Speed up VM create with work seeds

Beat VM create wall time without changing VM semantics.

Generate a work-seed ext4 sidecar during image builds and rootfs rebuilds, then clone and resize that seed for each new VM instead of rebuilding /root from scratch. Plumb the new seed artifact through config, runtime metadata, store state, runtime-bundle defaults, doctor checks, and default-image reconciliation so older images still fall back cleanly.

Add a daemon TAP pool to keep idle bridge-attached devices warm, expose stage timing in lifecycle logs, add a create/SSH benchmark script plus Make target, and teach verify.sh that tap-pool-* devices are reusable capacity rather than cleanup leaks.

Validated with go test ./..., make build, ./verify.sh, and make bench-create ARGS="--runs 2".

AGENTS.md

@@ -10,6 +10,7 @@
 
 ## Build, Test, and Development Commands
 - `make build` builds `./banger`, `./bangerd`, and the bundled `./runtime/banger-vsock-pingd` guest helper.
+- `make bench-create` benchmarks `vm create` and first-SSH readiness on the current host.
 - `make runtime-bundle` bootstraps `./runtime/` from the archive referenced by `RUNTIME_MANIFEST`; the checked-in `runtime-bundle.toml` is only a template.
 - `banger` validates required host tools per command and reports actionable missing-tool errors; do not assume one workstation's package set.
 - `./banger vm create --name testbox` creates and starts a VM.
@@ -32,6 +33,8 @@
 - Manual verification for VM lifecycle changes: `./banger vm create`, confirm SSH access, then stop/delete the VM.
 - For host-integration changes, run `./banger doctor` as a quick readiness check before the live VM smoke.
 - Rebuilt images now include `mise`, `opencode`, `tmux-resurrect`/`tmux-continuum` defaults for `root`, and the `banger-vsock-pingd` service used by the SSH reminder path; if you change guest provisioning, document whether users need to rebuild `./runtime/rootfs-docker.ext4` or another base image to pick it up.
+- Rebuilt images also emit a `work-seed.ext4` sidecar used to speed up future VM creates. If you touch `/root` provisioning, verify both the rootfs and the work-seed output.
+- The daemon may keep idle TAP devices in a pool for faster creates. Smoke tests should treat `tap-pool-*` devices as reusable capacity, not cleanup leaks.
 - If you add a new operational workflow, document how to exercise it in `README.md`.
 - For NAT changes, verify both guest outbound access and host rule cleanup, for example with `./verify.sh --nat`.
 

Makefile

@@ -16,13 +16,13 @@ RUNTIME_HELPERS := $(RUNTIME_SOURCE_DIR)/banger-vsock-pingd
 GO_SOURCES := $(shell find cmd internal -type f -name '*.go' | sort)
 RUNTIME_EXECUTABLES := firecracker customize.sh packages.sh namegen banger-vsock-pingd
 RUNTIME_DATA_FILES := packages.apt id_ed25519 rootfs-docker.ext4
-RUNTIME_OPTIONAL_DATA_FILES := rootfs.ext4 bundle.json
+RUNTIME_OPTIONAL_DATA_FILES := rootfs.ext4 rootfs-docker.work-seed.ext4 bundle.json
 RUNTIME_BOOT_FILES := wtf/root/boot/vmlinux-6.8.0-94-generic wtf/root/boot/initrd.img-6.8.0-94-generic
 RUNTIME_MODULES_DIR := wtf/root/lib/modules/6.8.0-94-generic
 
 .DEFAULT_GOAL := help
 
-.PHONY: help build banger bangerd test fmt tidy clean rootfs install runtime-bundle runtime-package check-runtime
+.PHONY: help build banger bangerd test fmt tidy clean rootfs install runtime-bundle runtime-package check-runtime bench-create
 
 help:
 	@printf '%s\n' \
@@ -30,6 +30,7 @@ help:
 	  '  make build   Build ./banger and ./bangerd' \
 	  '  make runtime-bundle Fetch and unpack ./runtime from the archive referenced by $(RUNTIME_MANIFEST)' \
 	  '  make runtime-package Package $(RUNTIME_SOURCE_DIR) into $(RUNTIME_ARCHIVE) and print its SHA256' \
+	  '  make bench-create Benchmark vm create and SSH readiness with scripts/bench-create.sh' \
 	  '  make install Build and install binaries plus the runtime bundle into $(DESTDIR)$(BINDIR) and $(DESTDIR)$(RUNTIMEDIR)' \
 	  '  make test    Run go test ./...' \
 	  '  make fmt     Format Go sources under cmd/ and internal/' \
@@ -67,6 +68,9 @@ runtime-bundle:
 runtime-package:
 	$(GO) run ./cmd/runtimebundle package --manifest "$(RUNTIME_MANIFEST)" --runtime-dir "$(RUNTIME_SOURCE_DIR)" --out "$(RUNTIME_ARCHIVE)"
 
+bench-create: build
+	bash ./scripts/bench-create.sh $(ARGS)
+
 check-runtime:
 	@test -d "$(RUNTIME_SOURCE_DIR)" || { echo "missing runtime bundle directory: $(RUNTIME_SOURCE_DIR); run 'make runtime-bundle'" >&2; exit 1; }
 	@for path in $(RUNTIME_EXECUTABLES) $(RUNTIME_DATA_FILES) $(RUNTIME_BOOT_FILES) $(RUNTIME_MODULES_DIR); do \

README.md

@@ -26,6 +26,8 @@ The bundle contains:
 - `bundle.json` with the bundle's default kernel/initrd/modules/rootfs paths
 - a kernel, initrd, and modules tree referenced by `bundle.json`
 - `rootfs-docker.ext4`
+- `rootfs-docker.work-seed.ext4` when present, used to seed `/root` quickly on
+  new VM creates
 - `rootfs.ext4` when present
 - `packages.apt`
 - `id_ed25519`
@@ -162,12 +164,14 @@ repo-built `./banger`. You can override either with `runtime_dir` in
 Useful config keys:
 - `log_level`
 - `runtime_dir`
+- `tap_pool_size`
 - `firecracker_bin`
 - `ssh_key_path`
 - `namegen_path`
 - `customize_script` (manual helper compatibility; `banger image build` is Go-native)
 - `vsock_ping_helper_path`
 - `default_rootfs`
+- `default_work_seed`
 - `default_base_rootfs`
 - `default_kernel`
 - `default_initrd`
@@ -207,7 +211,9 @@ Rebuilt images install a pinned `mise` at `/usr/local/bin/mise`, activate it
 for bash login and interactive shells, install `opencode` through `mise`,
 configure `tmux-resurrect` plus `tmux-continuum` for `root` with periodic
 autosaves and manual-only restore by default, and bake in the
-`banger-vsock-pingd` systemd service used by the post-SSH reminder path.
+`banger-vsock-pingd` systemd service used by the post-SSH reminder path. They
+also emit a `work-seed.ext4` sidecar that lets new VMs clone a prepared `/root`
+work disk instead of rebuilding it from scratch on every create.
 
 Show or delete images:
 ```bash
@@ -240,6 +246,12 @@ transparent `.vm` lookups on the host.
 - VMs share a read-only base rootfs image.
 - Each VM gets its own sparse writable system overlay for `/`.
 - Each VM gets its own persistent ext4 work disk mounted at `/root`.
+- When an image has a `work-seed.ext4` sidecar, new VM creates clone that seed
+  and only resize it when needed. Older images still work, but create more
+  slowly because `/root` must be built from scratch.
+- The daemon can keep a small idle TAP pool warm in the background so VM create
+  does not need to synchronously create a fresh TAP every time. `tap_pool_size`
+  controls the pool depth.
 
 ## Architecture Notes
 The Go daemon is the primary control plane. VM host integrations such as the
@@ -261,6 +273,9 @@ To rebuild the source-checkout default image in `./runtime/rootfs-docker.ext4`:
 make rootfs
 ```
 
+That rebuild also regenerates `./runtime/rootfs-docker.work-seed.ext4`, which
+the daemon uses to speed up future `vm create` calls.
+
 If your runtime bundle does not include `./runtime/rootfs.ext4`, pass an
 explicit base image instead:
 ```bash
@@ -293,6 +308,22 @@ That writes `dist/banger-runtime.tar.gz` and prints its SHA256 so you can update
 a local manifest copy before testing bootstrap changes or publishing the
 archive elsewhere.
 
+## Benchmarking Create Time
+Benchmark the current host's `vm create` wall time plus first-SSH readiness:
+```bash
+make bench-create
+```
+
+Pass options through `ARGS`, for example:
+```bash
+make bench-create ARGS="--runs 3 --image docker-dev"
+```
+
+The benchmark prints JSON with:
+- `create_ms`: wall time for `banger vm create`
+- `ssh_ready_ms`: wall time from create start until `banger vm ssh <vm> -- true`
+  succeeds
+
 ## Remaining Shell Helpers
 The runtime VM lifecycle is managed through `banger`. The remaining shell scripts are not the primary user interface:
 - `customize.sh`: manual reference flow for rootfs customization; `banger image build` is now Go-native, but the script still reads

customize.sh

@@ -174,6 +174,11 @@ if [[ -z "$OUT_ROOTFS" ]]; then
   base_name="$(basename "$BASE_ROOTFS")"
   OUT_ROOTFS="${base_dir}/docker-${base_name}"
 fi
+if [[ "$OUT_ROOTFS" == *.ext4 ]]; then
+  WORK_SEED="${OUT_ROOTFS%.ext4}.work-seed.ext4"
+else
+  WORK_SEED="${OUT_ROOTFS}.work-seed"
+fi
 if [[ ! -f "$KERNEL" ]]; then
   log "kernel not found: $KERNEL"
   exit 1
@@ -547,4 +552,6 @@ for _ in $(seq 1 200); do
   sleep 0.05
 done
 banger_write_rootfs_manifest_metadata "$OUT_ROOTFS" "$PACKAGES_HASH"
+log "building work seed $WORK_SEED"
+"$BANGER_BIN" internal work-seed --rootfs "$OUT_ROOTFS" --out "$WORK_SEED"
 log "done"

internal/cli/banger.go

@@ -87,7 +87,34 @@ func newInternalCommand() *cobra.Command {
 		Hidden: true,
 		RunE:   helpNoArgs,
 	}
-	cmd.AddCommand(newInternalNATCommand())
+	cmd.AddCommand(newInternalNATCommand(), newInternalWorkSeedCommand())
+	return cmd
+}
+
+func newInternalWorkSeedCommand() *cobra.Command {
+	var rootfsPath string
+	var outPath string
+	cmd := &cobra.Command{
+		Use:    "work-seed",
+		Hidden: true,
+		Args:   noArgsUsage("usage: banger internal work-seed --rootfs <path> [--out <path>]"),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			rootfsPath = strings.TrimSpace(rootfsPath)
+			outPath = strings.TrimSpace(outPath)
+			if rootfsPath == "" {
+				return errors.New("rootfs path is required")
+			}
+			if outPath == "" {
+				outPath = system.WorkSeedPath(rootfsPath)
+			}
+			if err := system.EnsureSudo(cmd.Context()); err != nil {
+				return err
+			}
+			return system.BuildWorkSeedImage(cmd.Context(), system.NewRunner(), rootfsPath, outPath)
+		},
+	}
+	cmd.Flags().StringVar(&rootfsPath, "rootfs", "", "rootfs image path")
+	cmd.Flags().StringVar(&outPath, "out", "", "output work-seed image path")
 	return cmd
 }
 

internal/config/config.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"os"
 	"path/filepath"
+	"strings"
 	"time"
 
 	toml "github.com/pelletier/go-toml"
@@ -22,6 +23,7 @@ type fileConfig struct {
 	NamegenPath        string `toml:"namegen_path"`
 	CustomizeScript    string `toml:"customize_script"`
 	VSockPingHelper    string `toml:"vsock_ping_helper_path"`
+	DefaultWorkSeed    string `toml:"default_work_seed"`
 	DefaultImageName   string `toml:"default_image_name"`
 	DefaultRootfs      string `toml:"default_rootfs"`
 	DefaultBaseRootfs  string `toml:"default_base_rootfs"`
@@ -35,6 +37,7 @@ type fileConfig struct {
 	BridgeName         string `toml:"bridge_name"`
 	BridgeIP           string `toml:"bridge_ip"`
 	CIDR               string `toml:"cidr"`
+	TapPoolSize        int    `toml:"tap_pool_size"`
 	DefaultDNS         string `toml:"default_dns"`
 }
 
@@ -47,6 +50,7 @@ func Load(layout paths.Layout) (model.DaemonConfig, error) {
 		BridgeName:          model.DefaultBridgeName,
 		BridgeIP:            model.DefaultBridgeIP,
 		CIDR:                model.DefaultCIDR,
+		TapPoolSize:         4,
 		DefaultDNS:          model.DefaultDNS,
 		DefaultImageName:    "default",
 	}
@@ -91,6 +95,9 @@ func Load(layout paths.Layout) (model.DaemonConfig, error) {
 	if file.VSockPingHelper != "" {
 		cfg.VSockPingHelperPath = file.VSockPingHelper
 	}
+	if file.DefaultWorkSeed != "" {
+		cfg.DefaultWorkSeed = file.DefaultWorkSeed
+	}
 	if file.DefaultImageName != "" {
 		cfg.DefaultImageName = file.DefaultImageName
 	}
@@ -121,6 +128,9 @@ func Load(layout paths.Layout) (model.DaemonConfig, error) {
 	if file.CIDR != "" {
 		cfg.CIDR = file.CIDR
 	}
+	if file.TapPoolSize > 0 {
+		cfg.TapPoolSize = file.TapPoolSize
+	}
 	if file.DefaultDNS != "" {
 		cfg.DefaultDNS = file.DefaultDNS
 	}
@@ -176,6 +186,9 @@ func applyRuntimeDefaults(cfg *model.DaemonConfig) error {
 			cfg.DefaultRootfs,
 		)
 	}
+	if cfg.DefaultWorkSeed == "" && cfg.DefaultRootfs != "" {
+		cfg.DefaultWorkSeed = firstExistingRuntimePath(associatedWorkSeedPath(cfg.DefaultRootfs))
+	}
 	return nil
 }
 
@@ -185,6 +198,7 @@ func applyBundleMetadataDefaults(cfg *model.DaemonConfig, runtimeDir string, met
 	cfg.NamegenPath = defaultRuntimePath(cfg.NamegenPath, runtimeDir, meta.NamegenPath)
 	cfg.CustomizeScript = defaultRuntimePath(cfg.CustomizeScript, runtimeDir, meta.CustomizeScript)
 	cfg.VSockPingHelperPath = defaultRuntimePath(cfg.VSockPingHelperPath, runtimeDir, meta.VSockPingHelperPath)
+	cfg.DefaultWorkSeed = defaultRuntimePath(cfg.DefaultWorkSeed, runtimeDir, meta.DefaultWorkSeed)
 	cfg.DefaultKernel = defaultRuntimePath(cfg.DefaultKernel, runtimeDir, meta.DefaultKernel)
 	cfg.DefaultInitrd = defaultRuntimePath(cfg.DefaultInitrd, runtimeDir, meta.DefaultInitrd)
 	cfg.DefaultModulesDir = defaultRuntimePath(cfg.DefaultModulesDir, runtimeDir, meta.DefaultModulesDir)
@@ -199,6 +213,7 @@ func applyLegacyRuntimeDefaults(cfg *model.DaemonConfig) {
 	cfg.NamegenPath = defaultRuntimePath(cfg.NamegenPath, cfg.RuntimeDir, "namegen")
 	cfg.CustomizeScript = defaultRuntimePath(cfg.CustomizeScript, cfg.RuntimeDir, "customize.sh")
 	cfg.VSockPingHelperPath = defaultRuntimePath(cfg.VSockPingHelperPath, cfg.RuntimeDir, "banger-vsock-pingd")
+	cfg.DefaultWorkSeed = defaultRuntimePath(cfg.DefaultWorkSeed, cfg.RuntimeDir, "rootfs-docker.work-seed.ext4")
 	cfg.DefaultKernel = defaultRuntimePath(cfg.DefaultKernel, cfg.RuntimeDir, "wtf/root/boot/vmlinux-6.8.0-94-generic")
 	cfg.DefaultInitrd = defaultRuntimePath(cfg.DefaultInitrd, cfg.RuntimeDir, "wtf/root/boot/initrd.img-6.8.0-94-generic")
 	cfg.DefaultModulesDir = defaultRuntimePath(cfg.DefaultModulesDir, cfg.RuntimeDir, "wtf/root/lib/modules/6.8.0-94-generic")
@@ -223,3 +238,14 @@ func firstExistingRuntimePath(paths ...string) string {
 	}
 	return ""
 }
+
+func associatedWorkSeedPath(rootfsPath string) string {
+	rootfsPath = strings.TrimSpace(rootfsPath)
+	if rootfsPath == "" {
+		return ""
+	}
+	if strings.HasSuffix(rootfsPath, ".ext4") {
+		return strings.TrimSuffix(rootfsPath, ".ext4") + ".work-seed.ext4"
+	}
+	return rootfsPath + ".work-seed"
+}

internal/config/config_test.go

@@ -20,6 +20,7 @@ func TestLoadDerivesArtifactPathsFromRuntimeDir(t *testing.T) {
 		VSockPingHelperPath: "bin/banger-vsock-pingd",
 		DefaultPackages:     "config/packages.apt",
 		DefaultRootfs:       "images/rootfs-docker.ext4",
+		DefaultWorkSeed:     "images/rootfs-docker.work-seed.ext4",
 		DefaultKernel:       "kernels/vmlinux",
 		DefaultInitrd:       "kernels/initrd.img",
 		DefaultModulesDir:   "modules/current",
@@ -32,6 +33,7 @@ func TestLoadDerivesArtifactPathsFromRuntimeDir(t *testing.T) {
 		meta.VSockPingHelperPath,
 		meta.DefaultPackages,
 		meta.DefaultRootfs,
+		meta.DefaultWorkSeed,
 		meta.DefaultKernel,
 		meta.DefaultInitrd,
 		filepath.Join(meta.DefaultModulesDir, "modules.dep"),
@@ -79,6 +81,9 @@ func TestLoadDerivesArtifactPathsFromRuntimeDir(t *testing.T) {
 	if cfg.DefaultRootfs != filepath.Join(runtimeDir, meta.DefaultRootfs) {
 		t.Fatalf("DefaultRootfs = %q", cfg.DefaultRootfs)
 	}
+	if cfg.DefaultWorkSeed != filepath.Join(runtimeDir, meta.DefaultWorkSeed) {
+		t.Fatalf("DefaultWorkSeed = %q", cfg.DefaultWorkSeed)
+	}
 	if cfg.DefaultBaseRootfs != filepath.Join(runtimeDir, meta.DefaultRootfs) {
 		t.Fatalf("DefaultBaseRootfs = %q", cfg.DefaultBaseRootfs)
 	}
@@ -106,6 +111,7 @@ func TestLoadFallsBackToLegacyRuntimeLayoutWithoutBundleMetadata(t *testing.T) {
 		"banger-vsock-pingd",
 		"packages.apt",
 		"rootfs-docker.ext4",
+		"rootfs-docker.work-seed.ext4",
 		"wtf/root/boot/vmlinux-6.8.0-94-generic",
 		"wtf/root/boot/initrd.img-6.8.0-94-generic",
 		"wtf/root/lib/modules/6.8.0-94-generic/modules.dep",
@@ -131,6 +137,9 @@ func TestLoadFallsBackToLegacyRuntimeLayoutWithoutBundleMetadata(t *testing.T) {
 	if cfg.VSockPingHelperPath != filepath.Join(runtimeDir, "banger-vsock-pingd") {
 		t.Fatalf("VSockPingHelperPath = %q", cfg.VSockPingHelperPath)
 	}
+	if cfg.DefaultWorkSeed != filepath.Join(runtimeDir, "rootfs-docker.work-seed.ext4") {
+		t.Fatalf("DefaultWorkSeed = %q", cfg.DefaultWorkSeed)
+	}
 	if cfg.DefaultKernel != filepath.Join(runtimeDir, "wtf/root/boot/vmlinux-6.8.0-94-generic") {
 		t.Fatalf("DefaultKernel = %q", cfg.DefaultKernel)
 	}

internal/daemon/capabilities.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"net"
+	"os"
 	"strings"
 
 	"banger/internal/firecracker"
@@ -150,10 +151,21 @@ type workDiskCapability struct{}
 
 func (workDiskCapability) Name() string { return "work-disk" }
 
-func (workDiskCapability) AddStartPreflight(_ context.Context, _ *Daemon, checks *system.Preflight, vm model.VMRecord, _ model.Image) {
+func (workDiskCapability) AddStartPreflight(_ context.Context, _ *Daemon, checks *system.Preflight, vm model.VMRecord, image model.Image) {
 	if exists(vm.Runtime.WorkDiskPath) {
 		return
 	}
+	imageSeed := ""
+	if image.RootfsPath != "" {
+		imageSeed = image.WorkSeedPath
+	}
+	if exists(imageSeed) {
+		if info, err := os.Stat(imageSeed); err == nil && vm.Spec.WorkDiskSizeBytes > info.Size() {
+			checks.RequireCommand("e2fsck", toolHint("e2fsck"))
+			checks.RequireCommand("resize2fs", toolHint("resize2fs"))
+		}
+		return
+	}
 	for _, command := range []string{"mkfs.ext4", "mount", "umount", "cp"} {
 		checks.RequireCommand(command, toolHint(command))
 	}
@@ -178,16 +190,23 @@ func (workDiskCapability) ContributeMachine(cfg *firecracker.MachineConfig, vm m
 	})
 }
 
-func (workDiskCapability) PrepareHost(ctx context.Context, d *Daemon, vm *model.VMRecord, _ model.Image) error {
+func (workDiskCapability) PrepareHost(ctx context.Context, d *Daemon, vm *model.VMRecord, image model.Image) error {
-	return d.ensureWorkDisk(ctx, vm)
+	return d.ensureWorkDisk(ctx, vm, image)
 }
 
-func (workDiskCapability) AddDoctorChecks(_ context.Context, _ *Daemon, report *system.Report) {
+func (workDiskCapability) AddDoctorChecks(_ context.Context, d *Daemon, report *system.Report) {
+	if strings.TrimSpace(d.config.DefaultWorkSeed) != "" && exists(d.config.DefaultWorkSeed) {
+		checks := system.NewPreflight()
+		checks.RequireFile(d.config.DefaultWorkSeed, "default work seed image", `rebuild the default runtime rootfs to regenerate the /root seed`)
+		report.AddPreflight("feature /root work disk", checks, "seeded /root work disk artifact available")
+		return
+	}
 	checks := system.NewPreflight()
 	for _, command := range []string{"mkfs.ext4", "mount", "umount", "cp"} {
 		checks.RequireCommand(command, toolHint(command))
 	}
-	report.AddPreflight("feature /root work disk", checks, "guest /root work disk tooling available")
+	report.AddPreflight("feature /root work disk", checks, "fallback /root work disk tooling available")
+	report.AddWarn("feature /root work disk", "default image has no work-seed artifact; new VM creates will be slower until the image is rebuilt")
 }
 
 type dnsCapability struct{}

internal/daemon/daemon.go

@@ -34,6 +34,9 @@ type Daemon struct {
 	mu             sync.Mutex
 	vmLocksMu      sync.Mutex
 	vmLocks        map[string]*sync.Mutex
+	tapPoolMu      sync.Mutex
+	tapPool        []string
+	tapPoolNext    int
 	closing        chan struct{}
 	once           sync.Once
 	pid            int
@@ -92,6 +95,11 @@ func Open(ctx context.Context) (d *Daemon, err error) {
 		d.logger.Error("daemon open failed", "stage", "reconcile", "error", err.Error())
 		return nil, err
 	}
+	if err = d.initializeTapPool(ctx); err != nil {
+		d.logger.Error("daemon open failed", "stage", "initialize_tap_pool", "error", err.Error())
+		return nil, err
+	}
+	go d.ensureTapPool(context.Background())
 	return d, nil
 }
 
@@ -436,7 +444,7 @@ func (d *Daemon) ensureDefaultImage(ctx context.Context) error {
 			return err
 		}
 		if d.logger != nil {
-			d.logger.Info("default image reconciled", append(imageLogAttrs(updated), "previous_rootfs_path", image.RootfsPath, "previous_kernel_path", image.KernelPath)...)
+			d.logger.Info("default image reconciled", append(imageLogAttrs(updated), "previous_rootfs_path", image.RootfsPath, "previous_work_seed_path", image.WorkSeedPath, "previous_kernel_path", image.KernelPath)...)
 		}
 		return nil
 	case errors.Is(err, sql.ErrNoRows):
@@ -471,6 +479,7 @@ func (d *Daemon) desiredDefaultImage() (model.Image, bool) {
 		Managed:      false,
 		ArtifactDir:  "",
 		RootfsPath:   rootfs,
+		WorkSeedPath: d.config.DefaultWorkSeed,
 		KernelPath:   kernel,
 		InitrdPath:   d.config.DefaultInitrd,
 		ModulesDir:   d.config.DefaultModulesDir,
@@ -484,6 +493,7 @@ func defaultImageMatches(current, desired model.Image) bool {
 		current.Managed == desired.Managed &&
 		current.ArtifactDir == desired.ArtifactDir &&
 		current.RootfsPath == desired.RootfsPath &&
+		current.WorkSeedPath == desired.WorkSeedPath &&
 		current.KernelPath == desired.KernelPath &&
 		current.InitrdPath == desired.InitrdPath &&
 		current.ModulesDir == desired.ModulesDir &&

internal/daemon/fastpath_test.go

@@ -0,0 +1,92 @@
+package daemon
+
+import (
+	"context"
+	"errors"
+	"os"
+	"path/filepath"
+	"strconv"
+	"testing"
+
+	"banger/internal/model"
+)
+
+func TestEnsureWorkDiskClonesSeedImageAndResizes(t *testing.T) {
+	t.Parallel()
+
+	vmDir := t.TempDir()
+	seedPath := filepath.Join(t.TempDir(), "root.work-seed.ext4")
+	if err := os.WriteFile(seedPath, []byte("seed-data"), 0o644); err != nil {
+		t.Fatalf("WriteFile(seed): %v", err)
+	}
+	workDiskPath := filepath.Join(vmDir, "root.ext4")
+	runner := &scriptedRunner{
+		t: t,
+		steps: []runnerStep{
+			{call: runnerCall{name: "e2fsck", args: []string{"-p", "-f", workDiskPath}}},
+			{call: runnerCall{name: "resize2fs", args: []string{workDiskPath}}},
+		},
+	}
+	d := &Daemon{runner: runner}
+	vm := testVM("seeded", "image-seeded", "172.16.0.60")
+	vm.Runtime.WorkDiskPath = workDiskPath
+	vm.Spec.WorkDiskSizeBytes = 2 * 1024 * 1024
+	image := testImage("image-seeded")
+	image.WorkSeedPath = seedPath
+
+	if err := d.ensureWorkDisk(context.Background(), &vm, image); err != nil {
+		t.Fatalf("ensureWorkDisk: %v", err)
+	}
+	runner.assertExhausted()
+
+	info, err := os.Stat(workDiskPath)
+	if err != nil {
+		t.Fatalf("Stat(work disk): %v", err)
+	}
+	if info.Size() != vm.Spec.WorkDiskSizeBytes {
+		t.Fatalf("work disk size = %d, want %d", info.Size(), vm.Spec.WorkDiskSizeBytes)
+	}
+}
+
+func TestTapPoolWarmsAndReusesIdleTap(t *testing.T) {
+	t.Parallel()
+
+	runner := &scriptedRunner{
+		t: t,
+		steps: []runnerStep{
+			{call: runnerCall{name: "ip", args: []string{"link", "show", "tap-pool-0"}}, err: errors.New("exit status 1")},
+			sudoStep("", nil, "ip", "tuntap", "add", "dev", "tap-pool-0", "mode", "tap", "user", strconv.Itoa(os.Getuid()), "group", strconv.Itoa(os.Getgid())),
+			sudoStep("", nil, "ip", "link", "set", "tap-pool-0", "master", model.DefaultBridgeName),
+			sudoStep("", nil, "ip", "link", "set", "tap-pool-0", "up"),
+			sudoStep("", nil, "ip", "link", "set", model.DefaultBridgeName, "up"),
+		},
+	}
+	d := &Daemon{
+		runner: runner,
+		config: model.DaemonConfig{
+			BridgeName:  model.DefaultBridgeName,
+			TapPoolSize: 1,
+		},
+		closing: make(chan struct{}),
+	}
+
+	d.ensureTapPool(context.Background())
+	tapName, err := d.acquireTap(context.Background(), "tap-fallback")
+	if err != nil {
+		t.Fatalf("acquireTap: %v", err)
+	}
+	if tapName != "tap-pool-0" {
+		t.Fatalf("tapName = %q, want tap-pool-0", tapName)
+	}
+	if err := d.releaseTap(context.Background(), tapName); err != nil {
+		t.Fatalf("releaseTap: %v", err)
+	}
+	tapName, err = d.acquireTap(context.Background(), "tap-fallback")
+	if err != nil {
+		t.Fatalf("acquireTap second time: %v", err)
+	}
+	if tapName != "tap-pool-0" {
+		t.Fatalf("tapName second = %q, want tap-pool-0", tapName)
+	}
+	runner.assertExhausted()
+}

internal/daemon/images.go

@@ -60,6 +60,7 @@ func (d *Daemon) BuildImage(ctx context.Context, params api.ImageBuildParams) (i
 	}
 	defer logFile.Close()
 	rootfsPath := filepath.Join(artifactDir, "rootfs.ext4")
+	workSeedPath := filepath.Join(artifactDir, "work-seed.ext4")
 	kernelPath := params.KernelPath
 	if kernelPath == "" {
 		kernelPath = d.config.DefaultKernel
@@ -90,10 +91,17 @@ func (d *Daemon) BuildImage(ctx context.Context, params api.ImageBuildParams) (i
 	}
 	op.stage("launch_builder", "build_log_path", buildLogPath, "artifact_dir", artifactDir)
 	if err := d.runImageBuild(ctx, spec); err != nil {
+		_ = logFile.Sync()
+		_ = os.RemoveAll(artifactDir)
+		return model.Image{}, err
+	}
+	if err := system.BuildWorkSeedImage(ctx, d.runner, rootfsPath, workSeedPath); err != nil {
+		_ = logFile.Sync()
 		_ = os.RemoveAll(artifactDir)
 		return model.Image{}, err
 	}
 	if err := writePackagesMetadata(rootfsPath, d.config.DefaultPackagesFile); err != nil {
+		_ = logFile.Sync()
 		_ = os.RemoveAll(artifactDir)
 		return model.Image{}, err
 	}
@@ -103,6 +111,7 @@ func (d *Daemon) BuildImage(ctx context.Context, params api.ImageBuildParams) (i
 		Managed:      true,
 		ArtifactDir:  artifactDir,
 		RootfsPath:   rootfsPath,
+		WorkSeedPath: workSeedPath,
 		KernelPath:   kernelPath,
 		InitrdPath:   initrdPath,
 		ModulesDir:   modulesDir,
@@ -119,6 +128,7 @@ func (d *Daemon) BuildImage(ctx context.Context, params api.ImageBuildParams) (i
 	if d.logger != nil {
 		d.logger.Info("image build log preserved", append(imageLogAttrs(image), "build_log_path", buildLogPath)...)
 	}
+	_ = logFile.Sync()
 	return image, nil
 }
 

internal/daemon/logger.go

@@ -35,14 +35,16 @@ func parseLogLevel(raw string) (slog.Level, string, error) {
 	}
 }
 
-func (d *Daemon) beginOperation(name string, attrs ...any) operationLog {
+func (d *Daemon) beginOperation(name string, attrs ...any) *operationLog {
 	if d.logger != nil {
 		d.logger.Info("operation started", append([]any{"operation", name}, attrs...)...)
 	}
-	return operationLog{
+	now := time.Now()
+	return &operationLog{
 		logger:  d.logger,
 		name:    name,
-		started: time.Now(),
+		started: now,
+		last:    now,
 		attrs:   append([]any(nil), attrs...),
 	}
 }
@@ -51,22 +53,35 @@ type operationLog struct {
 	logger  *slog.Logger
 	name    string
 	started time.Time
+	last    time.Time
 	attrs   []any
 }
 
-func (o operationLog) stage(stage string, attrs ...any) {
+func (o *operationLog) stage(stage string, attrs ...any) {
-	o.log(slog.LevelInfo, "operation stage", append([]any{"stage", stage}, attrs...)...)
+	now := time.Now()
+	o.log(slog.LevelInfo, "operation stage", append([]any{
+		"stage", stage,
+		"since_start_ms", now.Sub(o.started).Milliseconds(),
+		"since_last_stage_ms", now.Sub(o.last).Milliseconds(),
+	}, attrs...)...)
+	o.last = now
 }
 
-func (o operationLog) debugStage(stage string, attrs ...any) {
+func (o *operationLog) debugStage(stage string, attrs ...any) {
-	o.log(slog.LevelDebug, "operation stage", append([]any{"stage", stage}, attrs...)...)
+	now := time.Now()
+	o.log(slog.LevelDebug, "operation stage", append([]any{
+		"stage", stage,
+		"since_start_ms", now.Sub(o.started).Milliseconds(),
+		"since_last_stage_ms", now.Sub(o.last).Milliseconds(),
+	}, attrs...)...)
+	o.last = now
 }
 
-func (o operationLog) done(attrs ...any) {
+func (o *operationLog) done(attrs ...any) {
 	o.log(slog.LevelInfo, "operation completed", append([]any{"duration_ms", time.Since(o.started).Milliseconds()}, attrs...)...)
 }
 
-func (o operationLog) fail(err error, attrs ...any) error {
+func (o *operationLog) fail(err error, attrs ...any) error {
 	if err == nil {
 		return nil
 	}
@@ -118,6 +133,9 @@ func imageLogAttrs(image model.Image) []any {
 	if image.RootfsPath != "" {
 		attrs = append(attrs, "rootfs_path", image.RootfsPath)
 	}
+	if image.WorkSeedPath != "" {
+		attrs = append(attrs, "work_seed_path", image.WorkSeedPath)
+	}
 	return attrs
 }
 

internal/daemon/logger_test.go

@@ -141,7 +141,7 @@ func TestBuildImagePreservesBuildLogOnFailure(t *testing.T) {
 	}
 
 	binDir := t.TempDir()
-	for _, name := range []string{"sudo", "ip", "pgrep", "chown", "chmod", "kill", "iptables", "sysctl", "e2fsck", "resize2fs"} {
+	for _, name := range []string{"sudo", "ip", "pgrep", "chown", "chmod", "kill", "iptables", "sysctl", "e2fsck", "resize2fs", "mkfs.ext4", "mount", "umount", "cp"} {
 		writeFakeExecutable(t, filepath.Join(binDir, name))
 	}
 	t.Setenv("PATH", binDir)

internal/daemon/preflight.go

@@ -75,6 +75,9 @@ func (d *Daemon) addImageBuildPrereqs(ctx context.Context, checks *system.Prefli
 	for _, command := range []string{"sudo", "ip", "pgrep", "chown", "chmod", "kill"} {
 		checks.RequireCommand(command, toolHint(command))
 	}
+	for _, command := range []string{"mkfs.ext4", "mount", "umount", "cp"} {
+		checks.RequireCommand(command, toolHint(command))
+	}
 	checks.RequireExecutable(d.config.FirecrackerBin, "firecracker binary", hint)
 	checks.RequireFile(d.config.SSHKeyPath, "ssh private key", `set "ssh_key_path" or refresh the runtime bundle`)
 	checks.RequireExecutable(d.config.VSockPingHelperPath, "vsock ping helper", `run 'make build' or refresh the runtime bundle`)

internal/daemon/tap_pool.go

@@ -0,0 +1,121 @@
+package daemon
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+const tapPoolPrefix = "tap-pool-"
+
+func (d *Daemon) initializeTapPool(ctx context.Context) error {
+	if d.config.TapPoolSize <= 0 || d.store == nil {
+		return nil
+	}
+	vms, err := d.store.ListVMs(ctx)
+	if err != nil {
+		return err
+	}
+	next := 0
+	for _, vm := range vms {
+		if index, ok := parseTapPoolIndex(vm.Runtime.TapDevice); ok && index >= next {
+			next = index + 1
+		}
+	}
+	d.tapPoolMu.Lock()
+	d.tapPoolNext = next
+	d.tapPoolMu.Unlock()
+	return nil
+}
+
+func (d *Daemon) ensureTapPool(ctx context.Context) {
+	if d.config.TapPoolSize <= 0 {
+		return
+	}
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-d.closing:
+			return
+		default:
+		}
+
+		d.tapPoolMu.Lock()
+		if len(d.tapPool) >= d.config.TapPoolSize {
+			d.tapPoolMu.Unlock()
+			return
+		}
+		tapName := fmt.Sprintf("%s%d", tapPoolPrefix, d.tapPoolNext)
+		d.tapPoolNext++
+		d.tapPoolMu.Unlock()
+
+		if err := d.createTap(ctx, tapName); err != nil {
+			if d.logger != nil {
+				d.logger.Warn("tap pool warmup failed", "tap_device", tapName, "error", err.Error())
+			}
+			return
+		}
+
+		d.tapPoolMu.Lock()
+		d.tapPool = append(d.tapPool, tapName)
+		d.tapPoolMu.Unlock()
+
+		if d.logger != nil {
+			d.logger.Debug("tap added to idle pool", "tap_device", tapName)
+		}
+	}
+}
+
+func (d *Daemon) acquireTap(ctx context.Context, fallbackName string) (string, error) {
+	d.tapPoolMu.Lock()
+	if n := len(d.tapPool); n > 0 {
+		tapName := d.tapPool[n-1]
+		d.tapPool = d.tapPool[:n-1]
+		d.tapPoolMu.Unlock()
+		return tapName, nil
+	}
+	d.tapPoolMu.Unlock()
+
+	if err := d.createTap(ctx, fallbackName); err != nil {
+		return "", err
+	}
+	return fallbackName, nil
+}
+
+func (d *Daemon) releaseTap(ctx context.Context, tapName string) error {
+	tapName = strings.TrimSpace(tapName)
+	if tapName == "" {
+		return nil
+	}
+	if isTapPoolName(tapName) {
+		d.tapPoolMu.Lock()
+		if len(d.tapPool) < d.config.TapPoolSize {
+			d.tapPool = append(d.tapPool, tapName)
+			d.tapPoolMu.Unlock()
+			return nil
+		}
+		d.tapPoolMu.Unlock()
+	}
+	_, err := d.runner.RunSudo(ctx, "ip", "link", "del", tapName)
+	if err == nil {
+		go d.ensureTapPool(context.Background())
+	}
+	return err
+}
+
+func isTapPoolName(tapName string) bool {
+	return strings.HasPrefix(strings.TrimSpace(tapName), tapPoolPrefix)
+}
+
+func parseTapPoolIndex(tapName string) (int, bool) {
+	if !isTapPoolName(tapName) {
+		return 0, false
+	}
+	value, err := strconv.Atoi(strings.TrimPrefix(strings.TrimSpace(tapName), tapPoolPrefix))
+	if err != nil {
+		return 0, false
+	}
+	return value, true
+}

internal/daemon/vm.go

@@ -188,8 +188,8 @@ func (d *Daemon) startVMLocked(ctx context.Context, vm model.VMRecord, image mod
 
 	shortID := system.ShortID(vm.ID)
 	apiSock := filepath.Join(d.layout.RuntimeDir, "fc-"+shortID+".sock")
-	tap := "tap-fc-" + shortID
 	dmName := "fc-rootfs-" + shortID
+	tapName := "tap-fc-" + shortID
 	if strings.TrimSpace(vm.Runtime.VSockPath) == "" {
 		vm.Runtime.VSockPath = defaultVSockPath(d.layout.RuntimeDir, vm.ID)
 	}
@@ -221,7 +221,6 @@ func (d *Daemon) startVMLocked(ctx context.Context, vm model.VMRecord, image mod
 	vm.Runtime.DMName = handles.DMName
 	vm.Runtime.DMDev = handles.DMDev
 	vm.Runtime.APISockPath = apiSock
-	vm.Runtime.TapDevice = tap
 	vm.Runtime.State = model.VMStateRunning
 	vm.State = model.VMStateRunning
 	vm.Runtime.LastError = ""
@@ -247,10 +246,12 @@ func (d *Daemon) startVMLocked(ctx context.Context, vm model.VMRecord, image mod
 	if err := d.prepareCapabilityHosts(ctx, &vm, image); err != nil {
 		return cleanupOnErr(err)
 	}
-	op.stage("tap", "tap_device", tap)
+	op.stage("tap")
-	if err := d.createTap(ctx, tap); err != nil {
+	tap, err := d.acquireTap(ctx, tapName)
+	if err != nil {
 		return cleanupOnErr(err)
 	}
+	vm.Runtime.TapDevice = tap
 	op.stage("metrics_file", "metrics_path", vm.Runtime.MetricsPath)
 	if err := os.WriteFile(vm.Runtime.MetricsPath, nil, 0o644); err != nil {
 		return cleanupOnErr(err)
@@ -766,10 +767,28 @@ func (d *Daemon) patchRootOverlay(ctx context.Context, vm model.VMRecord, image
 	return nil
 }
 
-func (d *Daemon) ensureWorkDisk(ctx context.Context, vm *model.VMRecord) error {
+func (d *Daemon) ensureWorkDisk(ctx context.Context, vm *model.VMRecord, image model.Image) error {
 	if exists(vm.Runtime.WorkDiskPath) {
 		return nil
 	}
+	if exists(image.WorkSeedPath) {
+		if err := system.CopyFilePreferClone(image.WorkSeedPath, vm.Runtime.WorkDiskPath); err != nil {
+			return err
+		}
+		seedInfo, err := os.Stat(image.WorkSeedPath)
+		if err != nil {
+			return err
+		}
+		if vm.Spec.WorkDiskSizeBytes < seedInfo.Size() {
+			return fmt.Errorf("requested work disk size %d is smaller than seed image %d", vm.Spec.WorkDiskSizeBytes, seedInfo.Size())
+		}
+		if vm.Spec.WorkDiskSizeBytes > seedInfo.Size() {
+			if err := system.ResizeExt4Image(ctx, d.runner, vm.Runtime.WorkDiskPath, vm.Spec.WorkDiskSizeBytes); err != nil {
+				return err
+			}
+		}
+		return nil
+	}
 	if _, err := d.runner.Run(ctx, "truncate", "-s", strconv.FormatInt(vm.Spec.WorkDiskSizeBytes, 10), vm.Runtime.WorkDiskPath); err != nil {
 		return err
 	}
@@ -936,15 +955,6 @@ func (d *Daemon) cleanupRuntime(ctx context.Context, vm model.VMRecord, preserve
 			return err
 		}
 	}
-	if vm.Runtime.TapDevice != "" {
-		_, _ = d.runner.RunSudo(ctx, "ip", "link", "del", vm.Runtime.TapDevice)
-	}
-	if vm.Runtime.APISockPath != "" {
-		_ = os.Remove(vm.Runtime.APISockPath)
-	}
-	if vm.Runtime.VSockPath != "" {
-		_ = os.Remove(vm.Runtime.VSockPath)
-	}
 	snapshotErr := d.cleanupDMSnapshot(ctx, dmSnapshotHandles{
 		BaseLoop: vm.Runtime.BaseLoop,
 		COWLoop:  vm.Runtime.COWLoop,
@@ -952,10 +962,20 @@ func (d *Daemon) cleanupRuntime(ctx context.Context, vm model.VMRecord, preserve
 		DMDev:    vm.Runtime.DMDev,
 	})
 	featureErr := d.cleanupCapabilityState(ctx, vm)
-	if !preserveDisks && vm.Runtime.VMDir != "" {
+	var tapErr error
-		return errors.Join(snapshotErr, featureErr, os.RemoveAll(vm.Runtime.VMDir))
+	if vm.Runtime.TapDevice != "" {
+		tapErr = d.releaseTap(ctx, vm.Runtime.TapDevice)
 	}
-	return errors.Join(snapshotErr, featureErr)
+	if vm.Runtime.APISockPath != "" {
+		_ = os.Remove(vm.Runtime.APISockPath)
+	}
+	if vm.Runtime.VSockPath != "" {
+		_ = os.Remove(vm.Runtime.VSockPath)
+	}
+	if !preserveDisks && vm.Runtime.VMDir != "" {
+		return errors.Join(snapshotErr, featureErr, tapErr, os.RemoveAll(vm.Runtime.VMDir))
+	}
+	return errors.Join(snapshotErr, featureErr, tapErr)
 }
 
 func clearRuntimeHandles(vm *model.VMRecord) {

internal/model/types.go

@@ -42,12 +42,14 @@ type DaemonConfig struct {
 	NamegenPath         string
 	CustomizeScript     string
 	VSockPingHelperPath string
+	DefaultWorkSeed     string
 	AutoStopStaleAfter  time.Duration
 	StatsPollInterval   time.Duration
 	MetricsPollInterval time.Duration
 	BridgeName          string
 	BridgeIP            string
 	CIDR                string
+	TapPoolSize         int
 	DefaultDNS          string
 	DefaultImageName    string
 	DefaultRootfs       string
@@ -64,6 +66,7 @@ type Image struct {
 	Managed      bool      `json:"managed"`
 	ArtifactDir  string    `json:"artifact_dir,omitempty"`
 	RootfsPath   string    `json:"rootfs_path"`
+	WorkSeedPath string    `json:"work_seed_path,omitempty"`
 	KernelPath   string    `json:"kernel_path"`
 	InitrdPath   string    `json:"initrd_path,omitempty"`
 	ModulesDir   string    `json:"modules_dir,omitempty"`

internal/runtimebundle/bundle.go

@@ -38,6 +38,7 @@ type BundleMetadata struct {
 	DefaultPackages     string `json:"default_packages_file" toml:"default_packages_file"`
 	DefaultRootfs       string `json:"default_rootfs" toml:"default_rootfs"`
 	DefaultBaseRootfs   string `json:"default_base_rootfs,omitempty" toml:"default_base_rootfs"`
+	DefaultWorkSeed     string `json:"default_work_seed,omitempty" toml:"default_work_seed"`
 	DefaultKernel       string `json:"default_kernel" toml:"default_kernel"`
 	DefaultInitrd       string `json:"default_initrd,omitempty" toml:"default_initrd"`
 	DefaultModulesDir   string `json:"default_modules_dir,omitempty" toml:"default_modules_dir"`
@@ -233,6 +234,7 @@ func validateBundleMetadata(runtimeDir string, meta BundleMetadata) error {
 		{meta.DefaultPackages, "default_packages_file", true},
 		{meta.DefaultRootfs, "default_rootfs", true},
 		{meta.DefaultBaseRootfs, "default_base_rootfs", false},
+		{meta.DefaultWorkSeed, "default_work_seed", false},
 		{meta.DefaultKernel, "default_kernel", true},
 		{meta.DefaultInitrd, "default_initrd", false},
 		{meta.DefaultModulesDir, "default_modules_dir", false},
@@ -271,6 +273,7 @@ func metadataArchiveBytes(runtimeDir string, meta BundleMetadata) ([]byte, error
 		strings.TrimSpace(meta.DefaultPackages) == "" &&
 		strings.TrimSpace(meta.DefaultRootfs) == "" &&
 		strings.TrimSpace(meta.DefaultBaseRootfs) == "" &&
+		strings.TrimSpace(meta.DefaultWorkSeed) == "" &&
 		strings.TrimSpace(meta.DefaultKernel) == "" &&
 		strings.TrimSpace(meta.DefaultInitrd) == "" &&
 		strings.TrimSpace(meta.DefaultModulesDir) == "" {
@@ -291,6 +294,7 @@ func normalizeBundleMetadata(meta BundleMetadata) BundleMetadata {
 	meta.DefaultPackages = strings.TrimSpace(meta.DefaultPackages)
 	meta.DefaultRootfs = strings.TrimSpace(meta.DefaultRootfs)
 	meta.DefaultBaseRootfs = strings.TrimSpace(meta.DefaultBaseRootfs)
+	meta.DefaultWorkSeed = strings.TrimSpace(meta.DefaultWorkSeed)
 	meta.DefaultKernel = strings.TrimSpace(meta.DefaultKernel)
 	meta.DefaultInitrd = strings.TrimSpace(meta.DefaultInitrd)
 	meta.DefaultModulesDir = strings.TrimSpace(meta.DefaultModulesDir)

internal/store/store.go

@@ -74,6 +74,7 @@ func (s *Store) migrate() error {
 			managed INTEGER NOT NULL DEFAULT 0,
 			artifact_dir TEXT,
 			rootfs_path TEXT NOT NULL,
+			work_seed_path TEXT,
 			kernel_path TEXT NOT NULL,
 			initrd_path TEXT,
 			modules_dir TEXT,
@@ -103,6 +104,9 @@ func (s *Store) migrate() error {
 			return err
 		}
 	}
+	if err := ensureColumnExists(s.db, "images", "work_seed_path", "TEXT"); err != nil {
+		return err
+	}
 	return nil
 }
 
@@ -111,14 +115,15 @@ func (s *Store) UpsertImage(ctx context.Context, image model.Image) error {
 	defer s.writeMu.Unlock()
 	const query = `
 	INSERT INTO images (
-		id, name, managed, artifact_dir, rootfs_path, kernel_path, initrd_path,
+		id, name, managed, artifact_dir, rootfs_path, work_seed_path, kernel_path, initrd_path,
 		modules_dir, packages_path, build_size, docker, created_at, updated_at
-	) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+	) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
 	ON CONFLICT(id) DO UPDATE SET
 		name=excluded.name,
 		managed=excluded.managed,
 		artifact_dir=excluded.artifact_dir,
 		rootfs_path=excluded.rootfs_path,
+		work_seed_path=excluded.work_seed_path,
 		kernel_path=excluded.kernel_path,
 		initrd_path=excluded.initrd_path,
 		modules_dir=excluded.modules_dir,
@@ -132,6 +137,7 @@ func (s *Store) UpsertImage(ctx context.Context, image model.Image) error {
 		boolToInt(image.Managed),
 		image.ArtifactDir,
 		image.RootfsPath,
+		image.WorkSeedPath,
 		image.KernelPath,
 		image.InitrdPath,
 		image.ModulesDir,
@@ -145,15 +151,15 @@ func (s *Store) UpsertImage(ctx context.Context, image model.Image) error {
 }
 
 func (s *Store) GetImageByName(ctx context.Context, name string) (model.Image, error) {
-	return s.getImage(ctx, "SELECT id, name, managed, artifact_dir, rootfs_path, kernel_path, initrd_path, modules_dir, packages_path, build_size, docker, created_at, updated_at FROM images WHERE name = ?", name)
+	return s.getImage(ctx, "SELECT id, name, managed, artifact_dir, rootfs_path, work_seed_path, kernel_path, initrd_path, modules_dir, packages_path, build_size, docker, created_at, updated_at FROM images WHERE name = ?", name)
 }
 
 func (s *Store) GetImageByID(ctx context.Context, id string) (model.Image, error) {
-	return s.getImage(ctx, "SELECT id, name, managed, artifact_dir, rootfs_path, kernel_path, initrd_path, modules_dir, packages_path, build_size, docker, created_at, updated_at FROM images WHERE id = ?", id)
+	return s.getImage(ctx, "SELECT id, name, managed, artifact_dir, rootfs_path, work_seed_path, kernel_path, initrd_path, modules_dir, packages_path, build_size, docker, created_at, updated_at FROM images WHERE id = ?", id)
 }
 
 func (s *Store) ListImages(ctx context.Context) ([]model.Image, error) {
-	rows, err := s.db.QueryContext(ctx, "SELECT id, name, managed, artifact_dir, rootfs_path, kernel_path, initrd_path, modules_dir, packages_path, build_size, docker, created_at, updated_at FROM images ORDER BY created_at ASC")
+	rows, err := s.db.QueryContext(ctx, "SELECT id, name, managed, artifact_dir, rootfs_path, work_seed_path, kernel_path, initrd_path, modules_dir, packages_path, build_size, docker, created_at, updated_at FROM images ORDER BY created_at ASC")
 	if err != nil {
 		return nil, err
 	}
@@ -330,6 +336,7 @@ type scanner interface {
 func scanImageRow(row scanner) (model.Image, error) {
 	var image model.Image
 	var managed, docker int
+	var workSeedPath sql.NullString
 	var createdAt, updatedAt string
 	err := row.Scan(
 		&image.ID,
@@ -337,6 +344,7 @@ func scanImageRow(row scanner) (model.Image, error) {
 		&managed,
 		&image.ArtifactDir,
 		&image.RootfsPath,
+		&workSeedPath,
 		&image.KernelPath,
 		&image.InitrdPath,
 		&image.ModulesDir,
@@ -351,6 +359,7 @@ func scanImageRow(row scanner) (model.Image, error) {
 	}
 	image.Managed = managed == 1
 	image.Docker = docker == 1
+	image.WorkSeedPath = workSeedPath.String
 	image.CreatedAt, err = time.Parse(time.RFC3339, createdAt)
 	if err != nil {
 		return image, err
@@ -417,6 +426,35 @@ func scanVMInto(row scanner) (model.VMRecord, error) {
 	return vm, nil
 }
 
+func ensureColumnExists(db *sql.DB, table, column, columnType string) error {
+	rows, err := db.Query(fmt.Sprintf("PRAGMA table_info(%s)", table))
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+	for rows.Next() {
+		var (
+			cid       int
+			name      string
+			valueType string
+			notNull   int
+			defaultV  sql.NullString
+			pk        int
+		)
+		if err := rows.Scan(&cid, &name, &valueType, &notNull, &defaultV, &pk); err != nil {
+			return err
+		}
+		if name == column {
+			return nil
+		}
+	}
+	if err := rows.Err(); err != nil {
+		return err
+	}
+	_, err = db.Exec(fmt.Sprintf("ALTER TABLE %s ADD COLUMN %s %s", table, column, columnType))
+	return err
+}
+
 func boolToInt(value bool) int {
 	if value {
 		return 1

internal/store/store_test.go

@@ -340,6 +340,7 @@ func sampleImage(name string) model.Image {
 		Managed:      true,
 		ArtifactDir:  "/artifacts/" + name,
 		RootfsPath:   "/images/" + name + ".ext4",
+		WorkSeedPath: "/images/" + name + ".work-seed.ext4",
 		KernelPath:   "/kernels/" + name,
 		InitrdPath:   "/initrd/" + name,
 		ModulesDir:   "/modules/" + name,

internal/system/files.go

@@ -1,14 +1,22 @@
 package system
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"os"
+	"path/filepath"
 	"strings"
 
 	"golang.org/x/sys/unix"
 )
 
+const (
+	minWorkSeedBytes   int64 = 512 * 1024 * 1024
+	workSeedSlackBytes int64 = 256 * 1024 * 1024
+	workSeedRoundBytes int64 = 64 * 1024 * 1024
+)
+
 func CopyFilePreferClone(sourcePath, targetPath string) error {
 	source, err := os.Open(sourcePath)
 	if err != nil {
@@ -48,6 +56,79 @@ func CopyFilePreferClone(sourcePath, targetPath string) error {
 	return nil
 }
 
+func WorkSeedPath(rootfsPath string) string {
+	rootfsPath = strings.TrimSpace(rootfsPath)
+	if rootfsPath == "" {
+		return ""
+	}
+	if strings.HasSuffix(rootfsPath, ".ext4") {
+		return strings.TrimSuffix(rootfsPath, ".ext4") + ".work-seed.ext4"
+	}
+	return rootfsPath + ".work-seed"
+}
+
+func BuildWorkSeedImage(ctx context.Context, runner CommandRunner, rootfsPath, outPath string) error {
+	rootMount, cleanupRoot, err := MountTempDir(ctx, runner, rootfsPath, true)
+	if err != nil {
+		return err
+	}
+	defer cleanupRoot()
+
+	rootHome := filepath.Join(rootMount, "root")
+	sizeBytes, err := estimateWorkSeedSize(rootHome)
+	if err != nil {
+		return err
+	}
+	if err := os.RemoveAll(outPath); err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	file, err := os.OpenFile(outPath, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o644)
+	if err != nil {
+		return err
+	}
+	if err := file.Close(); err != nil {
+		return err
+	}
+	if err := os.Truncate(outPath, sizeBytes); err != nil {
+		return err
+	}
+	if _, err := runner.Run(ctx, "mkfs.ext4", "-F", outPath); err != nil {
+		return err
+	}
+
+	workMount, cleanupWork, err := MountTempDir(ctx, runner, outPath, false)
+	if err != nil {
+		return err
+	}
+	defer cleanupWork()
+
+	return CopyDirContents(ctx, runner, rootHome, workMount, true)
+}
+
+func estimateWorkSeedSize(rootHome string) (int64, error) {
+	var usedBytes int64
+	err := filepath.Walk(rootHome, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		if info.Mode().IsRegular() {
+			usedBytes += info.Size()
+		}
+		return nil
+	})
+	if err != nil {
+		return 0, err
+	}
+	sizeBytes := usedBytes*2 + workSeedSlackBytes
+	if sizeBytes < minWorkSeedBytes {
+		sizeBytes = minWorkSeedBytes
+	}
+	if rem := sizeBytes % workSeedRoundBytes; rem != 0 {
+		sizeBytes += workSeedRoundBytes - rem
+	}
+	return sizeBytes, nil
+}
+
 func ReadNormalizedLines(path string) ([]string, error) {
 	data, err := os.ReadFile(path)
 	if err != nil {

runtime-bundle.toml

@@ -27,6 +27,7 @@ customize_script = "customize.sh"
 vsock_ping_helper_path = "banger-vsock-pingd"
 default_packages_file = "packages.apt"
 default_rootfs = "rootfs-docker.ext4"
+default_work_seed = "rootfs-docker.work-seed.ext4"
 default_kernel = "wtf/root/boot/vmlinux-6.8.0-94-generic"
 default_initrd = "wtf/root/boot/initrd.img-6.8.0-94-generic"
 default_modules_dir = "wtf/root/lib/modules/6.8.0-94-generic"

scripts/bench-create.sh

@@ -0,0 +1,114 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+log() {
+  printf '[bench-create] %s\n' "$*" >&2
+}
+
+usage() {
+  cat <<'EOF'
+Usage: ./scripts/bench-create.sh [--runs N] [--image NAME] [--keep]
+
+Measures:
+  - create_ms: time for `banger vm create`
+  - ssh_ready_ms: time until `banger vm ssh <vm> -- true` succeeds
+EOF
+}
+
+RUNS=5
+IMAGE_NAME=""
+KEEP=0
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --runs)
+      RUNS="${2:-}"
+      shift 2
+      ;;
+    --image)
+      IMAGE_NAME="${2:-}"
+      shift 2
+      ;;
+    --keep)
+      KEEP=1
+      shift
+      ;;
+    -h|--help)
+      usage
+      exit 0
+      ;;
+    *)
+      log "unknown option: $1"
+      usage
+      exit 1
+      ;;
+  esac
+done
+
+if ! [[ "$RUNS" =~ ^[0-9]+$ ]] || [[ "$RUNS" -le 0 ]]; then
+  log "--runs must be a positive integer"
+  exit 1
+fi
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+BANGER_BIN="${BANGER_BIN:-$REPO_ROOT/banger}"
+if [[ ! -x "$BANGER_BIN" ]]; then
+  log "banger binary not found: $BANGER_BIN"
+  log "run 'make build' or set BANGER_BIN"
+  exit 1
+fi
+
+timestamp_ms() {
+  date +%s%3N
+}
+
+json_escape() {
+  python3 - <<'PY' "$1"
+import json, sys
+print(json.dumps(sys.argv[1]))
+PY
+}
+
+printf '[\n'
+for run in $(seq 1 "$RUNS"); do
+  vm_name="bench-$(date +%s)-$run"
+  create_args=("$BANGER_BIN" vm create --name "$vm_name")
+  if [[ -n "$IMAGE_NAME" ]]; then
+    create_args+=(--image "$IMAGE_NAME")
+  fi
+
+  create_start="$(timestamp_ms)"
+  if ! "${create_args[@]}" >/dev/null; then
+    log "create failed for $vm_name"
+    exit 1
+  fi
+  create_end="$(timestamp_ms)"
+
+  ssh_start="$create_end"
+  ssh_ready=0
+  deadline=$((ssh_start + 60000))
+  while (( $(timestamp_ms) < deadline )); do
+    if "$BANGER_BIN" vm ssh "$vm_name" -- true >/dev/null 2>&1; then
+      ssh_ready="$(timestamp_ms)"
+      break
+    fi
+    sleep 0.5
+  done
+  if [[ "$ssh_ready" -eq 0 ]]; then
+    log "ssh did not become ready for $vm_name"
+    exit 1
+  fi
+
+  if [[ "$KEEP" -ne 1 ]]; then
+    "$BANGER_BIN" vm delete "$vm_name" >/dev/null || true
+  fi
+
+  printf '  {"run": %d, "vm_name": %s, "create_ms": %d, "ssh_ready_ms": %d}%s\n' \
+    "$run" \
+    "$(json_escape "$vm_name")" \
+    "$((create_end - create_start))" \
+    "$((ssh_ready - create_start))" \
+    "$( [[ "$run" -lt "$RUNS" ]] && printf ',' )"
+done
+printf ']\n'

verify.sh

@@ -38,6 +38,11 @@ firecracker_running() {
   [[ "$cmdline" == *firecracker* && "$cmdline" == *"$api_sock"* ]]
 }
 
+pooled_tap() {
+  local tap="$1"
+  [[ "$tap" == tap-pool-* ]]
+}
+
 wait_for_ssh() {
   local guest_ip="$1"
   local deadline="$2"
@@ -228,8 +233,12 @@ if ./banger vm show "$VM_NAME" >/dev/null 2>&1; then
   exit 1
 fi
 if ip link show "$TAP" >/dev/null 2>&1; then
-  log "tap still exists: $TAP"
+  if pooled_tap "$TAP"; then
-  exit 1
+    log "tap returned to idle pool: $TAP"
+  else
+    log "tap still exists: $TAP"
+    exit 1
+  fi
 fi
 if [[ -d "$VM_DIR" ]]; then
   log "vm dir still exists: $VM_DIR"