Env names in reload diff; monitor shows last VRAM check result; harden control channel against floods

- diffConfig reports the env var names (from new struct tags) instead of
  Go field names, so the reload-env reply names what the user can change
- the monitor's GPU line now shows the game detector's last finding
  (external holders or none) and how long ago the check ran
- control channel: 10s per-connection watchdog (abortive force-close),
  cap of 32 concurrent connections, reload-env rate-limited; command
  read was already capped at 4 KiB

cmd/gpu-turnstile/main.go

@@ -728,9 +728,10 @@ func run(ctx context.Context, cfg config.Config, log *slog.Logger, logOut io.Wri
 
 	// Foreign GPU holders (games, other ML jobs) — enabled by GAME_PROCS
 	// and/or GPU_FOREIGN_VRAM_MB — hold the lock externally while they run.
-	// gw collects the VRAM reading for the status channel.
-	gw := &gpuWatch{}
-	if len(cfg.GameProcs) > 0 || cfg.GPUForeignVRAMMB > 0 {
+	// gw collects the VRAM reading and the last check result for the status
+	// channel.
+	gw := &gpuWatch{enabled: len(cfg.GameProcs) > 0 || cfg.GPUForeignVRAMMB > 0}
+	if gw.enabled {
 		det := game.New(cfg.GameProcs, cfg.GPUForeignVRAMMB, cfg.GPUIgnoreProcs, log)
 		go gameLoop(ctx, cfg, log, det, lk, ollamaClient, comfySup, gw)
 	}
@@ -836,26 +837,40 @@ func run(ctx context.Context, cfg config.Config, log *slog.Logger, logOut io.Wri
 // (idle); health checks skip it instead of logging an outage.
 var errManagedDown = errors.New("managed upstream intentionally stopped")
 
-// gpuWatch records the latest VRAM reading from the game detector's poll
-// loop, for the status channel. Known stays false when game detection is
-// not configured (no nvidia-smi polling happens then).
+// gpuWatch records the latest VRAM reading and game-detector finding from
+// the game detector's poll loop, for the status channel. Enabled is false
+// when game detection is not configured (no polling happens then); Known is
+// false until the first successful nvidia-smi reading.
 type gpuWatch struct {
-	mu     sync.Mutex
-	usedMB int
-	total  int
-	known  bool
+	mu      sync.Mutex
+	enabled bool
+	usedMB  int
+	total   int
+	known   bool
+	foreign string // last Check result: external holders, "" when none
+	at      time.Time
 }
 
-func (g *gpuWatch) set(used, total int) {
+func (g *gpuWatch) setVRAM(used, total int) {
 	g.mu.Lock()
 	g.usedMB, g.total, g.known = used, total, true
 	g.mu.Unlock()
 }
 
-func (g *gpuWatch) get() (used, total int, known bool) {
+func (g *gpuWatch) setCheck(foreign string) {
+	g.mu.Lock()
+	g.foreign, g.at = foreign, time.Now()
+	g.mu.Unlock()
+}
+
+func (g *gpuWatch) get() (used, total int, known bool, foreign string, ageS int64) {
 	g.mu.Lock()
 	defer g.mu.Unlock()
-	return g.usedMB, g.total, g.known
+	ageS = -1
+	if !g.at.IsZero() {
+		ageS = int64(time.Since(g.at).Seconds())
+	}
+	return g.usedMB, g.total, g.known, g.foreign, ageS
 }
 
 // gameLoop polls for foreign GPU holders (a game, another ML job). While one
@@ -877,8 +892,9 @@ func gameLoop(ctx context.Context, cfg config.Config, log *slog.Logger, det *gam
 		if err != nil && ctx.Err() == nil {
 			log.Warn("game detection failed", "err", err)
 		}
+		gw.setCheck(summarizeHolders(holders))
 		if used, total, verr := game.QueryVRAMMB(ctx); verr == nil {
-			gw.set(used, total)
+			gw.setVRAM(used, total)
 		}
 		switch {
 		case len(holders) > 0 && !held:
@@ -1012,12 +1028,21 @@ func updateLoop(ctx context.Context, interval time.Duration, log *slog.Logger, u
 // restarts. u is nil when AUTO_UPDATE=false.
 func serveControl(ctx context.Context, log *slog.Logger, u *update.Updater, exePath string, applyStaged func(to string), status func() string, reload func() string) {
 	var mu sync.Mutex
-	var lastTrigger time.Time
+	var lastTrigger, lastReload time.Time
 	h := func(cmd string) string {
 		switch cmd {
 		case control.CmdStatus:
 			return "OK " + status()
 		case control.CmdReloadEnv:
+			// reload re-reads the config file from disk; a short limiter
+			// keeps a local flood from turning into disk churn.
+			mu.Lock()
+			if wait := 2*time.Second - time.Since(lastReload); wait > 0 {
+				mu.Unlock()
+				return fmt.Sprintf("ERR rate limited: retry in %ds", int(wait.Seconds())+1)
+			}
+			lastReload = time.Now()
+			mu.Unlock()
 			return reload()
 		case control.CmdUpdateNow:
 		default:
@@ -1097,8 +1122,9 @@ type statusSnapshot struct {
 	UptimeS     int64              `json:"uptime_s"`
 	Downstreams []statusDownstream `json:"downstreams"`
 	Lock        statusLock         `json:"lock"`
-	// GPU carries the latest VRAM reading; Known is false when game
-	// detection (and with it nvidia-smi polling) is not configured.
+	// GPU carries the latest VRAM reading and detector finding; Enabled is
+	// false when game detection (and with it nvidia-smi polling) is not
+	// configured.
 	GPU statusGPU `json:"gpu"`
 	// MonitorNote is set client-side (never over the wire) when the
 	// monitor's own binary differs from the service's version.
@@ -1106,9 +1132,17 @@ type statusSnapshot struct {
 }
 
 type statusGPU struct {
+	// Enabled reports whether game detection is configured (and with it
+	// VRAM polling); when false the other fields carry no information.
+	Enabled bool `json:"enabled"`
 	UsedMB  int  `json:"used_mb"`
 	TotalMB int  `json:"total_mb"`
 	Known   bool `json:"known"`
+	// Foreign is the last detector finding (external GPU holders), empty
+	// when the last check found none.
+	Foreign string `json:"foreign,omitempty"`
+	// AgeS is how long ago the last check ran; -1 before the first check.
+	AgeS int64 `json:"age_s"`
 }
 
 // reloadHandler re-reads and validates the service's config file for
@@ -1130,15 +1164,19 @@ func reloadHandler(current config.Config, configPath string, restartWhenIdle fun
 	}
 }
 
-// diffConfig lists the names of fields whose values differ between two
-// configs.
+// diffConfig lists the env names of settings whose values differ between
+// two configs (from each field's env tag, so users recognize them).
 func diffConfig(a, b config.Config) []string {
 	va, vb := reflect.ValueOf(a), reflect.ValueOf(b)
 	t := va.Type()
 	var out []string
 	for i := 0; i < t.NumField(); i++ {
 		if !reflect.DeepEqual(va.Field(i).Interface(), vb.Field(i).Interface()) {
-			out = append(out, t.Field(i).Name)
+			name := t.Field(i).Tag.Get("env")
+			if name == "" {
+				name = t.Field(i).Name
+			}
+			out = append(out, name)
 		}
 	}
 	return out
@@ -1151,8 +1189,12 @@ func statusProvider(cfg config.Config, lk *lock.Lock, comfySup *supervise.Proces
 			Version: version,
 			UptimeS: int64(time.Since(started).Seconds()),
 		}
-		used, total, known := gw.get()
-		snap.GPU = statusGPU{UsedMB: used, TotalMB: total, Known: known}
+		used, total, known, foreign, ageS := gw.get()
+		snap.GPU = statusGPU{
+			Enabled: gw.enabled,
+			UsedMB:  used, TotalMB: total, Known: known,
+			Foreign: foreign, AgeS: ageS,
+		}
 		if cfg.OllamaURL != "" {
 			snap.Downstreams = append(snap.Downstreams, statusDownstream{
 				Name: "ollama", URL: cfg.OllamaURL, Up: health.get("ollama"),

cmd/gpu-turnstile/monitor.go

@@ -196,8 +196,8 @@ func renderMonitor(snap statusSnapshot, width int) string {
 		b.WriteString(fmt.Sprintf(" Queue: %s%d image job(s) waiting%s\x1b[K\n",
 			cYellow, snap.Lock.ImageQueue, cReset))
 	}
-	if snap.GPU.Known {
-		b.WriteString(" GPU: " + renderVRAM(snap.GPU.UsedMB, snap.GPU.TotalMB) + "\x1b[K\n")
+	if snap.GPU.Enabled {
+		b.WriteString(renderGPU(snap.GPU) + "\x1b[K\n")
 	}
 	if snap.MonitorNote != "" {
 		b.WriteString(" " + cYellow + snap.MonitorNote + cReset + "\x1b[K\n")
@@ -207,6 +207,26 @@ func renderMonitor(snap statusSnapshot, width int) string {
 	return b.String()
 }
 
+// renderGPU renders the GPU line: VRAM usage (when nvidia-smi answered),
+// the game detector's last finding, and how long ago it ran.
+func renderGPU(g statusGPU) string {
+	s := " GPU: "
+	if g.Known {
+		s += renderVRAM(g.UsedMB, g.TotalMB)
+	} else {
+		s += cDim + "VRAM unknown (nvidia-smi not answering)" + cReset
+	}
+	if g.Foreign != "" {
+		s += " · external: " + cRed + g.Foreign + cReset
+	} else {
+		s += cDim + " · no external process" + cReset
+	}
+	if g.AgeS >= 0 {
+		s += cDim + fmt.Sprintf(" (checked %s ago)", fmtDur(g.AgeS)) + cReset
+	}
+	return s
+}
+
 // renderVRAM renders "4.2 / 16.0 GiB used" (or MiB below 1 GiB).
 func renderVRAM(used, total int) string {
 	format := func(mb int) string {

cmd/gpu-turnstile/monitor_test.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"gpu-turnstile/internal/config"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -30,6 +31,22 @@ func TestRenderMonitor(t *testing.T) {
 			t.Errorf("frame missing %q:\n%s", want, frame)
 		}
 	}
+
+	snap.GPU = statusGPU{Enabled: true, Known: true, UsedMB: 4300, TotalMB: 16384, Foreign: "cyberpunk2077.exe (pid 1234)", AgeS: 12}
+	frame = renderMonitor(snap, 80)
+	for _, want := range []string{"GPU:", "4.2 GiB / 16.0 GiB used", "external:", "checked 12s ago"} {
+		if !strings.Contains(frame, want) {
+			t.Errorf("frame missing %q:\n%s", want, frame)
+		}
+	}
+
+	snap.GPU = statusGPU{Enabled: true, AgeS: 4}
+	frame = renderMonitor(snap, 80)
+	for _, want := range []string{"VRAM unknown", "no external process"} {
+		if !strings.Contains(frame, want) {
+			t.Errorf("frame missing %q:\n%s", want, frame)
+		}
+	}
 }
 
 func TestFmtDur(t *testing.T) {
@@ -50,7 +67,19 @@ func TestDiffConfig(t *testing.T) {
 	b.LogLevel = -4
 	b.GameProcs = []string{"game.exe"}
 	got := diffConfig(a, b)
-	if len(got) != 2 || got[0] != "GameProcs" || got[1] != "LogLevel" {
-		t.Fatalf("got %v, want [GameProcs LogLevel]", got)
+	if len(got) != 2 || got[0] != "GAME_PROCS" || got[1] != "LOGLEVEL" {
+		t.Fatalf("got %v, want [GAME_PROCS LOGLEVEL]", got)
+	}
+}
+
+// Every Config field must carry an env tag so user-facing output (the
+// reload diff) can name the setting the user would actually change.
+func TestConfigFieldsHaveEnvTags(t *testing.T) {
+	typ := reflect.TypeOf(config.Config{})
+	for i := 0; i < typ.NumField(); i++ {
+		f := typ.Field(i)
+		if f.Tag.Get("env") == "" {
+			t.Errorf("config.Config.%s has no env tag", f.Name)
+		}
 	}
 }

internal/config/config.go

@@ -13,43 +13,45 @@ import (
 	"time"
 )
 
-// Config holds every gpu-turnstile setting.
+// Config holds every gpu-turnstile setting. Each field's env tag names the
+// environment variable / config-file key that sets it; user-facing output
+// (e.g. the reload diff) uses those names, never the Go field names.
 type Config struct {
-	ListenOllama   string
-	ListenComfy    string
-	OllamaURL      string
-	ComfyURL       string
-	UnloadTimeout  time.Duration
-	JobTimeout     time.Duration
-	LLMWaitTimeout time.Duration
+	ListenOllama   string        `env:"LISTEN_OLLAMA"`
+	ListenComfy    string        `env:"LISTEN_COMFY"`
+	OllamaURL      string        `env:"OLLAMA_URL"`
+	ComfyURL       string        `env:"COMFY_URL"`
+	UnloadTimeout  time.Duration `env:"UNLOAD_TIMEOUT"`
+	JobTimeout     time.Duration `env:"JOB_TIMEOUT"`
+	LLMWaitTimeout time.Duration `env:"LLM_WAIT_TIMEOUT"`
 
-	UnloadPollInterval  time.Duration
-	HistoryPollInterval time.Duration
-	ProbeTimeout        time.Duration
-	HealthInterval      time.Duration
-	FreeTimeout         time.Duration
-	WarmTimeout         time.Duration
-	ShutdownTimeout     time.Duration
-	BackoffInitial      time.Duration
-	BackoffMax          time.Duration
-	PromptCaptureLimit  int64
+	UnloadPollInterval  time.Duration `env:"UNLOAD_POLL_INTERVAL"`
+	HistoryPollInterval time.Duration `env:"HISTORY_POLL_INTERVAL"`
+	ProbeTimeout        time.Duration `env:"PROBE_TIMEOUT"`
+	HealthInterval      time.Duration `env:"HEALTH_INTERVAL"`
+	FreeTimeout         time.Duration `env:"FREE_TIMEOUT"`
+	WarmTimeout         time.Duration `env:"WARM_TIMEOUT"`
+	ShutdownTimeout     time.Duration `env:"SHUTDOWN_TIMEOUT"`
+	BackoffInitial      time.Duration `env:"BACKOFF_INITIAL"`
+	BackoffMax          time.Duration `env:"BACKOFF_MAX"`
+	PromptCaptureLimit  int64         `env:"PROMPT_CAPTURE_LIMIT"`
 
-	AutoUpdate     bool
-	UpdateInterval time.Duration
-	UpdateRepo     string
-	UpdateAsset    string
+	AutoUpdate     bool          `env:"AUTO_UPDATE"`
+	UpdateInterval time.Duration `env:"UPDATE_INTERVAL"`
+	UpdateRepo     string        `env:"UPDATE_REPO"`
+	UpdateAsset    string        `env:"UPDATE_ASSET"`
 
 	// AppVersion is the version the user wants to run: "dev" disables
 	// updates, "stable" tracks the latest release, anything else is an
 	// exact vX.Y.Z release to pin. From APP_VER; defaults to "stable".
-	AppVersion string
+	AppVersion string `env:"APP_VER"`
 
 	// LLMBusyMode is "wait" (hold requests until the lock is free or
 	// LLMWaitTimeout expires) or "reject" (immediately answer with
 	// LLMBusyStatus + Retry-After when an image job is active or pending).
-	LLMBusyMode    string
-	LLMBusyStatus  int
-	BusyRetryAfter int
+	LLMBusyMode    string `env:"LLM_BUSY_MODE"`
+	LLMBusyStatus  int    `env:"LLM_BUSY_STATUS"`
+	BusyRetryAfter int    `env:"BUSY_RETRY_AFTER"`
 
 	// ComfyCmd spawns and supervises a ComfyUI server on demand. When
 	// ComfyCmd is empty but ComfyDir is set, management is enabled with the
@@ -59,10 +61,10 @@ type Config struct {
 	// set explicitly. The managed server is stopped after ComfyIdleTimeout
 	// without requests, freeing its VRAM; ComfyStartTimeout bounds how long
 	// a request waits for it to come up.
-	ComfyCmd          string
-	ComfyDir          string
-	ComfyIdleTimeout  time.Duration
-	ComfyStartTimeout time.Duration
+	ComfyCmd          string        `env:"COMFY_CMD"`
+	ComfyDir          string        `env:"COMFY_DIR"`
+	ComfyIdleTimeout  time.Duration `env:"COMFY_IDLE_TIMEOUT"`
+	ComfyStartTimeout time.Duration `env:"COMFY_START_TIMEOUT"`
 
 	// GameProcs (GAME_PROCS) is a watch list of process names; while any of
 	// them runs, the GPU is treated as held by a foreign process. The
@@ -70,15 +72,15 @@ type Config struct {
 	// when a process not in GPUIgnoreProcs (GPU_IGNORE_PROCS) holds more than
 	// that many MiB of VRAM. GamePollInterval (GAME_POLL_INTERVAL) is how
 	// often both checks run.
-	GameProcs        []string
-	GPUForeignVRAMMB int
-	GPUIgnoreProcs   []string
-	GamePollInterval time.Duration
+	GameProcs        []string      `env:"GAME_PROCS"`
+	GPUForeignVRAMMB int           `env:"GPU_FOREIGN_VRAM_MB"`
+	GPUIgnoreProcs   []string      `env:"GPU_IGNORE_PROCS"`
+	GamePollInterval time.Duration `env:"GAME_POLL_INTERVAL"`
 
-	WarmModel string
-	LogLevel  slog.Level
-	LogJSON   bool
-	LogFile   string
+	WarmModel string     `env:"WARM_MODEL"`
+	LogLevel  slog.Level `env:"LOGLEVEL"`
+	LogJSON   bool       `env:"LOG_FORMAT"`
+	LogFile   string     `env:"LOG_FILE"`
 }
 
 // Defaults returns the configuration used when neither the environment nor

internal/control/control.go

@@ -7,6 +7,13 @@
 // triggers, so the worst a local user can cause is a cheap, throttled
 // check and a GPU-idle-gated restart onto a signed binary.
 //
+// Abuse hardening: the command read is capped (4 KiB), each connection is
+// force-closed after connTimeout so a stalled client cannot pin a goroutine
+// (or a Windows pipe instance) forever, and concurrently served connections
+// are capped at maxConns — beyond that, connections are closed on arrival.
+// On Windows the pipe's ACL additionally denies network logons, so the
+// channel cannot be reached from another machine.
+//
 // Protocol: the client writes one command line, the server answers with
 // one reply line ("OK ..." or "ERR ...") and hangs up.
 package control
@@ -17,6 +24,7 @@ import (
 	"fmt"
 	"io"
 	"strings"
+	"time"
 )
 
 // CmdUpdateNow asks the service to check for, stage and (once the GPU is
@@ -37,9 +45,50 @@ var ErrUnavailable = errors.New("control channel unavailable")
 // line. It must start with "OK " or "ERR ".
 type Handler func(cmd string) string
 
+// connTimeout bounds one connection's lifetime: a client that stops
+// mid-command or never reads the reply would otherwise pin its goroutine
+// (and on Windows one of the pipe instances) indefinitely. A var so tests
+// can shrink it.
+var connTimeout = 10 * time.Second
+
+// maxConns caps concurrently served connections; beyond it, new
+// connections are closed on arrival. Bound on the goroutines a local
+// flood can pile up.
+const maxConns = 32
+
+var connSem = make(chan struct{}, maxConns)
+
+// serve dispatches connection handling under the concurrency cap. It
+// returns false when the cap is reached — the caller must then close the
+// connection itself.
+func serve(c io.ReadWriteCloser, h Handler) bool {
+	select {
+	case connSem <- struct{}{}:
+		go func() {
+			defer func() { <-connSem }()
+			serveConn(c, h)
+		}()
+		return true
+	default:
+		return false
+	}
+}
+
+// forceCloser is implemented by connections that can be torn down
+// abortively, unblocking pending reads and writes (Windows pipe:
+// DisconnectNamedPipe; unix socket: a deadline in the past). The
+// connection watchdog uses it; normal closes still flush the reply.
+type forceCloser interface {
+	ForceClose() error
+}
+
 // serveConn runs the line protocol on one accepted connection.
 func serveConn(c io.ReadWriteCloser, h Handler) {
 	defer c.Close()
+	if fc, ok := c.(forceCloser); ok {
+		timer := time.AfterFunc(connTimeout, func() { fc.ForceClose() })
+		defer timer.Stop()
+	}
 	line, err := bufio.NewReader(io.LimitReader(c, 4096)).ReadString('\n')
 	cmd := strings.TrimSpace(line)
 	if cmd == "" {

internal/control/control_linux.go

@@ -37,12 +37,24 @@ func Serve(ctx context.Context, h Handler, log *slog.Logger) error {
 			if err != nil {
 				return // shutting down
 			}
-			go serveConn(c, h)
+			uc := unixConn{c}
+			if !serve(uc, h) {
+				uc.ForceClose()
+			}
 		}
 	}()
 	return nil
 }
 
+// unixConn adds an abortive ForceClose to net.Conn: a deadline in the
+// past fails pending and future I/O immediately.
+type unixConn struct{ net.Conn }
+
+func (c unixConn) ForceClose() error {
+	c.SetDeadline(time.Now().Add(-time.Second)) //nolint:errcheck // best effort
+	return c.Conn.Close()
+}
+
 // Ask sends one command to the running service and returns its reply.
 func Ask(cmd string) (string, error) {
 	c, err := net.DialTimeout("unix", sockPath, 2*time.Second)

internal/control/control_test.go

@@ -5,6 +5,7 @@ import (
 	"net"
 	"strings"
 	"testing"
+	"time"
 )
 
 func TestRoundTrip(t *testing.T) {
@@ -44,3 +45,59 @@ func TestEmptyReplyIsUnavailable(t *testing.T) {
 		t.Fatalf("err = %v, want ErrUnavailable", err)
 	}
 }
+
+func TestServeCap(t *testing.T) {
+	for i := 0; i < maxConns; i++ {
+		connSem <- struct{}{}
+	}
+	defer func() {
+		for i := 0; i < maxConns; i++ {
+			<-connSem
+		}
+	}()
+	server, client := net.Pipe()
+	defer server.Close()
+	defer client.Close()
+	if serve(server, func(string) string { return "OK" }) {
+		t.Fatal("serve accepted a connection beyond the cap")
+	}
+}
+
+// forcePipe records ForceClose calls for the watchdog test.
+type forcePipe struct {
+	net.Conn
+	forced chan struct{}
+}
+
+func (c forcePipe) ForceClose() error {
+	err := c.Conn.Close()
+	close(c.forced)
+	return err
+}
+
+func TestConnWatchdog(t *testing.T) {
+	old := connTimeout
+	connTimeout = 50 * time.Millisecond
+	defer func() { connTimeout = old }()
+
+	server, client := net.Pipe()
+	defer client.Close()
+	fc := forcePipe{Conn: server, forced: make(chan struct{})}
+	done := make(chan struct{})
+	go func() {
+		serveConn(fc, func(string) string { return "OK" })
+		close(done)
+	}()
+	// The client never sends anything; the watchdog must tear the
+	// connection down instead of blocking forever.
+	select {
+	case <-fc.forced:
+	case <-time.After(5 * time.Second):
+		t.Fatal("watchdog did not force-close the stalled connection")
+	}
+	select {
+	case <-done:
+	case <-time.After(5 * time.Second):
+		t.Fatal("serveConn still blocked after the force close")
+	}
+}

internal/control/control_windows.go

@@ -86,7 +86,10 @@ func Serve(ctx context.Context, h Handler, log *slog.Logger) error {
 				windows.CloseHandle(pipe)
 				continue
 			}
-			go serveConn(&pipeConn{f: os.NewFile(uintptr(pipe), pipePath), h: pipe}, h)
+			conn := &pipeConn{f: os.NewFile(uintptr(pipe), pipePath), h: pipe}
+			if !serve(conn, h) {
+				conn.ForceClose()
+			}
 		}
 	}()
 	return nil
@@ -114,6 +117,14 @@ func (c *pipeConn) Close() error {
 	return c.f.Close()
 }
 
+// ForceClose aborts the connection without flushing: disconnecting
+// unblocks pending reads and writes at the cost of possibly discarding an
+// unread reply. Used by the connection watchdog; normal closes flush.
+func (c *pipeConn) ForceClose() error {
+	windows.DisconnectNamedPipe(c.h) //nolint:errcheck // best effort
+	return c.f.Close()
+}
+
 // Ask sends one command to the running service and returns its reply.
 func Ask(cmd string) (string, error) {
 	name, err := windows.UTF16PtrFromString(pipePath)