 +1027,43 @@ EOF
     run_podman network rm podman-default-kube-network
 }
 
+@test "quadlet - list images" {
+    local quadlet_tmpdir=$PODMAN_TMPDIR/quadlets
+    mkdir -p $quadlet_tmpdir
+
+    local image_name_1=quay.io/quadlet/image:1
+    local image_name_2=quay.io/quadlet/image:2
+    local image_name_3=quay.io/quadlet/image:3
+
+    cat > $PODMAN_TMPDIR/1.image <<EOF
+[Image]
+Image=$image_name_1
+EOF
+    cat > $quadlet_tmpdir/2.image <<EOF
+[Image]
+Image=$image_name_2
+EOF
+    cat > $quadlet_tmpdir/3.image <<EOF
+[Image]
+Image=$image_name_3
+EOF
+    cat > $quadlet_tmpdir/1.container <<EOF
+[Image]
+Image=quay.io/do/not/parse:me
+EOF
+
+    local image_file=$quadlet_tmpdir/image_file
+    touch $image_file
+
+    QUADLET_UNIT_DIRS=$PODMAN_TMPDIR run \
+                    timeout --foreground -v --kill=10 $PODMAN_TIMEOUT \
+                    $QUADLET -list-images=$image_file
+
+    assert "$(< $image_file)" = "$image_name_1
+$image_name_2
+$image_name_3" "-list-images=FILE lists all images referenced in .image Quadlets"
+}
+
 @test "quadlet - image files" {
     local quadlet_tmpdir=$PODMAN_TMPDIR/quadlets