xref: /netbsd-src/sys/rump/net/lib/libshmif/if_shmem.c (revision ba65fde2d7fefa7d39838fa5fa855e62bd606b5e)
1 /*	$NetBSD: if_shmem.c,v 1.47 2013/01/14 20:21:32 pooka Exp $	*/
2 
3 /*
4  * Copyright (c) 2009, 2010 Antti Kantee.  All Rights Reserved.
5  *
6  * Development of this software was supported by The Nokia Foundation.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  *
17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
18  * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
20  * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
23  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27  * SUCH DAMAGE.
28  */
29 
30 #include <sys/cdefs.h>
31 __KERNEL_RCSID(0, "$NetBSD: if_shmem.c,v 1.47 2013/01/14 20:21:32 pooka Exp $");
32 
33 #include <sys/param.h>
34 #include <sys/atomic.h>
35 #include <sys/fcntl.h>
36 #include <sys/kmem.h>
37 #include <sys/kthread.h>
38 #include <sys/lock.h>
39 #include <sys/vmem.h>
40 #include <sys/cprng.h>
41 
42 #include <net/bpf.h>
43 #include <net/if.h>
44 #include <net/if_dl.h>
45 #include <net/if_ether.h>
46 
47 #include <netinet/in.h>
48 #include <netinet/in_var.h>
49 
50 #include <rump/rump.h>
51 #include <rump/rumpuser.h>
52 
53 #include "rump_private.h"
54 #include "rump_net_private.h"
55 
56 static int shmif_clone(struct if_clone *, int);
57 static int shmif_unclone(struct ifnet *);
58 
59 struct if_clone shmif_cloner =
60     IF_CLONE_INITIALIZER("shmif", shmif_clone, shmif_unclone);
61 
62 /*
63  * Do r/w prefault for backend pages when attaching the interface.
64  * At least logically thinking improves performance (although no
65  * mlocking is done, so they might go away).
66  */
67 #define PREFAULT_RW
68 
69 /*
70  * A virtual ethernet interface which uses shared memory from a
71  * memory mapped file as the bus.
72  */
73 
74 static int	shmif_init(struct ifnet *);
75 static int	shmif_ioctl(struct ifnet *, u_long, void *);
76 static void	shmif_start(struct ifnet *);
77 static void	shmif_stop(struct ifnet *, int);
78 
79 #include "shmifvar.h"
80 
81 struct shmif_sc {
82 	struct ethercom sc_ec;
83 	struct shmif_mem *sc_busmem;
84 	int sc_memfd;
85 	int sc_kq;
86 	int sc_unit;
87 
88 	char *sc_backfile;
89 	size_t sc_backfilelen;
90 
91 	uint64_t sc_devgen;
92 	uint32_t sc_nextpacket;
93 
94 	kmutex_t sc_mtx;
95 	kcondvar_t sc_cv;
96 
97 	struct lwp *sc_rcvl;
98 	bool sc_dying;
99 };
100 
101 static const uint32_t busversion = SHMIF_VERSION;
102 
103 static void shmif_rcv(void *);
104 
105 #define LOCK_UNLOCKED	0
106 #define LOCK_LOCKED	1
107 #define LOCK_COOLDOWN	1001
108 
109 vmem_t *shmif_units;
110 
111 /*
112  * This locking needs work and will misbehave severely if:
113  * 1) the backing memory has to be paged in
114  * 2) some lockholder exits while holding the lock
115  */
116 static void
117 shmif_lockbus(struct shmif_mem *busmem)
118 {
119 	int i = 0;
120 
121 	while (__predict_false(atomic_cas_32(&busmem->shm_lock,
122 	    LOCK_UNLOCKED, LOCK_LOCKED) == LOCK_LOCKED)) {
123 		if (__predict_false(++i > LOCK_COOLDOWN)) {
124 			uint64_t sec, nsec;
125 			int error;
126 
127 			sec = 0;
128 			nsec = 1000*1000; /* 1ms */
129 			rumpuser_nanosleep(&sec, &nsec, &error);
130 			i = 0;
131 		}
132 		continue;
133 	}
134 	membar_enter();
135 }
136 
137 static void
138 shmif_unlockbus(struct shmif_mem *busmem)
139 {
140 	unsigned int old;
141 
142 	membar_exit();
143 	old = atomic_swap_32(&busmem->shm_lock, LOCK_UNLOCKED);
144 	KASSERT(old == LOCK_LOCKED);
145 }
146 
147 static int
148 allocif(int unit, struct shmif_sc **scp)
149 {
150 	uint8_t enaddr[ETHER_ADDR_LEN] = { 0xb2, 0xa0, 0x00, 0x00, 0x00, 0x00 };
151 	struct shmif_sc *sc;
152 	struct ifnet *ifp;
153 	uint32_t randnum;
154 	int error;
155 
156 	randnum = cprng_fast32();
157 	memcpy(&enaddr[2], &randnum, sizeof(randnum));
158 
159 	sc = kmem_zalloc(sizeof(*sc), KM_SLEEP);
160 	sc->sc_memfd = -1;
161 	sc->sc_unit = unit;
162 
163 	ifp = &sc->sc_ec.ec_if;
164 
165 	sprintf(ifp->if_xname, "shmif%d", unit);
166 	ifp->if_softc = sc;
167 	ifp->if_flags = IFF_BROADCAST | IFF_MULTICAST;
168 	ifp->if_init = shmif_init;
169 	ifp->if_ioctl = shmif_ioctl;
170 	ifp->if_start = shmif_start;
171 	ifp->if_stop = shmif_stop;
172 	ifp->if_mtu = ETHERMTU;
173 	ifp->if_dlt = DLT_EN10MB;
174 
175 	mutex_init(&sc->sc_mtx, MUTEX_DEFAULT, IPL_NONE);
176 	cv_init(&sc->sc_cv, "shmifcv");
177 
178 	if_attach(ifp);
179 	ether_ifattach(ifp, enaddr);
180 
181 	aprint_verbose("shmif%d: Ethernet address %s\n",
182 	    unit, ether_sprintf(enaddr));
183 
184 	if (scp)
185 		*scp = sc;
186 
187 	error = 0;
188 	if (rump_threads) {
189 		error = kthread_create(PRI_NONE,
190 		    KTHREAD_MPSAFE | KTHREAD_MUSTJOIN, NULL,
191 		    shmif_rcv, ifp, &sc->sc_rcvl, "shmif");
192 	} else {
193 		printf("WARNING: threads not enabled, shmif NOT working\n");
194 	}
195 
196 	if (error) {
197 		shmif_unclone(ifp);
198 	}
199 
200 	return error;
201 }
202 
203 static int
204 initbackend(struct shmif_sc *sc, int memfd)
205 {
206 	volatile uint8_t v;
207 	volatile uint8_t *p;
208 	int error;
209 
210 	sc->sc_busmem = rumpuser_filemmap(memfd, 0, BUSMEM_SIZE,
211 	    RUMPUSER_FILEMMAP_TRUNCATE | RUMPUSER_FILEMMAP_SHARED
212 	    | RUMPUSER_FILEMMAP_READ | RUMPUSER_FILEMMAP_WRITE, &error);
213 	if (error)
214 		return error;
215 
216 	if (sc->sc_busmem->shm_magic
217 	    && sc->sc_busmem->shm_magic != SHMIF_MAGIC) {
218 		printf("bus is not magical");
219 		rumpuser_unmap(sc->sc_busmem, BUSMEM_SIZE);
220 		return ENOEXEC;
221 	}
222 
223 	/*
224 	 * Prefault in pages to minimize runtime penalty with buslock.
225 	 * Use 512 instead of PAGE_SIZE to make sure we catch cases where
226 	 * rump kernel PAGE_SIZE > host page size.
227 	 */
228 	for (p = (uint8_t *)sc->sc_busmem;
229 	    p < (uint8_t *)sc->sc_busmem + BUSMEM_SIZE;
230 	    p += 512)
231 		v = *p;
232 
233 	shmif_lockbus(sc->sc_busmem);
234 	/* we're first?  initialize bus */
235 	if (sc->sc_busmem->shm_magic == 0) {
236 		sc->sc_busmem->shm_magic = SHMIF_MAGIC;
237 		sc->sc_busmem->shm_first = BUSMEM_DATASIZE;
238 	}
239 
240 	sc->sc_nextpacket = sc->sc_busmem->shm_last;
241 	sc->sc_devgen = sc->sc_busmem->shm_gen;
242 
243 #ifdef PREFAULT_RW
244 	for (p = (uint8_t *)sc->sc_busmem;
245 	    p < (uint8_t *)sc->sc_busmem + BUSMEM_SIZE;
246 	    p += PAGE_SIZE) {
247 		v = *p;
248 		*p = v;
249 	}
250 #endif
251 	shmif_unlockbus(sc->sc_busmem);
252 
253 	sc->sc_kq = rumpuser_writewatchfile_setup(-1, memfd, 0, &error);
254 	if (sc->sc_kq == -1) {
255 		rumpuser_unmap(sc->sc_busmem, BUSMEM_SIZE);
256 		return error;
257 	}
258 
259 	sc->sc_memfd = memfd;
260 
261 	return error;
262 }
263 
264 static void
265 finibackend(struct shmif_sc *sc)
266 {
267 
268 	if (sc->sc_backfile == NULL)
269 		return;
270 
271 	if (sc->sc_backfile) {
272 		kmem_free(sc->sc_backfile, sc->sc_backfilelen);
273 		sc->sc_backfile = NULL;
274 		sc->sc_backfilelen = 0;
275 	}
276 
277 	rumpuser_unmap(sc->sc_busmem, BUSMEM_SIZE);
278 	rumpuser_close(sc->sc_memfd, NULL);
279 	rumpuser_close(sc->sc_kq, NULL);
280 
281 	sc->sc_memfd = -1;
282 }
283 
284 int
285 rump_shmif_create(const char *path, int *ifnum)
286 {
287 	struct shmif_sc *sc;
288 	vmem_addr_t t;
289 	int unit, error;
290 	int memfd = -1; /* XXXgcc */
291 
292 	if (path) {
293 		memfd = rumpuser_open(path,
294 		    RUMPUSER_OPEN_RDWR | RUMPUSER_OPEN_CREATE, &error);
295 		if (memfd == -1)
296 			return error;
297 	}
298 
299 	error = vmem_xalloc(shmif_units, 1, 0, 0, 0,
300 	    VMEM_ADDR_MIN, VMEM_ADDR_MAX, VM_INSTANTFIT | VM_SLEEP, &t);
301 
302 	if (error != 0) {
303 		if (path)
304 			rumpuser_close(memfd, NULL);
305 		return error;
306 	}
307 
308 	unit = t - 1;
309 
310 	if ((error = allocif(unit, &sc)) != 0) {
311 		if (path)
312 			rumpuser_close(memfd, NULL);
313 		return error;
314 	}
315 
316 	if (!path)
317 		goto out;
318 
319 	error = initbackend(sc, memfd);
320 	if (error) {
321 		shmif_unclone(&sc->sc_ec.ec_if);
322 		return error;
323 	}
324 
325 	sc->sc_backfilelen = strlen(path)+1;
326 	sc->sc_backfile = kmem_alloc(sc->sc_backfilelen, KM_SLEEP);
327 	strcpy(sc->sc_backfile, path);
328 
329  out:
330 	if (ifnum)
331 		*ifnum = unit;
332 
333 	return 0;
334 }
335 
336 static int
337 shmif_clone(struct if_clone *ifc, int unit)
338 {
339 	int rc;
340 	vmem_addr_t unit2;
341 
342 	/*
343 	 * Ok, we know the unit number, but we must still reserve it.
344 	 * Otherwise the wildcard-side of things might get the same one.
345 	 * This is slightly offset-happy due to vmem.  First, we offset
346 	 * the range of unit numbers by +1 since vmem cannot deal with
347 	 * ranges starting from 0.  Talk about uuuh.
348 	 */
349 	rc = vmem_xalloc(shmif_units, 1, 0, 0, 0, unit+1, unit+1,
350 	    VM_SLEEP | VM_INSTANTFIT, &unit2);
351 	KASSERT(rc == 0 && unit2-1 == unit);
352 
353 	return allocif(unit, NULL);
354 }
355 
356 static int
357 shmif_unclone(struct ifnet *ifp)
358 {
359 	struct shmif_sc *sc = ifp->if_softc;
360 
361 	shmif_stop(ifp, 1);
362 	if_down(ifp);
363 	finibackend(sc);
364 
365 	mutex_enter(&sc->sc_mtx);
366 	sc->sc_dying = true;
367 	cv_broadcast(&sc->sc_cv);
368 	mutex_exit(&sc->sc_mtx);
369 
370 	if (sc->sc_rcvl)
371 		kthread_join(sc->sc_rcvl);
372 	sc->sc_rcvl = NULL;
373 
374 	vmem_xfree(shmif_units, sc->sc_unit+1, 1);
375 
376 	ether_ifdetach(ifp);
377 	if_detach(ifp);
378 
379 	cv_destroy(&sc->sc_cv);
380 	mutex_destroy(&sc->sc_mtx);
381 
382 	kmem_free(sc, sizeof(*sc));
383 
384 	return 0;
385 }
386 
387 static int
388 shmif_init(struct ifnet *ifp)
389 {
390 	struct shmif_sc *sc = ifp->if_softc;
391 	int error = 0;
392 
393 	if (sc->sc_memfd == -1)
394 		return ENXIO;
395 	KASSERT(sc->sc_busmem);
396 
397 	ifp->if_flags |= IFF_RUNNING;
398 
399 	mutex_enter(&sc->sc_mtx);
400 	sc->sc_nextpacket = sc->sc_busmem->shm_last;
401 	sc->sc_devgen = sc->sc_busmem->shm_gen;
402 
403 	cv_broadcast(&sc->sc_cv);
404 	mutex_exit(&sc->sc_mtx);
405 
406 	return error;
407 }
408 
409 static int
410 shmif_ioctl(struct ifnet *ifp, u_long cmd, void *data)
411 {
412 	struct shmif_sc *sc = ifp->if_softc;
413 	struct ifdrv *ifd;
414 	char *path;
415 	int s, rv, memfd;
416 
417 	s = splnet();
418 	switch (cmd) {
419 	case SIOCGLINKSTR:
420 		ifd = data;
421 
422 		if (sc->sc_backfilelen == 0) {
423 			rv = ENOENT;
424 			break;
425 		}
426 
427 		ifd->ifd_len = sc->sc_backfilelen;
428 		if (ifd->ifd_cmd == IFLINKSTR_QUERYLEN) {
429 			rv = 0;
430 			break;
431 		}
432 
433 		if (ifd->ifd_cmd != 0) {
434 			rv = EINVAL;
435 			break;
436 		}
437 
438 		rv = copyoutstr(sc->sc_backfile, ifd->ifd_data,
439 		    MIN(sc->sc_backfilelen, ifd->ifd_len), NULL);
440 		break;
441 	case SIOCSLINKSTR:
442 		if (ifp->if_flags & IFF_UP) {
443 			rv = EBUSY;
444 			break;
445 		}
446 
447 		ifd = data;
448 		if (ifd->ifd_cmd == IFLINKSTR_UNSET) {
449 			finibackend(sc);
450 			rv = 0;
451 			break;
452 		} else if (ifd->ifd_cmd != 0) {
453 			rv = EINVAL;
454 			break;
455 		} else if (sc->sc_backfile) {
456 			rv = EBUSY;
457 			break;
458 		}
459 
460 		if (ifd->ifd_len > MAXPATHLEN) {
461 			rv = E2BIG;
462 			break;
463 		} else if (ifd->ifd_len < 1) {
464 			rv = EINVAL;
465 			break;
466 		}
467 
468 		path = kmem_alloc(ifd->ifd_len, KM_SLEEP);
469 		rv = copyinstr(ifd->ifd_data, path, ifd->ifd_len, NULL);
470 		if (rv) {
471 			kmem_free(path, ifd->ifd_len);
472 			break;
473 		}
474 		memfd = rumpuser_open(path,
475 		    RUMPUSER_OPEN_RDWR | RUMPUSER_OPEN_CREATE, &rv);
476 		if (memfd == -1) {
477 			kmem_free(path, ifd->ifd_len);
478 			break;
479 		}
480 		rv = initbackend(sc, memfd);
481 		if (rv) {
482 			kmem_free(path, ifd->ifd_len);
483 			rumpuser_close(memfd, NULL);
484 			break;
485 		}
486 		sc->sc_backfile = path;
487 		sc->sc_backfilelen = ifd->ifd_len;
488 
489 		break;
490 	default:
491 		rv = ether_ioctl(ifp, cmd, data);
492 		if (rv == ENETRESET)
493 			rv = 0;
494 		break;
495 	}
496 	splx(s);
497 
498 	return rv;
499 }
500 
501 /* send everything in-context since it's just a matter of mem-to-mem copy */
502 static void
503 shmif_start(struct ifnet *ifp)
504 {
505 	struct shmif_sc *sc = ifp->if_softc;
506 	struct shmif_mem *busmem = sc->sc_busmem;
507 	struct mbuf *m, *m0;
508 	uint32_t dataoff;
509 	uint32_t pktsize, pktwrote;
510 	bool wrote = false;
511 	bool wrap;
512 	int error;
513 
514 	ifp->if_flags |= IFF_OACTIVE;
515 
516 	for (;;) {
517 		struct shmif_pkthdr sp;
518 		struct timeval tv;
519 
520 		IF_DEQUEUE(&ifp->if_snd, m0);
521 		if (m0 == NULL) {
522 			break;
523 		}
524 
525 		pktsize = 0;
526 		for (m = m0; m != NULL; m = m->m_next) {
527 			pktsize += m->m_len;
528 		}
529 		KASSERT(pktsize <= ETHERMTU + ETHER_HDR_LEN);
530 
531 		getmicrouptime(&tv);
532 		sp.sp_len = pktsize;
533 		sp.sp_sec = tv.tv_sec;
534 		sp.sp_usec = tv.tv_usec;
535 
536 		bpf_mtap(ifp, m0);
537 
538 		shmif_lockbus(busmem);
539 		KASSERT(busmem->shm_magic == SHMIF_MAGIC);
540 		busmem->shm_last = shmif_nextpktoff(busmem, busmem->shm_last);
541 
542 		wrap = false;
543 		dataoff = shmif_buswrite(busmem,
544 		    busmem->shm_last, &sp, sizeof(sp), &wrap);
545 		pktwrote = 0;
546 		for (m = m0; m != NULL; m = m->m_next) {
547 			pktwrote += m->m_len;
548 			dataoff = shmif_buswrite(busmem, dataoff,
549 			    mtod(m, void *), m->m_len, &wrap);
550 		}
551 		KASSERT(pktwrote == pktsize);
552 		if (wrap) {
553 			busmem->shm_gen++;
554 			DPRINTF(("bus generation now %" PRIu64 "\n",
555 			    busmem->shm_gen));
556 		}
557 		shmif_unlockbus(busmem);
558 
559 		m_freem(m0);
560 		wrote = true;
561 
562 		DPRINTF(("shmif_start: send %d bytes at off %d\n",
563 		    pktsize, busmem->shm_last));
564 	}
565 
566 	ifp->if_flags &= ~IFF_OACTIVE;
567 
568 	/* wakeup? */
569 	if (wrote)
570 		rumpuser_pwrite(sc->sc_memfd,
571 		    &busversion, sizeof(busversion), IFMEM_WAKEUP, &error);
572 }
573 
574 static void
575 shmif_stop(struct ifnet *ifp, int disable)
576 {
577 	struct shmif_sc *sc = ifp->if_softc;
578 
579 	ifp->if_flags &= ~IFF_RUNNING;
580 	membar_producer();
581 
582 	/*
583 	 * wakeup thread.  this will of course wake up all bus
584 	 * listeners, but that's life.
585 	 */
586 	if (sc->sc_memfd != -1)
587 		rumpuser_pwrite(sc->sc_memfd,
588 		    &busversion, sizeof(busversion), IFMEM_WAKEUP, NULL);
589 }
590 
591 
592 /*
593  * Check if we have been sleeping too long.  Basically,
594  * our in-sc nextpkt must by first <= nextpkt <= last"+1".
595  * We use the fact that first is guaranteed to never overlap
596  * with the last frame in the ring.
597  */
598 static __inline bool
599 stillvalid_p(struct shmif_sc *sc)
600 {
601 	struct shmif_mem *busmem = sc->sc_busmem;
602 	unsigned gendiff = busmem->shm_gen - sc->sc_devgen;
603 	uint32_t lastoff, devoff;
604 
605 	KASSERT(busmem->shm_first != busmem->shm_last);
606 
607 	/* normalize onto a 2x busmem chunk */
608 	devoff = sc->sc_nextpacket;
609 	lastoff = shmif_nextpktoff(busmem, busmem->shm_last);
610 
611 	/* trivial case */
612 	if (gendiff > 1)
613 		return false;
614 	KASSERT(gendiff <= 1);
615 
616 	/* Normalize onto 2x busmem chunk */
617 	if (busmem->shm_first >= lastoff) {
618 		lastoff += BUSMEM_DATASIZE;
619 		if (gendiff == 0)
620 			devoff += BUSMEM_DATASIZE;
621 	} else {
622 		if (gendiff)
623 			return false;
624 	}
625 
626 	return devoff >= busmem->shm_first && devoff <= lastoff;
627 }
628 
629 static void
630 shmif_rcv(void *arg)
631 {
632 	struct ifnet *ifp = arg;
633 	struct shmif_sc *sc = ifp->if_softc;
634 	struct shmif_mem *busmem;
635 	struct mbuf *m = NULL;
636 	struct ether_header *eth;
637 	uint32_t nextpkt;
638 	bool wrap, passup;
639 	int error;
640 
641  reup:
642 	mutex_enter(&sc->sc_mtx);
643 	while ((ifp->if_flags & IFF_RUNNING) == 0 && !sc->sc_dying)
644 		cv_wait(&sc->sc_cv, &sc->sc_mtx);
645 	mutex_exit(&sc->sc_mtx);
646 
647 	busmem = sc->sc_busmem;
648 
649 	while (ifp->if_flags & IFF_RUNNING) {
650 		struct shmif_pkthdr sp;
651 
652 		if (m == NULL) {
653 			m = m_gethdr(M_WAIT, MT_DATA);
654 			MCLGET(m, M_WAIT);
655 		}
656 
657 		DPRINTF(("waiting %d/%" PRIu64 "\n",
658 		    sc->sc_nextpacket, sc->sc_devgen));
659 		KASSERT(m->m_flags & M_EXT);
660 
661 		shmif_lockbus(busmem);
662 		KASSERT(busmem->shm_magic == SHMIF_MAGIC);
663 		KASSERT(busmem->shm_gen >= sc->sc_devgen);
664 
665 		/* need more data? */
666 		if (sc->sc_devgen == busmem->shm_gen &&
667 		    shmif_nextpktoff(busmem, busmem->shm_last)
668 		     == sc->sc_nextpacket) {
669 			shmif_unlockbus(busmem);
670 			error = 0;
671 			rumpuser_writewatchfile_wait(sc->sc_kq, NULL, &error);
672 			if (__predict_false(error))
673 				printf("shmif_rcv: wait failed %d\n", error);
674 			membar_consumer();
675 			continue;
676 		}
677 
678 		if (stillvalid_p(sc)) {
679 			nextpkt = sc->sc_nextpacket;
680 		} else {
681 			KASSERT(busmem->shm_gen > 0);
682 			nextpkt = busmem->shm_first;
683 			if (busmem->shm_first > busmem->shm_last)
684 				sc->sc_devgen = busmem->shm_gen - 1;
685 			else
686 				sc->sc_devgen = busmem->shm_gen;
687 			DPRINTF(("dev %p overrun, new data: %d/%" PRIu64 "\n",
688 			    sc, nextpkt, sc->sc_devgen));
689 		}
690 
691 		/*
692 		 * If our read pointer is ahead the bus last write, our
693 		 * generation must be one behind.
694 		 */
695 		KASSERT(!(nextpkt > busmem->shm_last
696 		    && sc->sc_devgen == busmem->shm_gen));
697 
698 		wrap = false;
699 		nextpkt = shmif_busread(busmem, &sp,
700 		    nextpkt, sizeof(sp), &wrap);
701 		KASSERT(sp.sp_len <= ETHERMTU + ETHER_HDR_LEN);
702 		nextpkt = shmif_busread(busmem, mtod(m, void *),
703 		    nextpkt, sp.sp_len, &wrap);
704 
705 		DPRINTF(("shmif_rcv: read packet of length %d at %d\n",
706 		    sp.sp_len, nextpkt));
707 
708 		sc->sc_nextpacket = nextpkt;
709 		shmif_unlockbus(sc->sc_busmem);
710 
711 		if (wrap) {
712 			sc->sc_devgen++;
713 			DPRINTF(("dev %p generation now %" PRIu64 "\n",
714 			    sc, sc->sc_devgen));
715 		}
716 
717 		m->m_len = m->m_pkthdr.len = sp.sp_len;
718 		m->m_pkthdr.rcvif = ifp;
719 
720 		/*
721 		 * Test if we want to pass the packet upwards
722 		 */
723 		eth = mtod(m, struct ether_header *);
724 		if (memcmp(eth->ether_dhost, CLLADDR(ifp->if_sadl),
725 		    ETHER_ADDR_LEN) == 0) {
726 			passup = true;
727 		} else if (ETHER_IS_MULTICAST(eth->ether_dhost)) {
728 			passup = true;
729 		} else if (ifp->if_flags & IFF_PROMISC) {
730 			m->m_flags |= M_PROMISC;
731 			passup = true;
732 		} else {
733 			passup = false;
734 		}
735 
736 		if (passup) {
737 			KERNEL_LOCK(1, NULL);
738 			bpf_mtap(ifp, m);
739 			ifp->if_input(ifp, m);
740 			KERNEL_UNLOCK_ONE(NULL);
741 			m = NULL;
742 		}
743 		/* else: reuse mbuf for a future packet */
744 	}
745 	m_freem(m);
746 	m = NULL;
747 
748 	if (!sc->sc_dying)
749 		goto reup;
750 
751 	kthread_exit(0);
752 }
753