xref: /original-bsd/sys/net/bpf.c (revision 93ab02a6)

/*-
 * Copyright (c) 1991 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from the Stanford/CMU enet packet filter,
 * (net/enet.c) distributed as part of 4.3BSD, and code contributed
 * to Berkeley by Steven McCanne of Lawrence Berkeley Laboratory.
 *
 * %sccs.include.redist.c%
 *
 *	@(#)bpf.c	7.1 (Berkeley) 05/07/91
 *
 * static char rcsid[] =
 * "$Header: bpf.c,v 1.23 91/01/30 18:22:13 mccanne Exp $";
 */

#include "bpfilter.h"

#if (NBPFILTER > 0)

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/buf.h>
#include <sys/dir.h>
#include <sys/proc.h>
#include <sys/user.h>
#include <sys/ioctl.h>
#include <sys/map.h>

#include <sys/file.h>
#ifdef sparc
#include <sys/stream.h>
#endif
#include <sys/tty.h>
#include <sys/uio.h>

#include <sys/protosw.h>
#include <sys/socket.h>
#include <net/if.h>

#include <net/bpf.h>
#include <net/bpfdesc.h>

#include <sys/errno.h>

#include <netinet/in.h>
#include <netinet/if_ether.h>
#include <sys/kernel.h>

#define PRINET  26			/* interruptible */

/*
 * The default read buffer size is patchable.
 */
int bpf_bufsize = MCLBYTES;

/*
 *  bpf_iflist is the list of interfaces; each corresponds to an ifnet
 *  bpf_dtab holds the descriptors, indexed by minor device #
 *
 * We really don't need NBPFILTER bpf_if entries, but this eliminates
 * the need to account for all possible drivers here.
 * This problem will go away when these structures are allocated dynamically.
 */
static struct bpf_if 	*bpf_iflist;
static struct bpf_d	bpf_dtab[NBPFILTER];

static void	bpf_ifname();
static void	catchpacket();
static int	bpf_setif();
static int	bpf_initd();

static int
bpf_movein(uio, linktype, mp, sockp)
	register struct uio *uio;
	int linktype;
	register struct mbuf **mp;
	register struct sockaddr *sockp;
{
	struct mbuf *m;
	int error;
	int len;
	int hlen;

	/*
	 * Build a sockaddr based on the data link layer type.
	 * We do this at this level because the ethernet header
	 * is copied directly into the data field of the sockaddr.
	 * In the case of SLIP, there is no header and the packet
	 * is forwarded as is.
	 * Also, we are careful to leave room at the front of the mbuf
	 * for the link level header.
	 */
	switch (linktype) {
	case DLT_SLIP:
		sockp->sa_family = AF_INET;
		hlen = 0;
		break;

	case DLT_EN10MB:
		sockp->sa_family = AF_UNSPEC;
		/* XXX Would MAXLINKHDR be better? */
		hlen = sizeof(struct ether_header);
		break;

       case DLT_FDDI:
		sockp->sa_family = AF_UNSPEC;
		/* XXX 4(FORMAC)+6(dst)+6(src)+3(LLC)+5(SNAP) */
		hlen = 24;
		break;

	default:
		return (EIO);
	}

	len = uio->uio_resid;
	if ((unsigned)len > MCLBYTES)
		return (EIO);

	MGET(m, M_WAIT, MT_DATA);
	if (m == 0)
		return (ENOBUFS);
	if (len > MLEN) {
		MCLGET(m, M_WAIT);
		if ((m->m_flags & M_EXT) == 0) {
			error = ENOBUFS;
			goto bad;
		}
	}
	m->m_len = len;
	*mp = m;
	/*
	 * Make room for link header.
	 */
	if (hlen) {
		m->m_len -= hlen;
		m->m_data += hlen; /* XXX */

		error = uiomove((caddr_t)sockp->sa_data, hlen, uio);
		if (error)
			goto bad;
	}
	error = uiomove(mtod(m, caddr_t), len - hlen, uio);
	if (!error)
		return (0);
 bad:
	m_freem(m);
	return (error);
}

/*
 * Attach 'd' to the bpf interface 'bp', i.e. make 'd' listen on 'bp'.
 * Must be called at splimp.
 */
static void
bpf_attachd(d, bp)
	struct bpf_d *d;
	struct bpf_if *bp;
{
	/* Point d at bp. */
	d->bd_bif = bp;

	/* Add d to bp's list of listeners. */
	d->bd_next = bp->bif_dlist;
	bp->bif_dlist = d;

	/*
	 * Let the driver know we're here (if it doesn't already).
	 */
	*bp->bif_driverp = bp;
}

static void
bpf_detachd(d)
	struct bpf_d *d;
{
	struct bpf_d **p;
	struct bpf_if *bp;

	bp = d->bd_bif;
	/*
	 * Check if this descriptor had requested promiscuous mode.
	 * If so, turn it off.
	 */
	if (d->bd_promisc) {
		d->bd_promisc = 0;
		if (ifpromisc(bp->bif_ifp, 0))
			/*
			 * Something is really wrong if we were able to put
			 * the driver into promiscuous mode, but can't
			 * take it out.
			 */
			panic("bpf_detachd: ifpromisc failed");
	}
	/* Remove 'd' from the interface's descriptor list. */
	p = &bp->bif_dlist;
	while (*p != d) {
		p = &(*p)->bd_next;
		if (*p == 0)
			panic("bpf_detachd: descriptor not in list");
	}
	*p = (*p)->bd_next;
	if (bp->bif_dlist == 0)
		/*
		 * Let the driver know that there are no more listeners.
		 */
		*d->bd_bif->bif_driverp = 0;
	d->bd_bif = 0;
}


/*
 * Mark a descriptor free by making it point to itself.
 * This is probably cheaper than marking with a constant since
 * the address should be in a register anyway.
 */
#define D_ISFREE(d) ((d) == (d)->bd_next)
#define D_MARKFREE(d) ((d)->bd_next = (d))
#define D_MARKUSED(d) ((d)->bd_next = 0)

/*
 *  bpfopen - open ethernet device
 *
 *  Errors:	ENXIO	- illegal minor device number
 *		EBUSY	- too many files open
 */
/* ARGSUSED */
int
bpfopen(dev, flag)
	dev_t dev;
	int flag;
{
	int error, s;
	register struct bpf_d *d;

	if (minor(dev) >= NBPFILTER)
		return (ENXIO);

	/*
	 * Each minor can be opened by only one process.  If the requested
	 * minor is in use, return EBUSY.
	 */
	s = splimp();
	d = &bpf_dtab[minor(dev)];
	if (!D_ISFREE(d)) {
		splx(s);
		return (EBUSY);
	} else
		/* Mark "free" and do most initialization. */
		bzero((char *)d, sizeof(*d));
	splx(s);

	error = bpf_initd(d);
	if (error) {
		D_MARKFREE(d);
		return (error);
	}
	return (0);
}

/*
 * Close the descriptor by detaching it from its interface,
 * deallocating its buffers, and marking it free.
 */
/* ARGSUSED */
bpfclose(dev, flag)
	dev_t dev;
	int flag;
{
	register struct bpf_d *d = &bpf_dtab[minor(dev)];
	int s;

	s = splimp();
	if (d->bd_bif)
		bpf_detachd(d);
	splx(s);

	/* Free the buffer space. */
	if (d->bd_hbuf)
		free(d->bd_hbuf, M_DEVBUF);
	if (d->bd_fbuf)
		free(d->bd_fbuf, M_DEVBUF);
	free(d->bd_sbuf, M_DEVBUF);
	if (d->bd_filter)
		free((caddr_t)d->bd_filter, M_DEVBUF);

	D_MARKFREE(d);
}

/*
 * Rotate the packet buffers in descriptor d.  Move the store buffer
 * into the hold slot, and the free buffer into the store slot.
 * Zero the length of the new store buffer.
 */
#define ROTATE_BUFFERS(d) \
	(d)->bd_hbuf = (d)->bd_sbuf; \
	(d)->bd_hlen = (d)->bd_slen; \
	(d)->bd_sbuf = (d)->bd_fbuf; \
	(d)->bd_slen = 0; \
	(d)->bd_fbuf = 0;
/*
 *  bpfread - read next chunk of packets from buffers
 */
int
bpfread(dev, uio)
	dev_t dev;
	register struct uio *uio;
{
	register struct bpf_d *d = &bpf_dtab[minor(dev)];
	int error;
	int s;

	/*
	 * Restrict application to use a buffer the same size as
	 * as kernel buffers.
	 */
	if (uio->uio_resid != d->bd_bufsize)
		return (EINVAL);

	s = splimp();
	/*
	 * If the hold buffer is empty, then set a timer and sleep
	 * until either the timeout has occurred or enough packets have
	 * arrived to fill the store buffer.
	 */
	while (d->bd_hbuf == 0) {
		if (d->bd_immediate && d->bd_slen != 0) {
			/*
			 * A packet(s) either arrived since the previous
			 * read or arrived while we were asleep.
			 * Rotate the buffers and return what's here.
			 */
			ROTATE_BUFFERS(d);
			break;
		}
		error = tsleep((caddr_t)d, PRINET|PCATCH, "bpf", d->bd_rtout);
		if (error == EINTR || error == ERESTART) {
			splx(s);
			return (error);
		}
		if (error == EWOULDBLOCK) {
			/*
			 * On a timeout, return what's in the buffer,
			 * which may be nothing.  If there is something
			 * in the store buffer, we can rotate the buffers.
			 */
			if (d->bd_hbuf)
				/*
				 * We filled up the buffer in between
				 * getting the timeout and arriving
				 * here, so we don't need to rotate.
				 */
				break;

			if (d->bd_slen == 0) {
				splx(s);
				return (0);
			}
			ROTATE_BUFFERS(d);
			break;
		}
	}
	/*
	 * At this point, we know we have something in the hold slot.
	 */
	splx(s);

	/*
	 * Move data from hold buffer into user space.
	 * We know the entire buffer is transferred since
	 * we checked above that the read buffer is bpf_bufsize bytes.
	 */
	error = uiomove(d->bd_hbuf, d->bd_hlen, uio);

	s = splimp();
	d->bd_fbuf = d->bd_hbuf;
	d->bd_hbuf = 0;
	splx(s);

	return (error);
}


/*
 * If there are processes sleeping on this descriptor, wake them up.
 */
static inline void
bpf_wakeup(d)
	register struct bpf_d *d;
{
	wakeup((caddr_t)d);
	if (d->bd_selproc) {
		selwakeup(d->bd_selproc, (int)d->bd_selcoll);
		d->bd_selcoll = 0;
		d->bd_selproc = 0;
	}
}

int
bpfwrite(dev, uio)
	dev_t dev;
	struct uio *uio;
{
	register struct bpf_d *d = &bpf_dtab[minor(dev)];
	struct ifnet *ifp;
	struct mbuf *m;
	int error, s;
	static struct sockaddr dst;

	if (d->bd_bif == 0)
		return (ENXIO);

	ifp = d->bd_bif->bif_ifp;

	if (uio->uio_resid == 0)
		return (0);
	if (uio->uio_resid > ifp->if_mtu)
		return (EMSGSIZE);

	error = bpf_movein(uio, (int)d->bd_bif->bif_dlt, &m, &dst);
	if (error)
		return (error);

	s = splnet();
	error = (*ifp->if_output)(ifp, m, &dst);
	splx(s);
	/*
	 * The driver frees the mbuf.
	 */
	return (error);
}

/*
 * Reset a descriptor by flushing its packet bufferand clearing the receive
 * and drop counts.  Should be called at splimp.
 */
static void
reset_d(d)
	struct bpf_d *d;
{
	if (d->bd_hbuf) {
		/* Free the hold buffer. */
		d->bd_fbuf = d->bd_hbuf;
		d->bd_hbuf = 0;
	}
	d->bd_slen = 0;
	d->bd_rcount = 0;
	d->bd_dcount = 0;
}

/*
 *  FIONREAD		Check for read packet available.
 *  SIOCGIFADDR		Get interface address - convenient hook to driver.
 *  BIOCGFLEN		Get max filter len.
 *  BIOCGBLEN		Get buffer len [for read()].
 *  BIOCSETF		Set ethernet read filter.
 *  BIOCFLUSH		Flush read packet buffer.
 *  BIOCPROMISC		Put interface into promiscuous mode.
 *  BIOCGDLT		Get link layer type.
 *  BIOCGETIF		Get interface name.
 *  BIOCSETIF		Set interface.
 *  BIOCSRTIMEOUT	Set read timeout.
 *  BIOCGRTIMEOUT	Get read timeout.
 *  BIOCGSTATS		Get packet stats.
 *  BIOCIMMEDIATE	Set immediate mode.
 */
/* ARGSUSED */
int
bpfioctl(dev, cmd, addr, flag)
	dev_t dev;
	int cmd;
	caddr_t addr;
	int flag;
{
	register struct bpf_d *d = &bpf_dtab[minor(dev)];
	int s, error = 0;

	switch (cmd) {

	default:
		error = EINVAL;
		break;

	/*
	 * Check for read packet available.
	 */
	case FIONREAD:
		{
			int n;

			s = splimp();
			n = d->bd_slen;
			if (d->bd_hbuf)
				n += d->bd_hlen;
			splx(s);

			*(int *)addr = n;
			break;
		}

	case SIOCGIFADDR:
		{
			struct ifnet *ifp;

			if (d->bd_bif == 0)
				error = EINVAL;
			else {
				ifp = d->bd_bif->bif_ifp;
				error =  (*ifp->if_ioctl)(ifp, cmd, addr);
			}
			break;
		}

	/*
	 * Get max filter len.
	 */
	case BIOCGFLEN:
		*(u_int *)addr = BPF_MAXINSNS;
		break;
	/*
	 * Get buffer len [for read()].
	 */
	case BIOCGBLEN:
		*(u_int *)addr = d->bd_bufsize;
		break;

	/*
	 * Set ethernet read filter.
	 */
        case BIOCSETF:
		error = bpf_setf(d, (struct bpf_program *)addr);
		break;

	/*
	 * Flush read packet buffer.
	 */
	case BIOCFLUSH:
		s = splimp();
		reset_d(d);
		splx(s);
		break;

	/*
	 * Put interface into promiscuous mode.
	 */
	case BIOCPROMISC:
		if (d->bd_bif == 0) {
			/*
			 * No interface attached yet.
			 */
			error = EINVAL;
			break;
		}
		s = splimp();
		if (d->bd_promisc == 0) {
			d->bd_promisc = 1;
			error = ifpromisc(d->bd_bif->bif_ifp, 1);
		}
		splx(s);
		break;

	/*
	 * Get device parameters.
	 */
	case BIOCGDLT:
		if (d->bd_bif == 0)
			error = EINVAL;
		else
			*(u_int *)addr = d->bd_bif->bif_dlt;
		break;

	/*
	 * Set interface name.
	 */
	case BIOCGETIF:
		if (d->bd_bif == 0)
			error = EINVAL;
		else
			bpf_ifname(d->bd_bif->bif_ifp, (struct ifreq *)addr);
		break;

	/*
	 * Set interface.
	 */
	case BIOCSETIF:
		error = bpf_setif(d, (struct ifreq *)addr);
		break;

	/*
	 * Set read timeout.
	 */
 	case BIOCSRTIMEOUT:
		{
			struct timeval *tv = (struct timeval *)addr;
			u_long msec;

			/* Compute number of milliseconds. */
			msec = tv->tv_sec * 1000 + tv->tv_usec / 1000;
			/* Scale milliseconds to ticks.  Assume hard
			   clock has millisecond or greater resolution
			   (i.e. tick >= 1000).  For 10ms hardclock,
			   tick/1000 = 10, so rtout<-msec/10. */
			d->bd_rtout = msec / (tick / 1000);
			break;
		}

	/*
	 * Get read timeout.
	 */
 	case BIOCGRTIMEOUT:
		{
			struct timeval *tv = (struct timeval *)addr;
			u_long msec = d->bd_rtout;

			msec *= tick / 1000;
			tv->tv_sec = msec / 1000;
			tv->tv_usec = msec % 1000;
			break;
		}

	/*
	 * Get packet stats.
	 */
	case BIOCGSTATS:
		{
			struct bpf_stat *bs = (struct bpf_stat *)addr;

			bs->bs_recv = d->bd_rcount;
			bs->bs_drop = d->bd_dcount;
			break;
		}

	/*
	 * Set immediate mode.
	 */
	case BIOCIMMEDIATE:
		d->bd_immediate = *(u_int *)addr;
		break;
	}
	return (error);
}

/*
 * Set d's packet filter program to 'fp'.  If 'd' already has a filter,
 * free it and replace it.  Returns EINVAL for bogus requests.
 */
int
bpf_setf(d, fp)
	struct bpf_d *d;
	struct bpf_program *fp;
{
	struct bpf_insn *fcode, *old;
	u_int flen, size;
	int s;

	old = d->bd_filter;
	if (fp->bf_insns == 0) {
		if (fp->bf_len != 0)
			return (EINVAL);
		s = splimp();
		d->bd_filter = 0;
		reset_d(d);
		splx(s);
		if (old != 0)
			free((caddr_t)old, M_DEVBUF);
		return (0);
	}
	flen = fp->bf_len;
	if (flen > BPF_MAXINSNS)
		return (EINVAL);

	size = flen * sizeof(*fp->bf_insns);
	fcode = (struct bpf_insn *)malloc(size, M_DEVBUF, M_WAITOK);
	if (copyin((caddr_t)fp->bf_insns, (caddr_t)fcode, size))
		return (EINVAL);

	if (bpf_validate(fcode, (int)flen)) {
		s = splimp();
		d->bd_filter = fcode;
		reset_d(d);
		splx(s);
		if (old != 0)
			free((caddr_t)old, M_DEVBUF);

		return (0);
	}
	free((caddr_t)fcode, M_DEVBUF);
	return (EINVAL);
}

/*
 * Detach 'd' from its current interface (if attached at all) and attach to
 * the interface named 'name'.  Return ioctl error code or 0.
 */
static int
bpf_setif(d, ifr)
	struct bpf_d *d;
	struct ifreq *ifr;
{
	struct bpf_if *bp;
	char *cp;
	int unit, s;

	/*
	 * Separate string into name part and unit number.  Put a null
	 * byte at the end of the name part, and compute the number.
	 * If the a unit number is unspecified, the default is 0,
	 * as initialized above.  XXX This should be common code.
	 */
	unit = 0;
	cp = ifr->ifr_name;
	cp[sizeof(ifr->ifr_name) - 1] = '\0';
	while (*cp++) {
		if (*cp >= '0' && *cp <= '9') {
			unit = *cp - '0';
			*cp++ = '\0';
			while (*cp)
				unit = 10 * unit + *cp++ - '0';
			break;
		}
	}
	/*
	 * Look through attached interfaces for the named one.
	 */
	for (bp = bpf_iflist; bp != 0; bp = bp->bif_next) {
		struct ifnet *ifp = bp->bif_ifp;

		if (ifp == 0 || unit != ifp->if_unit
		    || strcmp(ifp->if_name, ifr->ifr_name) != 0)
			continue;
		/*
		 * We found the requested interface.  If we're
		 * already attached to it, just flush the buffer.
		 * If it's not up, return an error.
		 */
		if ((ifp->if_flags & IFF_UP) == 0)
			return (ENETDOWN);
		s = splimp();
		if (bp != d->bd_bif) {
			if (d->bd_bif)
				/*
				 * Detach if attached to something else.
				 */
				bpf_detachd(d);

			bpf_attachd(d, bp);
		}
		reset_d(d);
		splx(s);
		return (0);
	}
	/* Not found. */
	return (ENXIO);
}

/*
 * Lookup the name of the 'ifp' interface and return it in 'ifr->ifr_name'.
 * We augment the ifp's base name with its unit number.
 */
static void
bpf_ifname(ifp, ifr)
	struct ifnet *ifp;
	struct ifreq *ifr;
{
	char *s = ifp->if_name;
	char *d = ifr->ifr_name;

	while (*d++ = *s++)
		;
	/* XXX Assume that unit number is less than 10. */
	*d++ = ifp->if_unit + '0';
	*d = '\0';
}

/*
 * Support for select() system call
 * Inspired by the code in tty.c for the same purpose.
 *
 * bpfselect - returns true iff the specific operation
 *	will not block indefinitely.  Otherwise, return
 *	false but make a note that a selwakeup() must be done.
 */
int
bpfselect(dev, rw, p)
	register dev_t dev;
	int rw;
	struct proc *p;
{
	register struct bpf_d *d;
	register int s;

	if (rw != FREAD)
		return (0);
	/*
	 * An imitation of the FIONREAD ioctl code.
	 */
	d = &bpf_dtab[minor(dev)];

	s = splimp();
	if (d->bd_slen != 0 || d->bd_hbuf && d->bd_hlen != 0) {
		/*
		 * There is data waiting.
		 */
		splx(s);
		return (1);
	}
	/*
	 * No data ready.  If there's already a select() waiting on this
	 * minor device then this is a collision.  This shouldn't happen
	 * because minors really should not be shared, but if a process
	 * forks while one of these is open, it is possible that both
	 * processes could select on the same descriptor.
	 */
	if (d->bd_selproc && d->bd_selproc->p_wchan == (caddr_t)&selwait)
		d->bd_selcoll = 1;
	else
		d->bd_selproc = p;

	splx(s);
	return (0);
}

/*
 * bpf_tap - incoming linkage from device drivers
 */
void
bpf_tap(arg, pkt, pktlen)
	caddr_t arg;
	register u_char *pkt;
	register u_int pktlen;
{
	struct bpf_if *bp;
	register struct bpf_d *d;
	register u_int slen;
	/*
	 * Note that the ipl does not have to be raised at this point.
	 * The only problem that could arise here is that if two different
	 * interfaces shared any data.  This is not the case.
	 */
	bp = (struct bpf_if *)arg;
	for (d = bp->bif_dlist; d != 0; d = d->bd_next) {
		++d->bd_rcount;
		if (d->bd_filter == 0) {
			catchpacket(d, pkt, pktlen, (u_int)-1, bcopy);
			continue;
		}
		slen = bpf_filter(d->bd_filter, pkt, pktlen, pktlen);
		if (slen != 0)
			catchpacket(d, pkt, pktlen, slen, bcopy);
	}
}

/*
 * Copy data from an mbuf chain into a buffer.  This code is derived
 * from m_copydata in sys/uipc_mbuf.c.
 */
static void
bpf_mcopy(src, dst, len)
	u_char *src;
	u_char *dst;
	register int len;
{
	register struct mbuf *m = (struct mbuf *)src;
	register unsigned count;

	while (len > 0) {
		if (m == 0)
			panic("bpf_mcopy");
		count = MIN(m->m_len, len);
		bcopy(mtod(m, caddr_t), (caddr_t)dst, count);
		m = m->m_next;
		dst += count;
		len -= count;
	}
}

/*
 * Length of ethernet and TCP/IP header with no IP options.
 */
#define BPF_MIN_SNAPLEN 50

/*
 * bpf_mtap - incoming linkage from device drivers, when packet
 *   is in an mbuf chain
 */
void
bpf_mtap(arg, m)
	caddr_t arg;
	struct mbuf *m;
{
	struct bpf_if *bp = (struct bpf_if *)arg;
	struct bpf_d *d;
	u_int pktlen, slen;
	struct mbuf *m0;

	pktlen = 0;
	m0 = m;
	while (m0) {
		pktlen += m0->m_len;
		m0 = m0->m_next;
	}
	for (d = bp->bif_dlist; d != 0; d = d->bd_next) {
		++d->bd_rcount;
		if (d->bd_filter == 0) {
			catchpacket(d, (u_char *)m, pktlen, (u_int)-1,
				    bpf_mcopy);
			continue;
		}
		slen = bpf_filter(d->bd_filter, (u_char *)m, pktlen, 0);
		if (slen != 0)
			catchpacket(d, (u_char *)m, pktlen, slen, bpf_mcopy);
	}
}

/*
 * Move the packet data from interface memory (pkt) into the
 * store buffer.  Return 1 if it's time to wakeup a listener (buffer full),
 * otherwise 0.  'copy' is the routine called to do the actual data
 * transfer.  'bcopy' is passed in to copy contiguous chunks, while
 * 'bpf_mcopy' is passed in to copy mbuf chains.  In the latter
 * case, 'pkt' is really an mbuf.
 */
static void
catchpacket(d, pkt, pktlen, snaplen, cpfn)
	register struct bpf_d *d;
	register u_char *pkt;
	register u_int pktlen, snaplen;
	register void (*cpfn)();
{
	register struct bpf_hdr *hp;
	register int totlen, curlen;
	register int hdrlen = d->bd_bif->bif_hdrlen;
	/*
	 * Figure out how many bytes to move.  If the packet is
	 * greater or equal to the snapshot length, transfer that
	 * much.  Otherwise, transfer the whole packet (unless
	 * we hit the buffer size limit).
	 */
	if (snaplen <= pktlen)
		totlen = snaplen + hdrlen;
	else {
		totlen = pktlen + hdrlen;
		if (totlen > d->bd_bufsize)
			totlen = d->bd_bufsize;
	}

	/*
	 * Round up the end of the previous packet to the next longword.
	 */
	curlen = BPF_WORDALIGN(d->bd_slen);
	if (curlen + totlen > d->bd_bufsize) {
		/*
		 * This packet will overflow the storage buffer.
		 * Rotate the buffers if we can, then wakeup any
		 * pending reads.
		 */
		if (d->bd_fbuf == 0) {
			/*
			 * We haven't completed the previous read yet,
			 * so drop the packet.
			 */
			++d->bd_dcount;
			return;
		}
		ROTATE_BUFFERS(d);
		bpf_wakeup(d);
		curlen = 0;
	}
	else if (d->bd_immediate)
		/*
		 * Immediate mode is set.  A packet arrived so any
		 * reads should be woken up.
		 */
		bpf_wakeup(d);

	/*
	 * Append the bpf header.
	 */
	hp = (struct bpf_hdr *)(d->bd_sbuf + curlen);
#ifdef sun
	uniqtime(&hp->bh_tstamp);
#else
#ifdef hp300
	microtime(&hp->bh_tstamp);
#else
	hp->bh_tstamp = time;
#endif
#endif
	hp->bh_datalen = pktlen;
	hp->bh_hdrlen = hdrlen;
	/*
	 * Copy the packet data into the store buffer and update its length.
	 */
	(*cpfn)(pkt, (u_char *)hp + hdrlen, (hp->bh_caplen = totlen - hdrlen));
	d->bd_slen = curlen + totlen;
}

/*
 * Initialize all nonzero fields of a descriptor.
 */
static int
bpf_initd(d)
	register struct bpf_d *d;
{
	d->bd_bufsize = bpf_bufsize;
	d->bd_fbuf = (caddr_t)malloc(d->bd_bufsize, M_DEVBUF, M_WAITOK);
	if (d->bd_fbuf == 0)
		return (ENOBUFS);

	d->bd_sbuf = (caddr_t)malloc(d->bd_bufsize, M_DEVBUF, M_WAITOK);
	if (d->bd_sbuf == 0) {
		free(d->bd_fbuf, M_DEVBUF);
		return (ENOBUFS);
	}
	d->bd_slen = 0;
	d->bd_hlen = 0;
	return (0);
}

/*
 * Register 'ifp' with bpf.  XXX
 * and 'driverp' is a pointer to the 'struct bpf_if *' in the driver's softc.
 */
void
bpfattach(driverp, ifp, dlt, hdrlen)
	caddr_t *driverp;
	struct ifnet *ifp;
	u_int dlt, hdrlen;
{
	struct bpf_if *bp;
	int i;

	bp = (struct bpf_if *)malloc(sizeof(*bp), M_DEVBUF, M_DONTWAIT);
	if (bp == 0)
		panic("bpfattach");

	bp->bif_dlist = 0;
	bp->bif_driverp = (struct bpf_if **)driverp;
	bp->bif_ifp = ifp;
	bp->bif_dlt = dlt;

	bp->bif_next = bpf_iflist;
	bpf_iflist = bp;

	*bp->bif_driverp = 0;

	/*
	 * Compute the length of the bpf header.  This is not necessarily
	 * equal to SIZEOF_BPF_HDR because we want to insert spacing such
	 * that the network layer header begins on a longword boundary (for
	 * performance reasons and to alleviate alignment restrictions).
	 */
	bp->bif_hdrlen = BPF_WORDALIGN(hdrlen + SIZEOF_BPF_HDR) - hdrlen;

	/*
	 * Mark all the descriptors free if this hasn't been done.
	 */
	if (!D_ISFREE(&bpf_dtab[0]))
		for (i = 0; i < NBPFILTER; ++i)
			D_MARKFREE(&bpf_dtab[i]);

	printf("bpf: %s%d attached\n", ifp->if_name, ifp->if_unit);
}

/* XXX This routine belongs in net/if.c. */
/*
 * Set/clear promiscuous mode on interface ifp based on the truth value`
 * of pswitch.  The calls are reference counted so that only the first
 * on request actually has an effect, as does the final off request.
 * Results are undefined if the off and on requests are not matched.
 */
int
ifpromisc(ifp, pswitch)
	struct ifnet *ifp;
	int pswitch;
{
	/*
	 * If the device is not configured up, we cannot put it in
	 * promiscuous mode.
	 */
	if ((ifp->if_flags & IFF_UP) == 0)
		return (ENETDOWN);

	if (pswitch) {
		if (ifp->if_pcount++ != 0)
			return (0);
		ifp->if_flags |= IFF_PROMISC;
	} else {
		if (--ifp->if_pcount > 0)
			return (0);
		ifp->if_flags &= ~IFF_PROMISC;
	}
	return ((*ifp->if_ioctl)(ifp, SIOCSIFFLAGS, (caddr_t)0));
}

#endif (NBPFILTER > 0)