fix(vm): fail fast when cidata profiles lack cloud-localds

docs/env-reference.md

@@ -131,6 +131,7 @@ Generated by `bpfcompat env --markdown`. Do not edit by hand.
 |---|---|---|
 | `BPFCOMPAT_AARCH64_UEFI_CODE` | /usr/share/AAVMF/AAVMF_CODE.fd | Path to the aarch64 UEFI firmware CODE image (pflash). aarch64 `virt` has no built-in firmware, so VM boots need it; install qemu-efi-aarch64 or point this at your distro's edk2 build. Ignored on x86_64. |
 | `BPFCOMPAT_AARCH64_UEFI_VARS` | /usr/share/AAVMF/AAVMF_VARS.fd | Path to the aarch64 UEFI vars template (pflash). A per-VM writable copy is staged from it so guest NVRAM writes don't touch the shared template. Ignored on x86_64. |
+| `BPFCOMPAT_ALLOW_VVFAT_SEED` | false | Re-enable the legacy vvfat config-drive seed for RHEL-family/Amazon/Oracle/SUSE profiles when cloud-localds is missing. Off by default: those guests are known not to boot from the vvfat fallback on some hosts (0-byte serial, then an SSH timeout), so seed selection fails fast with an install hint instead. Prefer installing cloud-image-utils (provides cloud-localds). |
 | `BPFCOMPAT_ENABLE_RHCOS` | false | Enable the RHEL CoreOS (rhcos) profile. RHCOS boots via the same Ignition path as Fedora CoreOS, but its image ships with an OpenShift release rather than a public URL. Stage the image with `make rhcos-image` and set this to 1/true once it is present; left off, rhcos stays unsupported so it is never claimed runnable without a real image. |
 
 ## Validator

internal/envref/envref.go

@@ -299,6 +299,11 @@ var catalog = []Var{
 		Category:    "VM Runner",
 		Description: "Enable the RHEL CoreOS (rhcos) profile. RHCOS boots via the same Ignition path as Fedora CoreOS, but its image ships with an OpenShift release rather than a public URL. Stage the image with `make rhcos-image` and set this to 1/true once it is present; left off, rhcos stays unsupported so it is never claimed runnable without a real image.",
 	},
+	{
+		Name: "BPFCOMPAT_ALLOW_VVFAT_SEED", Default: "false",
+		Category:    "VM Runner",
+		Description: "Re-enable the legacy vvfat config-drive seed for RHEL-family/Amazon/Oracle/SUSE profiles when cloud-localds is missing. Off by default: those guests are known not to boot from the vvfat fallback on some hosts (0-byte serial, then an SSH timeout), so seed selection fails fast with an install hint instead. Prefer installing cloud-image-utils (provides cloud-localds).",
+	},
 	{
 		Name: "BPFCOMPAT_AARCH64_UEFI_CODE", Default: "/usr/share/AAVMF/AAVMF_CODE.fd",
 		Category:    "VM Runner",

internal/vm/ignition_test.go

@@ -48,8 +48,8 @@ func TestIsCoreOSIgnitionDistro(t *testing.T) {
 }
 
 func TestSeedDeliveryForCoreOS(t *testing.T) {
-	if got := seedDeliveryForProfile(Profile{Distro: "fedora-coreos"}); got != seedDeliveryIgnition {
-		t.Errorf("fedora-coreos seed delivery = %q, want %q", got, seedDeliveryIgnition)
+	if got, err := seedDeliveryForProfile(Profile{Distro: "fedora-coreos"}); err != nil || got != seedDeliveryIgnition {
+		t.Errorf("fedora-coreos seed delivery = %q (err %v), want %q", got, err, seedDeliveryIgnition)
 	}
 }
 

internal/vm/qemu.go

@@ -237,7 +237,11 @@ func ExecuteProfile(ctx context.Context, req ExecutionRequest) (result Execution
 		return
 	}
 
-	seedMode := seedDeliveryForProfile(req.Profile)
+	seedMode, err := seedDeliveryForProfile(req.Profile)
+	if err != nil {
+		result.InfraError = err.Error()
+		return
+	}
 	seedDir := filepath.Join(vmRunDir, "seed")
 	seedURL := ""
 	seedImagePath := ""
@@ -272,7 +276,7 @@ func ExecuteProfile(ctx context.Context, req ExecutionRequest) (result Execution
 		}
 		result.Notes = append(result.Notes, "seed delivery: local NoCloud config drive image (cloud-localds)")
 	case seedDeliveryNoCloudConfigFS:
-		result.Notes = append(result.Notes, "seed delivery: local NoCloud config drive (vvfat, label=cidata)")
+		result.Notes = append(result.Notes, "seed delivery: local NoCloud config drive (vvfat, label=cidata) — legacy fallback enabled via BPFCOMPAT_ALLOW_VVFAT_SEED; if this guest never reaches SSH, install cloud-image-utils instead")
 	default:
 		seedSrv, err := startSeedServer(seedDir)
 		if err != nil {
@@ -937,17 +941,40 @@ func needsCIDATASeed(profile Profile) bool {
 	return strings.EqualFold(strings.TrimSpace(profile.ID), "rhel-8-4.18")
 }
 
-func seedDeliveryForProfile(profile Profile) seedDeliveryMode {
+func seedDeliveryForProfile(profile Profile) (seedDeliveryMode, error) {
 	if isCoreOSIgnitionDistro(profile) {
-		return seedDeliveryIgnition
+		return seedDeliveryIgnition, nil
 	}
 	if needsCIDATASeed(profile) {
 		if commandAvailable("cloud-localds") {
-			return seedDeliveryNoCloudConfigDrive
+			return seedDeliveryNoCloudConfigDrive, nil
+		}
+		// The vvfat config-drive fallback is known NOT to boot RHEL-family/
+		// Amazon/Oracle/SUSE guests on some hosts (0-byte serial, SSH
+		// timeout) — and because the guest simply never comes up, the
+		// failure surfaces 15 minutes later as an opaque SSH timeout.
+		// Fail fast with the actionable fix instead; the legacy fallback
+		// stays reachable behind an explicit opt-in.
+		if allowVVFATSeedFallback() {
+			return seedDeliveryNoCloudConfigFS, nil
 		}
-		return seedDeliveryNoCloudConfigFS
+		return "", fmt.Errorf("profile %s needs a cloud-init cidata seed ISO but cloud-localds is not installed; "+
+			"install cloud-image-utils (Debian/Ubuntu: apt-get install cloud-image-utils), "+
+			"or set BPFCOMPAT_ALLOW_VVFAT_SEED=1 to try the legacy vvfat config-drive fallback "+
+			"(known not to boot RHEL-family/Amazon/Oracle/SUSE guests on some hosts)", profile.ID)
+	}
+	return seedDeliveryNoCloudNet, nil
+}
+
+// allowVVFATSeedFallback reports whether the operator explicitly re-enabled
+// the legacy vvfat config-drive seed for cidata profiles when cloud-localds
+// is missing.
+func allowVVFATSeedFallback() bool {
+	switch strings.ToLower(strings.TrimSpace(os.Getenv("BPFCOMPAT_ALLOW_VVFAT_SEED"))) {
+	case "1", "true", "yes", "on":
+		return true
 	}
-	return seedDeliveryNoCloudNet
+	return false
 }
 
 func commandAvailable(name string) bool {

internal/vm/qemu_test.go

@@ -395,23 +395,55 @@ func TestParseFirecrackerMarkedOutput(t *testing.T) {
 }
 
 func TestSeedDeliveryForProfile(t *testing.T) {
-	if got := seedDeliveryForProfile(Profile{ID: "rhel-8-4.18"}); got != seedDeliveryNoCloudConfigDrive && got != seedDeliveryNoCloudConfigFS {
-		t.Fatalf("expected rhel-8-4.18 seed delivery %q or %q, got %q", seedDeliveryNoCloudConfigDrive, seedDeliveryNoCloudConfigFS, got)
+	if got, err := seedDeliveryForProfile(Profile{ID: "ubuntu-22.04-5.15", Distro: "ubuntu"}); err != nil || got != seedDeliveryNoCloudNet {
+		t.Fatalf("expected default seed delivery %q, got %q (err %v)", seedDeliveryNoCloudNet, got, err)
 	}
-	if got := seedDeliveryForProfile(Profile{ID: "ubuntu-22.04-5.15", Distro: "ubuntu"}); got != seedDeliveryNoCloudNet {
-		t.Fatalf("expected default seed delivery %q, got %q", seedDeliveryNoCloudNet, got)
-	}
-	if got := seedDeliveryForProfile(Profile{ID: "debian-12-6.1", Distro: "debian"}); got != seedDeliveryNoCloudNet {
-		t.Fatalf("expected debian seed delivery %q, got %q", seedDeliveryNoCloudNet, got)
+	if got, err := seedDeliveryForProfile(Profile{ID: "debian-12-6.1", Distro: "debian"}); err != nil || got != seedDeliveryNoCloudNet {
+		t.Fatalf("expected debian seed delivery %q, got %q (err %v)", seedDeliveryNoCloudNet, got, err)
 	}
 	// EL-family / Amazon / SUSE must use the CIDATA disk seed (SMBIOS-net is
-	// ignored by their cloud-init).
+	// ignored by their cloud-init). With cloud-localds present that is the
+	// seed ISO; without it, selection must error rather than fall back.
 	for _, distro := range []string{"almalinux", "rocky", "rhel", "centos-stream", "oracle", "amazon-linux", "sles", "opensuse"} {
-		got := seedDeliveryForProfile(Profile{ID: distro + "-x", Distro: distro})
-		if got != seedDeliveryNoCloudConfigDrive && got != seedDeliveryNoCloudConfigFS {
-			t.Fatalf("expected CIDATA seed for distro %q, got %q", distro, got)
+		got, err := seedDeliveryForProfile(Profile{ID: distro + "-x", Distro: distro})
+		if err != nil {
+			continue // host without cloud-localds: covered by the fail-fast test below
+		}
+		if got != seedDeliveryNoCloudConfigDrive {
+			t.Fatalf("expected CIDATA seed ISO for distro %q, got %q", distro, got)
+		}
+	}
+}
+
+// Without cloud-localds on PATH, cidata profiles must fail fast with the
+// actionable install hint — the vvfat fallback boots to a 0-byte serial on
+// some hosts and only surfaces as an SSH timeout much later.
+func TestSeedDeliveryFailsFastWithoutCloudLocalds(t *testing.T) {
+	t.Setenv("PATH", t.TempDir()) // no cloud-localds resolvable
+	t.Setenv("BPFCOMPAT_ALLOW_VVFAT_SEED", "")
+
+	_, err := seedDeliveryForProfile(Profile{ID: "almalinux-8-4.18", Distro: "almalinux"})
+	if err == nil {
+		t.Fatal("expected error for cidata profile without cloud-localds")
+	}
+	for _, want := range []string{"cloud-localds", "cloud-image-utils", "BPFCOMPAT_ALLOW_VVFAT_SEED"} {
+		if !strings.Contains(err.Error(), want) {
+			t.Fatalf("error %q missing actionable hint %q", err.Error(), want)
 		}
 	}
+
+	// Explicit opt-in re-enables the legacy vvfat fallback.
+	t.Setenv("BPFCOMPAT_ALLOW_VVFAT_SEED", "1")
+	got, err := seedDeliveryForProfile(Profile{ID: "almalinux-8-4.18", Distro: "almalinux"})
+	if err != nil || got != seedDeliveryNoCloudConfigFS {
+		t.Fatalf("expected vvfat fallback with opt-in, got %q (err %v)", got, err)
+	}
+
+	// Ubuntu/Debian (NoCloud net seed) are unaffected by the missing tool.
+	got, err = seedDeliveryForProfile(Profile{ID: "ubuntu-22.04-5.15", Distro: "ubuntu"})
+	if err != nil || got != seedDeliveryNoCloudNet {
+		t.Fatalf("expected NoCloud net seed for ubuntu, got %q (err %v)", got, err)
+	}
 }
 
 func TestMapFixupArgs(t *testing.T) {