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Stop using kernel IP autoconfig for runtime VMs

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Avoid the Alpine boot stall caused by kernel ip= autoconfig running before
virtio_net is available.

Split runtime and image-build boot args so managed VMs boot without kernel
network autoconfig, inject a static guest network config plus bootstrap
script into the runtime overlay, and keep image builds on the old path for
compatibility with existing base images.

Preserve executable bits when patching guest files into ext4 images and add
coverage for the new boot-arg split and guest network config generation.

Validated with go test ./..., a rebuilt Alpine image, and a fresh alp-fast
create/ssh check that brought vm.start down to about 2.7s.
This commit is contained in:
Thales Maciel 2026-03-21 21:54:18 -03:00
parent 092d848620
commit 14d8563f3c
No known key found for this signature in database
GPG key ID: 33112E6833C34679
7 changed files with 186 additions and 28 deletions
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28
internal/system/system.go
View file

@ -318,6 +318,10 @@ func ReadDebugFSText(ctx context.Context, runner CommandRunner, imagePath, guest
}
func WriteExt4File(ctx context.Context, runner CommandRunner, imagePath, guestPath string, data []byte) error {
return WriteExt4FileMode(ctx, runner, imagePath, guestPath, 0o600, data)
}
func WriteExt4FileMode(ctx context.Context, runner CommandRunner, imagePath, guestPath string, mode os.FileMode, data []byte) error {
tmp, err := os.CreateTemp("", "banger-ext4-*")
if err != nil {
return err
@ -330,9 +334,20 @@ func WriteExt4File(ctx context.Context, runner CommandRunner, imagePath, guestPa
if err := tmp.Close(); err != nil {
return err
}
if err := os.Chmod(tmp.Name(), mode); err != nil {
return err
}
_, _ = runner.RunSudo(ctx, "e2rm", imagePath+":"+guestPath)
_, err = runner.RunSudo(ctx, "e2cp", tmp.Name(), imagePath+":"+guestPath)
return err
if _, err := runner.RunSudo(ctx, "e2cp", tmp.Name(), imagePath+":"+guestPath); err != nil {
return err
}
if mode.Perm()&0o111 != 0 {
modeValue := fmt.Sprintf("%#o", uint32(0o100000|mode.Perm()))
if _, err := runner.RunSudo(ctx, "debugfs", "-w", "-R", "sif "+guestPath+" mode "+modeValue, imagePath); err != nil {
return err
}
}
return nil
}
func MountTempDir(ctx context.Context, runner CommandRunner, source string, readOnly bool) (string, func() error, error) {
@ -415,7 +430,14 @@ func UpdateFSTab(existing string) string {
return strings.Join(out, "\n") + "\n"
}
func BuildBootArgs(vmName, guestIP, bridgeIP, dns string) string {
func BuildBootArgs(vmName string) string {
return fmt.Sprintf(
"console=ttyS0 reboot=k panic=1 pci=off root=/dev/vda rootfstype=ext4 rw hostname=%s systemd.mask=home.mount systemd.mask=var.mount",
vmName,
)
}
func BuildBootArgsWithKernelIP(vmName, guestIP, bridgeIP, dns string) string {
return fmt.Sprintf(
"console=ttyS0 reboot=k panic=1 pci=off root=/dev/vda rootfstype=ext4 rw ip=%s::%s:255.255.255.0:%s:eth0:off:%s hostname=%s systemd.mask=home.mount systemd.mask=var.mount",
guestIP,

56
internal/system/system_test.go
View file

@ -167,16 +167,26 @@ func TestReadNormalizedLines(t *testing.T) {
}
}
func TestBuildBootArgsIncludesHostnameInIPField(t *testing.T) {
func TestBuildBootArgsOmitsKernelIPAutoconfig(t *testing.T) {
t.Parallel()
got := BuildBootArgs("devbox", "172.16.0.2", "172.16.0.1", "1.1.1.1")
want := "console=ttyS0 reboot=k panic=1 pci=off root=/dev/vda rootfstype=ext4 rw ip=172.16.0.2::172.16.0.1:255.255.255.0:devbox:eth0:off:1.1.1.1 hostname=devbox systemd.mask=home.mount systemd.mask=var.mount"
got := BuildBootArgs("devbox")
want := "console=ttyS0 reboot=k panic=1 pci=off root=/dev/vda rootfstype=ext4 rw hostname=devbox systemd.mask=home.mount systemd.mask=var.mount"
if got != want {
t.Fatalf("BuildBootArgs() = %q, want %q", got, want)
}
}
func TestBuildBootArgsWithKernelIPIncludesHostnameInIPField(t *testing.T) {
t.Parallel()
got := BuildBootArgsWithKernelIP("devbox", "172.16.0.2", "172.16.0.1", "1.1.1.1")
want := "console=ttyS0 reboot=k panic=1 pci=off root=/dev/vda rootfstype=ext4 rw ip=172.16.0.2::172.16.0.1:255.255.255.0:devbox:eth0:off:1.1.1.1 hostname=devbox systemd.mask=home.mount systemd.mask=var.mount"
if got != want {
t.Fatalf("BuildBootArgsWithKernelIP() = %q, want %q", got, want)
}
}
func TestWriteExt4FileRemovesTempFileAndReturnsCopyError(t *testing.T) {
t.Parallel()
@ -212,6 +222,46 @@ func TestWriteExt4FileRemovesTempFileAndReturnsCopyError(t *testing.T) {
}
}
func TestWriteExt4FileModeUsesRequestedPermissions(t *testing.T) {
t.Parallel()
debugfsCalled := false
runner := funcRunner{
runSudo: func(ctx context.Context, args ...string) ([]byte, error) {
switch args[0] {
case "e2rm":
return nil, nil
case "e2cp":
info, err := os.Stat(args[1])
if err != nil {
t.Fatalf("Stat(temp file): %v", err)
}
if got := info.Mode().Perm(); got != 0o755 {
t.Fatalf("temp file mode = %o, want 755", got)
}
return nil, nil
case "debugfs":
debugfsCalled = true
want := []string{"debugfs", "-w", "-R", "sif /usr/local/libexec/banger-network-bootstrap mode 0100755", "/tmp/root.ext4"}
if !reflect.DeepEqual(args, want) {
t.Fatalf("debugfs args = %v, want %v", args, want)
}
return nil, nil
default:
t.Fatalf("unexpected sudo call: %v", args)
return nil, nil
}
},
}
if err := WriteExt4FileMode(context.Background(), runner, "/tmp/root.ext4", "/usr/local/libexec/banger-network-bootstrap", 0o755, []byte("#!/bin/sh\n")); err != nil {
t.Fatalf("WriteExt4FileMode() error = %v", err)
}
if !debugfsCalled {
t.Fatal("expected debugfs mode fixup to run")
}
}
func TestMountTempDirUsesLoopForRegularFilesAndCleanupUsesBackgroundContext(t *testing.T) {
t.Parallel()