HAMMER 60I/Many: Mirroring

[dragonfly.git] / sys / kern / uipc_mbuf.c

/*
 * Copyright (c) 2004 Jeffrey M. Hsu.  All rights reserved.
 * Copyright (c) 2004 The DragonFly Project.  All rights reserved.
 * 
 * This code is derived from software contributed to The DragonFly Project
 * by Jeffrey M. Hsu.
 * 
 * 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. Neither the name of The DragonFly Project 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 COPYRIGHT HOLDERS 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
 * COPYRIGHT HOLDERS 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.
 */

/*
 * 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
 * $FreeBSD: src/sys/kern/uipc_mbuf.c,v 1.51.2.24 2003/04/15 06:59:29 silby Exp $
 * $DragonFly: src/sys/kern/uipc_mbuf.c,v 1.66 2008/06/05 18:06:32 swildner Exp $
 */

#include "opt_param.h"
#include "opt_ddb.h"
#include "opt_mbuf_stress_test.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/domain.h>
#include <sys/objcache.h>
#include <sys/tree.h>
#include <sys/protosw.h>
#include <sys/uio.h>
#include <sys/thread.h>
#include <sys/globaldata.h>
#include <sys/thread2.h>

#include <machine/atomic.h>

#include <vm/vm.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>

#ifdef INVARIANTS
#include <machine/cpu.h>
#endif

/*
 * mbuf cluster meta-data
 */
struct mbcluster {
        int32_t mcl_refs;
        void    *mcl_data;
};

/*
 * mbuf tracking for debugging purposes
 */
#ifdef MBUF_DEBUG

static MALLOC_DEFINE(M_MTRACK, "mtrack", "mtrack");

struct mbctrack;
RB_HEAD(mbuf_rb_tree, mbtrack);
RB_PROTOTYPE2(mbuf_rb_tree, mbtrack, rb_node, mbtrack_cmp, struct mbuf *);

struct mbtrack {
        RB_ENTRY(mbtrack) rb_node;
        int trackid;
        struct mbuf *m;
};

static int
mbtrack_cmp(struct mbtrack *mb1, struct mbtrack *mb2)
{
        if (mb1->m < mb2->m)
                return(-1);
        if (mb1->m > mb2->m)
                return(1);
        return(0);
}

RB_GENERATE2(mbuf_rb_tree, mbtrack, rb_node, mbtrack_cmp, struct mbuf *, m);

struct mbuf_rb_tree     mbuf_track_root;

static void
mbuftrack(struct mbuf *m)
{
        struct mbtrack *mbt;

        crit_enter();
        mbt = kmalloc(sizeof(*mbt), M_MTRACK, M_INTWAIT|M_ZERO);
        mbt->m = m;
        if (mbuf_rb_tree_RB_INSERT(&mbuf_track_root, mbt))
                panic("mbuftrack: mbuf %p already being tracked\n", m);
        crit_exit();
}

static void
mbufuntrack(struct mbuf *m)
{
        struct mbtrack *mbt;

        crit_enter();
        mbt = mbuf_rb_tree_RB_LOOKUP(&mbuf_track_root, m);
        if (mbt == NULL) {
                kprintf("mbufuntrack: mbuf %p was not tracked\n", m);
        } else {
                mbuf_rb_tree_RB_REMOVE(&mbuf_track_root, mbt);
                kfree(mbt, M_MTRACK);
        }
        crit_exit();
}

void
mbuftrackid(struct mbuf *m, int trackid)
{
        struct mbtrack *mbt;
        struct mbuf *n;

        crit_enter();
        while (m) { 
                n = m->m_nextpkt;
                while (m) {
                        mbt = mbuf_rb_tree_RB_LOOKUP(&mbuf_track_root, m);
                        if (mbt)
                                mbt->trackid = trackid;
                        m = m->m_next;
                }
                m = n;
        }
        crit_exit();
}

static int
mbuftrack_callback(struct mbtrack *mbt, void *arg)
{
        struct sysctl_req *req = arg;
        char buf[64];
        int error;

        ksnprintf(buf, sizeof(buf), "mbuf %p track %d\n", mbt->m, mbt->trackid);

        error = SYSCTL_OUT(req, buf, strlen(buf));
        if (error)      
                return(-error);
        return(0);
}

static int
mbuftrack_show(SYSCTL_HANDLER_ARGS)
{
        int error;

        crit_enter();
        error = mbuf_rb_tree_RB_SCAN(&mbuf_track_root, NULL,
                                     mbuftrack_callback, req);
        crit_exit();
        return (-error);
}
SYSCTL_PROC(_kern_ipc, OID_AUTO, showmbufs, CTLFLAG_RD|CTLTYPE_STRING,
            0, 0, mbuftrack_show, "A", "Show all in-use mbufs");

#else

#define mbuftrack(m)
#define mbufuntrack(m)

#endif

static void mbinit(void *);
SYSINIT(mbuf, SI_BOOT2_MACHDEP, SI_ORDER_FIRST, mbinit, NULL)

static u_long   mbtypes[SMP_MAXCPU][MT_NTYPES];

static struct mbstat mbstat[SMP_MAXCPU];
int     max_linkhdr;
int     max_protohdr;
int     max_hdr;
int     max_datalen;
int     m_defragpackets;
int     m_defragbytes;
int     m_defraguseless;
int     m_defragfailure;
#ifdef MBUF_STRESS_TEST
int     m_defragrandomfailures;
#endif

struct objcache *mbuf_cache, *mbufphdr_cache;
struct objcache *mclmeta_cache;
struct objcache *mbufcluster_cache, *mbufphdrcluster_cache;

int     nmbclusters;
int     nmbufs;

SYSCTL_INT(_kern_ipc, KIPC_MAX_LINKHDR, max_linkhdr, CTLFLAG_RW,
           &max_linkhdr, 0, "");
SYSCTL_INT(_kern_ipc, KIPC_MAX_PROTOHDR, max_protohdr, CTLFLAG_RW,
           &max_protohdr, 0, "");
SYSCTL_INT(_kern_ipc, KIPC_MAX_HDR, max_hdr, CTLFLAG_RW, &max_hdr, 0, "");
SYSCTL_INT(_kern_ipc, KIPC_MAX_DATALEN, max_datalen, CTLFLAG_RW,
           &max_datalen, 0, "");
SYSCTL_INT(_kern_ipc, OID_AUTO, mbuf_wait, CTLFLAG_RW,
           &mbuf_wait, 0, "");
static int do_mbstat(SYSCTL_HANDLER_ARGS);

SYSCTL_PROC(_kern_ipc, KIPC_MBSTAT, mbstat, CTLTYPE_STRUCT|CTLFLAG_RD,
        0, 0, do_mbstat, "S,mbstat", "");

static int do_mbtypes(SYSCTL_HANDLER_ARGS);

SYSCTL_PROC(_kern_ipc, OID_AUTO, mbtypes, CTLTYPE_ULONG|CTLFLAG_RD,
        0, 0, do_mbtypes, "LU", "");

static int
do_mbstat(SYSCTL_HANDLER_ARGS)
{
        struct mbstat mbstat_total;
        struct mbstat *mbstat_totalp;
        int i;

        bzero(&mbstat_total, sizeof(mbstat_total));
        mbstat_totalp = &mbstat_total;

        for (i = 0; i < ncpus; i++)
        {
                mbstat_total.m_mbufs += mbstat[i].m_mbufs;      
                mbstat_total.m_clusters += mbstat[i].m_clusters;        
                mbstat_total.m_spare += mbstat[i].m_spare;      
                mbstat_total.m_clfree += mbstat[i].m_clfree;    
                mbstat_total.m_drops += mbstat[i].m_drops;      
                mbstat_total.m_wait += mbstat[i].m_wait;        
                mbstat_total.m_drain += mbstat[i].m_drain;      
                mbstat_total.m_mcfail += mbstat[i].m_mcfail;    
                mbstat_total.m_mpfail += mbstat[i].m_mpfail;    

        }
        /*
         * The following fields are not cumulative fields so just
         * get their values once.
         */
        mbstat_total.m_msize = mbstat[0].m_msize;       
        mbstat_total.m_mclbytes = mbstat[0].m_mclbytes; 
        mbstat_total.m_minclsize = mbstat[0].m_minclsize;       
        mbstat_total.m_mlen = mbstat[0].m_mlen; 
        mbstat_total.m_mhlen = mbstat[0].m_mhlen;       

        return(sysctl_handle_opaque(oidp, mbstat_totalp, sizeof(mbstat_total), req));
}

static int
do_mbtypes(SYSCTL_HANDLER_ARGS)
{
        u_long totals[MT_NTYPES];
        int i, j;

        for (i = 0; i < MT_NTYPES; i++)
                totals[i] = 0;

        for (i = 0; i < ncpus; i++)
        {
                for (j = 0; j < MT_NTYPES; j++)
                        totals[j] += mbtypes[i][j];
        }

        return(sysctl_handle_opaque(oidp, totals, sizeof(totals), req));
}

/*
 * These are read-only because we do not currently have any code
 * to adjust the objcache limits after the fact.  The variables
 * may only be set as boot-time tunables.
 */
SYSCTL_INT(_kern_ipc, KIPC_NMBCLUSTERS, nmbclusters, CTLFLAG_RD,
           &nmbclusters, 0, "Maximum number of mbuf clusters available");
SYSCTL_INT(_kern_ipc, OID_AUTO, nmbufs, CTLFLAG_RD, &nmbufs, 0,
           "Maximum number of mbufs available"); 

SYSCTL_INT(_kern_ipc, OID_AUTO, m_defragpackets, CTLFLAG_RD,
           &m_defragpackets, 0, "");
SYSCTL_INT(_kern_ipc, OID_AUTO, m_defragbytes, CTLFLAG_RD,
           &m_defragbytes, 0, "");
SYSCTL_INT(_kern_ipc, OID_AUTO, m_defraguseless, CTLFLAG_RD,
           &m_defraguseless, 0, "");
SYSCTL_INT(_kern_ipc, OID_AUTO, m_defragfailure, CTLFLAG_RD,
           &m_defragfailure, 0, "");
#ifdef MBUF_STRESS_TEST
SYSCTL_INT(_kern_ipc, OID_AUTO, m_defragrandomfailures, CTLFLAG_RW,
           &m_defragrandomfailures, 0, "");
#endif

static MALLOC_DEFINE(M_MBUF, "mbuf", "mbuf");
static MALLOC_DEFINE(M_MBUFCL, "mbufcl", "mbufcl");
static MALLOC_DEFINE(M_MCLMETA, "mclmeta", "mclmeta");

static void m_reclaim (void);
static void m_mclref(void *arg);
static void m_mclfree(void *arg);

#ifndef NMBCLUSTERS
#define NMBCLUSTERS     (512 + maxusers * 16)
#endif
#ifndef NMBUFS
#define NMBUFS          (nmbclusters * 2)
#endif

/*
 * Perform sanity checks of tunables declared above.
 */
static void
tunable_mbinit(void *dummy)
{
        /*
         * This has to be done before VM init.
         */
        nmbclusters = NMBCLUSTERS;
        TUNABLE_INT_FETCH("kern.ipc.nmbclusters", &nmbclusters);
        nmbufs = NMBUFS;
        TUNABLE_INT_FETCH("kern.ipc.nmbufs", &nmbufs);
        /* Sanity checks */
        if (nmbufs < nmbclusters * 2)
                nmbufs = nmbclusters * 2;
}
SYSINIT(tunable_mbinit, SI_BOOT1_TUNABLES, SI_ORDER_ANY,
        tunable_mbinit, NULL);

/* "number of clusters of pages" */
#define NCL_INIT        1

#define NMB_INIT        16

/*
 * The mbuf object cache only guarantees that m_next and m_nextpkt are
 * NULL and that m_data points to the beginning of the data area.  In
 * particular, m_len and m_pkthdr.len are uninitialized.  It is the
 * responsibility of the caller to initialize those fields before use.
 */

static boolean_t __inline
mbuf_ctor(void *obj, void *private, int ocflags)
{
        struct mbuf *m = obj;

        m->m_next = NULL;
        m->m_nextpkt = NULL;
        m->m_data = m->m_dat;
        m->m_flags = 0;

        return (TRUE);
}

/*
 * Initialize the mbuf and the packet header fields.
 */
static boolean_t
mbufphdr_ctor(void *obj, void *private, int ocflags)
{
        struct mbuf *m = obj;

        m->m_next = NULL;
        m->m_nextpkt = NULL;
        m->m_data = m->m_pktdat;
        m->m_flags = M_PKTHDR | M_PHCACHE;

        m->m_pkthdr.rcvif = NULL;       /* eliminate XXX JH */
        SLIST_INIT(&m->m_pkthdr.tags);
        m->m_pkthdr.csum_flags = 0;     /* eliminate XXX JH */
        m->m_pkthdr.fw_flags = 0;       /* eliminate XXX JH */

        return (TRUE);
}

/*
 * A mbcluster object consists of 2K (MCLBYTES) cluster and a refcount.
 */
static boolean_t
mclmeta_ctor(void *obj, void *private, int ocflags)
{
        struct mbcluster *cl = obj;
        void *buf;

        if (ocflags & M_NOWAIT)
                buf = kmalloc(MCLBYTES, M_MBUFCL, M_NOWAIT | M_ZERO);
        else
                buf = kmalloc(MCLBYTES, M_MBUFCL, M_INTWAIT | M_ZERO);
        if (buf == NULL)
                return (FALSE);
        cl->mcl_refs = 0;
        cl->mcl_data = buf;
        return (TRUE);
}

static void
mclmeta_dtor(void *obj, void *private)
{
        struct mbcluster *mcl = obj;

        KKASSERT(mcl->mcl_refs == 0);
        kfree(mcl->mcl_data, M_MBUFCL);
}

static void
linkcluster(struct mbuf *m, struct mbcluster *cl)
{
        /*
         * Add the cluster to the mbuf.  The caller will detect that the
         * mbuf now has an attached cluster.
         */
        m->m_ext.ext_arg = cl;
        m->m_ext.ext_buf = cl->mcl_data;
        m->m_ext.ext_ref = m_mclref;
        m->m_ext.ext_free = m_mclfree;
        m->m_ext.ext_size = MCLBYTES;
        atomic_add_int(&cl->mcl_refs, 1);

        m->m_data = m->m_ext.ext_buf;
        m->m_flags |= M_EXT | M_EXT_CLUSTER;
}

static boolean_t
mbufphdrcluster_ctor(void *obj, void *private, int ocflags)
{
        struct mbuf *m = obj;
        struct mbcluster *cl;

        mbufphdr_ctor(obj, private, ocflags);
        cl = objcache_get(mclmeta_cache, ocflags);
        if (cl == NULL)
                return (FALSE);
        m->m_flags |= M_CLCACHE;
        linkcluster(m, cl);
        return (TRUE);
}

static boolean_t
mbufcluster_ctor(void *obj, void *private, int ocflags)
{
        struct mbuf *m = obj;
        struct mbcluster *cl;

        mbuf_ctor(obj, private, ocflags);
        cl = objcache_get(mclmeta_cache, ocflags);
        if (cl == NULL)
                return (FALSE);
        m->m_flags |= M_CLCACHE;
        linkcluster(m, cl);
        return (TRUE);
}

/*
 * Used for both the cluster and cluster PHDR caches.
 *
 * The mbuf may have lost its cluster due to sharing, deal
 * with the situation by checking M_EXT.
 */
static void
mbufcluster_dtor(void *obj, void *private)
{
        struct mbuf *m = obj;
        struct mbcluster *mcl;

        if (m->m_flags & M_EXT) {
                KKASSERT((m->m_flags & M_EXT_CLUSTER) != 0);
                mcl = m->m_ext.ext_arg;
                KKASSERT(mcl->mcl_refs == 1);
                mcl->mcl_refs = 0;
                objcache_put(mclmeta_cache, mcl);
        }
}

struct objcache_malloc_args mbuf_malloc_args = { MSIZE, M_MBUF };
struct objcache_malloc_args mclmeta_malloc_args =
        { sizeof(struct mbcluster), M_MCLMETA };

/* ARGSUSED*/
static void
mbinit(void *dummy)
{
        int i;

        for (i = 0; i < ncpus; i++)
        {
                atomic_set_long_nonlocked(&mbstat[i].m_msize, MSIZE);
                atomic_set_long_nonlocked(&mbstat[i].m_mclbytes, MCLBYTES);
                atomic_set_long_nonlocked(&mbstat[i].m_minclsize, MINCLSIZE);
                atomic_set_long_nonlocked(&mbstat[i].m_mlen, MLEN);
                atomic_set_long_nonlocked(&mbstat[i].m_mhlen, MHLEN);
        }

        mbuf_cache = objcache_create("mbuf", nmbufs, 0,
            mbuf_ctor, NULL, NULL,
            objcache_malloc_alloc, objcache_malloc_free, &mbuf_malloc_args);
        mbufphdr_cache = objcache_create("mbuf pkt hdr", nmbufs, 64,
            mbufphdr_ctor, NULL, NULL,
            objcache_malloc_alloc, objcache_malloc_free, &mbuf_malloc_args);
        mclmeta_cache = objcache_create("cluster mbuf", nmbclusters , 0,
            mclmeta_ctor, mclmeta_dtor, NULL,
            objcache_malloc_alloc, objcache_malloc_free, &mclmeta_malloc_args);
        mbufcluster_cache = objcache_create("mbuf + cluster", nmbclusters, 0,
            mbufcluster_ctor, mbufcluster_dtor, NULL,
            objcache_malloc_alloc, objcache_malloc_free, &mbuf_malloc_args);
        mbufphdrcluster_cache = objcache_create("mbuf pkt hdr + cluster",
            nmbclusters, 64, mbufphdrcluster_ctor, mbufcluster_dtor, NULL,
            objcache_malloc_alloc, objcache_malloc_free, &mbuf_malloc_args);
        return;
}

/*
 * Return the number of references to this mbuf's data.  0 is returned
 * if the mbuf is not M_EXT, a reference count is returned if it is
 * M_EXT | M_EXT_CLUSTER, and 99 is returned if it is a special M_EXT.
 */
int
m_sharecount(struct mbuf *m)
{
        switch (m->m_flags & (M_EXT | M_EXT_CLUSTER)) {
        case 0:
                return (0);
        case M_EXT:
                return (99);
        case M_EXT | M_EXT_CLUSTER:
                return (((struct mbcluster *)m->m_ext.ext_arg)->mcl_refs);
        }
        /* NOTREACHED */
        return (0);             /* to shut up compiler */
}

/*
 * change mbuf to new type
 */
void
m_chtype(struct mbuf *m, int type)
{
        struct globaldata *gd = mycpu;

        atomic_add_long_nonlocked(&mbtypes[gd->gd_cpuid][type], 1);
        atomic_subtract_long_nonlocked(&mbtypes[gd->gd_cpuid][m->m_type], 1);
        atomic_set_short_nonlocked(&m->m_type, type);
}

static void
m_reclaim(void)
{
        struct domain *dp;
        struct protosw *pr;

        crit_enter();
        SLIST_FOREACH(dp, &domains, dom_next) {
                for (pr = dp->dom_protosw; pr < dp->dom_protoswNPROTOSW; pr++) {
                        if (pr->pr_drain)
                                (*pr->pr_drain)();
                }
        }
        crit_exit();
        atomic_add_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_drain, 1);
}

static void __inline
updatestats(struct mbuf *m, int type)
{
        struct globaldata *gd = mycpu;
        m->m_type = type;

        mbuftrack(m);

        atomic_add_long_nonlocked(&mbtypes[gd->gd_cpuid][type], 1);
        atomic_add_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_mbufs, 1);

}

/*
 * Allocate an mbuf.
 */
struct mbuf *
m_get(int how, int type)
{
        struct mbuf *m;
        int ntries = 0;
        int ocf = MBTOM(how);

retryonce:

        m = objcache_get(mbuf_cache, ocf);

        if (m == NULL) {
                if ((how & MB_TRYWAIT) && ntries++ == 0) {
                        struct objcache *reclaimlist[] = {
                                mbufphdr_cache,
                                mbufcluster_cache, mbufphdrcluster_cache
                        };
                        const int nreclaims = __arysize(reclaimlist);

                        if (!objcache_reclaimlist(reclaimlist, nreclaims, ocf))
                                m_reclaim();
                        goto retryonce;
                }
                return (NULL);
        }

        updatestats(m, type);
        return (m);
}

struct mbuf *
m_gethdr(int how, int type)
{
        struct mbuf *m;
        int ocf = MBTOM(how);
        int ntries = 0;

retryonce:

        m = objcache_get(mbufphdr_cache, ocf);

        if (m == NULL) {
                if ((how & MB_TRYWAIT) && ntries++ == 0) {
                        struct objcache *reclaimlist[] = {
                                mbuf_cache,
                                mbufcluster_cache, mbufphdrcluster_cache
                        };
                        const int nreclaims = __arysize(reclaimlist);

                        if (!objcache_reclaimlist(reclaimlist, nreclaims, ocf))
                                m_reclaim();
                        goto retryonce;
                }
                return (NULL);
        }

        updatestats(m, type);
        return (m);
}

/*
 * Get a mbuf (not a mbuf cluster!) and zero it.
 * Deprecated.
 */
struct mbuf *
m_getclr(int how, int type)
{
        struct mbuf *m;

        m = m_get(how, type);
        if (m != NULL)
                bzero(m->m_data, MLEN);
        return (m);
}

/*
 * Returns an mbuf with an attached cluster.
 * Because many network drivers use this kind of buffers a lot, it is
 * convenient to keep a small pool of free buffers of this kind.
 * Even a small size such as 10 gives about 10% improvement in the
 * forwarding rate in a bridge or router.
 */
struct mbuf *
m_getcl(int how, short type, int flags)
{
        struct mbuf *m;
        int ocflags = MBTOM(how);
        int ntries = 0;

retryonce:

        if (flags & M_PKTHDR)
                m = objcache_get(mbufphdrcluster_cache, ocflags);
        else
                m = objcache_get(mbufcluster_cache, ocflags);

        if (m == NULL) {
                if ((how & MB_TRYWAIT) && ntries++ == 0) {
                        struct objcache *reclaimlist[1];

                        if (flags & M_PKTHDR)
                                reclaimlist[0] = mbufcluster_cache;
                        else
                                reclaimlist[0] = mbufphdrcluster_cache;
                        if (!objcache_reclaimlist(reclaimlist, 1, ocflags))
                                m_reclaim();
                        goto retryonce;
                }
                return (NULL);
        }

        m->m_type = type;

        mbuftrack(m);

        atomic_add_long_nonlocked(&mbtypes[mycpu->gd_cpuid][type], 1);
        atomic_add_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_clusters, 1);
        return (m);
}

/*
 * Allocate chain of requested length.
 */
struct mbuf *
m_getc(int len, int how, int type)
{
        struct mbuf *n, *nfirst = NULL, **ntail = &nfirst;
        int nsize;

        while (len > 0) {
                n = m_getl(len, how, type, 0, &nsize);
                if (n == NULL)
                        goto failed;
                n->m_len = 0;
                *ntail = n;
                ntail = &n->m_next;
                len -= nsize;
        }
        return (nfirst);

failed:
        m_freem(nfirst);
        return (NULL);
}

/*
 * Allocate len-worth of mbufs and/or mbuf clusters (whatever fits best)
 * and return a pointer to the head of the allocated chain. If m0 is
 * non-null, then we assume that it is a single mbuf or an mbuf chain to
 * which we want len bytes worth of mbufs and/or clusters attached, and so
 * if we succeed in allocating it, we will just return a pointer to m0.
 *
 * If we happen to fail at any point during the allocation, we will free
 * up everything we have already allocated and return NULL.
 *
 * Deprecated.  Use m_getc() and m_cat() instead.
 */
struct mbuf *
m_getm(struct mbuf *m0, int len, int type, int how)
{
        struct mbuf *nfirst;

        nfirst = m_getc(len, how, type);

        if (m0 != NULL) {
                m_last(m0)->m_next = nfirst;
                return (m0);
        }

        return (nfirst);
}

/*
 * Adds a cluster to a normal mbuf, M_EXT is set on success.
 * Deprecated.  Use m_getcl() instead.
 */
void
m_mclget(struct mbuf *m, int how)
{
        struct mbcluster *mcl;

        KKASSERT((m->m_flags & M_EXT) == 0);
        mcl = objcache_get(mclmeta_cache, MBTOM(how));
        if (mcl != NULL) {
                linkcluster(m, mcl);
                atomic_add_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_clusters, 1);
        }
}

/*
 * Updates to mbcluster must be MPSAFE.  Only an entity which already has
 * a reference to the cluster can ref it, so we are in no danger of 
 * racing an add with a subtract.  But the operation must still be atomic
 * since multiple entities may have a reference on the cluster.
 *
 * m_mclfree() is almost the same but it must contend with two entities
 * freeing the cluster at the same time.  If there is only one reference
 * count we are the only entity referencing the cluster and no further
 * locking is required.  Otherwise we must protect against a race to 0
 * with the serializer.
 */
static void
m_mclref(void *arg)
{
        struct mbcluster *mcl = arg;

        atomic_add_int(&mcl->mcl_refs, 1);
}

/*
 * When dereferencing a cluster we have to deal with a N->0 race, where
 * N entities free their references simultaniously.  To do this we use
 * atomic_cmpset_int().
 */
static void
m_mclfree(void *arg)
{
        struct mbcluster *mcl = arg;
        int refs;

        do {
                refs = mcl->mcl_refs;
        } while (atomic_cmpset_int(&mcl->mcl_refs, refs, refs - 1) == 0);
        if (refs == 1)
                objcache_put(mclmeta_cache, mcl);
}

extern void db_print_backtrace(void);

/*
 * Free a single mbuf and any associated external storage.  The successor,
 * if any, is returned.
 *
 * We do need to check non-first mbuf for m_aux, since some of existing
 * code does not call M_PREPEND properly.
 * (example: call to bpf_mtap from drivers)
 */
struct mbuf *
m_free(struct mbuf *m)
{
        struct mbuf *n;
        struct globaldata *gd = mycpu;

        KASSERT(m->m_type != MT_FREE, ("freeing free mbuf %p", m));
        atomic_subtract_long_nonlocked(&mbtypes[gd->gd_cpuid][m->m_type], 1);

        n = m->m_next;

        /*
         * Make sure the mbuf is in constructed state before returning it
         * to the objcache.
         */
        m->m_next = NULL;
        mbufuntrack(m);
#ifdef notyet
        KKASSERT(m->m_nextpkt == NULL);
#else
        if (m->m_nextpkt != NULL) {
#ifdef DDB
                static int afewtimes = 10;

                if (afewtimes-- > 0) {
                        kprintf("mfree: m->m_nextpkt != NULL\n");
                        db_print_backtrace();
                }
#endif
                m->m_nextpkt = NULL;
        }
#endif
        if (m->m_flags & M_PKTHDR) {
                m_tag_delete_chain(m);          /* eliminate XXX JH */
        }

        m->m_flags &= (M_EXT | M_EXT_CLUSTER | M_CLCACHE | M_PHCACHE);

        /*
         * Clean the M_PKTHDR state so we can return the mbuf to its original
         * cache.  This is based on the PHCACHE flag which tells us whether
         * the mbuf was originally allocated out of a packet-header cache
         * or a non-packet-header cache.
         */
        if (m->m_flags & M_PHCACHE) {
                m->m_flags |= M_PKTHDR;
                m->m_pkthdr.rcvif = NULL;       /* eliminate XXX JH */
                m->m_pkthdr.csum_flags = 0;     /* eliminate XXX JH */
                m->m_pkthdr.fw_flags = 0;       /* eliminate XXX JH */
                SLIST_INIT(&m->m_pkthdr.tags);
        }

        /*
         * Handle remaining flags combinations.  M_CLCACHE tells us whether
         * the mbuf was originally allocated from a cluster cache or not,
         * and is totally separate from whether the mbuf is currently
         * associated with a cluster.
         */
        crit_enter();
        switch(m->m_flags & (M_CLCACHE | M_EXT | M_EXT_CLUSTER)) {
        case M_CLCACHE | M_EXT | M_EXT_CLUSTER:
                /*
                 * mbuf+cluster cache case.  The mbuf was allocated from the
                 * combined mbuf_cluster cache and can be returned to the
                 * cache if the cluster hasn't been shared.
                 */
                if (m_sharecount(m) == 1) {
                        /*
                         * The cluster has not been shared, we can just
                         * reset the data pointer and return the mbuf
                         * to the cluster cache.  Note that the reference
                         * count is left intact (it is still associated with
                         * an mbuf).
                         */
                        m->m_data = m->m_ext.ext_buf;
                        if (m->m_flags & M_PHCACHE)
                                objcache_put(mbufphdrcluster_cache, m);
                        else
                                objcache_put(mbufcluster_cache, m);
                        atomic_subtract_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_clusters, 1);
                } else {
                        /*
                         * Hell.  Someone else has a ref on this cluster,
                         * we have to disconnect it which means we can't
                         * put it back into the mbufcluster_cache, we
                         * have to destroy the mbuf.
                         *
                         * Other mbuf references to the cluster will typically
                         * be M_EXT | M_EXT_CLUSTER but without M_CLCACHE.
                         *
                         * XXX we could try to connect another cluster to
                         * it.
                         */
                        m->m_ext.ext_free(m->m_ext.ext_arg); 
                        m->m_flags &= ~(M_EXT | M_EXT_CLUSTER);
                        if (m->m_flags & M_PHCACHE)
                                objcache_dtor(mbufphdrcluster_cache, m);
                        else
                                objcache_dtor(mbufcluster_cache, m);
                }
                break;
        case M_EXT | M_EXT_CLUSTER:
                /*
                 * Normal cluster associated with an mbuf that was allocated
                 * from the normal mbuf pool rather then the cluster pool.
                 * The cluster has to be independantly disassociated from the
                 * mbuf.
                 */
                if (m_sharecount(m) == 1)
                        atomic_subtract_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_clusters, 1);
                /* fall through */
        case M_EXT:
                /*
                 * Normal cluster association case, disconnect the cluster from
                 * the mbuf.  The cluster may or may not be custom.
                 */
                m->m_ext.ext_free(m->m_ext.ext_arg); 
                m->m_flags &= ~(M_EXT | M_EXT_CLUSTER);
                /* fall through */
        case 0:
                /*
                 * return the mbuf to the mbuf cache.
                 */
                if (m->m_flags & M_PHCACHE) {
                        m->m_data = m->m_pktdat;
                        objcache_put(mbufphdr_cache, m);
                } else {
                        m->m_data = m->m_dat;
                        objcache_put(mbuf_cache, m);
                }
                atomic_subtract_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_mbufs, 1);
                break;
        default:
                if (!panicstr)
                        panic("bad mbuf flags %p %08x\n", m, m->m_flags);
                break;
        }
        crit_exit();
        return (n);
}

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

/*
 * mbuf utility routines
 */

/*
 * Lesser-used path for M_PREPEND: allocate new mbuf to prepend to chain and
 * copy junk along.
 */
struct mbuf *
m_prepend(struct mbuf *m, int len, int how)
{
        struct mbuf *mn;

        if (m->m_flags & M_PKTHDR)
            mn = m_gethdr(how, m->m_type);
        else
            mn = m_get(how, m->m_type);
        if (mn == NULL) {
                m_freem(m);
                return (NULL);
        }
        if (m->m_flags & M_PKTHDR)
                M_MOVE_PKTHDR(mn, m);
        mn->m_next = m;
        m = mn;
        if (len < MHLEN)
                MH_ALIGN(m, len);
        m->m_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 MB_WAIT/MB_DONTWAIT from caller.
 * Note that the copy is read-only, because clusters are not copied,
 * only their reference counts are incremented.
 */
struct mbuf *
m_copym(const struct mbuf *m, int off0, int len, int wait)
{
        struct mbuf *n, **np;
        int off = off0;
        struct mbuf *top;
        int copyhdr = 0;

        KASSERT(off >= 0, ("m_copym, negative off %d", off));
        KASSERT(len >= 0, ("m_copym, negative len %d", len));
        if (off == 0 && m->m_flags & M_PKTHDR)
                copyhdr = 1;
        while (off > 0) {
                KASSERT(m != NULL, ("m_copym, offset > size of mbuf chain"));
                if (off < m->m_len)
                        break;
                off -= m->m_len;
                m = m->m_next;
        }
        np = &top;
        top = 0;
        while (len > 0) {
                if (m == NULL) {
                        KASSERT(len == M_COPYALL, 
                            ("m_copym, length > size of mbuf chain"));
                        break;
                }
                /*
                 * Because we are sharing any cluster attachment below,
                 * be sure to get an mbuf that does not have a cluster
                 * associated with it.
                 */
                if (copyhdr)
                        n = m_gethdr(wait, m->m_type);
                else
                        n = m_get(wait, m->m_type);
                *np = n;
                if (n == NULL)
                        goto nospace;
                if (copyhdr) {
                        if (!m_dup_pkthdr(n, m, wait))
                                goto nospace;
                        if (len == M_COPYALL)
                                n->m_pkthdr.len -= off0;
                        else
                                n->m_pkthdr.len = len;
                        copyhdr = 0;
                }
                n->m_len = min(len, m->m_len - off);
                if (m->m_flags & M_EXT) {
                        KKASSERT((n->m_flags & M_EXT) == 0);
                        n->m_data = m->m_data + off;
                        m->m_ext.ext_ref(m->m_ext.ext_arg); 
                        n->m_ext = m->m_ext;
                        n->m_flags |= m->m_flags & (M_EXT | M_EXT_CLUSTER);
                } 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;
        }
        if (top == NULL)
                atomic_add_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_mcfail, 1);
        return (top);
nospace:
        m_freem(top);
        atomic_add_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_mcfail, 1);
        return (NULL);
}

/*
 * Copy an entire packet, including header (which must be present).
 * An optimization of the common case `m_copym(m, 0, M_COPYALL, how)'.
 * Note that the copy is read-only, because clusters are not copied,
 * only their reference counts are incremented.
 * Preserve alignment of the first mbuf so if the creator has left
 * some room at the beginning (e.g. for inserting protocol headers)
 * the copies also have the room available.
 */
struct mbuf *
m_copypacket(struct mbuf *m, int how)
{
        struct mbuf *top, *n, *o;

        n = m_gethdr(how, m->m_type);
        top = n;
        if (!n)
                goto nospace;

        if (!m_dup_pkthdr(n, m, how))
                goto nospace;
        n->m_len = m->m_len;
        if (m->m_flags & M_EXT) {
                KKASSERT((n->m_flags & M_EXT) == 0);
                n->m_data = m->m_data;
                m->m_ext.ext_ref(m->m_ext.ext_arg); 
                n->m_ext = m->m_ext;
                n->m_flags |= m->m_flags & (M_EXT | M_EXT_CLUSTER);
        } else {
                n->m_data = n->m_pktdat + (m->m_data - m->m_pktdat );
                bcopy(mtod(m, char *), mtod(n, char *), n->m_len);
        }

        m = m->m_next;
        while (m) {
                o = m_get(how, m->m_type);
                if (!o)
                        goto nospace;

                n->m_next = o;
                n = n->m_next;

                n->m_len = m->m_len;
                if (m->m_flags & M_EXT) {
                        KKASSERT((n->m_flags & M_EXT) == 0);
                        n->m_data = m->m_data;
                        m->m_ext.ext_ref(m->m_ext.ext_arg); 
                        n->m_ext = m->m_ext;
                        n->m_flags |= m->m_flags & (M_EXT | M_EXT_CLUSTER);
                } else {
                        bcopy(mtod(m, char *), mtod(n, char *), n->m_len);
                }

                m = m->m_next;
        }
        return top;
nospace:
        m_freem(top);
        atomic_add_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_mcfail, 1);
        return (NULL);
}

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

        KASSERT(off >= 0, ("m_copydata, negative off %d", off));
        KASSERT(len >= 0, ("m_copydata, negative len %d", len));
        while (off > 0) {
                KASSERT(m != NULL, ("m_copydata, offset > size of mbuf chain"));
                if (off < m->m_len)
                        break;
                off -= m->m_len;
                m = m->m_next;
        }
        while (len > 0) {
                KASSERT(m != NULL, ("m_copydata, length > size of mbuf chain"));
                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;
        }
}

/*
 * Copy a packet header mbuf chain into a completely new chain, including
 * copying any mbuf clusters.  Use this instead of m_copypacket() when
 * you need a writable copy of an mbuf chain.
 */
struct mbuf *
m_dup(struct mbuf *m, int how)
{
        struct mbuf **p, *top = NULL;
        int remain, moff, nsize;

        /* Sanity check */
        if (m == NULL)
                return (NULL);
        KASSERT((m->m_flags & M_PKTHDR) != 0, ("%s: !PKTHDR", __func__));

        /* While there's more data, get a new mbuf, tack it on, and fill it */
        remain = m->m_pkthdr.len;
        moff = 0;
        p = &top;
        while (remain > 0 || top == NULL) {     /* allow m->m_pkthdr.len == 0 */
                struct mbuf *n;

                /* Get the next new mbuf */
                n = m_getl(remain, how, m->m_type, top == NULL ? M_PKTHDR : 0,
                           &nsize);
                if (n == NULL)
                        goto nospace;
                if (top == NULL)
                        if (!m_dup_pkthdr(n, m, how))
                                goto nospace0;

                /* Link it into the new chain */
                *p = n;
                p = &n->m_next;

                /* Copy data from original mbuf(s) into new mbuf */
                n->m_len = 0;
                while (n->m_len < nsize && m != NULL) {
                        int chunk = min(nsize - n->m_len, m->m_len - moff);

                        bcopy(m->m_data + moff, n->m_data + n->m_len, chunk);
                        moff += chunk;
                        n->m_len += chunk;
                        remain -= chunk;
                        if (moff == m->m_len) {
                                m = m->m_next;
                                moff = 0;
                        }
                }

                /* Check correct total mbuf length */
                KASSERT((remain > 0 && m != NULL) || (remain == 0 && m == NULL),
                        ("%s: bogus m_pkthdr.len", __func__));
        }
        return (top);

nospace:
        m_freem(top);
nospace0:
        atomic_add_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_mcfail, 1);
        return (NULL);
}

/*
 * 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(struct mbuf *m, struct mbuf *n)
{
        m = m_last(m);
        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(struct mbuf *mp, int req_len)
{
        int len = req_len;
        struct mbuf *m;
        int 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 (mp->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;
                        if (mp->m_flags & M_PKTHDR)
                                mp->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_next)
                        (m = m->m_next) ->m_len = 0;
        }
}

/*
 * Rearrange an mbuf chain so that len bytes are contiguous
 * and in the data area of an mbuf (so that mtod 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.
 */
struct mbuf *
m_pullup(struct mbuf *n, int len)
{
        struct mbuf *m;
        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) &&
            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;
                if (n->m_flags & M_PKTHDR)
                        m = m_gethdr(MB_DONTWAIT, n->m_type);
                else
                        m = m_get(MB_DONTWAIT, n->m_type);
                if (m == NULL)
                        goto bad;
                m->m_len = 0;
                if (n->m_flags & M_PKTHDR)
                        M_MOVE_PKTHDR(m, n);
        }
        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) {
                m_free(m);
                goto bad;
        }
        m->m_next = n;
        return (m);
bad:
        m_freem(n);
        atomic_add_long_nonlocked(&mbstat[mycpu->gd_cpuid].m_mcfail, 1);
        return (NULL);
}

/*
 * 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.
 *
 * Note that the resulting mbufs might be read-only, because the new
 * mbuf can end up sharing an mbuf cluster with the original mbuf if
 * the "breaking point" happens to lie within a cluster mbuf. Use the
 * M_WRITABLE() macro to check for this case.
 */
struct mbuf *
m_split(struct mbuf *m0, int len0, int wait)
{
        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 == NULL)
                return (NULL);
        remain = m->m_len - len;
        if (m0->m_flags & M_PKTHDR) {
                n = m_gethdr(wait, m0->m_type);
                if (n == NULL)
                        return (NULL);
                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 == NULL) {
                                m_free(n);
                                return (NULL);
                        } else {
                                n->m_len = 0;
                                return (n);
                        }
                } else
                        MH_ALIGN(n, remain);
        } else if (remain == 0) {
                n = m->m_next;
                m->m_next = 0;
                return (n);
        } else {
                n = m_get(wait, m->m_type);
                if (n == NULL)
                        return (NULL);
                M_ALIGN(n, remain);
        }
extpacket:
        if (m->m_flags & M_EXT) {
                KKASSERT((n->m_flags & M_EXT) == 0);
                n->m_data = m->m_data + len;
                m->m_ext.ext_ref(m->m_ext.ext_arg); 
                n->m_ext = m->m_ext;
                n->m_flags |= m->m_flags & (M_EXT | M_EXT_CLUSTER);
        } 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.
 * Note: "offset" is ill-defined and always called as 0, so ignore it.
 */
struct mbuf *
m_devget(char *buf, int len, int offset, struct ifnet *ifp,
    void (*copy)(volatile const void *from, volatile void *to, size_t length))
{
        struct mbuf *m, *mfirst = NULL, **mtail;
        int nsize, flags;

        if (copy == NULL)
                copy = bcopy;
        mtail = &mfirst;
        flags = M_PKTHDR;

        while (len > 0) {
                m = m_getl(len, MB_DONTWAIT, MT_DATA, flags, &nsize);
                if (m == NULL) {
                        m_freem(mfirst);
                        return (NULL);
                }
                m->m_len = min(len, nsize);

                if (flags & M_PKTHDR) {
                        if (len + max_linkhdr <= nsize)
                                m->m_data += max_linkhdr;
                        m->m_pkthdr.rcvif = ifp;
                        m->m_pkthdr.len = len;
                        flags = 0;
                }

                copy(buf, m->m_data, (unsigned)m->m_len);
                buf += m->m_len;
                len -= m->m_len;
                *mtail = m;
                mtail = &m->m_next;
        }

        return (mfirst);
}

/*
 * 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(struct mbuf *m0, int off, int len, caddr_t cp)
{
        int mlen;
        struct mbuf *m = m0, *n;
        int totlen = 0;

        if (m0 == NULL)
                return;
        while (off > (mlen = m->m_len)) {
                off -= mlen;
                totlen += mlen;
                if (m->m_next == NULL) {
                        n = m_getclr(MB_DONTWAIT, m->m_type);
                        if (n == NULL)
                                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 == NULL) {
                        n = m_get(MB_DONTWAIT, m->m_type);
                        if (n == NULL)
                                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;
}

void
m_print(const struct mbuf *m)
{
        int len;
        const struct mbuf *m2;

        len = m->m_pkthdr.len;
        m2 = m;
        while (len) {
                kprintf("%p %*D\n", m2, m2->m_len, (u_char *)m2->m_data, "-");
                len -= m2->m_len;
                m2 = m2->m_next;
        }
        return;
}

/*
 * "Move" mbuf pkthdr from "from" to "to".
 * "from" must have M_PKTHDR set, and "to" must be empty.
 */
void
m_move_pkthdr(struct mbuf *to, struct mbuf *from)
{
        KASSERT((to->m_flags & M_PKTHDR), ("m_move_pkthdr: not packet header"));

        to->m_flags |= from->m_flags & M_COPYFLAGS;
        to->m_pkthdr = from->m_pkthdr;          /* especially tags */
        SLIST_INIT(&from->m_pkthdr.tags);       /* purge tags from src */
}

/*
 * Duplicate "from"'s mbuf pkthdr in "to".
 * "from" must have M_PKTHDR set, and "to" must be empty.
 * In particular, this does a deep copy of the packet tags.
 */
int
m_dup_pkthdr(struct mbuf *to, const struct mbuf *from, int how)
{
        KASSERT((to->m_flags & M_PKTHDR), ("m_dup_pkthdr: not packet header"));

        to->m_flags = (from->m_flags & M_COPYFLAGS) |
                      (to->m_flags & ~M_COPYFLAGS);
        to->m_pkthdr = from->m_pkthdr;
        SLIST_INIT(&to->m_pkthdr.tags);
        return (m_tag_copy_chain(to, from, how));
}

/*
 * Defragment a mbuf chain, returning the shortest possible
 * chain of mbufs and clusters.  If allocation fails and
 * this cannot be completed, NULL will be returned, but
 * the passed in chain will be unchanged.  Upon success,
 * the original chain will be freed, and the new chain
 * will be returned.
 *
 * If a non-packet header is passed in, the original
 * mbuf (chain?) will be returned unharmed.
 *
 * m_defrag_nofree doesn't free the passed in mbuf.
 */
struct mbuf *
m_defrag(struct mbuf *m0, int how)
{
        struct mbuf *m_new;

        if ((m_new = m_defrag_nofree(m0, how)) == NULL)
                return (NULL);
        if (m_new != m0)
                m_freem(m0);
        return (m_new);
}

struct mbuf *
m_defrag_nofree(struct mbuf *m0, int how)
{
        struct mbuf     *m_new = NULL, *m_final = NULL;
        int             progress = 0, length, nsize;

        if (!(m0->m_flags & M_PKTHDR))
                return (m0);

#ifdef MBUF_STRESS_TEST
        if (m_defragrandomfailures) {
                int temp = karc4random() & 0xff;
                if (temp == 0xba)
                        goto nospace;
        }
#endif
        
        m_final = m_getl(m0->m_pkthdr.len, how, MT_DATA, M_PKTHDR, &nsize);
        if (m_final == NULL)
                goto nospace;
        m_final->m_len = 0;     /* in case m0->m_pkthdr.len is zero */

        if (m_dup_pkthdr(m_final, m0, how) == 0)
                goto nospace;

        m_new = m_final;

        while (progress < m0->m_pkthdr.len) {
                length = m0->m_pkthdr.len - progress;
                if (length > MCLBYTES)
                        length = MCLBYTES;

                if (m_new == NULL) {
                        m_new = m_getl(length, how, MT_DATA, 0, &nsize);
                        if (m_new == NULL)
                                goto nospace;
                }

                m_copydata(m0, progress, length, mtod(m_new, caddr_t));
                progress += length;
                m_new->m_len = length;
                if (m_new != m_final)
                        m_cat(m_final, m_new);
                m_new = NULL;
        }
        if (m0->m_next == NULL)
                m_defraguseless++;
        m_defragpackets++;
        m_defragbytes += m_final->m_pkthdr.len;
        return (m_final);
nospace:
        m_defragfailure++;
        if (m_new)
                m_free(m_new);
        m_freem(m_final);
        return (NULL);
}

/*
 * Move data from uio into mbufs.
 */
struct mbuf *
m_uiomove(struct uio *uio)
{
        struct mbuf *m;                 /* current working mbuf */
        struct mbuf *head = NULL;       /* result mbuf chain */
        struct mbuf **mp = &head;
        int resid = uio->uio_resid, nsize, flags = M_PKTHDR, error;

        do {
                m = m_getl(resid, MB_WAIT, MT_DATA, flags, &nsize);
                if (flags) {
                        m->m_pkthdr.len = 0;
                        /* Leave room for protocol headers. */
                        if (resid < MHLEN)
                                MH_ALIGN(m, resid);
                        flags = 0;
                }
                m->m_len = min(nsize, resid);
                error = uiomove(mtod(m, caddr_t), m->m_len, uio);
                if (error) {
                        m_free(m);
                        goto failed;
                }
                *mp = m;
                mp = &m->m_next;
                head->m_pkthdr.len += m->m_len;
                resid -= m->m_len;
        } while (resid > 0);

        return (head);

failed:
        m_freem(head);
        return (NULL);
}

struct mbuf *
m_last(struct mbuf *m)
{
        while (m->m_next)
                m = m->m_next;
        return (m);
}

/*
 * Return the number of bytes in an mbuf chain.
 * If lastm is not NULL, also return the last mbuf.
 */
u_int
m_lengthm(struct mbuf *m, struct mbuf **lastm)
{
        u_int len = 0;
        struct mbuf *prev = m;

        while (m) {
                len += m->m_len;
                prev = m;
                m = m->m_next;
        }
        if (lastm != NULL)
                *lastm = prev;
        return (len);
}

/*
 * Like m_lengthm(), except also keep track of mbuf usage.
 */
u_int
m_countm(struct mbuf *m, struct mbuf **lastm, u_int *pmbcnt)
{
        u_int len = 0, mbcnt = 0;
        struct mbuf *prev = m;

        while (m) {
                len += m->m_len;
                mbcnt += MSIZE;
                if (m->m_flags & M_EXT)
                        mbcnt += m->m_ext.ext_size;
                prev = m;
                m = m->m_next;
        }
        if (lastm != NULL)
                *lastm = prev;
        *pmbcnt = mbcnt;
        return (len);
}