xnu-517.11.1.tar.gz

[apple/xnu.git] / bsd / kern / uipc_mbuf.c

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * Copyright (c) 1982, 1986, 1988, 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)uipc_mbuf.c 8.2 (Berkeley) 1/4/94
 */
/* HISTORY
 *
 *      10/15/97 Annette DeSchon (deschon@apple.com)
 *              Fixed bug in which all cluster mbufs were broken up 
 *              into regular mbufs: Some clusters are now reserved.
 *              When a cluster is needed, regular mbufs are no longer
 *              used.  (Radar 1683621)
 *      20-May-95 Mac Gillon (mgillon) at NeXT
 *              New version based on 4.4
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/kernel.h>
#include <sys/syslog.h>
#include <sys/protosw.h>
#include <sys/domain.h>
#include <net/netisr.h>

#include <kern/queue.h>
#include <kern/kern_types.h>
#include <kern/sched_prim.h>

#include <IOKit/IOMapper.h>

#define _MCLREF(p)       (++mclrefcnt[mtocl(p)])
#define _MCLUNREF(p)     (--mclrefcnt[mtocl(p)] == 0)
#define _M_CLEAR_PKTHDR(mbuf_ptr)       (mbuf_ptr)->m_pkthdr.rcvif = NULL; \
                                                                        (mbuf_ptr)->m_pkthdr.len = 0; \
                                                                        (mbuf_ptr)->m_pkthdr.header = NULL; \
                                                                        (mbuf_ptr)->m_pkthdr.csum_flags = 0; \
                                                                        (mbuf_ptr)->m_pkthdr.csum_data = 0; \
                                                                        (mbuf_ptr)->m_pkthdr.aux = (struct mbuf*)NULL; \
                                                                        (mbuf_ptr)->m_pkthdr.reserved_1 = 0; \
                                                                        (mbuf_ptr)->m_pkthdr.vlan_tag = 0; \
                                                                        (mbuf_ptr)->m_pkthdr.reserved2 = NULL;

extern pmap_t kernel_pmap;    /* The kernel's pmap */
/* kernel translater */
extern ppnum_t pmap_find_phys(pmap_t pmap, addr64_t va);

decl_simple_lock_data(, mbuf_slock);
struct mbuf     *mfree;         /* mbuf free list */
struct  mbuf *mfreelater;       /* mbuf deallocation list */
extern vm_map_t mb_map;         /* special map */
int             m_want;         /* sleepers on mbufs */
extern int      nmbclusters;    /* max number of mapped clusters */
short           *mclrefcnt;     /* mapped cluster reference counts */
int             *mcl_paddr;
static ppnum_t mcl_paddr_base;  /* Handle returned by IOMapper::iovmAlloc() */
union mcluster  *mclfree;       /* mapped cluster free list */
int             max_linkhdr;    /* largest link-level header */
int             max_protohdr;   /* largest protocol header */
int             max_hdr;        /* largest link+protocol header */
int             max_datalen;    /* MHLEN - max_hdr */
struct mbstat   mbstat;         /* statistics */
union mcluster  *mbutl;         /* first mapped cluster address */
union mcluster  *embutl;        /* ending virtual address of mclusters */

static int      nclpp;          /* # clusters per physical page */
static char     mbfail[] = "mbuf not mapped";

static int m_howmany();

/* The number of cluster mbufs that are allocated, to start. */
#define MINCL   max(16, 2)

static int mbuf_expand_thread_wakeup = 0;
static int mbuf_expand_mcl = 0;
static int mbuf_expand_thread_initialized = 0;

static void mbuf_expand_thread_init(void);

#if 0
static int mfree_munge = 0;
#if 0
#define _MFREE_MUNGE(m) {                                               \
    if (mfree_munge)                                                    \
        {   int i;                                                      \
            vm_offset_t *element = (vm_offset_t *)(m);                  \
            for (i = 0;                                                 \
                 i < sizeof(struct mbuf)/sizeof(vm_offset_t);           \
                 i++)                                                   \
                    (element)[i] = 0xdeadbeef;                          \
        }                                                               \
}
#else
void
munge_mbuf(struct mbuf *m)
{
    int i;
    vm_offset_t *element = (vm_offset_t *)(m);
    for (i = 0;
            i < sizeof(struct mbuf)/sizeof(vm_offset_t);
            i++)
            (element)[i] = 0xdeadbeef;
}
#define _MFREE_MUNGE(m) {  \
    if (mfree_munge)       \
        munge_mbuf(m);     \
}
#endif
#else
#define _MFREE_MUNGE(m)
#endif


#define _MINTGET(m, type) {                                             \
        MBUF_LOCK();                                                    \
        if (((m) = mfree) != 0) {                                       \
                MCHECK(m);                                              \
                ++mclrefcnt[mtocl(m)];                                  \
                mbstat.m_mtypes[MT_FREE]--;                             \
                mbstat.m_mtypes[(type)]++;                              \
                mfree = (m)->m_next;                                    \
        }                                                               \
        MBUF_UNLOCK();                                                  \
}
        

void
mbinit()
{
        int s,m;
        int initmcl = 32;
        int mcl_pages;

        if (nclpp)
                return;
        nclpp = round_page_32(MCLBYTES) / MCLBYTES;     /* see mbufgc() */
        if (nclpp < 1) nclpp = 1;
        MBUF_LOCKINIT();
//      NETISR_LOCKINIT();

        mbstat.m_msize = MSIZE;
        mbstat.m_mclbytes = MCLBYTES;
        mbstat.m_minclsize = MINCLSIZE;
        mbstat.m_mlen = MLEN;
        mbstat.m_mhlen = MHLEN;

        if (nmbclusters == 0)
                nmbclusters = NMBCLUSTERS;
        MALLOC(mclrefcnt, short *, nmbclusters * sizeof (short),
                                        M_TEMP, M_WAITOK);
        if (mclrefcnt == 0)
                panic("mbinit");
        for (m = 0; m < nmbclusters; m++)
                mclrefcnt[m] = -1;

        /* Calculate the number of pages assigned to the cluster pool */
        mcl_pages = nmbclusters/(PAGE_SIZE/CLBYTES);
        MALLOC(mcl_paddr, int *, mcl_pages * sizeof(int), M_TEMP, M_WAITOK);
        if (mcl_paddr == 0)
                panic("mbinit1");
        /* Register with the I/O Bus mapper */
        mcl_paddr_base = IOMapperIOVMAlloc(mcl_pages);
        bzero((char *)mcl_paddr, mcl_pages * sizeof(int));

        embutl = (union mcluster *)((unsigned char *)mbutl + (nmbclusters * MCLBYTES));

        PE_parse_boot_arg("initmcl", &initmcl);
        
        if (m_clalloc(max(PAGE_SIZE/CLBYTES, 1) * initmcl, M_WAIT) == 0)
                goto bad;
        MBUF_UNLOCK();

    (void) kernel_thread(kernel_task, mbuf_expand_thread_init);

        return;
bad:
                panic("mbinit");
}

/*
 * Allocate some number of mbuf clusters
 * and place on cluster free list.
 */
/* ARGSUSED */
m_clalloc(ncl, nowait)
        register int ncl;
        int nowait;
{
        register union mcluster *mcl;
        register int i;
        vm_size_t size;
        static char doing_alloc;

        /*
         * Honor the caller's wish to block or not block.
         * We have a way to grow the pool asynchronously,
         * by kicking the dlil_input_thread.
         */
        if ((i = m_howmany()) <= 0)
                goto out;

        if ((nowait == M_DONTWAIT))
                goto out;

        if (ncl < i) 
                ncl = i;
        size = round_page_32(ncl * MCLBYTES);
        mcl = (union mcluster *)kmem_mb_alloc(mb_map, size);

        if (mcl == 0 && ncl > 1) {
                size = round_page_32(MCLBYTES); /* Try for 1 if failed */
                mcl = (union mcluster *)kmem_mb_alloc(mb_map, size);
        }

        if (mcl) {
                MBUF_LOCK();
                ncl = size / MCLBYTES;
                for (i = 0; i < ncl; i++) {
                        if (++mclrefcnt[mtocl(mcl)] != 0)
                                panic("m_clalloc already there");
                        if (((int)mcl & PAGE_MASK) == 0) {
                                ppnum_t offset = ((char *)mcl - (char *)mbutl)/PAGE_SIZE;
                                ppnum_t new_page = pmap_find_phys(kernel_pmap, (vm_address_t) mcl);

                                /*
                                 * In the case of no mapper being available
                                 * the following code nops and returns the
                                 * input page, if there is a mapper the I/O
                                 * page appropriate is returned.
                                 */
                                new_page = IOMapperInsertPage(mcl_paddr_base, offset, new_page);
                                mcl_paddr[offset] = new_page << 12;
                        }

                        mcl->mcl_next = mclfree;
                        mclfree = mcl++;
                }
                mbstat.m_clfree += ncl;
                mbstat.m_clusters += ncl;
                return (ncl);
        } /* else ... */
out:
        MBUF_LOCK();

        /* 
         * When non-blocking we kick the dlil thread if we havve to grow the 
         * pool or if the number of free clusters is less than requested.
         */
        if ((nowait == M_DONTWAIT) && (i > 0 || ncl >= mbstat.m_clfree)) {
                mbuf_expand_mcl = 1; 
                if (mbuf_expand_thread_initialized)
                        wakeup((caddr_t)&mbuf_expand_thread_wakeup);
        }

        if (mbstat.m_clfree >= ncl) 
             return 1;

        return 0;
}

/*
 * Add more free mbufs by cutting up a cluster.
 */
m_expand(canwait)
        int canwait;
{
        register caddr_t mcl;

        if (mbstat.m_clfree < (mbstat.m_clusters >> 4))
          /* 1/16th of the total number of cluster mbufs allocated is
             reserved for large packets.  The number reserved must
             always be < 1/2, or future allocation will be prevented.
          */
                return 0;

        MCLALLOC(mcl, canwait);
        if (mcl) {
                register struct mbuf *m = (struct mbuf *)mcl;
                register int i = NMBPCL;
                MBUF_LOCK();
                mbstat.m_mtypes[MT_FREE] += i;
                mbstat.m_mbufs += i;
                while (i--) {
                        _MFREE_MUNGE(m);
                        m->m_type = MT_FREE;
                        m->m_next = mfree;
                        mfree = m++;
                }
                i = m_want;
                m_want = 0;
                MBUF_UNLOCK();
                if (i) wakeup((caddr_t)&mfree);
                return 1;
        }
        return 0;
}

/*
 * When MGET failes, ask protocols to free space when short of memory,
 * then re-attempt to allocate an mbuf.
 */
struct mbuf *
m_retry(canwait, type)
        int canwait, type;
{
        register struct mbuf *m;
        int wait, s;
        funnel_t * fnl;
        int fnl_switch = 0;
        boolean_t funnel_state;

        for (;;) {
                (void) m_expand(canwait);
                _MINTGET(m, type);
                if (m) {
                        (m)->m_next = (m)->m_nextpkt = 0;
                        (m)->m_type = (type);
                        (m)->m_data = (m)->m_dat;
                        (m)->m_flags = 0;
                }
                if (m || canwait == M_DONTWAIT)
                        break;
                MBUF_LOCK();
                wait = m_want++;
                mbuf_expand_mcl = 1;
                if (wait == 0)
                        mbstat.m_drain++;
                else
                        mbstat.m_wait++;
                MBUF_UNLOCK();
        
                if (mbuf_expand_thread_initialized)
                        wakeup((caddr_t)&mbuf_expand_thread_wakeup);

                /* 
                 * Need to be inside network funnel for m_reclaim because it calls into the 
                 * socket domains and tsleep end-up calling splhigh
                 */
                fnl = thread_funnel_get();
                if (wait == 0 && fnl == network_flock) {
                        m_reclaim();
                } else if (fnl != THR_FUNNEL_NULL) {
                        /* Sleep with a small timeout as insurance */
                        (void) tsleep((caddr_t)&mfree, PZERO-1, "m_retry", hz); 
                } else {
                        /* We are called from a non-BSD context: use mach primitives */
                        u_int64_t       abstime = 0;

                        assert_wait((event_t)&mfree, THREAD_UNINT);
                        clock_interval_to_deadline(hz, NSEC_PER_SEC / hz, &abstime);
                        thread_set_timer_deadline(abstime);
                        if (thread_block(THREAD_CONTINUE_NULL) != THREAD_TIMED_OUT)
                                thread_cancel_timer();
                }
        }
        if (m == 0)
                mbstat.m_drops++;
        return (m);
}

/*
 * As above; retry an MGETHDR.
 */
struct mbuf *
m_retryhdr(canwait, type)
        int canwait, type;
{
        register struct mbuf *m;

        if (m = m_retry(canwait, type)) {
                m->m_flags |= M_PKTHDR;
                m->m_data = m->m_pktdat;
                _M_CLEAR_PKTHDR(m);
        }
        return (m);
}

m_reclaim()
{
        register struct domain *dp;
        register struct protosw *pr;

        for (dp = domains; dp; dp = dp->dom_next)
                for (pr = dp->dom_protosw; pr; pr = pr->pr_next)
                        if (pr->pr_drain)
                                (*pr->pr_drain)();
        mbstat.m_drain++;
}

/*
 * Space allocation routines.
 * These are also available as macros
 * for critical paths.
 */
struct mbuf *
m_get(nowait, type)
        int nowait, type;
{
        register struct mbuf *m;

        _MINTGET(m, type);
        if (m) {
                m->m_next = m->m_nextpkt = 0;
                m->m_type = type;
                m->m_data = m->m_dat;
                m->m_flags = 0;
        } else
                (m) = m_retry(nowait, type);

        return (m);
}

struct mbuf *
m_gethdr(nowait, type)
        int nowait, type;
{
        register struct mbuf *m;

        _MINTGET(m, type);
        if (m) {
                m->m_next = m->m_nextpkt = 0;
                m->m_type = type;
                m->m_data = m->m_pktdat;
                m->m_flags = M_PKTHDR;
                _M_CLEAR_PKTHDR(m)
        } else
                m = m_retryhdr(nowait, type);

        return m;
}

struct mbuf *
m_getclr(nowait, type)
        int nowait, type;
{
        register struct mbuf *m;

        MGET(m, nowait, type);
        if (m == 0)
                return (0);
        bzero(mtod(m, caddr_t), MLEN);
        return (m);
}

struct mbuf *
m_free(m)
        struct mbuf *m;
{
        struct mbuf *n = m->m_next;
        int i, s;

        if (m->m_type == MT_FREE)
                panic("freeing free mbuf");

        /* Free the aux data if there is any */
        if ((m->m_flags & M_PKTHDR) && m->m_pkthdr.aux)
        {
                m_freem(m->m_pkthdr.aux);
        }

        MBUF_LOCK();
        if ((m->m_flags & M_EXT)) 
    {
                if (MCLHASREFERENCE(m)) {
                        remque((queue_t)&m->m_ext.ext_refs);
                } else if (m->m_ext.ext_free == NULL) {
                        union mcluster *mcl= (union mcluster *)m->m_ext.ext_buf;
                        if (_MCLUNREF(mcl)) {
                                mcl->mcl_next = mclfree;
                                mclfree = mcl;
                                ++mbstat.m_clfree;
                        } 
#ifdef COMMENT_OUT
/* *** Since m_split() increments "mclrefcnt[mtocl(m->m_ext.ext_buf)]", 
       and AppleTalk ADSP uses m_split(), this incorrect sanity check
       caused a panic.  
*** */
                        else    /* sanity check - not referenced this way */
                                panic("m_free m_ext cluster not free");
#endif
                } else {
                        (*(m->m_ext.ext_free))(m->m_ext.ext_buf,
                            m->m_ext.ext_size, m->m_ext.ext_arg);
                }
        }
        mbstat.m_mtypes[m->m_type]--;
        (void) _MCLUNREF(m);
        _MFREE_MUNGE(m);
        m->m_type = MT_FREE;
        mbstat.m_mtypes[m->m_type]++;
        m->m_flags = 0;
        m->m_next = mfree;
        m->m_len = 0;
        mfree = m;
        i = m_want;
        m_want = 0;
        MBUF_UNLOCK();
        if (i) wakeup((caddr_t)&mfree);
        return (n);
}

/* m_mclget() add an mbuf cluster to a normal mbuf */
struct mbuf *
m_mclget(m, nowait)
        struct mbuf *m;
        int nowait;
{
        MCLALLOC(m->m_ext.ext_buf, nowait);
        if (m->m_ext.ext_buf) {
                m->m_data = m->m_ext.ext_buf;
                m->m_flags |= M_EXT;
                m->m_ext.ext_size = MCLBYTES;
                m->m_ext.ext_free = 0;
                m->m_ext.ext_refs.forward = m->m_ext.ext_refs.backward =
                        &m->m_ext.ext_refs;
        }
        
    return m;
}

/* m_mclalloc() allocate an mbuf cluster */
caddr_t
m_mclalloc( nowait)
    int nowait;
{
    caddr_t p;
        
        (void)m_clalloc(1, nowait);
        if ((p = (caddr_t)mclfree)) {
                ++mclrefcnt[mtocl(p)];
                mbstat.m_clfree--;
                mclfree = ((union mcluster *)p)->mcl_next;
        } else {
                mbstat.m_drops++;
        }
        MBUF_UNLOCK();
        
        return p;
}

/* m_mclfree() releases a reference to a cluster allocated by MCLALLOC,
 * freeing the cluster if the reference count has reached 0. */
void
m_mclfree(p)
    caddr_t p;
{
        MBUF_LOCK();
        if (--mclrefcnt[mtocl(p)] == 0) {
                ((union mcluster *)(p))->mcl_next = mclfree;
                mclfree = (union mcluster *)(p);
                mbstat.m_clfree++;
        }
        MBUF_UNLOCK();
}

/* mcl_hasreference() checks if a cluster of an mbuf is referenced by another mbuf */
int
m_mclhasreference(m)
    struct mbuf *m;
{
    return (m->m_ext.ext_refs.forward != &(m->m_ext.ext_refs));
}

/* */
void
m_copy_pkthdr(to, from)
    struct mbuf *to, *from;
{
        to->m_pkthdr = from->m_pkthdr;
        from->m_pkthdr.aux = (struct mbuf *)NULL;
        to->m_flags = from->m_flags & M_COPYFLAGS;
        to->m_data = (to)->m_pktdat;
}

/* Best effort to get a mbuf cluster + pkthdr under one lock.
 * If we don't have them avail, just bail out and use the regular
 * path.
 * Used by drivers to allocated packets on receive ring.
 */
struct mbuf *
m_getpacket(void)
{
        struct mbuf *m;
        m_clalloc(1, M_DONTWAIT); /* takes the MBUF_LOCK, but doesn't release it... */
        if ((mfree != 0) && (mclfree != 0)) {   /* mbuf + cluster are available */
                m = mfree;
                mfree = m->m_next;
                MCHECK(m);
                ++mclrefcnt[mtocl(m)];
                mbstat.m_mtypes[MT_FREE]--;
                mbstat.m_mtypes[MT_DATA]++;
                m->m_ext.ext_buf = (caddr_t)mclfree; /* get the cluster */
                ++mclrefcnt[mtocl(m->m_ext.ext_buf)];
                mbstat.m_clfree--;
                mclfree = ((union mcluster *)(m->m_ext.ext_buf))->mcl_next;

                m->m_next = m->m_nextpkt = 0;
                m->m_type = MT_DATA;
                m->m_data = m->m_ext.ext_buf;
                m->m_flags = M_PKTHDR | M_EXT;
                _M_CLEAR_PKTHDR(m)
                          m->m_ext.ext_free = 0;
                m->m_ext.ext_size = MCLBYTES;
                m->m_ext.ext_refs.forward = m->m_ext.ext_refs.backward =
                     &m->m_ext.ext_refs;
                MBUF_UNLOCK();
        }
        else { /* slow path: either mbuf or cluster need to be allocated anyway */
                MBUF_UNLOCK();

                MGETHDR(m, M_WAITOK, MT_DATA );

                if ( m == 0 ) 
                        return (NULL); 

                MCLGET( m, M_WAITOK );
                if ( ( m->m_flags & M_EXT ) == 0 )
                {
                     m_free(m); m = 0;
                }
        }
        return (m);
}


/*
 * return a list of mbuf hdrs that point to clusters...
 * try for num_needed, if this can't be met, return whatever
 * number were available... set up the first num_with_pkthdrs
 * with mbuf hdrs configured as packet headers... these are
 * chained on the m_nextpkt field... any packets requested beyond
 * this are chained onto the last packet header's m_next field.
 */
struct mbuf *
m_getpackets(int num_needed, int num_with_pkthdrs, int how)
{
        struct mbuf *m;
        struct mbuf **np, *top;

        top = NULL;
        np = &top;

        m_clalloc(num_needed, how);     /* takes the MBUF_LOCK, but doesn't release it... */

        while (num_needed--) {
            if (mfree && mclfree) {     /* mbuf + cluster are available */
                m = mfree;
                MCHECK(m);
                mfree = m->m_next;
                ++mclrefcnt[mtocl(m)];
                mbstat.m_mtypes[MT_FREE]--;
                mbstat.m_mtypes[MT_DATA]++;
                m->m_ext.ext_buf = (caddr_t)mclfree; /* get the cluster */
                ++mclrefcnt[mtocl(m->m_ext.ext_buf)];
                mbstat.m_clfree--;
                mclfree = ((union mcluster *)(m->m_ext.ext_buf))->mcl_next;

                m->m_next = m->m_nextpkt = 0;
                m->m_type = MT_DATA;
                m->m_data = m->m_ext.ext_buf;
                m->m_ext.ext_free = 0;
                m->m_ext.ext_size = MCLBYTES;
                m->m_ext.ext_refs.forward = m->m_ext.ext_refs.backward = &m->m_ext.ext_refs;

                if (num_with_pkthdrs == 0)
                    m->m_flags = M_EXT;
                else {
                    m->m_flags = M_PKTHDR | M_EXT;
                    _M_CLEAR_PKTHDR(m);

                    num_with_pkthdrs--;
                }

            } else {

                MBUF_UNLOCK();

                if (num_with_pkthdrs == 0) {
                    MGET(m, how, MT_DATA );
                } else {
                    MGETHDR(m, how, MT_DATA);

                    num_with_pkthdrs--;
                }
                if (m == 0)
                    return(top);

                MCLGET(m, how);
                if ((m->m_flags & M_EXT) == 0) {
                    m_free(m);
                    return(top);
                }
                MBUF_LOCK();
            }
            *np = m; 

            if (num_with_pkthdrs)
                np = &m->m_nextpkt;
            else
                np = &m->m_next;
        }
        MBUF_UNLOCK();

        return (top);
}


/*
 * return a list of mbuf hdrs set up as packet hdrs
 * chained together on the m_nextpkt field
 */
struct mbuf *
m_getpackethdrs(int num_needed, int how)
{
        struct mbuf *m;
        struct mbuf **np, *top;

        top = NULL;
        np = &top;

        MBUF_LOCK();

        while (num_needed--) {
            if (m = mfree) {    /* mbufs are available */
                MCHECK(m);
                mfree = m->m_next;
                ++mclrefcnt[mtocl(m)];
                mbstat.m_mtypes[MT_FREE]--;
                mbstat.m_mtypes[MT_DATA]++;

                m->m_next = m->m_nextpkt = 0;
                m->m_type = MT_DATA;
                m->m_flags = M_PKTHDR;
                m->m_data = m->m_pktdat;
                _M_CLEAR_PKTHDR(m);

            } else {

                MBUF_UNLOCK();

                m = m_retryhdr(how, MT_DATA);

                if (m == 0)
                    return(top);

                MBUF_LOCK();
            }
            *np = m; 
            np = &m->m_nextpkt;
        }
        MBUF_UNLOCK();

        return (top);
}


/* free and mbuf list (m_nextpkt) while following m_next under one lock.
 * returns the count for mbufs packets freed. Used by the drivers.
 */
int 
m_freem_list(m)
        struct mbuf *m;
{
        struct mbuf *nextpkt;
        int i, count=0;

        MBUF_LOCK();

        while (m) {
                if (m) 
                        nextpkt = m->m_nextpkt; /* chain of linked mbufs from driver */
                else 
                        nextpkt = 0;

                count++;

                while (m) { /* free the mbuf chain (like mfreem) */
                        
                        struct mbuf *n;

                        /* Free the aux data if there is any */
                        if ((m->m_flags & M_PKTHDR) && m->m_pkthdr.aux) {
                                /*
                                 * Treat the current m as the nextpkt and set m
                                 * to the aux data. Preserve nextpkt in m->m_nextpkt.
                                 * This lets us free the aux data in this loop
                                 * without having to call m_freem recursively,
                                 * which wouldn't work because we've still got
                                 * the lock.
                                 */
                                m->m_nextpkt = nextpkt;
                                nextpkt = m;
                                m = nextpkt->m_pkthdr.aux;
                                nextpkt->m_pkthdr.aux = NULL;
                        }

                        n = m->m_next;

                        if (n && n->m_nextpkt)
                                panic("m_freem_list: m_nextpkt of m_next != NULL");
                        if (m->m_type == MT_FREE)
                                panic("freeing free mbuf");

                        if (m->m_flags & M_EXT) {
                                if (MCLHASREFERENCE(m)) {
                                        remque((queue_t)&m->m_ext.ext_refs);
                                } else if (m->m_ext.ext_free == NULL) {
                                        union mcluster *mcl= (union mcluster *)m->m_ext.ext_buf;
                                        if (_MCLUNREF(mcl)) {
                                                mcl->mcl_next = mclfree;
                                                mclfree = mcl;
                                                ++mbstat.m_clfree;
                                        } 
                                } else {
                                        (*(m->m_ext.ext_free))(m->m_ext.ext_buf,
                                            m->m_ext.ext_size, m->m_ext.ext_arg);
                                }
                        }
                        mbstat.m_mtypes[m->m_type]--;
                        (void) _MCLUNREF(m);
              _MFREE_MUNGE(m);
                        mbstat.m_mtypes[MT_FREE]++;
                        m->m_type = MT_FREE;
                        m->m_flags = 0;
                        m->m_len = 0;
                        m->m_next = mfree;
                        mfree = m;
                        m = n;
                }
                m = nextpkt; /* bump m with saved nextpkt if any */
        }
        if (i = m_want)
                m_want = 0;

        MBUF_UNLOCK();

        if (i)
                wakeup((caddr_t)&mfree);

        return (count);
}

void
m_freem(m)
        register struct mbuf *m;
{
        while (m)
                m = m_free(m);
}

/*
 * Mbuffer utility routines.
 */
/*
 * Compute the amount of space available
 * before the current start of data in an mbuf.
 */
m_leadingspace(m)
register struct mbuf *m;
{
        if (m->m_flags & M_EXT) {
                if (MCLHASREFERENCE(m))
                        return(0);
                return (m->m_data - m->m_ext.ext_buf);
        }
        if (m->m_flags & M_PKTHDR)
                return (m->m_data - m->m_pktdat);
        return (m->m_data - m->m_dat);
}

/*
 * Compute the amount of space available
 * after the end of data in an mbuf.
 */
m_trailingspace(m)
register struct mbuf *m;
{
        if (m->m_flags & M_EXT) {
                if (MCLHASREFERENCE(m))
                        return(0);
                return (m->m_ext.ext_buf + m->m_ext.ext_size -
                        (m->m_data + m->m_len));
        }
        return (&m->m_dat[MLEN] - (m->m_data + m->m_len));
}

/*
 * Lesser-used path for M_PREPEND:
 * allocate new mbuf to prepend to chain,
 * copy junk along.
 * Does not adjust packet header length.
 */
struct mbuf *
m_prepend(m, len, how)
        register struct mbuf *m;
        int len, how;
{
        struct mbuf *mn;

        MGET(mn, how, m->m_type);
        if (mn == (struct mbuf *)NULL) {
                m_freem(m);
                return ((struct mbuf *)NULL);
        }
        if (m->m_flags & M_PKTHDR) {
                M_COPY_PKTHDR(mn, m);
                m->m_flags &= ~M_PKTHDR;
        }
        mn->m_next = m;
        m = mn;
        if (len < MHLEN)
                MH_ALIGN(m, len);
        m->m_len = len;
        return (m);
}

/*
 * Replacement for old M_PREPEND macro:
 * allocate new mbuf to prepend to chain,
 * copy junk along, and adjust length.
 * 
 */
struct mbuf *
m_prepend_2(m, len, how)
        register struct mbuf *m;
        int len, how;
{
        if (M_LEADINGSPACE(m) >= len) {
                m->m_data -= len;
                m->m_len += len;
        } else {
                m = m_prepend(m, len, how);
        }
        if ((m) && (m->m_flags & M_PKTHDR))
                m->m_pkthdr.len += len;
        return (m);
}

/*
 * Make a copy of an mbuf chain starting "off0" bytes from the beginning,
 * continuing for "len" bytes.  If len is M_COPYALL, copy to end of mbuf.
 * The wait parameter is a choice of M_WAIT/M_DONTWAIT from caller.
 */
int MCFail;

struct mbuf *
m_copym(m, off0, len, wait)
        register struct mbuf *m;
        int off0, wait;
        register int len;
{
        register struct mbuf *n, **np;
        register int off = off0;
        struct mbuf *top;
        int copyhdr = 0;

        if (off < 0 || len < 0)
                panic("m_copym");
        if (off == 0 && m->m_flags & M_PKTHDR)
                copyhdr = 1;

        while (off >= m->m_len) {
                if (m == 0)
                        panic("m_copym");
                off -= m->m_len;
                m = m->m_next;
        }
        np = &top;
        top = 0;

        MBUF_LOCK();

        while (len > 0) {
                if (m == 0) {
                        if (len != M_COPYALL)
                                panic("m_copym");
                        break;
                }
                if (n = mfree) {
                        MCHECK(n);
                        ++mclrefcnt[mtocl(n)];
                        mbstat.m_mtypes[MT_FREE]--;
                        mbstat.m_mtypes[m->m_type]++;
                        mfree = n->m_next;
                        n->m_next = n->m_nextpkt = 0;
                        n->m_type = m->m_type;
                        n->m_data = n->m_dat;
                        n->m_flags = 0;
                } else {
                        MBUF_UNLOCK();
                        n = m_retry(wait, m->m_type);
                        MBUF_LOCK();
                }
                *np = n;

                if (n == 0)
                        goto nospace;
                if (copyhdr) {
                        M_COPY_PKTHDR(n, m);
                        if (len == M_COPYALL)
                                n->m_pkthdr.len -= off0;
                        else
                                n->m_pkthdr.len = len;
                        copyhdr = 0;
                }
                if (len == M_COPYALL) {
                    if (min(len, (m->m_len - off)) == len) {
                        printf("m->m_len %d - off %d = %d, %d\n", 
                               m->m_len, off, m->m_len - off,
                               min(len, (m->m_len - off)));
                    }
                }
                n->m_len = min(len, (m->m_len - off));
                if (n->m_len == M_COPYALL) {
                    printf("n->m_len == M_COPYALL, fixing\n");
                    n->m_len = MHLEN;
                }
                if (m->m_flags & M_EXT) {
                        n->m_ext = m->m_ext;
                        insque((queue_t)&n->m_ext.ext_refs, (queue_t)&m->m_ext.ext_refs);
                        n->m_data = m->m_data + off;
                        n->m_flags |= M_EXT;
                } else {
                        bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
                            (unsigned)n->m_len);
                }
                if (len != M_COPYALL)
                        len -= n->m_len;
                off = 0;
                m = m->m_next;
                np = &n->m_next;
        }
        MBUF_UNLOCK();

        if (top == 0)
                MCFail++;

        return (top);
nospace:
        MBUF_UNLOCK();

        m_freem(top);
        MCFail++;
        return (0);
}


/*
 * equivilent to m_copym except that all necessary
 * mbuf hdrs are allocated within this routine
 * also, the last mbuf and offset accessed are passed
 * out and can be passed back in to avoid having to
 * rescan the entire mbuf list (normally hung off of the socket)
 */
struct mbuf *
m_copym_with_hdrs(m, off0, len, wait, m_last, m_off)
        register struct mbuf *m;
        int off0, wait;
        register int len;
        struct mbuf **m_last;
        int          *m_off;
{
        register struct mbuf *n, **np;
        register int off = off0;
        struct mbuf *top = 0;
        int copyhdr = 0;
        int type;

        if (off == 0 && m->m_flags & M_PKTHDR)
                copyhdr = 1;

        if (*m_last) {
                m   = *m_last;
                off = *m_off;
        } else {
                while (off >= m->m_len) {
                        off -= m->m_len;
                        m = m->m_next;
                }
        }
        MBUF_LOCK();

        while (len > 0) {
                if (top == 0)
                        type = MT_HEADER;
                else {
                        if (m == 0)
                                panic("m_gethdr_and_copym");
                        type = m->m_type;
                }
                if (n = mfree) {
                        MCHECK(n);
                        ++mclrefcnt[mtocl(n)];
                        mbstat.m_mtypes[MT_FREE]--;
                        mbstat.m_mtypes[type]++;
                        mfree = n->m_next;
                        n->m_next = n->m_nextpkt = 0;
                        n->m_type = type;

                        if (top) {
                                n->m_data = n->m_dat;
                                n->m_flags = 0;
                        } else {
                                n->m_data = n->m_pktdat;
                                n->m_flags = M_PKTHDR;
                                _M_CLEAR_PKTHDR(n);
                        }
                } else {
                        MBUF_UNLOCK();
                        if (top)
                                n = m_retry(wait, type);
                        else
                                n = m_retryhdr(wait, type);
                        MBUF_LOCK();
                }
                if (n == 0)
                        goto nospace;
                if (top == 0) {
                        top = n;
                        np = &top->m_next;
                        continue;
                } else
                        *np = n;

                if (copyhdr) {
                        M_COPY_PKTHDR(n, m);
                        n->m_pkthdr.len = len;
                        copyhdr = 0;
                }
                n->m_len = min(len, (m->m_len - off));

                if (m->m_flags & M_EXT) {
                        n->m_ext = m->m_ext;
                        insque((queue_t)&n->m_ext.ext_refs, (queue_t)&m->m_ext.ext_refs);
                        n->m_data = m->m_data + off;
                        n->m_flags |= M_EXT;
                } else {
                        bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
                            (unsigned)n->m_len);
                }
                len -= n->m_len;
                
                if (len == 0) {
                        if ((off + n->m_len) == m->m_len) {
                               *m_last = m->m_next;
                               *m_off  = 0;
                        } else {
                               *m_last = m;
                               *m_off  = off + n->m_len;
                        }
                        break;
                }
                off = 0;
                m = m->m_next;
                np = &n->m_next;
        }
        MBUF_UNLOCK();

        return (top);
nospace:
        MBUF_UNLOCK();

        if (top)
                m_freem(top);
        MCFail++;
        return (0);
}


/*
 * Copy data from an mbuf chain starting "off" bytes from the beginning,
 * continuing for "len" bytes, into the indicated buffer.
 */
void m_copydata(m, off, len, cp)
        register struct mbuf *m;
        register int off;
        register int len;
        caddr_t cp;
{
        register unsigned count;

        if (off < 0 || len < 0)
                panic("m_copydata");
        while (off > 0) {
                if (m == 0)
                        panic("m_copydata");
                if (off < m->m_len)
                        break;
                off -= m->m_len;
                m = m->m_next;
        }
        while (len > 0) {
                if (m == 0)
                        panic("m_copydata");
                count = min(m->m_len - off, len);
                bcopy(mtod(m, caddr_t) + off, cp, count);
                len -= count;
                cp += count;
                off = 0;
                m = m->m_next;
        }
}

/*
 * Concatenate mbuf chain n to m.
 * Both chains must be of the same type (e.g. MT_DATA).
 * Any m_pkthdr is not updated.
 */
void m_cat(m, n)
        register struct mbuf *m, *n;
{
        while (m->m_next)
                m = m->m_next;
        while (n) {
                if (m->m_flags & M_EXT ||
                    m->m_data + m->m_len + n->m_len >= &m->m_dat[MLEN]) {
                        /* just join the two chains */
                        m->m_next = n;
                        return;
                }
                /* splat the data from one into the other */
                bcopy(mtod(n, caddr_t), mtod(m, caddr_t) + m->m_len,
                    (u_int)n->m_len);
                m->m_len += n->m_len;
                n = m_free(n);
        }
}

void
m_adj(mp, req_len)
        struct mbuf *mp;
        int req_len;
{
        register int len = req_len;
        register struct mbuf *m;
        register count;

        if ((m = mp) == NULL)
                return;
        if (len >= 0) {
                /*
                 * Trim from head.
                 */
                while (m != NULL && len > 0) {
                        if (m->m_len <= len) {
                                len -= m->m_len;
                                m->m_len = 0;
                                m = m->m_next;
                        } else {
                                m->m_len -= len;
                                m->m_data += len;
                                len = 0;
                        }
                }
                m = mp;
                if (m->m_flags & M_PKTHDR)
                        m->m_pkthdr.len -= (req_len - len);
        } else {
                /*
                 * Trim from tail.  Scan the mbuf chain,
                 * calculating its length and finding the last mbuf.
                 * If the adjustment only affects this mbuf, then just
                 * adjust and return.  Otherwise, rescan and truncate
                 * after the remaining size.
                 */
                len = -len;
                count = 0;
                for (;;) {
                        count += m->m_len;
                        if (m->m_next == (struct mbuf *)0)
                                break;
                        m = m->m_next;
                }
                if (m->m_len >= len) {
                        m->m_len -= len;
                        m = mp;
                        if (m->m_flags & M_PKTHDR)
                                m->m_pkthdr.len -= len;
                        return;
                }
                count -= len;
                if (count < 0)
                        count = 0;
                /*
                 * Correct length for chain is "count".
                 * Find the mbuf with last data, adjust its length,
                 * and toss data from remaining mbufs on chain.
                 */
                m = mp;
                if (m->m_flags & M_PKTHDR)
                        m->m_pkthdr.len = count;
                for (; m; m = m->m_next) {
                        if (m->m_len >= count) {
                                m->m_len = count;
                                break;
                        }
                        count -= m->m_len;
                }
                while (m = m->m_next)
                        m->m_len = 0;
        }
}

/*
 * Rearange an mbuf chain so that len bytes are contiguous
 * and in the data area of an mbuf (so that mtod and dtom
 * will work for a structure of size len).  Returns the resulting
 * mbuf chain on success, frees it and returns null on failure.
 * If there is room, it will add up to max_protohdr-len extra bytes to the
 * contiguous region in an attempt to avoid being called next time.
 */
int MPFail;

struct mbuf *
m_pullup(n, len)
        register struct mbuf *n;
        int len;
{
        register struct mbuf *m;
        register int count;
        int space;

        /*
         * If first mbuf has no cluster, and has room for len bytes
         * without shifting current data, pullup into it,
         * otherwise allocate a new mbuf to prepend to the chain.
         */
        if ((n->m_flags & M_EXT) == 0 &&
            n->m_data + len < &n->m_dat[MLEN] && n->m_next) {
                if (n->m_len >= len)
                        return (n);
                m = n;
                n = n->m_next;
                len -= m->m_len;
        } else {
                if (len > MHLEN)
                        goto bad;
                MGET(m, M_DONTWAIT, n->m_type);
                if (m == 0)
                        goto bad;
                m->m_len = 0;
                if (n->m_flags & M_PKTHDR) {
                        M_COPY_PKTHDR(m, n);
                        n->m_flags &= ~M_PKTHDR;
                }
        }
        space = &m->m_dat[MLEN] - (m->m_data + m->m_len);
        do {
                count = min(min(max(len, max_protohdr), space), n->m_len);
                bcopy(mtod(n, caddr_t), mtod(m, caddr_t) + m->m_len,
                  (unsigned)count);
                len -= count;
                m->m_len += count;
                n->m_len -= count;
                space -= count;
                if (n->m_len)
                        n->m_data += count;
                else
                        n = m_free(n);
        } while (len > 0 && n);
        if (len > 0) {
                (void) m_free(m);
                goto bad;
        }
        m->m_next = n;
        return (m);
bad:
        m_freem(n);
        MPFail++;
        return (0);
}

/*
 * Partition an mbuf chain in two pieces, returning the tail --
 * all but the first len0 bytes.  In case of failure, it returns NULL and
 * attempts to restore the chain to its original state.
 */
struct mbuf *
m_split(m0, len0, wait)
        register struct mbuf *m0;
        int len0, wait;
{
        register struct mbuf *m, *n;
        unsigned len = len0, remain;

        for (m = m0; m && len > m->m_len; m = m->m_next)
                len -= m->m_len;
        if (m == 0)
                return (0);
        remain = m->m_len - len;
        if (m0->m_flags & M_PKTHDR) {
                MGETHDR(n, wait, m0->m_type);
                if (n == 0)
                        return (0);
                n->m_pkthdr.rcvif = m0->m_pkthdr.rcvif;
                n->m_pkthdr.len = m0->m_pkthdr.len - len0;
                m0->m_pkthdr.len = len0;
                if (m->m_flags & M_EXT)
                        goto extpacket;
                if (remain > MHLEN) {
                        /* m can't be the lead packet */
                        MH_ALIGN(n, 0);
                        n->m_next = m_split(m, len, wait);
                        if (n->m_next == 0) {
                                (void) m_free(n);
                                return (0);
                        } else
                                return (n);
                } else
                        MH_ALIGN(n, remain);
        } else if (remain == 0) {
                n = m->m_next;
                m->m_next = 0;
                return (n);
        } else {
                MGET(n, wait, m->m_type);
                if (n == 0)
                        return (0);
                M_ALIGN(n, remain);
        }
extpacket:
        if (m->m_flags & M_EXT) {
                n->m_flags |= M_EXT;
                MBUF_LOCK();
                n->m_ext = m->m_ext;
                insque((queue_t)&n->m_ext.ext_refs, (queue_t)&m->m_ext.ext_refs);
                MBUF_UNLOCK();
                n->m_data = m->m_data + len;
        } else {
                bcopy(mtod(m, caddr_t) + len, mtod(n, caddr_t), remain);
        }
        n->m_len = remain;
        m->m_len = len;
        n->m_next = m->m_next;
        m->m_next = 0;
        return (n);
}
/*
 * Routine to copy from device local memory into mbufs.
 */
struct mbuf *
m_devget(buf, totlen, off0, ifp, copy)
        char *buf;
        int totlen, off0;
        struct ifnet *ifp;
        void (*copy)();
{
        register struct mbuf *m;
        struct mbuf *top = 0, **mp = &top;
        register int off = off0, len;
        register char *cp;
        char *epkt;

        cp = buf;
        epkt = cp + totlen;
        if (off) {
                /*
                 * If 'off' is non-zero, packet is trailer-encapsulated,
                 * so we have to skip the type and length fields.
                 */
                cp += off + 2 * sizeof(u_int16_t);
                totlen -= 2 * sizeof(u_int16_t);
        }
        MGETHDR(m, M_DONTWAIT, MT_DATA);
        if (m == 0)
                return (0);
        m->m_pkthdr.rcvif = ifp;
        m->m_pkthdr.len = totlen;
        m->m_len = MHLEN;

        while (totlen > 0) {
                if (top) {
                        MGET(m, M_DONTWAIT, MT_DATA);
                        if (m == 0) {
                                m_freem(top);
                                return (0);
                        }
                        m->m_len = MLEN;
                }
                len = min(totlen, epkt - cp);
                if (len >= MINCLSIZE) {
                        MCLGET(m, M_DONTWAIT);
                        if (m->m_flags & M_EXT)
                                m->m_len = len = min(len, MCLBYTES);
                        else {
                                /* give up when it's out of cluster mbufs */
                                if (top)
                                   m_freem(top);
                                m_freem(m);
                                return (0);
                        }
                } else {
                        /*
                         * Place initial small packet/header at end of mbuf.
                         */
                        if (len < m->m_len) {
                                if (top == 0 && len + max_linkhdr <= m->m_len)
                                        m->m_data += max_linkhdr;
                                m->m_len = len;
                        } else
                                len = m->m_len;
                }
                if (copy)
                        copy(cp, mtod(m, caddr_t), (unsigned)len);
                else
                        bcopy(cp, mtod(m, caddr_t), (unsigned)len);
                cp += len;
                *mp = m;
                mp = &m->m_next;
                totlen -= len;
                if (cp == epkt)
                        cp = buf;
        }
        return (top);
}

/*
 * Cluster freelist allocation check. The mbuf lock  must be held.
 * Ensure hysteresis between hi/lo.
 */
static int
m_howmany()
{
        register int i;

        /* Under minimum */
        if (mbstat.m_clusters < MINCL)
                return (MINCL - mbstat.m_clusters);
        /* Too few (free < 1/2 total) and not over maximum */
        if (mbstat.m_clusters < nmbclusters &&
            (i = ((mbstat.m_clusters >> 1) - mbstat.m_clfree)) > 0)
                return i;
        return 0;
}


/*
 * Copy data from a buffer back into the indicated mbuf chain,
 * starting "off" bytes from the beginning, extending the mbuf
 * chain if necessary.
 */
void
m_copyback(m0, off, len, cp)
        struct  mbuf *m0;
        register int off;
        register int len;
        caddr_t cp;
{
        register int mlen;
        register struct mbuf *m = m0, *n;
        int totlen = 0;

        if (m0 == 0)
                return;
        while (off > (mlen = m->m_len)) {
                off -= mlen;
                totlen += mlen;
                if (m->m_next == 0) {
                        n = m_getclr(M_DONTWAIT, m->m_type);
                        if (n == 0)
                                goto out;
                        n->m_len = min(MLEN, len + off);
                        m->m_next = n;
                }
                m = m->m_next;
        }
        while (len > 0) {
                mlen = min (m->m_len - off, len);
                bcopy(cp, off + mtod(m, caddr_t), (unsigned)mlen);
                cp += mlen;
                len -= mlen;
                mlen += off;
                off = 0;
                totlen += mlen;
                if (len == 0)
                        break;
                if (m->m_next == 0) {
                        n = m_get(M_DONTWAIT, m->m_type);
                        if (n == 0)
                                break;
                        n->m_len = min(MLEN, len);
                        m->m_next = n;
                }
                m = m->m_next;
        }
out:    if (((m = m0)->m_flags & M_PKTHDR) && (m->m_pkthdr.len < totlen))
                m->m_pkthdr.len = totlen;
}


char *mcl_to_paddr(register char *addr) {
        register int base_phys;
  
        if (addr < (char *)mbutl || addr >= (char *)embutl)
                return (0);
        base_phys = mcl_paddr[(addr - (char *)mbutl) >> PAGE_SHIFT];

        if (base_phys == 0)
                return (0);
        return ((char *)((int)base_phys | ((int)addr & PAGE_MASK)));
}

/*
 * Dup the mbuf chain passed in.  The whole thing.  No cute additional cruft.
 * And really copy the thing.  That way, we don't "precompute" checksums
 *  for unsuspecting consumers.
 * Assumption: m->m_nextpkt == 0.
 * Trick: for small packets, don't dup into a cluster.  That way received
 *  packets don't take up too much room in the sockbuf (cf. sbspace()).
 */
int MDFail;

struct mbuf *
m_dup(register struct mbuf *m, int how)
{       register struct mbuf *n, **np;
        struct mbuf *top;
        int copyhdr = 0;

        np = &top;
        top = 0;
        if (m->m_flags & M_PKTHDR)
                copyhdr = 1;

        /*
         * Quick check: if we have one mbuf and its data fits in an
         *  mbuf with packet header, just copy and go.
         */
        if (m->m_next == NULL)
        {       /* Then just move the data into an mbuf and be done... */
                if (copyhdr)
                {       if (m->m_pkthdr.len <= MHLEN)
                        {       if ((n = m_gethdr(how, m->m_type)) == NULL)
                                        return(NULL);
                                n->m_len = m->m_len;
                                n->m_flags |= (m->m_flags & M_COPYFLAGS);
                                n->m_pkthdr.len = m->m_pkthdr.len;
                                n->m_pkthdr.rcvif = m->m_pkthdr.rcvif;
                                n->m_pkthdr.header = NULL;
                                n->m_pkthdr.csum_flags = 0;
                                n->m_pkthdr.csum_data = 0;
                                n->m_pkthdr.aux = NULL;
                                n->m_pkthdr.vlan_tag = 0;
                                n->m_pkthdr.reserved_1 = 0;
                                n->m_pkthdr.reserved2 = 0;
                                bcopy(m->m_data, n->m_data, m->m_pkthdr.len);
                                return(n);
                        }
                } else if (m->m_len <= MLEN)
                {       if ((n = m_get(how, m->m_type)) == NULL)
                                return(NULL);
                        bcopy(m->m_data, n->m_data, m->m_len);
                        n->m_len = m->m_len;
                        return(n);
                }
        }
        while (m)
        {
#if BLUE_DEBUG
                kprintf("<%x: %x, %x, %x\n", m, m->m_flags, m->m_len,
                        m->m_data);
#endif
                if (copyhdr)
                        n = m_gethdr(how, m->m_type);
                else
                        n = m_get(how, m->m_type);
                if (n == 0)
                        goto nospace;
                if (m->m_flags & M_EXT)
                {       MCLGET(n, how);
                        if ((n->m_flags & M_EXT) == 0)
                                goto nospace;
                }
                *np = n;
                if (copyhdr)
                {       /* Don't use M_COPY_PKTHDR: preserve m_data */
                        n->m_pkthdr = m->m_pkthdr;
                        n->m_flags |= (m->m_flags & M_COPYFLAGS);
                        copyhdr = 0;
                        if ((n->m_flags & M_EXT) == 0)
                                n->m_data = n->m_pktdat;
                }
                n->m_len = m->m_len;
                /*
                 * Get the dup on the same bdry as the original
                 * Assume that the two mbufs have the same offset to data area
                 *  (up to word bdries)
                 */
                bcopy(mtod(m, caddr_t), mtod(n, caddr_t), (unsigned)n->m_len);
                m = m->m_next;
                np = &n->m_next;
#if BLUE_DEBUG
                kprintf(">%x: %x, %x, %x\n", n, n->m_flags, n->m_len,
                        n->m_data);
#endif
        }

        if (top == 0)
                MDFail++;
        return (top);
 nospace:
        m_freem(top);
        MDFail++;
        return (0);
}

int
m_mclref(struct mbuf *p)
{
        return (_MCLREF(p));
}

int
m_mclunref(struct mbuf *p)
{
        return (_MCLUNREF(p));
}

/* change mbuf to new type */
void
m_mchtype(struct mbuf *m, int t)
{
        MBUF_LOCK();
        mbstat.m_mtypes[(m)->m_type]--;
        mbstat.m_mtypes[t]++;
        (m)->m_type = t;
        MBUF_UNLOCK();
}

void *m_mtod(struct mbuf *m)
{
        return ((m)->m_data);
}

struct mbuf *m_dtom(void *x)
{
        return ((struct mbuf *)((u_long)(x) & ~(MSIZE-1)));
}

int m_mtocl(void *x)
{
        return (((char *)(x) - (char *)mbutl) / sizeof(union mcluster));
}

union mcluster *m_cltom(int x)
{
        return ((union mcluster *)(mbutl + (x)));
}


void m_mcheck(struct mbuf *m)
{
        if (m->m_type != MT_FREE) 
                panic("mget MCHECK: m_type=%x m=%x", m->m_type, m);
}

void
mbuf_expand_thread(void)
{
    while (1) {
        int expand_mcl;
        MBUF_LOCK();
        expand_mcl = mbuf_expand_mcl;
        mbuf_expand_mcl = 0;
        MBUF_UNLOCK();
        if (expand_mcl) {
                caddr_t p;
                MCLALLOC(p, M_WAIT);
                if (p) MCLFREE(p);
        }
        assert_wait(&mbuf_expand_thread_wakeup, THREAD_UNINT);
        (void) thread_block(mbuf_expand_thread);
    }
}

void
mbuf_expand_thread_init(void)
{
        mbuf_expand_thread_initialized++;
        mbuf_expand_thread();
}