udev: finish the kqueue code path so the BSDs no longer need libepoll-shim

udev_input.c had a half-written kqueue alternative to epoll behind a
"#if 1 / TODO" that hard-selected epoll everywhere, which is why the
FreeBSD games/retroarch port has to link the udev input driver against
libepoll-shim (UDEV_LIB_DEPENDS/UDEV_CFLAGS/UDEV_LDFLAGS in the port).

Complete it: on FreeBSD, OpenBSD, NetBSD, DragonFly and macOS the evdev
fds are registered with EV_SET(EVFILT_READ, EV_ADD, udata = device)
(the placeholder referenced an undefined LISTENSOCKET), the poll uses a
zero timespec like the epoll_wait(..., 0) it mirrors (the placeholder
referenced an undefined `timeout`), and the event loop tests
filter == EVFILT_READ && !(flags & EV_ERROR) instead of the epoll-only
`events & EPOLLIN`.  kqueue is level-triggered by default so the
drain-until-EAGAIN read loop is unchanged, and closing a device fd
removes it from the kqueue just as it does from the epoll set.
NetBSD's kevent.udata is intptr_t rather than void *, hence the
UDEV_KQ_UDATA cast.

Linux still uses epoll; that object is unchanged.  The kqueue variant
was compiled with libkqueue's <sys/event.h> to catch type errors.

CI: the FreeBSD job now fails if the linked retroarch binary still
imports any epoll_* symbol.

.github/workflows/FreeBSD.yml

@@ -71,6 +71,11 @@ jobs:
             gmake -j$NCPU clean
             gmake -j$NCPU info all
             ./retroarch --version
+            # udev input must multiplex with kqueue here, so the binary
+            # must not need libepoll-shim's epoll_* at all.
+            if nm -u retroarch | grep -q 'epoll_'; then
+              echo "retroarch still references epoll (libepoll-shim)"; exit 1
+            fi
 
             # With v4l_compat the V4L2 camera and video processor core
             # must still compile; only those two objects are rebuilt.

input/drivers/udev_input.c

@@ -14,18 +14,12 @@
  *  If not, see <http://www.gnu.org/licenses/>.
  */
 
-/* TODO/FIXME - set this once the kqueue codepath is implemented and working properly,
- * also remove libepoll-shim from the Makefile when that happens. */
-#if 1
-#define HAVE_EPOLL
-#else
-#ifdef __linux__
-#define HAVE_EPOLL 1
-#endif
-
-#if defined(__APPLE__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined (__NetBSD__)
+/* Linux multiplexes the evdev fds with epoll; the BSDs and macOS use
+ * kqueue natively so no libepoll-shim is needed there. */
+#if defined(__APPLE__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) || defined(__DragonFly__)
 #define HAVE_KQUEUE 1
-#endif
+#else
+#define HAVE_EPOLL 1
 #endif
 
 #include <stdint.h>
@@ -43,6 +37,13 @@
 #include <sys/epoll.h>
 #elif defined(HAVE_KQUEUE)
 #include <sys/event.h>
+#include <sys/time.h>
+/* NetBSD declares kevent.udata as intptr_t, everyone else as void *. */
+#if defined(__NetBSD__)
+#define UDEV_KQ_UDATA(ptr) ((intptr_t)(ptr))
+#else
+#define UDEV_KQ_UDATA(ptr) ((void*)(ptr))
+#endif
 #endif
 #include <poll.h>
 
@@ -3295,7 +3296,7 @@ static int udev_input_add_device(udev_input_t *udev,
             fd, strerror(errno));
    }
 #elif defined(HAVE_KQUEUE)
-   EV_SET(&event, fd, EVFILT_READ, EV_ADD, 0, 0, LISTENSOCKET);
+   EV_SET(&event, fd, EVFILT_READ, EV_ADD, 0, 0, UDEV_KQ_UDATA(device));
    if (kevent(udev->fd, &event, 1, NULL, 0, NULL) == -1)
    {
       RARCH_ERR("[udev] Failed to add FD (%d) to kqueue list (%s).\n",
@@ -3540,8 +3541,9 @@ static void udev_input_poll(void *data)
    ret = epoll_wait(udev->fd, events, ARRAY_SIZE(events), 0);
 #elif defined(HAVE_KQUEUE)
    {
+      /* Zero timeout: drain what is pending, never block the frame. */
       struct timespec timeoutspec;
-      timeoutspec.tv_sec  = timeout;
+      timeoutspec.tv_sec  = 0;
       timeoutspec.tv_nsec = 0;
       ret                 = kevent(udev->fd, NULL, 0, events,
             ARRAY_SIZE(events), &timeoutspec);
@@ -3550,8 +3552,12 @@ static void udev_input_poll(void *data)
 
    for (i = 0; i < ret; i++)
    {
-      /* TODO/FIXME - add HAVE_EPOLL/HAVE_KQUEUE codepaths here */
+#if defined(HAVE_EPOLL)
       if (events[i].events & EPOLLIN)
+#elif defined(HAVE_KQUEUE)
+      if (     events[i].filter == EVFILT_READ
+            && !(events[i].flags & EV_ERROR))
+#endif
       {
          int j, len;
          struct input_event input_events[32];