refactor: drop the stop flood's warble to match the launch

app/src/main/java/com/droiddeck/launcher/MainActivity.kt

@@ -89,6 +89,9 @@ class MainActivity : ComponentActivity() {
     private var flood by mutableStateOf<PendingFlood?>(null)
     private var floodProgress by androidx.compose.runtime.mutableFloatStateOf(0f)
     private class PendingFlood(val from: androidx.compose.ui.geometry.Rect, val intent: Intent)
+    /** A session stopped behind a flood: its blue, drawn back into the button it started from (FloodReturn). */
+    private var returning by mutableStateOf<ReturningFlood?>(null)
+    private class ReturningFlood(val color: Int, val to: androidx.compose.ui.geometry.Rect?)
     private var ready by mutableStateOf(false)
     private var available by mutableStateOf<LinuxRuntimeInstaller.Release?>(null)
     private var busy by mutableStateOf(false)
@@ -481,6 +484,13 @@ class MainActivity : ComponentActivity() {
                 )
                 if (showCredits) CreditsDialog { showCredits = false }
                 flood?.let { f -> com.droiddeck.launcher.ui.LaunchFlood(f.from, onProgress = { floodProgress = it }) { launchFlooded(f) } }
+                returning?.let { r ->
+                    com.droiddeck.launcher.ui.FloodReturn(androidx.compose.ui.graphics.Color(r.color), r.to, onProgress = { floodProgress = it }) {
+                        returning = null
+                        floodProgress = 0f
+                        com.droiddeck.launcher.ui.LaunchOrigin.flooding = null
+                    }
+                }
             }
         }
 
@@ -557,6 +567,10 @@ class MainActivity : ComponentActivity() {
     override fun onResume() {
         super.onResume()
         com.droiddeck.launcher.ui.Motion.refresh(this)
+        // Back from a session stopped behind a flood: open on its blue, before the first frame.
+        com.droiddeck.launcher.ui.QuitFlood.take()?.let { c ->
+            returning = ReturningFlood(c, com.droiddeck.launcher.ui.LaunchOrigin.takeReturn())
+        }
         refreshPhantomStatus()
         // Swaps queued while a game ran on that Proton go in once nothing uses it (usually the
         // session has just ended). Cheap when nothing is queued.
@@ -592,6 +606,7 @@ class MainActivity : ComponentActivity() {
         displayManager.unregisterDisplayListener(secondScreenDisplayListener)
         // The session covers the page by now; coming back finds it as it was.
         flood = null
+        returning = null
         floodProgress = 0f
         com.droiddeck.launcher.ui.LaunchOrigin.flooding = null
         super.onStop()

app/src/main/java/com/droiddeck/launcher/SessionActivity.kt

@@ -29,6 +29,8 @@ import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.ComposeView
+import androidx.compose.ui.graphics.toArgb
+import androidx.compose.ui.unit.dp
 import com.droiddeck.launcher.core.FileUtils
 import com.droiddeck.launcher.frontend.Library
 import com.droiddeck.launcher.gpu.FrameGen
@@ -144,6 +146,10 @@ class SessionActivity : ComponentActivity(), SurfaceHolder.Callback {
 
     // Compose reads these; the activity writes them.
     private var drawerOpen by mutableStateOf(false)
+    /** A stop growing out of the dialog's Stop (overlay px); the session ends once it covers the screen. */
+    private var quitFrom by mutableStateOf<androidx.compose.ui.geometry.Rect?>(null)
+    /** Left behind that flood: the front end opens on its blue, so no sink of our own. */
+    private var quitFlooded = false
     /** The drawer's Components tab: the Protons as last read (ComponentsManager). */
     private var drawerComponents by mutableStateOf<ComponentsManager.Snapshot?>(null)
     private var drawerPage by mutableIntStateOf(0)
@@ -394,6 +400,15 @@ class SessionActivity : ComponentActivity(), SurfaceHolder.Callback {
                     onBackground = { drawerOpen = false; moveTaskToBack(true) },
                     onShareLogs = { drawerOpen = false; shareCurrentSessionLogs() },
                     onStop = { drawerOpen = false; SessionService.stop(this@SessionActivity); finish() },
+                    onStopFrom = { onScreen ->
+                        drawerOpen = false
+                        if (onScreen == null || com.droiddeck.launcher.ui.Motion.scale == 0f || quitFrom != null) {
+                            if (quitFrom == null) { SessionService.stop(this@SessionActivity); finish() }
+                        } else {
+                            val at = IntArray(2).also { sessionOverlay.getLocationOnScreen(it) }
+                            quitFrom = onScreen.translate(-at[0].toFloat(), -at[1].toFloat())
+                        }
+                    },
                     onClose = { drawerOpen = false },
                     components = drawerComponents,
                     onComponentsRefresh = { refreshDrawerComponents() },
@@ -403,6 +418,14 @@ class SessionActivity : ComponentActivity(), SurfaceHolder.Callback {
                     title = pausedTitle(),
                     onResume = { SessionService.resume(this@SessionActivity) },
                 )
+                quitFrom?.let { from ->
+                    val error = androidx.compose.material3.MaterialTheme.colorScheme.error
+                    com.droiddeck.launcher.ui.LaunchFlood(
+                        from, onProgress = {},
+                        fromColors = error to androidx.compose.ui.graphics.lerp(error, androidx.compose.ui.graphics.Color.Black, 0.12f),
+                        cornerAtRest = 20.dp,
+                    ) { finishFlooded() }
+                }
             }
         }
     }
@@ -1554,10 +1577,22 @@ class SessionActivity : ComponentActivity(), SurfaceHolder.Callback {
         super.onDestroy()
     }
 
+    /** The screen is all blue: the session stops and the front end opens on the same blue (FloodReturn). */
+    private fun finishFlooded() {
+        if (isFinishing) return
+        val signal = com.droiddeck.launcher.ui.Themes.byId(SessionPrefs.theme(this)).signal
+        com.droiddeck.launcher.ui.QuitFlood.mark(signal.toArgb())
+        window.setBackgroundDrawable(android.graphics.drawable.ColorDrawable(signal.toArgb()))
+        quitFlooded = true
+        SessionService.stop(this)
+        finish()
+    }
+
     /** Leaving the session sinks its surface back down onto the front end. */
     override fun finish() {
         super.finish()
-        overridePendingTransition(R.anim.session_hold, R.anim.session_sink)
+        if (quitFlooded) overridePendingTransition(0, 0)
+        else overridePendingTransition(R.anim.session_hold, R.anim.session_sink)
     }
 
     companion object {

app/src/main/java/com/droiddeck/launcher/session/SessionService.kt

@@ -736,6 +736,24 @@ class SessionService : Service() {
         return try { Pair(fields[1].toInt(), fields[19].toLong()) } catch (e: NumberFormatException) { null }
     }
 
+    private fun askSteamToExit(prootPid: Int) {
+        if (!File("/proc/$prootPid").exists()) return
+        val request = File(LinuxRuntime.sessionRoot(this), "steam-stop")
+        try {
+            request.writeText("")
+        } catch (e: Exception) {
+            Log.w(TAG, "could not ask the Steam client to exit", e)
+            return
+        }
+        val started = System.currentTimeMillis()
+        if (waitForExit(prootPid, STEAM_PICKUP_MS) || request.exists()) {
+            request.delete()
+            return
+        }
+        val exited = waitForExit(prootPid, STEAM_EXIT_MS)
+        Log.i(TAG, "Steam client ${if (exited) "exited" else "did not exit"} after ${System.currentTimeMillis() - started} ms")
+    }
+
     private fun waitForExit(pid: Int, timeoutMs: Long): Boolean {
         val deadline = System.currentTimeMillis() + timeoutMs
         while (System.currentTimeMillis() < deadline) {
@@ -953,9 +971,11 @@ class SessionService : Service() {
         }
         components.clear()
         FakeInputWriter.releaseAllRingSlots()
+        val steamClientMayRun = SessionState.mode == MODE_STEAM || SessionState.mode == MODE_DESKTOP
         val finishAfterTeardown: () -> Unit = {
             if (prootPid > 1 || auxiliary.isNotEmpty()) {
                 Thread({
+                    if (prootPid > 1 && steamClientMayRun) askSteamToExit(prootPid)
                     auxiliary.forEach { (pid, started) -> teardown(pid, started) }
                     if (prootPid > 1) teardown(prootPid)
                     killGuestLeftovers()
@@ -1114,6 +1134,8 @@ class SessionService : Service() {
             "steamwebhelper", "linuxfs/opt/android-host/proot", "/libproot.so", "pulseaudio/libpulseaudio.so")
         /** How long proot gets to run its own cleanup before it is killed outright. */
         private const val GRACE_MS = 1200L
+        private const val STEAM_PICKUP_MS = 1500L
+        private const val STEAM_EXIT_MS = 10_000L
         private const val NO_PAD_SWITCH = "Download/droiddeck-no-pad"
         private const val PAD_LOG_SWITCH = "Download/droiddeck-pad-log"
 

app/src/main/java/com/droiddeck/launcher/ui/LaunchFlood.kt

@@ -36,9 +36,18 @@ import kotlinx.coroutines.coroutineScope
 import androidx.compose.ui.layout.onSizeChanged
 import androidx.compose.runtime.snapshotFlow
 import androidx.compose.animation.core.spring
+import androidx.compose.ui.graphics.drawscope.DrawScope
+import androidx.compose.ui.layout.LayoutCoordinates
+import androidx.compose.ui.layout.boundsInRoot
+import androidx.compose.ui.unit.Dp
+import java.lang.ref.WeakReference
+import kotlin.math.PI
+import kotlin.math.sin
 
 // Starting a session from a blue button: the button grows until the page is its blue, and the
 // loading screen opens on that blue and gathers it into the ball of the throbber.
+// Stopping one from the drawer runs it the other way: Stop grows until the page is blue, and the
+// front end opens on that blue and draws it back down into the button the session came from.
 
 /** Carries the flood's colour to the session, which opens on it. */
 const val EXTRA_FLOOD = "com.droiddeck.launcher.FLOOD"
@@ -48,6 +57,8 @@ internal object LaunchOrigin {
     private var bounds: Rect? = null
     private var button: Any? = null
     private var at = 0L
+    /** The last button a session was started from, for a stop to return into. */
+    private var last: WeakReference<Any>? = null
 
     /** The button a flood is growing out of: it steps aside so only the flood shows. */
     var flooding by mutableStateOf<Any?>(null)
@@ -55,9 +66,22 @@ internal object LaunchOrigin {
     fun mark(r: Rect, key: Any) {
         bounds = r
         button = key
+        last = WeakReference(key)
         at = SystemClock.uptimeMillis()
     }
 
+    /**
+     * Where the button the running session was started from sits now, if it is still on screen;
+     * it hides for the return, as for the flood.
+     */
+    fun takeReturn(): Rect? {
+        val key = last?.get() as? Array<*> ?: return null
+        val c = key.getOrNull(0) as? LayoutCoordinates ?: return null
+        if (!c.isAttached) return null
+        flooding = key
+        return c.boundsInRoot()
+    }
+
     /** The button behind a launch starting now, if one was pressed just before; it hides for the flood. */
     fun take(): Rect? {
         val b = bounds?.takeIf { SystemClock.uptimeMillis() - at < 1_500 }
@@ -68,6 +92,23 @@ internal object LaunchOrigin {
     }
 }
 
+/** A session stopped behind a flood: the blue the front end opens on, for a few seconds. */
+internal object QuitFlood {
+    private var color: Int? = null
+    private var at = 0L
+
+    fun mark(argb: Int) {
+        color = argb
+        at = SystemClock.uptimeMillis()
+    }
+
+    fun take(): Int? {
+        val c = color?.takeIf { SystemClock.uptimeMillis() - at < 3_000 }
+        color = null
+        return c
+    }
+}
+
 /** The page a flood grows over, sinking back a touch as it is covered; [progress] is the flood's. */
 @Composable
 internal fun FloodBehind(progress: () -> Float, content: @Composable () -> Unit) {
@@ -87,9 +128,17 @@ private val Gather = CubicBezierEasing(0.6f, 0f, 0.15f, 1f)
  * Swallows touches while it runs.
  */
 @Composable
-internal fun LaunchFlood(from: Rect, onProgress: (Float) -> Unit, onCovered: () -> Unit) {
+internal fun LaunchFlood(
+    from: Rect,
+    onProgress: (Float) -> Unit,
+    /** The button's own colours, where it is not the page's blue one (a red Stop). */
+    fromColors: Pair<Color, Color>? = null,
+    cornerAtRest: Dp = 12.dp,
+    onCovered: () -> Unit,
+) {
     val colors = MaterialTheme.colorScheme
     val pal = LocalPalette.current
+    val start = fromColors ?: (colors.primary to pal.primary2)
     // Left, top, right, bottom: 0 on the button, 1 on the page's edge. Springs overshoot past the
     // edge, off the page, so the wobble is felt in the pull and never seen as a shrink.
     val edges = remember { List(4) { Animatable(0f) } }
@@ -117,30 +166,83 @@ internal fun LaunchFlood(from: Rect, onProgress: (Float) -> Unit, onCovered: ()
         }
     }
     Canvas(Modifier.fillMaxSize().onSizeChanged { page = Size(it.width.toFloat(), it.height.toFloat()) }.pointerInput(Unit) { awaitEachGesture { while (true) awaitPointerEvent().changes.forEach { it.consume() } } }) {
-        val (l, t, r, b) = edges.map { it.value }
-        val mean = edges.sumOf { it.value.coerceIn(0f, 1f).toDouble() }.toFloat() / 4f
-        // The button sinks with the page behind (FloodBehind), so the flood leaves from where it is now.
-        val k = sinkScale(mean)
-        val cx = size.width / 2f
-        val cy = size.height / 2f
-        val left = lerp(cx + (from.left - cx) * k, 0f, l)
-        val top = lerp(cy + (from.top - cy) * k, 0f, t)
-        val right = lerp(cx + (from.right - cx) * k, size.width, r)
-        val bottom = lerp(cy + (from.bottom - cy) * k, size.height, b)
-        val w = (right - left).coerceAtLeast(0f)
-        val h = (bottom - top).coerceAtLeast(0f)
-        // A button's corners at rest, a blob in flight, square once it fills the page.
-        val blob = kotlin.math.sin(Math.PI * mean).toFloat().coerceAtLeast(0f)
-        val corner = lerp(12.dp.toPx() * (1f - mean), minOf(w, h) * 0.42f, blob)
-        // The button's gradient gives way to the ball's flat blue in the first half.
-        val mix = (mean * 2f).coerceAtMost(1f)
-        drawRoundRect(
-            Brush.linearGradient(
-                listOf(lerp(colors.primary, pal.signal, mix), lerp(pal.primary2, pal.signal, mix)),
-                start = Offset(left, top), end = Offset(right, bottom),
-            ),
-            topLeft = Offset(left, top), size = Size(w, h), cornerRadius = CornerRadius(corner),
-        )
+        drawFlood(from, edges.map { it.value }, start, pal.signal, cornerAtRest.toPx())
+    }
+}
+
+/**
+ * The flood from a button at [from] with its edges [v] of the way to the page's (left, top, right,
+ * bottom): the button sinking with the page behind, blobby in flight, its colours [start] giving
+ * way to the flat [signal] in the first half.
+ */
+private fun DrawScope.drawFlood(from: Rect, v: List<Float>, start: Pair<Color, Color>, signal: Color, cornerAtRest: Float) {
+    val (l, t, r, b) = v
+    val mean = v.sumOf { it.coerceIn(0f, 1f).toDouble() }.toFloat() / 4f
+    // The button sinks with the page behind (FloodBehind), so the flood leaves from where it is now.
+    val k = sinkScale(mean)
+    val cx = size.width / 2f
+    val cy = size.height / 2f
+    val left = lerp(cx + (from.left - cx) * k, 0f, l)
+    val top = lerp(cy + (from.top - cy) * k, 0f, t)
+    val right = lerp(cx + (from.right - cx) * k, size.width, r)
+    val bottom = lerp(cy + (from.bottom - cy) * k, size.height, b)
+    val w = (right - left).coerceAtLeast(0f)
+    val h = (bottom - top).coerceAtLeast(0f)
+    // A button's corners at rest, a blob in flight, square once it fills the page.
+    val blob = sin(PI * mean).toFloat().coerceAtLeast(0f)
+    val corner = lerp(cornerAtRest * (1f - mean), minOf(w, h) * 0.42f, blob)
+    // The button's gradient gives way to the ball's flat blue in the first half.
+    val mix = (mean * 2f).coerceAtMost(1f)
+    val brush = Brush.linearGradient(
+        listOf(lerp(start.first, signal, mix), lerp(start.second, signal, mix)),
+        start = Offset(left, top), end = Offset(right, bottom),
+    )
+    drawRoundRect(brush, topLeft = Offset(left, top), size = Size(w, h), cornerRadius = CornerRadius(corner))
+}
+
+/**
+ * The front end's first frames after a stop: the page in [flood] after a beat, drawn back down
+ * into the button at [to] (root px, measured before the page sank) on critically damped springs,
+ * the far edges first, so it sets down on the button without a bounce. [onProgress] (1 to 0) lets
+ * the page behind rise back. No button to return to: the blue fades. Calls [onLanded] at the end.
+ */
+@Composable
+internal fun FloodReturn(flood: Color, to: Rect?, onProgress: (Float) -> Unit, onLanded: () -> Unit) {
+    val colors = MaterialTheme.colorScheme
+    val pal = LocalPalette.current
+    val edges = remember { List(4) { Animatable(1f) } }
+    val fade = remember { Animatable(1f) }
+    val landed by rememberUpdatedState(onLanded)
+    val progress by rememberUpdatedState(onProgress)
+    var page by remember { mutableStateOf(Size.Zero) }
+    LaunchedEffect(page != Size.Zero) {
+        if (page == Size.Zero) return@LaunchedEffect
+        progress(1f)
+        // A beat of plain blue first, so the change of screen does not read as a cut.
+        delay(Motion.ms(220).toLong())
+        if (to == null || Motion.scale == 0f) {
+            fade.animateTo(0f, tween(Motion.ms(240).coerceAtLeast(1)))
+        } else {
+            val travel = listOf(to.left, to.top, page.width - to.right, page.height - to.bottom).map { it.coerceAtLeast(0f) }
+            val far = travel.max().coerceAtLeast(1f)
+            coroutineScope {
+                edges.mapIndexed { i, edge ->
+                    val lead = travel[i] / far
+                    launch {
+                        delay(Motion.ms((180 * (1f - lead)).toInt()).toLong())
+                        edge.animateTo(0f, spring(dampingRatio = 1f, stiffness = lerp(110f, 190f, lead))) {
+                            progress(edges.sumOf { it.value.coerceIn(0f, 1f).toDouble() }.toFloat() / 4f)
+                        }
+                    }
+                }.forEach { it.join() }
+            }
+        }
+        progress(0f)
+        landed()
+    }
+    Canvas(Modifier.fillMaxSize().onSizeChanged { page = Size(it.width.toFloat(), it.height.toFloat()) }.pointerInput(Unit) { awaitEachGesture { while (true) awaitPointerEvent().changes.forEach { it.consume() } } }) {
+        if (to == null) drawRect(flood, alpha = fade.value)
+        else drawFlood(to, edges.map { it.value }, colors.primary to pal.primary2, flood, 12.dp.toPx())
     }
 }
 

app/src/main/java/com/droiddeck/launcher/ui/SessionOverlay.kt

@@ -85,6 +85,9 @@ import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.input.InputMode
 import androidx.compose.ui.platform.LocalInputModeManager
 import androidx.compose.ui.platform.LocalFocusManager
+import androidx.compose.ui.platform.LocalView
+import androidx.compose.ui.layout.boundsInWindow
+import androidx.compose.ui.layout.onGloballyPositioned
 import androidx.compose.ui.semantics.contentDescription
 import androidx.compose.ui.semantics.semantics
 import androidx.compose.ui.text.font.FontWeight
@@ -172,6 +175,8 @@ class DrawerActions(
     val onBackground: () -> Unit,
     val onShareLogs: () -> Unit,
     val onStop: () -> Unit,
+    /** Stop with the dialog's button's bounds on screen, for the flood to grow out of; null falls back to [onStop]. */
+    val onStopFrom: ((androidx.compose.ui.geometry.Rect?) -> Unit)? = null,
     val onClose: () -> Unit,
     /** Components tab: every Proton with what it uses; null until first read. */
     val components: ComponentsManager.Snapshot? = null,
@@ -453,7 +458,14 @@ fun SessionDrawer(open: Boolean, page: Int, controllerActive: Boolean, onPageCha
     if (confirmStop) {
         val cancelFocus = remember { FocusRequester() }
         val cancel = { confirmStop = false }
-        val stop = { confirmStop = false; a.onStop() }
+        // Where Stop sits on screen: the dialog is a window of its own, so its bounds are taken
+        // against the screen and the session's overlay converts them back.
+        var stopOnScreen by remember { mutableStateOf<androidx.compose.ui.geometry.Rect?>(null) }
+        val stop = {
+            confirmStop = false
+            val from = a.onStopFrom
+            if (from != null) from(stopOnScreen) else a.onStop()
+        }
         LaunchedEffect(controllerActive) {
             if (controllerActive) {
                 androidx.compose.runtime.withFrameNanos { }
@@ -465,9 +477,13 @@ fun SessionDrawer(open: Boolean, page: Int, controllerActive: Boolean, onPageCha
             modifier = Modifier.controllerBack(onBack = cancel),
             title = { Text("Stop session?") },
             confirmButton = {
+                val dialogView = LocalView.current
                 TextButton(
                     onClick = stop,
-                    modifier = Modifier.controllerConfirm(onClick = stop),
+                    modifier = Modifier.controllerConfirm(onClick = stop).onGloballyPositioned { c ->
+                        val at = IntArray(2).also { dialogView.rootView.getLocationOnScreen(it) }
+                        stopOnScreen = c.boundsInWindow().translate(at[0].toFloat(), at[1].toFloat())
+                    },
                     colors = ButtonDefaults.textButtonColors(contentColor = colors.error),
                 ) { Text("Stop") }
             },

tools/linuxfs/overlay/usr/local/bin/bannerlator-session

@@ -547,6 +547,23 @@ BUSCONF
     # An update that cannot install asks for a restart (rc=42) every time; the count is capped so a
     # session can never again loop in silence, which reads as a menu opening and closing by itself.
     steam_updates=0
+    rm -f "$HOME/.bl-stop-requested"
+    if [ -n "${BL_LAUNCH_DIR:-}" ] && [ -d "$BL_LAUNCH_DIR" ]; then
+      rm -f "$BL_LAUNCH_DIR/steam-stop"
+      (
+        while :; do
+          if [ -e "$BL_LAUNCH_DIR/steam-stop" ]; then
+            rm -f "$BL_LAUNCH_DIR/steam-stop"
+            : > "$HOME/.bl-stop-requested"
+            echo "== steam: the app asked for a clean exit"
+            "$steam_root/steamrtarm64/steam" -shutdown >/dev/null 2>&1 || true
+            exit 0
+          fi
+          sleep 0.5
+        done
+      ) &
+      stop_watcher=$!
+    fi
     while :; do
       rm -f "$HOME/.bl-restart-once"
       if [ -f "$steam_beta" ] && [ "$(cat "$steam_beta" 2>/dev/null)" != "$steam_channel" ]; then
@@ -563,6 +580,10 @@ BUSCONF
       if [ -n "${BL_ADDED_GAMES:-}" ] && [ -f "$BL_ADDED_GAMES" ]; then
         bannerlator-steam-shortcuts "$steam_root" "$BL_ADDED_GAMES" || true
       fi
+      if [ -f "$HOME/.bl-stop-requested" ]; then
+        rm -f "$HOME/.bl-stop-requested" "$HOME/.bl-restart-once"
+        break
+      fi
       # The session asked for this exit (the ARM64 Proton landed): start again, without the URL
       # arguments, which were acted on. Not counted against the update cap.
       if [ -f "$HOME/.bl-restart-once" ]; then
@@ -579,6 +600,10 @@ BUSCONF
       # The URL arguments were acted on the first time; a restart must not repeat them.
       set --
     done
+    if [ -n "${stop_watcher:-}" ]; then
+      kill "$stop_watcher" 2>/dev/null || true
+      wait "$stop_watcher" 2>/dev/null || true
+    fi
     if [ -n "${games_watcher:-}" ]; then
       kill "$games_watcher" 2>/dev/null || true
       wait "$games_watcher" 2>/dev/null || true

tools/linuxfs/preload/inputudev.c

@@ -131,6 +131,9 @@ static struct pad *pad_for_syslink(const char *path) {
 
 static void *next_symbol(const char *name) { return dlsym(RTLD_NEXT, name); }
 
+char *bl_cached_realpath(const char *path, char *resolved, char *(*real)(const char *, char *))
+    __attribute__((visibility("hidden")));
+
 /* Wine reaches libudev from its HID bus driver, which is the only caller these pads are for. */
 static int caller_is_winebus(void *caller) {
   Dl_info info;
@@ -152,7 +155,7 @@ char *realpath(const char *path, char *resolved) {
   }
   if (real_realpath == NULL) real_realpath = next_symbol("realpath");
   if (real_realpath == NULL) return NULL;
-  return real_realpath(path, resolved);
+  return bl_cached_realpath(path, resolved, real_realpath);
 }
 
 void *udev_device_new_from_syspath(void *udev, const char *syspath) {

tools/linuxfs/preload/pathcache.c

@@ -0,0 +1,189 @@
+/*
+ * Path lookups the Steam client repeats, answered from a short-lived cache.
+ *
+ * While it registers its compatibility tools after logon, the client resolves the same few
+ * directories - its local tools under compatibilitytools.d and its own platform directory - with
+ * realpath() and access() thousands of times a second. Each realpath() is one readlinkat() per
+ * path component, and under proot every one of those is a trapped syscall with a round trip
+ * through the tracer. Measured on an AYN Thor, that loop was 23 of the client's 31 seconds of
+ * startup, with proot busy for 16 of them.
+ *
+ * Only the client itself uses the cache, never a game or a helper. Only successful answers are
+ * kept, and only for a moment: a path that stops existing is noticed within PATH_CACHE_TTL_NS, and
+ * one that starts existing is never hidden, since failures always go to the filesystem.
+ * BL_NO_PATH_CACHE=1 turns it off.
+ */
+#define _GNU_SOURCE
+#include <dlfcn.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+
+#define PATH_CACHE_SLOTS 256
+#define PATH_CACHE_KEY_MAX 512
+#define PATH_CACHE_TTL_NS 2000000000LL
+
+enum { KIND_REALPATH, KIND_ACCESS };
+
+struct entry {
+  long long stamp;
+  unsigned hash;
+  int kind;
+  int mode;
+  int flags;
+  char key[PATH_CACHE_KEY_MAX];
+  char *value;
+};
+
+static struct entry table[PATH_CACHE_SLOTS];
+static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
+
+static long long now_ns(void) {
+  struct timespec t;
+
+  clock_gettime(CLOCK_MONOTONIC_COARSE, &t);
+  return (long long)t.tv_sec * 1000000000LL + t.tv_nsec;
+}
+
+static int enabled(void) {
+  static int cached = -1;
+  const char *off;
+
+  if (cached >= 0) return cached;
+  off = getenv("BL_NO_PATH_CACHE");
+  cached = strcmp(program_invocation_short_name, "steam") == 0 &&
+           strstr(program_invocation_name, "steamrtarm64") != NULL &&
+           !(off != NULL && off[0] == '1');
+  return cached;
+}
+
+static unsigned hash_of(const char *s, int kind, int mode, int flags) {
+  unsigned h = 2166136261u ^ (unsigned)(kind * 31 + mode * 7 + flags);
+
+  while (*s) h = (h ^ (unsigned char)*s++) * 16777619u;
+  return h;
+}
+
+static int cacheable(const char *path) {
+  return path != NULL && path[0] == '/' && strlen(path) < PATH_CACHE_KEY_MAX && enabled();
+}
+
+static struct entry *find(const char *path, int kind, int mode, int flags, unsigned h) {
+  struct entry *e = &table[h % PATH_CACHE_SLOTS];
+
+  if (e->stamp == 0 || e->hash != h || e->kind != kind || e->mode != mode || e->flags != flags) return NULL;
+  if (now_ns() - e->stamp > PATH_CACHE_TTL_NS || strcmp(e->key, path) != 0) return NULL;
+  return e;
+}
+
+static void store(const char *path, int kind, int mode, int flags, unsigned h, const char *value) {
+  struct entry *e = &table[h % PATH_CACHE_SLOTS];
+  char *copy = value != NULL ? strdup(value) : NULL;
+
+  if (value != NULL && copy == NULL) return;
+  free(e->value);
+  e->value = copy;
+  e->hash = h;
+  e->kind = kind;
+  e->mode = mode;
+  e->flags = flags;
+  memcpy(e->key, path, strlen(path) + 1);
+  e->stamp = now_ns();
+}
+
+__attribute__((visibility("hidden")))
+char *bl_cached_realpath(const char *path, char *resolved, char *(*real)(const char *, char *)) {
+  char out[PATH_MAX];
+  unsigned h;
+  struct entry *e;
+
+  if (!cacheable(path)) return real(path, resolved);
+  h = hash_of(path, KIND_REALPATH, 0, 0);
+  pthread_mutex_lock(&lock);
+  e = find(path, KIND_REALPATH, 0, 0, h);
+  if (e != NULL && e->value != NULL) {
+    size_t n = strlen(e->value) + 1;
+    char *result = resolved != NULL ? resolved : malloc(n);
+    if (result != NULL) memcpy(result, e->value, n);
+    pthread_mutex_unlock(&lock);
+    return result;
+  }
+  pthread_mutex_unlock(&lock);
+  if (real(path, out) == NULL) return NULL;
+  pthread_mutex_lock(&lock);
+  store(path, KIND_REALPATH, 0, 0, h, out);
+  pthread_mutex_unlock(&lock);
+  if (resolved != NULL) {
+    memcpy(resolved, out, strlen(out) + 1);
+    return resolved;
+  }
+  return strdup(out);
+}
+
+static int cached_access(const char *path, int mode, int flags, int (*check)(const char *, int, int)) {
+  unsigned h;
+  int hit;
+  int result;
+
+  if (!cacheable(path)) return check(path, mode, flags);
+  h = hash_of(path, KIND_ACCESS, mode, flags);
+  pthread_mutex_lock(&lock);
+  hit = find(path, KIND_ACCESS, mode, flags, h) != NULL;
+  pthread_mutex_unlock(&lock);
+  if (hit) return 0;
+  result = check(path, mode, flags);
+  if (result == 0) {
+    pthread_mutex_lock(&lock);
+    store(path, KIND_ACCESS, mode, flags, h, NULL);
+    pthread_mutex_unlock(&lock);
+  }
+  return result;
+}
+
+static int (*next_faccessat(void))(int, const char *, int, int) {
+  static int (*real)(int, const char *, int, int);
+
+  if (real == NULL) real = (int (*)(int, const char *, int, int))dlsym(RTLD_NEXT, "faccessat");
+  return real;
+}
+
+static int check_cwd(const char *path, int mode, int flags) {
+  int (*real)(int, const char *, int, int) = next_faccessat();
+
+  if (real == NULL) {
+    errno = ENOSYS;
+    return -1;
+  }
+  return real(AT_FDCWD, path, mode, flags);
+}
+
+int access(const char *path, int mode) {
+  return cached_access(path, mode, 0, check_cwd);
+}
+
+int euidaccess(const char *path, int mode) {
+  return cached_access(path, mode, AT_EACCESS, check_cwd);
+}
+
+int eaccess(const char *path, int mode) {
+  return cached_access(path, mode, AT_EACCESS, check_cwd);
+}
+
+int faccessat(int dirfd, const char *path, int mode, int flags) {
+  int (*real)(int, const char *, int, int);
+
+  if (dirfd == AT_FDCWD) {
+    return cached_access(path, mode, flags, check_cwd);
+  }
+  real = next_faccessat();
+  if (real == NULL) {
+    errno = ENOSYS;
+    return -1;
+  }
+  return real(dirfd, path, mode, flags);
+}