Netlink uevent hotplug monitor (mechanism + headless diagnostic)

src/hidapi/SDL_hidapi.c

@@ -56,6 +56,7 @@
 
 #ifdef __WEBOS__
 #include "../joystick/webos/dev_presence.h"
+#include "../joystick/webos/uevent_monitor.h"
 #endif /* __WEBOS__ */
 
 #include "../core/linux/SDL_udev.h"
@@ -84,6 +85,7 @@ typedef enum
     ENUMERATION_FALLBACK,
 #ifdef __WEBOS__
     ENUMERATION_POLLING,
+    ENUMERATION_NETLINK,
 #endif
 } LinuxEnumerationMethod;
 
@@ -125,6 +127,7 @@ static struct
 #endif
 #ifdef __WEBOS__
     Uint32 m_unPresenceFlags;
+    SDL_webOSUeventMonitor *m_pUeventMonitor;
 #endif
 } SDL_HIDAPI_discovery;
 
@@ -343,7 +346,13 @@ static void HIDAPI_InitializeDiscovery(void)
     } else
 #endif /* SDL_USE_LIBUDEV */
 #ifdef __WEBOS__
-    if (linux_enumeration_method == ENUMERATION_POLLING) {
+    if (linux_enumeration_method == ENUMERATION_POLLING || linux_enumeration_method == ENUMERATION_NETLINK) {
+        /* Hidraw hotplug has its own monitor: netlink broadcasts a copy to
+         * every bound socket, but a single fd shared with the joystick
+         * backend would mean whichever drained first ate the other's
+         * events. Without one we keep the 3s presence poll below. */
+        SDL_HIDAPI_discovery.m_pUeventMonitor =
+            SDL_webOSUeventMonitorOpen(SDL_WEBOS_DEVICE_PRESENCE_CHECK_HIDRAW);
         SDL_HIDAPI_discovery.m_bCanGetNotifications = SDL_TRUE;
     } else
 #endif
@@ -454,7 +463,16 @@ static void HIDAPI_UpdateDiscovery(void)
     } else
 #endif /* SDL_USE_LIBUDEV */
 #ifdef __WEBOS__
-    if (linux_enumeration_method == ENUMERATION_POLLING) {
+    if (SDL_HIDAPI_discovery.m_pUeventMonitor != NULL) {
+        SDL_webOSUevent event;
+
+        /* Every add or remove counts; the enumeration behind
+         * SDL_hid_device_change_count() re-reads /dev/hidraw* anyway, so the
+         * node itself doesn't matter here, only that something moved. */
+        while (SDL_webOSUeventMonitorPoll(SDL_HIDAPI_discovery.m_pUeventMonitor, &event)) {
+            ++SDL_HIDAPI_discovery.m_unDeviceChangeCounter;
+        }
+    } else if (linux_enumeration_method == ENUMERATION_POLLING) {
         const Uint32 SDL_HIDAPI_DETECT_INTERVAL_MS = 3000; /* Update every 3 seconds */
         Uint32 now = SDL_GetTicks();
         Uint32 next_detect = SDL_HIDAPI_discovery.m_unLastDetect + SDL_HIDAPI_DETECT_INTERVAL_MS;
@@ -517,6 +535,11 @@ static void HIDAPI_ShutdownDiscovery(void)
         return;
     }
 
+#ifdef __WEBOS__
+    SDL_webOSUeventMonitorClose(SDL_HIDAPI_discovery.m_pUeventMonitor);
+    SDL_HIDAPI_discovery.m_pUeventMonitor = NULL;
+#endif
+
 #if defined(__WIN32__) || defined(__WINGDK__)
     if (SDL_HIDAPI_discovery.m_hNotify) {
         UnregisterDeviceNotification(SDL_HIDAPI_discovery.m_hNotify);

src/joystick/linux/SDL_sysjoystick.c

@@ -48,6 +48,9 @@
 #include "../../events/SDL_events_c.h"
 #include "../SDL_sysjoystick.h"
 #include "../SDL_joystick_c.h"
+#ifdef __WEBOS__
+#include "../webos/uevent_monitor.h"
+#endif
 #include "../steam/SDL_steamcontroller.h"
 #include "SDL_sysjoystick_c.h"
 #include "../hidapi/SDL_hidapijoystick_c.h"
@@ -147,6 +150,7 @@ typedef enum
     ENUMERATION_FALLBACK,
 #ifdef __WEBOS__
     ENUMERATION_POLLING,
+    ENUMERATION_NETLINK,
 #endif
 } EnumerationMethod;
 
@@ -190,6 +194,9 @@ static SDL_joylist_item *SDL_joylist_tail SDL_GUARDED_BY(SDL_joystick_lock) = NU
 static int numjoysticks SDL_GUARDED_BY(SDL_joystick_lock) = 0;
 static SDL_sensorlist_item *SDL_sensorlist SDL_GUARDED_BY(SDL_joystick_lock) = NULL;
 static int inotify_fd = -1;
+#ifdef __WEBOS__
+static SDL_webOSUeventMonitor *joystick_uevent_monitor = NULL;
+#endif
 
 static Uint32 last_joy_detect_time;
 static time_t last_input_dir_mtime;
@@ -1034,8 +1041,32 @@ static void LINUX_FallbackJoystickDetect(void)
     }
 }
 
+#ifdef __WEBOS__
+/* The uevent stream is explicit and ordered, so a device that disconnects and
+ * reconnects on the same index between two ticks produces a remove and an add
+ * rather than an unchanged presence bitmask. Devices already attached at init
+ * arrive here as ordinary adds, so there's no separate startup scan. */
+static void LINUX_NetlinkJoystickDetect(void)
+{
+    SDL_webOSUevent event;
+
+    while (SDL_webOSUeventMonitorPoll(joystick_uevent_monitor, &event)) {
+        if (event.action == SDL_WEBOS_UEVENT_ACTION_ADD) {
+            MaybeAddDevice(event.devnode);
+        } else {
+            MaybeRemoveDevice(event.devnode);
+        }
+    }
+}
+#endif
+
 static void LINUX_JoystickDetect(void)
 {
+#ifdef __WEBOS__
+    if (enumeration_method == ENUMERATION_NETLINK) {
+        LINUX_NetlinkJoystickDetect();
+    } else
+#endif
 #ifdef SDL_USE_LIBUDEV
     if (enumeration_method == ENUMERATION_LIBUDEV) {
         SDL_UDEV_Poll();
@@ -1103,7 +1134,13 @@ static int LINUX_JoystickInit(void)
             SDL_LogDebug(SDL_LOG_CATEGORY_INPUT,
                          "Container detected, disabling udev integration");
 #ifdef __WEBOS__
-            enumeration_method = ENUMERATION_POLLING;
+            /* No libudev in the app jail, so hotplug comes from a netlink
+             * uevent socket. Polling is the fallback for a kernel that won't
+             * let us bind one. */
+            joystick_uevent_monitor = SDL_webOSUeventMonitorOpen(
+                SDL_classic_joysticks ? SDL_WEBOS_DEVICE_PRESENCE_CHECK_JS
+                                      : SDL_WEBOS_DEVICE_PRESENCE_CHECK_EVDEV);
+            enumeration_method = joystick_uevent_monitor ? ENUMERATION_NETLINK : ENUMERATION_POLLING;
 #else
             enumeration_method = ENUMERATION_FALLBACK;
 #endif
@@ -2315,6 +2352,11 @@ static void LINUX_JoystickQuit(void)
         inotify_fd = -1;
     }
 
+#ifdef __WEBOS__
+    SDL_webOSUeventMonitorClose(joystick_uevent_monitor);
+    joystick_uevent_monitor = NULL;
+#endif
+
     for (item = SDL_joylist; item; item = next) {
         next = item->next;
         FreeJoylistItem(item);