/*	$NetBSD: if_tun.c,v 1.14 1994/06/29 06:36:25 cgd Exp $	*/

/*
 * Copyright (c) 1988, Julian Onions <jpo@cs.nott.ac.uk>
 * Nottingham University 1987.
 *
 * This source may be freely distributed, however I would be interested
 * in any changes that are made.
 *
 * This driver takes packets off the IP i/f and hands them up to a
 * user process to have its wicked way with. This driver has it's
 * roots in a similar driver written by Phil Cockcroft (formerly) at
 * UCL. This driver is based much more on read/write/poll mode of
 * operation though.
 *
 * $FreeBSD$
 */

#include "opt_atalk.h"
#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipx.h"
#include "opt_mac.h"

#include <sys/param.h>
#include <sys/proc.h>
#include <sys/systm.h>
#include <sys/mac.h>
#include <sys/mbuf.h>
#include <sys/module.h>
#include <sys/socket.h>
#include <sys/filio.h>
#include <sys/sockio.h>
#include <sys/ttycom.h>
#include <sys/poll.h>
#include <sys/signalvar.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/conf.h>
#include <sys/uio.h>
#include <sys/vnode.h>
#include <sys/malloc.h>
#include <sys/random.h>

#include <net/if.h>
#include <net/if_types.h>
#include <net/netisr.h>
#include <net/route.h>
#ifdef INET
#include <netinet/in.h>
#endif
#include <net/bpf.h>
#include <net/if_tun.h>

#include <sys/queue.h>

/*
 * tun_list is protected by global tunmtx.  Other mutable fields are
 * protected by tun->tun_mtx, or by their owning subsystem.  tun_dev is
 * static for the duration of a tunnel interface.
 */
struct tun_softc {
	TAILQ_ENTRY(tun_softc)	tun_list;
	dev_t			tun_dev;
	u_short	tun_flags;		/* misc flags */
#define	TUN_OPEN	0x0001
#define	TUN_INITED	0x0002
#define	TUN_RCOLL	0x0004
#define	TUN_IASET	0x0008
#define	TUN_DSTADDR	0x0010
#define	TUN_LMODE	0x0020
#define	TUN_RWAIT	0x0040
#define	TUN_ASYNC	0x0080
#define	TUN_IFHEAD	0x0100

#define TUN_READY       (TUN_OPEN | TUN_INITED)

	/*
	 * XXXRW: tun_pid is used to exclusively lock /dev/tun.  Is this
	 * actually needed?  Can we just return EBUSY if already open?
	 * Problem is that this involved inherent races when a tun device
	 * is handed off from one process to another, as opposed to just
	 * being slightly stale informationally.
	 */
	pid_t	tun_pid;		/* owning pid */
	struct	ifnet tun_if;		/* the interface */
	struct  sigio *tun_sigio;	/* information for async I/O */
	struct	selinfo	tun_rsel;	/* read select */
	struct mtx	tun_mtx;	/* protect mutable softc fields */
};

#define TUNDEBUG	if (tundebug) if_printf
#define	TUNNAME		"tun"

/*
 * All mutable global variables in if_tun are locked using tunmtx, with
 * the exception of tundebug, which is used unlocked, and tunclones,
 * which is static after setup.
 */
static struct mtx tunmtx;
static MALLOC_DEFINE(M_TUN, TUNNAME, "Tunnel Interface");
static int tundebug = 0;
static struct clonedevs *tunclones;
static TAILQ_HEAD(,tun_softc)	tunhead = TAILQ_HEAD_INITIALIZER(tunhead);
SYSCTL_INT(_debug, OID_AUTO, if_tun_debug, CTLFLAG_RW, &tundebug, 0, "");

static void	tunclone(void *arg, char *name, int namelen, dev_t *dev);
static void	tuncreate(dev_t dev);
static int	tunifioctl(struct ifnet *, u_long, caddr_t);
static int	tuninit(struct ifnet *);
static int	tunmodevent(module_t, int, void *);
static int	tunoutput(struct ifnet *, struct mbuf *, struct sockaddr *,
		    struct rtentry *rt);
static void	tunstart(struct ifnet *);

static d_open_t		tunopen;
static d_close_t	tunclose;
static d_read_t		tunread;
static d_write_t	tunwrite;
static d_ioctl_t	tunioctl;
static d_poll_t		tunpoll;

static struct cdevsw tun_cdevsw = {
	.d_version =	D_VERSION,
	.d_flags =	D_PSEUDO | D_NEEDGIANT,
	.d_open =	tunopen,
	.d_close =	tunclose,
	.d_read =	tunread,
	.d_write =	tunwrite,
	.d_ioctl =	tunioctl,
	.d_poll =	tunpoll,
	.d_name =	TUNNAME,
};

static void
tunclone(void *arg, char *name, int namelen, dev_t *dev)
{
	int u, i;

	if (*dev != NODEV)
		return;

	if (strcmp(name, TUNNAME) == 0) {
		u = -1;
	} else if (dev_stdclone(name, NULL, TUNNAME, &u) != 1)
		return;	/* Don't recognise the name */
	if (u != -1 && u > IF_MAXUNIT)
		return;	/* Unit number too high */

	/* find any existing device, or allocate new unit number */
	i = clone_create(&tunclones, &tun_cdevsw, &u, dev, 0);
	if (i) {
		/* No preexisting dev_t, create one */
		*dev = make_dev(&tun_cdevsw, unit2minor(u),
		    UID_UUCP, GID_DIALER, 0600, "tun%d", u);
		if (*dev != NULL)
			(*dev)->si_flags |= SI_CHEAPCLONE;
	}
}

static void
tun_destroy(struct tun_softc *tp)
{
	dev_t dev;

	/* Unlocked read. */
	KASSERT((tp->tun_flags & TUN_OPEN) == 0,
	    ("tununits is out of sync - unit %d", tp->tun_if.if_dunit));

	dev = tp->tun_dev;
	bpfdetach(&tp->tun_if);
	if_detach(&tp->tun_if);
	destroy_dev(dev);
	mtx_destroy(&tp->tun_mtx);
	free(tp, M_TUN);
}

static int
tunmodevent(module_t mod, int type, void *data)
{
	static eventhandler_tag tag;
	struct tun_softc *tp;

	switch (type) {
	case MOD_LOAD:
		mtx_init(&tunmtx, "tunmtx", NULL, MTX_DEF);
		clone_setup(&tunclones);
		tag = EVENTHANDLER_REGISTER(dev_clone, tunclone, 0, 1000);
		if (tag == NULL)
			return (ENOMEM);
		break;
	case MOD_UNLOAD:
		EVENTHANDLER_DEREGISTER(dev_clone, tag);

		mtx_lock(&tunmtx);
		while ((tp = TAILQ_FIRST(&tunhead)) != NULL) {
			TAILQ_REMOVE(&tunhead, tp, tun_list);
			mtx_unlock(&tunmtx);
			tun_destroy(tp);
			mtx_lock(&tunmtx);
		}
		mtx_unlock(&tunmtx);
		clone_cleanup(&tunclones);
		mtx_destroy(&tunmtx);
		break;
	}
	return 0;
}

static moduledata_t tun_mod = {
	"if_tun",
	tunmodevent,
	0
};

DECLARE_MODULE(if_tun, tun_mod, SI_SUB_PSEUDO, SI_ORDER_ANY);

static void
tunstart(struct ifnet *ifp)
{
	struct tun_softc *tp = ifp->if_softc;

	mtx_lock(&tp->tun_mtx);
	if (tp->tun_flags & TUN_RWAIT) {
		tp->tun_flags &= ~TUN_RWAIT;
		wakeup(tp);
	}
	if (tp->tun_flags & TUN_ASYNC && tp->tun_sigio) {
		mtx_unlock(&tp->tun_mtx);
		pgsigio(&tp->tun_sigio, SIGIO, 0);
	} else
		mtx_unlock(&tp->tun_mtx);
	selwakeuppri(&tp->tun_rsel, PZERO + 1);
}

static void
tuncreate(dev_t dev)
{
	struct tun_softc *sc;
	struct ifnet *ifp;

	dev->si_flags &= ~SI_CHEAPCLONE;

	MALLOC(sc, struct tun_softc *, sizeof(*sc), M_TUN, M_WAITOK | M_ZERO);
	mtx_init(&sc->tun_mtx, "tun_mtx", NULL, MTX_DEF);
	sc->tun_flags = TUN_INITED;
	sc->tun_dev = dev;
	mtx_lock(&tunmtx);
	TAILQ_INSERT_TAIL(&tunhead, sc, tun_list);
	mtx_unlock(&tunmtx);

	ifp = &sc->tun_if;
	if_initname(ifp, TUNNAME, dev2unit(dev));
	ifp->if_mtu = TUNMTU;
	ifp->if_ioctl = tunifioctl;
	ifp->if_output = tunoutput;
	ifp->if_start = tunstart;
	ifp->if_flags = IFF_POINTOPOINT | IFF_MULTICAST;
	ifp->if_type = IFT_PPP;
	ifp->if_snd.ifq_maxlen = ifqmaxlen;
	ifp->if_softc = sc;
	if_attach(ifp);
	bpfattach(ifp, DLT_NULL, sizeof(u_int));
	dev->si_drv1 = sc;
}

static int
tunopen(dev_t dev, int flag, int mode, struct thread *td)
{
	struct ifnet	*ifp;
	struct tun_softc *tp;

	/*
	 * XXXRW: Non-atomic test and set of dev->si_drv1 requires
	 * synchronization.
	 */
	tp = dev->si_drv1;
	if (!tp) {
		tuncreate(dev);
		tp = dev->si_drv1;
	}

	/*
	 * XXXRW: This use of tun_pid is subject to error due to the
	 * fact that a reference to the tunnel can live beyond the
	 * death of the process that created it.  Can we replace this
	 * with a simple busy flag?
	 */
	mtx_lock(&tp->tun_mtx);
	if (tp->tun_pid != 0 && tp->tun_pid != td->td_proc->p_pid) {
		mtx_unlock(&tp->tun_mtx);
		return (EBUSY);
	}
	tp->tun_pid = td->td_proc->p_pid;

	tp->tun_flags |= TUN_OPEN;
	mtx_unlock(&tp->tun_mtx);
	ifp = &tp->tun_if;
	TUNDEBUG(ifp, "open\n");

	return (0);
}

/*
 * tunclose - close the device - mark i/f down & delete
 * routing info
 */
static	int
tunclose(dev_t dev, int foo, int bar, struct thread *td)
{
	struct tun_softc *tp;
	struct ifnet *ifp;
	int s;

	tp = dev->si_drv1;
	ifp = &tp->tun_if;

	mtx_lock(&tp->tun_mtx);
	tp->tun_flags &= ~TUN_OPEN;
	tp->tun_pid = 0;
	mtx_unlock(&tp->tun_mtx);

	/*
	 * junk all pending output
	 */
	IF_DRAIN(&ifp->if_snd);

	if (ifp->if_flags & IFF_UP) {
		s = splimp();
		if_down(ifp);
		splx(s);
	}

	if (ifp->if_flags & IFF_RUNNING) {
		struct ifaddr *ifa;

		s = splimp();
		/* find internet addresses and delete routes */
		TAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link)
			if (ifa->ifa_addr->sa_family == AF_INET)
				/* Unlocked read. */
				rtinit(ifa, (int)RTM_DELETE,
				    tp->tun_flags & TUN_DSTADDR ? RTF_HOST : 0);
		ifp->if_flags &= ~IFF_RUNNING;
		splx(s);
	}

	funsetown(&tp->tun_sigio);
	selwakeuppri(&tp->tun_rsel, PZERO + 1);
	TUNDEBUG (ifp, "closed\n");
	return (0);
}

static int
tuninit(struct ifnet *ifp)
{
	struct tun_softc *tp = ifp->if_softc;
	struct ifaddr *ifa;
	int error = 0;

	TUNDEBUG(ifp, "tuninit\n");

	ifp->if_flags |= IFF_UP | IFF_RUNNING;
	getmicrotime(&ifp->if_lastchange);

	for (ifa = TAILQ_FIRST(&ifp->if_addrhead); ifa;
	     ifa = TAILQ_NEXT(ifa, ifa_link)) {
		if (ifa->ifa_addr == NULL)
			error = EFAULT;
			/* XXX: Should maybe return straight off? */
		else {
#ifdef INET
			if (ifa->ifa_addr->sa_family == AF_INET) {
			    struct sockaddr_in *si;

			    si = (struct sockaddr_in *)ifa->ifa_addr;
			    mtx_lock(&tp->tun_mtx);
			    if (si->sin_addr.s_addr)
				    tp->tun_flags |= TUN_IASET;

			    si = (struct sockaddr_in *)ifa->ifa_dstaddr;
			    if (si && si->sin_addr.s_addr)
				    tp->tun_flags |= TUN_DSTADDR;
			    mtx_unlock(&tp->tun_mtx);
			}
#endif
		}
	}
	return (error);
}

/*
 * Process an ioctl request.
 */
static int
tunifioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
{
	struct ifreq *ifr = (struct ifreq *)data;
	struct tun_softc *tp = ifp->if_softc;
	struct ifstat *ifs;
	int		error = 0, s;

	s = splimp();
	switch(cmd) {
	case SIOCGIFSTATUS:
		ifs = (struct ifstat *)data;
		mtx_lock(&tp->tun_mtx);
		if (tp->tun_pid)
			sprintf(ifs->ascii + strlen(ifs->ascii),
			    "\tOpened by PID %d\n", tp->tun_pid);
		mtx_unlock(&tp->tun_mtx);
		break;
	case SIOCSIFADDR:
		error = tuninit(ifp);
		TUNDEBUG(ifp, "address set, error=%d\n", error);
		break;
	case SIOCSIFDSTADDR:
		error = tuninit(ifp);
		TUNDEBUG(ifp, "destination address set, error=%d\n", error);
		break;
	case SIOCSIFMTU:
		ifp->if_mtu = ifr->ifr_mtu;
		TUNDEBUG(ifp, "mtu set\n");
		break;
	case SIOCSIFFLAGS:
	case SIOCADDMULTI:
	case SIOCDELMULTI:
		break;
	default:
		error = EINVAL;
	}
	splx(s);
	return (error);
}

/*
 * tunoutput - queue packets from higher level ready to put out.
 */
static int
tunoutput(
	struct ifnet *ifp,
	struct mbuf *m0,
	struct sockaddr *dst,
	struct rtentry *rt)
{
	struct tun_softc *tp = ifp->if_softc;
	u_short cached_tun_flags;
	int error;

	TUNDEBUG (ifp, "tunoutput\n");

#ifdef MAC
	error = mac_check_ifnet_transmit(ifp, m0);
	if (error) {
		m_freem(m0);
		return (error);
	}
#endif

	/* Could be unlocked read? */
	mtx_lock(&tp->tun_mtx);
	cached_tun_flags = tp->tun_flags;
	mtx_unlock(&tp->tun_mtx);
	if ((cached_tun_flags & TUN_READY) != TUN_READY) {
		TUNDEBUG (ifp, "not ready 0%o\n", tp->tun_flags);
		m_freem (m0);
		return (EHOSTDOWN);
	}

	if ((ifp->if_flags & IFF_UP) != IFF_UP) {
		m_freem (m0);
		return (EHOSTDOWN);
	}

	/* BPF write needs to be handled specially */
	if (dst->sa_family == AF_UNSPEC) {
		dst->sa_family = *(mtod(m0, int *));
		m0->m_len -= sizeof(int);
		m0->m_pkthdr.len -= sizeof(int);
		m0->m_data += sizeof(int);
	}

	if (ifp->if_bpf) {
		uint32_t af = dst->sa_family;
		bpf_mtap2(ifp->if_bpf, &af, sizeof(af), m0);
	}

	/* prepend sockaddr? this may abort if the mbuf allocation fails */
	if (cached_tun_flags & TUN_LMODE) {
		/* allocate space for sockaddr */
		M_PREPEND(m0, dst->sa_len, M_DONTWAIT);

		/* if allocation failed drop packet */
		if (m0 == NULL) {
			ifp->if_iqdrops++;
			ifp->if_oerrors++;
			return (ENOBUFS);
		} else {
			bcopy(dst, m0->m_data, dst->sa_len);
		}
	}

	if (cached_tun_flags & TUN_IFHEAD) {
		/* Prepend the address family */
		M_PREPEND(m0, 4, M_DONTWAIT);

		/* if allocation failed drop packet */
		if (m0 == NULL) {
			ifp->if_iqdrops++;
			ifp->if_oerrors++;
			return (ENOBUFS);
		} else
			*(u_int32_t *)m0->m_data = htonl(dst->sa_family);
	} else {
#ifdef INET
		if (dst->sa_family != AF_INET)
#endif
		{
			m_freem(m0);
			return (EAFNOSUPPORT);
		}
	}

	IFQ_HANDOFF(ifp, m0, error);
	if (error) {
		ifp->if_collisions++;
		return (ENOBUFS);
	}
	ifp->if_opackets++;
	return (0);
}

/*
 * the cdevsw interface is now pretty minimal.
 */
static	int
tunioctl(dev_t dev, u_long cmd, caddr_t data, int flag, struct thread *td)
{
	int		s;
	int		error;
	struct tun_softc *tp = dev->si_drv1;
	struct tuninfo *tunp;

	switch (cmd) {
	case TUNSIFINFO:
		tunp = (struct tuninfo *)data;
		if (tunp->mtu < IF_MINMTU)
			return (EINVAL);
		if (tp->tun_if.if_mtu != tunp->mtu
		&& (error = suser(td)) != 0)
			return (error);
		tp->tun_if.if_mtu = tunp->mtu;
		tp->tun_if.if_type = tunp->type;
		tp->tun_if.if_baudrate = tunp->baudrate;
		break;
	case TUNGIFINFO:
		tunp = (struct tuninfo *)data;
		tunp->mtu = tp->tun_if.if_mtu;
		tunp->type = tp->tun_if.if_type;
		tunp->baudrate = tp->tun_if.if_baudrate;
		break;
	case TUNSDEBUG:
		tundebug = *(int *)data;
		break;
	case TUNGDEBUG:
		*(int *)data = tundebug;
		break;
	case TUNSLMODE:
		mtx_lock(&tp->tun_mtx);
		if (*(int *)data) {
			tp->tun_flags |= TUN_LMODE;
			tp->tun_flags &= ~TUN_IFHEAD;
		} else
			tp->tun_flags &= ~TUN_LMODE;
		mtx_unlock(&tp->tun_mtx);
		break;
	case TUNSIFHEAD:
		mtx_lock(&tp->tun_mtx);
		if (*(int *)data) {
			tp->tun_flags |= TUN_IFHEAD;
			tp->tun_flags &= ~TUN_LMODE;
		} else
			tp->tun_flags &= ~TUN_IFHEAD;
		mtx_unlock(&tp->tun_mtx);
		break;
	case TUNGIFHEAD:
		/* Could be unlocked read? */
		mtx_lock(&tp->tun_mtx);
		*(int *)data = (tp->tun_flags & TUN_IFHEAD) ? 1 : 0;
		mtx_unlock(&tp->tun_mtx);
		break;
	case TUNSIFMODE:
		/* deny this if UP */
		if (tp->tun_if.if_flags & IFF_UP)
			return(EBUSY);

		switch (*(int *)data & ~IFF_MULTICAST) {
		case IFF_POINTOPOINT:
		case IFF_BROADCAST:
			tp->tun_if.if_flags &=
			    ~(IFF_BROADCAST|IFF_POINTOPOINT|IFF_MULTICAST);
			tp->tun_if.if_flags |= *(int *)data;
			break;
		default:
			return(EINVAL);
		}
		break;
	case TUNSIFPID:
		mtx_lock(&tp->tun_mtx);
		tp->tun_pid = curthread->td_proc->p_pid;
		mtx_unlock(&tp->tun_mtx);
		break;
	case FIONBIO:
		break;
	case FIOASYNC:
		mtx_lock(&tp->tun_mtx);
		if (*(int *)data)
			tp->tun_flags |= TUN_ASYNC;
		else
			tp->tun_flags &= ~TUN_ASYNC;
		mtx_unlock(&tp->tun_mtx);
		break;
	case FIONREAD:
		s = splimp();
		if (tp->tun_if.if_snd.ifq_head) {
			struct mbuf *mb = tp->tun_if.if_snd.ifq_head;
			for( *(int *)data = 0; mb != 0; mb = mb->m_next)
				*(int *)data += mb->m_len;
		} else
			*(int *)data = 0;
		splx(s);
		break;
	case FIOSETOWN:
		return (fsetown(*(int *)data, &tp->tun_sigio));

	case FIOGETOWN:
		*(int *)data = fgetown(&tp->tun_sigio);
		return (0);

	/* This is deprecated, FIOSETOWN should be used instead. */
	case TIOCSPGRP:
		return (fsetown(-(*(int *)data), &tp->tun_sigio));

	/* This is deprecated, FIOGETOWN should be used instead. */
	case TIOCGPGRP:
		*(int *)data = -fgetown(&tp->tun_sigio);
		return (0);

	default:
		return (ENOTTY);
	}
	return (0);
}

/*
 * The cdevsw read interface - reads a packet at a time, or at
 * least as much of a packet as can be read.
 */
static	int
tunread(dev_t dev, struct uio *uio, int flag)
{
	struct tun_softc *tp = dev->si_drv1;
	struct ifnet	*ifp = &tp->tun_if;
	struct mbuf	*m;
	int		error=0, len, s;

	TUNDEBUG (ifp, "read\n");
	mtx_lock(&tp->tun_mtx);
	if ((tp->tun_flags & TUN_READY) != TUN_READY) {
		mtx_unlock(&tp->tun_mtx);
		TUNDEBUG (ifp, "not ready 0%o\n", tp->tun_flags);
		return (EHOSTDOWN);
	}

	tp->tun_flags &= ~TUN_RWAIT;
	mtx_unlock(&tp->tun_mtx);

	s = splimp();
	do {
		IF_DEQUEUE(&ifp->if_snd, m);
		if (m == NULL) {
			if (flag & IO_NDELAY) {
				splx(s);
				return (EWOULDBLOCK);
			}
			mtx_lock(&tp->tun_mtx);
			tp->tun_flags |= TUN_RWAIT;
			mtx_unlock(&tp->tun_mtx);
			if((error = tsleep(tp, PCATCH | (PZERO + 1),
					"tunread", 0)) != 0) {
				splx(s);
				return (error);
			}
		}
	} while (m == NULL);
	splx(s);

	while (m && uio->uio_resid > 0 && error == 0) {
		len = min(uio->uio_resid, m->m_len);
		if (len != 0)
			error = uiomove(mtod(m, void *), len, uio);
		m = m_free(m);
	}

	if (m) {
		TUNDEBUG(ifp, "Dropping mbuf\n");
		m_freem(m);
	}
	return (error);
}

/*
 * the cdevsw write interface - an atomic write is a packet - or else!
 */
static	int
tunwrite(dev_t dev, struct uio *uio, int flag)
{
	struct tun_softc *tp = dev->si_drv1;
	struct ifnet	*ifp = &tp->tun_if;
	struct mbuf	*top, **mp, *m;
	int		error=0, tlen, mlen;
	uint32_t	family;
	int 		isr;

	TUNDEBUG(ifp, "tunwrite\n");

	if ((ifp->if_flags & IFF_UP) != IFF_UP)
		/* ignore silently */
		return (0);

	if (uio->uio_resid == 0)
		return (0);

	if (uio->uio_resid < 0 || uio->uio_resid > TUNMRU) {
		TUNDEBUG(ifp, "len=%d!\n", uio->uio_resid);
		return (EIO);
	}
	tlen = uio->uio_resid;

	/* get a header mbuf */
	MGETHDR(m, M_DONTWAIT, MT_DATA);
	if (m == NULL)
		return (ENOBUFS);
	mlen = MHLEN;

	top = 0;
	mp = &top;
	while (error == 0 && uio->uio_resid > 0) {
		m->m_len = min(mlen, uio->uio_resid);
		error = uiomove(mtod(m, void *), m->m_len, uio);
		*mp = m;
		mp = &m->m_next;
		if (uio->uio_resid > 0) {
			MGET (m, M_DONTWAIT, MT_DATA);
			if (m == 0) {
				error = ENOBUFS;
				break;
			}
			mlen = MLEN;
		}
	}
	if (error) {
		if (top)
			m_freem (top);
		ifp->if_ierrors++;
		return (error);
	}

	top->m_pkthdr.len = tlen;
	top->m_pkthdr.rcvif = ifp;
#ifdef MAC
	mac_create_mbuf_from_ifnet(ifp, top);
#endif

	/* Could be unlocked read? */
	mtx_lock(&tp->tun_mtx);
	if (tp->tun_flags & TUN_IFHEAD) {
		mtx_unlock(&tp->tun_mtx);
		if (top->m_len < sizeof(family) &&
		    (top = m_pullup(top, sizeof(family))) == NULL)
			return (ENOBUFS);
		family = ntohl(*mtod(top, u_int32_t *));
		m_adj(top, sizeof(family));
	} else {
		mtx_unlock(&tp->tun_mtx);
		family = AF_INET;
	}

	BPF_MTAP2(ifp, &family, sizeof(family), top);

	switch (family) {
#ifdef INET
	case AF_INET:
		isr = NETISR_IP;
		break;
#endif
#ifdef INET6
	case AF_INET6:
		isr = NETISR_IPV6;
		break;
#endif
#ifdef IPX
	case AF_IPX:
		isr = NETISR_IPX;
		break;
#endif
#ifdef NETATALK
	case AF_APPLETALK:
		isr = NETISR_ATALK2;
		break;
#endif
	default:
		m_freem(m);
		return (EAFNOSUPPORT);
	}
	/* First chunk of an mbuf contains good junk */
	if (harvest.point_to_point)
		random_harvest(m, 16, 3, 0, RANDOM_NET);
	ifp->if_ibytes += top->m_pkthdr.len;
	ifp->if_ipackets++;
	netisr_dispatch(isr, top);
	return (0);
}

/*
 * tunpoll - the poll interface, this is only useful on reads
 * really. The write detect always returns true, write never blocks
 * anyway, it either accepts the packet or drops it.
 */
static	int
tunpoll(dev_t dev, int events, struct thread *td)
{
	int		s;
	struct tun_softc *tp = dev->si_drv1;
	struct ifnet	*ifp = &tp->tun_if;
	int		revents = 0;

	s = splimp();
	TUNDEBUG(ifp, "tunpoll\n");

	if (events & (POLLIN | POLLRDNORM)) {
		if (ifp->if_snd.ifq_len > 0) {
			TUNDEBUG(ifp, "tunpoll q=%d\n", ifp->if_snd.ifq_len);
			revents |= events & (POLLIN | POLLRDNORM);
		} else {
			TUNDEBUG(ifp, "tunpoll waiting\n");
			selrecord(td, &tp->tun_rsel);
		}
	}
	if (events & (POLLOUT | POLLWRNORM))
		revents |= events & (POLLOUT | POLLWRNORM);

	splx(s);
	return (revents);
}