FreeBSD/Linux Kernel Cross Reference
sys/kern/uipc_mbuf.c

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * 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. 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
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_param.h"
    #include "opt_mbuf_stress_test.h"
    #include "opt_mbuf_profiling.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/limits.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/mbuf.h>
    #include <sys/sysctl.h>
    #include <sys/domain.h>
    #include <sys/protosw.h>
    #include <sys/uio.h>
    #include <sys/vmmeter.h>
    #include <sys/sbuf.h>
    #include <sys/sdt.h>
    #include <vm/vm.h>
    #include <vm/vm_pageout.h>
    #include <vm/vm_page.h>
    
    SDT_PROBE_DEFINE5_XLATE(sdt, , , m__init,
        "struct mbuf *", "mbufinfo_t *",
        "uint32_t", "uint32_t",
        "uint16_t", "uint16_t",
        "uint32_t", "uint32_t",
        "uint32_t", "uint32_t");
    
    SDT_PROBE_DEFINE3_XLATE(sdt, , , m__gethdr_raw,
        "uint32_t", "uint32_t",
        "uint16_t", "uint16_t",
        "struct mbuf *", "mbufinfo_t *");
    
    SDT_PROBE_DEFINE3_XLATE(sdt, , , m__gethdr,
        "uint32_t", "uint32_t",
        "uint16_t", "uint16_t",
        "struct mbuf *", "mbufinfo_t *");
    
    SDT_PROBE_DEFINE3_XLATE(sdt, , , m__get_raw,
        "uint32_t", "uint32_t",
        "uint16_t", "uint16_t",
        "struct mbuf *", "mbufinfo_t *");
    
    SDT_PROBE_DEFINE3_XLATE(sdt, , , m__get,
        "uint32_t", "uint32_t",
        "uint16_t", "uint16_t",
        "struct mbuf *", "mbufinfo_t *");
    
    SDT_PROBE_DEFINE4_XLATE(sdt, , , m__getcl,
        "uint32_t", "uint32_t",
        "uint16_t", "uint16_t",
        "uint32_t", "uint32_t",
        "struct mbuf *", "mbufinfo_t *");
    
    SDT_PROBE_DEFINE5_XLATE(sdt, , , m__getjcl,
        "uint32_t", "uint32_t",
        "uint16_t", "uint16_t",
        "uint32_t", "uint32_t",
        "uint32_t", "uint32_t",
        "struct mbuf *", "mbufinfo_t *");
    
    SDT_PROBE_DEFINE3_XLATE(sdt, , , m__clget,
       "struct mbuf *", "mbufinfo_t *",
       "uint32_t", "uint32_t",
       "uint32_t", "uint32_t");
   
   SDT_PROBE_DEFINE4_XLATE(sdt, , , m__cljget,
       "struct mbuf *", "mbufinfo_t *",
       "uint32_t", "uint32_t",
       "uint32_t", "uint32_t",
       "void*", "void*");
   
   SDT_PROBE_DEFINE(sdt, , , m__cljset);
   
   SDT_PROBE_DEFINE1_XLATE(sdt, , , m__free,
           "struct mbuf *", "mbufinfo_t *");
   
   SDT_PROBE_DEFINE1_XLATE(sdt, , , m__freem,
       "struct mbuf *", "mbufinfo_t *");
   
   #include <security/mac/mac_framework.h>
   
   /*
    * Provide minimum possible defaults for link and protocol header space,
    * assuming IPv4 over Ethernet.  Enabling IPv6, IEEE802.11 or some other
    * protocol may grow these values.
    */
   u_int   max_linkhdr = 16;
   u_int   max_protohdr = 40;
   u_int   max_hdr = 16 + 40;
   SYSCTL_INT(_kern_ipc, KIPC_MAX_LINKHDR, max_linkhdr, CTLFLAG_RD,
              &max_linkhdr, 16, "Size of largest link layer header");
   SYSCTL_INT(_kern_ipc, KIPC_MAX_PROTOHDR, max_protohdr, CTLFLAG_RD,
              &max_protohdr, 40, "Size of largest protocol layer header");
   SYSCTL_INT(_kern_ipc, KIPC_MAX_HDR, max_hdr, CTLFLAG_RD,
              &max_hdr, 16 + 40, "Size of largest link plus protocol header");
   
   static void
   max_hdr_grow(void)
   {
   
           max_hdr = max_linkhdr + max_protohdr;
           MPASS(max_hdr <= MHLEN);
   }
   
   void
   max_linkhdr_grow(u_int new)
   {
   
           if (new > max_linkhdr) {
                   max_linkhdr = new;
                   max_hdr_grow();
           }
   }
   
   void
   max_protohdr_grow(u_int new)
   {
   
           if (new > max_protohdr) {
                   max_protohdr = new;
                   max_hdr_grow();
           }
   }
   
   #ifdef MBUF_STRESS_TEST
   int     m_defragpackets;
   int     m_defragbytes;
   int     m_defraguseless;
   int     m_defragfailure;
   int     m_defragrandomfailures;
   
   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, "");
   SYSCTL_INT(_kern_ipc, OID_AUTO, m_defragrandomfailures, CTLFLAG_RW,
              &m_defragrandomfailures, 0, "");
   #endif
   
   /*
    * Ensure the correct size of various mbuf parameters.  It could be off due
    * to compiler-induced padding and alignment artifacts.
    */
   CTASSERT(MSIZE - offsetof(struct mbuf, m_dat) == MLEN);
   CTASSERT(MSIZE - offsetof(struct mbuf, m_pktdat) == MHLEN);
   
   /*
    * mbuf data storage should be 64-bit aligned regardless of architectural
    * pointer size; check this is the case with and without a packet header.
    */
   CTASSERT(offsetof(struct mbuf, m_dat) % 8 == 0);
   CTASSERT(offsetof(struct mbuf, m_pktdat) % 8 == 0);
   
   /*
    * While the specific values here don't matter too much (i.e., +/- a few
    * words), we do want to ensure that changes to these values are carefully
    * reasoned about and properly documented.  This is especially the case as
    * network-protocol and device-driver modules encode these layouts, and must
    * be recompiled if the structures change.  Check these values at compile time
    * against the ones documented in comments in mbuf.h.
    *
    * NB: Possibly they should be documented there via #define's and not just
    * comments.
    */
   #if defined(__LP64__)
   CTASSERT(offsetof(struct mbuf, m_dat) == 32);
   CTASSERT(sizeof(struct pkthdr) == 64);
   CTASSERT(sizeof(struct m_ext) == 160);
   #else
   CTASSERT(offsetof(struct mbuf, m_dat) == 24);
   CTASSERT(sizeof(struct pkthdr) == 56);
   #if defined(__powerpc__) && defined(BOOKE)
   /* PowerPC booke has 64-bit physical pointers. */
   CTASSERT(sizeof(struct m_ext) == 176);
   #else
   CTASSERT(sizeof(struct m_ext) == 172);
   #endif
   #endif
   
   /*
    * Assert that the queue(3) macros produce code of the same size as an old
    * plain pointer does.
    */
   #ifdef INVARIANTS
   static struct mbuf __used m_assertbuf;
   CTASSERT(sizeof(m_assertbuf.m_slist) == sizeof(m_assertbuf.m_next));
   CTASSERT(sizeof(m_assertbuf.m_stailq) == sizeof(m_assertbuf.m_next));
   CTASSERT(sizeof(m_assertbuf.m_slistpkt) == sizeof(m_assertbuf.m_nextpkt));
   CTASSERT(sizeof(m_assertbuf.m_stailqpkt) == sizeof(m_assertbuf.m_nextpkt));
   #endif
   
   /*
    * Attach the cluster from *m to *n, set up m_ext in *n
    * and bump the refcount of the cluster.
    */
   void
   mb_dupcl(struct mbuf *n, struct mbuf *m)
   {
           volatile u_int *refcnt;
   
           KASSERT(m->m_flags & (M_EXT|M_EXTPG),
               ("%s: M_EXT|M_EXTPG not set on %p", __func__, m));
           KASSERT(!(n->m_flags & (M_EXT|M_EXTPG)),
               ("%s: M_EXT|M_EXTPG set on %p", __func__, n));
   
           /*
            * Cache access optimization.
            *
            * o Regular M_EXT storage doesn't need full copy of m_ext, since
            *   the holder of the 'ext_count' is responsible to carry the free
            *   routine and its arguments.
            * o M_EXTPG data is split between main part of mbuf and m_ext, the
            *   main part is copied in full, the m_ext part is similar to M_EXT.
            * o EXT_EXTREF, where 'ext_cnt' doesn't point into mbuf at all, is
            *   special - it needs full copy of m_ext into each mbuf, since any
            *   copy could end up as the last to free.
            */
           if (m->m_flags & M_EXTPG) {
                   bcopy(&m->m_epg_startcopy, &n->m_epg_startcopy,
                       __rangeof(struct mbuf, m_epg_startcopy, m_epg_endcopy));
                   bcopy(&m->m_ext, &n->m_ext, m_epg_ext_copylen);
           } else if (m->m_ext.ext_type == EXT_EXTREF)
                   bcopy(&m->m_ext, &n->m_ext, sizeof(struct m_ext));
           else
                   bcopy(&m->m_ext, &n->m_ext, m_ext_copylen);
   
           n->m_flags |= m->m_flags & (M_RDONLY | M_EXT | M_EXTPG);
   
           /* See if this is the mbuf that holds the embedded refcount. */
           if (m->m_ext.ext_flags & EXT_FLAG_EMBREF) {
                   refcnt = n->m_ext.ext_cnt = &m->m_ext.ext_count;
                   n->m_ext.ext_flags &= ~EXT_FLAG_EMBREF;
           } else {
                   KASSERT(m->m_ext.ext_cnt != NULL,
                       ("%s: no refcounting pointer on %p", __func__, m));
                   refcnt = m->m_ext.ext_cnt;
           }
   
           if (*refcnt == 1)
                   *refcnt += 1;
           else
                   atomic_add_int(refcnt, 1);
   }
   
   void
   m_demote_pkthdr(struct mbuf *m)
   {
   
           M_ASSERTPKTHDR(m);
           M_ASSERT_NO_SND_TAG(m);
   
           m_tag_delete_chain(m, NULL);
           m->m_flags &= ~M_PKTHDR;
           bzero(&m->m_pkthdr, sizeof(struct pkthdr));
   }
   
   /*
    * Clean up mbuf (chain) from any tags and packet headers.
    * If "all" is set then the first mbuf in the chain will be
    * cleaned too.
    */
   void
   m_demote(struct mbuf *m0, int all, int flags)
   {
           struct mbuf *m;
   
           flags |= M_DEMOTEFLAGS;
   
           for (m = all ? m0 : m0->m_next; m != NULL; m = m->m_next) {
                   KASSERT(m->m_nextpkt == NULL, ("%s: m_nextpkt in m %p, m0 %p",
                       __func__, m, m0));
                   if (m->m_flags & M_PKTHDR)
                           m_demote_pkthdr(m);
                   m->m_flags &= flags;
           }
   }
   
   /*
    * Sanity checks on mbuf (chain) for use in KASSERT() and general
    * debugging.
    * Returns 0 or panics when bad and 1 on all tests passed.
    * Sanitize, 0 to run M_SANITY_ACTION, 1 to garble things so they
    * blow up later.
    */
   int
   m_sanity(struct mbuf *m0, int sanitize)
   {
           struct mbuf *m;
           caddr_t a, b;
           int pktlen = 0;
   
   #ifdef INVARIANTS
   #define M_SANITY_ACTION(s)      panic("mbuf %p: " s, m)
   #else
   #define M_SANITY_ACTION(s)      printf("mbuf %p: " s, m)
   #endif
   
           for (m = m0; m != NULL; m = m->m_next) {
                   /*
                    * Basic pointer checks.  If any of these fails then some
                    * unrelated kernel memory before or after us is trashed.
                    * No way to recover from that.
                    */
                   a = M_START(m);
                   b = a + M_SIZE(m);
                   if ((caddr_t)m->m_data < a)
                           M_SANITY_ACTION("m_data outside mbuf data range left");
                   if ((caddr_t)m->m_data > b)
                           M_SANITY_ACTION("m_data outside mbuf data range right");
                   if ((caddr_t)m->m_data + m->m_len > b)
                           M_SANITY_ACTION("m_data + m_len exeeds mbuf space");
   
                   /* m->m_nextpkt may only be set on first mbuf in chain. */
                   if (m != m0 && m->m_nextpkt != NULL) {
                           if (sanitize) {
                                   m_freem(m->m_nextpkt);
                                   m->m_nextpkt = (struct mbuf *)0xDEADC0DE;
                           } else
                                   M_SANITY_ACTION("m->m_nextpkt on in-chain mbuf");
                   }
   
                   /* packet length (not mbuf length!) calculation */
                   if (m0->m_flags & M_PKTHDR)
                           pktlen += m->m_len;
   
                   /* m_tags may only be attached to first mbuf in chain. */
                   if (m != m0 && m->m_flags & M_PKTHDR &&
                       !SLIST_EMPTY(&m->m_pkthdr.tags)) {
                           if (sanitize) {
                                   m_tag_delete_chain(m, NULL);
                                   /* put in 0xDEADC0DE perhaps? */
                           } else
                                   M_SANITY_ACTION("m_tags on in-chain mbuf");
                   }
   
                   /* M_PKTHDR may only be set on first mbuf in chain */
                   if (m != m0 && m->m_flags & M_PKTHDR) {
                           if (sanitize) {
                                   bzero(&m->m_pkthdr, sizeof(m->m_pkthdr));
                                   m->m_flags &= ~M_PKTHDR;
                                   /* put in 0xDEADCODE and leave hdr flag in */
                           } else
                                   M_SANITY_ACTION("M_PKTHDR on in-chain mbuf");
                   }
           }
           m = m0;
           if (pktlen && pktlen != m->m_pkthdr.len) {
                   if (sanitize)
                           m->m_pkthdr.len = 0;
                   else
                           M_SANITY_ACTION("m_pkthdr.len != mbuf chain length");
           }
           return 1;
   
   #undef  M_SANITY_ACTION
   }
   
   /*
    * Non-inlined part of m_init().
    */
   int
   m_pkthdr_init(struct mbuf *m, int how)
   {
   #ifdef MAC
           int error;
   #endif
           m->m_data = m->m_pktdat;
           bzero(&m->m_pkthdr, sizeof(m->m_pkthdr));
   #ifdef NUMA
           m->m_pkthdr.numa_domain = M_NODOM;
   #endif
   #ifdef MAC
           /* If the label init fails, fail the alloc */
           error = mac_mbuf_init(m, how);
           if (error)
                   return (error);
   #endif
   
           return (0);
   }
   
   /*
    * "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)
   {
   
   #if 0
           /* see below for why these are not enabled */
           M_ASSERTPKTHDR(to);
           /* Note: with MAC, this may not be a good assertion. */
           KASSERT(SLIST_EMPTY(&to->m_pkthdr.tags),
               ("m_move_pkthdr: to has tags"));
   #endif
   #ifdef MAC
           /*
            * XXXMAC: It could be this should also occur for non-MAC?
            */
           if (to->m_flags & M_PKTHDR)
                   m_tag_delete_chain(to, NULL);
   #endif
           to->m_flags = (from->m_flags & M_COPYFLAGS) |
               (to->m_flags & (M_EXT | M_EXTPG));
           if ((to->m_flags & M_EXT) == 0)
                   to->m_data = to->m_pktdat;
           to->m_pkthdr = from->m_pkthdr;          /* especially tags */
           SLIST_INIT(&from->m_pkthdr.tags);       /* purge tags from src */
           from->m_flags &= ~M_PKTHDR;
           if (from->m_pkthdr.csum_flags & CSUM_SND_TAG) {
                   from->m_pkthdr.csum_flags &= ~CSUM_SND_TAG;
                   from->m_pkthdr.snd_tag = NULL;
           }
   }
   
   /*
    * 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)
   {
   
   #if 0
           /*
            * The mbuf allocator only initializes the pkthdr
            * when the mbuf is allocated with m_gethdr(). Many users
            * (e.g. m_copy*, m_prepend) use m_get() and then
            * smash the pkthdr as needed causing these
            * assertions to trip.  For now just disable them.
            */
           M_ASSERTPKTHDR(to);
           /* Note: with MAC, this may not be a good assertion. */
           KASSERT(SLIST_EMPTY(&to->m_pkthdr.tags), ("m_dup_pkthdr: to has tags"));
   #endif
           MBUF_CHECKSLEEP(how);
   #ifdef MAC
           if (to->m_flags & M_PKTHDR)
                   m_tag_delete_chain(to, NULL);
   #endif
           to->m_flags = (from->m_flags & M_COPYFLAGS) |
               (to->m_flags & (M_EXT | M_EXTPG));
           if ((to->m_flags & M_EXT) == 0)
                   to->m_data = to->m_pktdat;
           to->m_pkthdr = from->m_pkthdr;
           if (from->m_pkthdr.csum_flags & CSUM_SND_TAG)
                   m_snd_tag_ref(from->m_pkthdr.snd_tag);
           SLIST_INIT(&to->m_pkthdr.tags);
           return (m_tag_copy_chain(to, from, how));
   }
   
   /*
    * Lesser-used path for M_PREPEND:
    * allocate new mbuf to prepend to chain,
    * 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 < M_SIZE(m))
                   M_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 M_WAITOK/M_NOWAIT from caller.
    * Note that the copy is read-only, because clusters are not copied,
    * only their reference counts are incremented.
    */
   struct mbuf *
   m_copym(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));
           MBUF_CHECKSLEEP(wait);
           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 = NULL;
           while (len > 0) {
                   if (m == NULL) {
                           KASSERT(len == M_COPYALL,
                               ("m_copym, length > size of mbuf chain"));
                           break;
                   }
                   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|M_EXTPG)) {
                           n->m_data = m->m_data + off;
                           mb_dupcl(n, m);
                   } else
                           bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
                               (u_int)n->m_len);
                   if (len != M_COPYALL)
                           len -= n->m_len;
                   off = 0;
                   m = m->m_next;
                   np = &n->m_next;
           }
   
           return (top);
   nospace:
           m_freem(top);
           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 still have the room available.
    */
   struct mbuf *
   m_copypacket(struct mbuf *m, int how)
   {
           struct mbuf *top, *n, *o;
   
           MBUF_CHECKSLEEP(how);
           n = m_get(how, m->m_type);
           top = n;
           if (n == NULL)
                   goto nospace;
   
           if (!m_dup_pkthdr(n, m, how))
                   goto nospace;
           n->m_len = m->m_len;
           if (m->m_flags & (M_EXT|M_EXTPG)) {
                   n->m_data = m->m_data;
                   mb_dupcl(n, m);
           } 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 == NULL)
                           goto nospace;
   
                   n->m_next = o;
                   n = n->m_next;
   
                   n->m_len = m->m_len;
                   if (m->m_flags & (M_EXT|M_EXTPG)) {
                           n->m_data = m->m_data;
                           mb_dupcl(n, m);
                   } else {
                           bcopy(mtod(m, char *), mtod(n, char *), n->m_len);
                   }
   
                   m = m->m_next;
           }
           return top;
   nospace:
           m_freem(top);
           return (NULL);
   }
   
   static void
   m_copyfromunmapped(const struct mbuf *m, int off, int len, caddr_t cp)
   {
           struct iovec iov;
           struct uio uio;
           int error __diagused;
   
           KASSERT(off >= 0, ("m_copyfromunmapped: negative off %d", off));
           KASSERT(len >= 0, ("m_copyfromunmapped: negative len %d", len));
           KASSERT(off < m->m_len,
               ("m_copyfromunmapped: len exceeds mbuf length"));
           iov.iov_base = cp;
           iov.iov_len = len;
           uio.uio_resid = len;
           uio.uio_iov = &iov;
           uio.uio_segflg = UIO_SYSSPACE;
           uio.uio_iovcnt = 1;
           uio.uio_offset = 0;
           uio.uio_rw = UIO_READ;
           error = m_unmapped_uiomove(m, off, &uio, len);
           KASSERT(error == 0, ("m_unmapped_uiomove failed: off %d, len %d", off,
              len));
   }
   
   /*
    * 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)
   {
           u_int 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);
                   if ((m->m_flags & M_EXTPG) != 0)
                           m_copyfromunmapped(m, off, count, cp);
                   else
                           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(const struct mbuf *m, int how)
   {
           struct mbuf **p, *top = NULL;
           int remain, moff, nsize;
   
           MBUF_CHECKSLEEP(how);
           /* Sanity check */
           if (m == NULL)
                   return (NULL);
           M_ASSERTPKTHDR(m);
   
           /* 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 */
                   if (remain >= MINCLSIZE) {
                           n = m_getcl(how, m->m_type, 0);
                           nsize = MCLBYTES;
                   } else {
                           n = m_get(how, m->m_type);
                           nsize = MLEN;
                   }
                   if (n == NULL)
                           goto nospace;
   
                   if (top == NULL) {              /* First one, must be PKTHDR */
                           if (!m_dup_pkthdr(n, m, how)) {
                                   m_free(n);
                                   goto nospace;
                           }
                           if ((n->m_flags & M_EXT) == 0)
                                   nsize = MHLEN;
                           n->m_flags &= ~M_RDONLY;
                   }
                   n->m_len = 0;
   
                   /* Link it into the new chain */
                   *p = n;
                   p = &n->m_next;
   
                   /* Copy data from original mbuf(s) into new mbuf */
                   while (n->m_len < nsize && m != NULL) {
                           int chunk = min(nsize - n->m_len, m->m_len - moff);
   
                           m_copydata(m, moff, chunk, n->m_data + n->m_len);
                           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);
           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)
   {
           while (m->m_next)
                   m = m->m_next;
           while (n) {
                   if (!M_WRITABLE(m) ||
                       (n->m_flags & M_EXTPG) != 0 ||
                       M_TRAILINGSPACE(m) < n->m_len) {
                           /* 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);
           }
   }
   
   /*
    * Concatenate two pkthdr mbuf chains.
    */
   void
   m_catpkt(struct mbuf *m, struct mbuf *n)
   {
   
           M_ASSERTPKTHDR(m);
           M_ASSERTPKTHDR(n);
   
           m->m_pkthdr.len += n->m_pkthdr.len;
           m_demote(n, 1, 0);
   
           m_cat(m, 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;
                           }
                   }
                   if (mp->m_flags & M_PKTHDR)
                           mp->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;
                                   if (m->m_next != NULL) {
                                           m_freem(m->m_next);
                                           m->m_next = NULL;
                                   }
                                   break;
                           }
                           count -= m->m_len;
                   }
           }
   }
   
   void
   m_adj_decap(struct mbuf *mp, int len)
   {
           uint8_t rsstype;
   
           m_adj(mp, len);
           if ((mp->m_flags & M_PKTHDR) != 0) {
                   /*
                    * If flowid was calculated by card from the inner
                    * headers, move flowid to the decapsulated mbuf
                    * chain, otherwise clear.  This depends on the
                    * internals of m_adj, which keeps pkthdr as is, in
                    * particular not changing rsstype and flowid.
                    */
                   rsstype = mp->m_pkthdr.rsstype;
                   if ((rsstype & M_HASHTYPE_INNER) != 0) {
                           M_HASHTYPE_SET(mp, rsstype & ~M_HASHTYPE_INNER);
                   } else {
                           M_HASHTYPE_CLEAR(mp);
                   }
           }
   }
   
   /*
    * Rearange 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;
   
           KASSERT((n->m_flags & M_EXTPG) == 0,
               ("%s: unmapped mbuf %p", __func__, n));
   
           /*
            * 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;
                   m = m_get(M_NOWAIT, n->m_type);
                   if (m == NULL)
                           goto bad;
                   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,
                     (u_int)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);
           return (NULL);
   }
   
   /*
    * Like m_pullup(), except a new mbuf is always allocated, and we allow
    * the amount of empty space before the data in the new mbuf to be specified
    * (in the event that the caller expects to prepend later).
    */
   struct mbuf *
   m_copyup(struct mbuf *n, int len, int dstoff)
   {
           struct mbuf *m;
           int count, space;
   
           if (len > (MHLEN - dstoff))
                   goto bad;
           m = m_get(M_NOWAIT, n->m_type);
           if (m == NULL)
                   goto bad;
          if (n->m_flags & M_PKTHDR)
                  m_move_pkthdr(m, n);
          m->m_data += dstoff;
          space = &m->m_dat[MLEN] - (m->m_data + m->m_len);
          do {
                  count = min(min(max(len, max_protohdr), space), n->m_len);
                  memcpy(mtod(m, caddr_t) + m->m_len, mtod(n, caddr_t),
                      (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);
          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;
          u_int len = len0, remain;
  
          MBUF_CHECKSLEEP(wait);
          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 && remain == 0) {
                  n = m_gethdr(wait, m0->m_type);
                  if (n == NULL)
                          return (NULL);
                  n->m_next = m->m_next;
                  m->m_next = NULL;
                  if (m0->m_pkthdr.csum_flags & CSUM_SND_TAG) {
                          n->m_pkthdr.snd_tag =
                              m_snd_tag_ref(m0->m_pkthdr.snd_tag);
                          n->m_pkthdr.csum_flags |= CSUM_SND_TAG;
                  } else
                          n->m_pkthdr.rcvif = m0->m_pkthdr.rcvif;
                  n->m_pkthdr.len = m0->m_pkthdr.len - len0;
                  m0->m_pkthdr.len = len0;
                  return (n);
          } else if (m0->m_flags & M_PKTHDR) {
                  n = m_gethdr(wait, m0->m_type);
                  if (n == NULL)
                          return (NULL);
                  if (m0->m_pkthdr.csum_flags & CSUM_SND_TAG) {
                          n->m_pkthdr.snd_tag =
                              m_snd_tag_ref(m0->m_pkthdr.snd_tag);
                          n->m_pkthdr.csum_flags |= CSUM_SND_TAG;
                  } else
                          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|M_EXTPG))
                          goto extpacket;
                  if (remain > MHLEN) {
                          /* m can't be the lead packet */
                          M_ALIGN(n, 0);
                          n->m_next = m_split(m, len, wait);
                          if (n->m_next == NULL) {
                                  (void) m_free(n);
                                  return (NULL);
                          } else {
                                  n->m_len = 0;
                                  return (n);
                          }
                  } else
                          M_ALIGN(n, remain);
          } else if (remain == 0) {
                  n = m->m_next;
                  m->m_next = NULL;
                  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|M_EXTPG)) {
                  n->m_data = m->m_data + len;
                  mb_dupcl(n, m);
          } 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 = NULL;
          return (n);
  }
  /*
   * Routine to copy from device local memory into mbufs.
   * Note that `off' argument is offset into first mbuf of target chain from
   * which to begin copying the data to.
   */
  struct mbuf *
  m_devget(char *buf, int totlen, int off, struct ifnet *ifp,
      void (*copy)(char *from, caddr_t to, u_int len))
  {
          struct mbuf *m;
          struct mbuf *top = NULL, **mp = &top;
          int len;
  
          if (off < 0 || off > MHLEN)
                  return (NULL);
  
          while (totlen > 0) {
                  if (top == NULL) {      /* First one, must be PKTHDR */
                          if (totlen + off >= MINCLSIZE) {
                                  m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
                                  len = MCLBYTES;
                          } else {
                                  m = m_gethdr(M_NOWAIT, MT_DATA);
                                  len = MHLEN;
  
                                  /* Place initial small packet/header at end of mbuf */
                                  if (m && totlen + off + max_linkhdr <= MHLEN) {
                                          m->m_data += max_linkhdr;
                                          len -= max_linkhdr;
                                  }
                          }
                          if (m == NULL)
                                  return NULL;
                          m->m_pkthdr.rcvif = ifp;
                          m->m_pkthdr.len = totlen;
                  } else {
                          if (totlen + off >= MINCLSIZE) {
                                  m = m_getcl(M_NOWAIT, MT_DATA, 0);
                                  len = MCLBYTES;
                          } else {
                                  m = m_get(M_NOWAIT, MT_DATA);
                                  len = MLEN;
                          }
                          if (m == NULL) {
                                  m_freem(top);
                                  return NULL;
                          }
                  }
                  if (off) {
                          m->m_data += off;
                          len -= off;
                          off = 0;
                  }
                  m->m_len = len = min(totlen, len);
                  if (copy)
                          copy(buf, mtod(m, caddr_t), (u_int)len);
                  else
                          bcopy(buf, mtod(m, caddr_t), (u_int)len);
                  buf += len;
                  *mp = m;
                  mp = &m->m_next;
                  totlen -= len;
          }
          return (top);
  }
  
  static void
  m_copytounmapped(const struct mbuf *m, int off, int len, c_caddr_t cp)
  {
          struct iovec iov;
          struct uio uio;
          int error __diagused;
  
          KASSERT(off >= 0, ("m_copytounmapped: negative off %d", off));
          KASSERT(len >= 0, ("m_copytounmapped: negative len %d", len));
          KASSERT(off < m->m_len, ("m_copytounmapped: len exceeds mbuf length"));
          iov.iov_base = __DECONST(caddr_t, cp);
          iov.iov_len = len;
          uio.uio_resid = len;
          uio.uio_iov = &iov;
          uio.uio_segflg = UIO_SYSSPACE;
          uio.uio_iovcnt = 1;
          uio.uio_offset = 0;
          uio.uio_rw = UIO_WRITE;
          error = m_unmapped_uiomove(m, off, &uio, len);
          KASSERT(error == 0, ("m_unmapped_uiomove failed: off %d, len %d", off,
             len));
  }
  
  /*
   * 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, c_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_get(M_NOWAIT, m->m_type);
                          if (n == NULL)
                                  goto out;
                          bzero(mtod(n, caddr_t), MLEN);
                          n->m_len = min(MLEN, len + off);
                          m->m_next = n;
                  }
                  m = m->m_next;
          }
          while (len > 0) {
                  if (m->m_next == NULL && (len > m->m_len - off)) {
                          m->m_len += min(len - (m->m_len - off),
                              M_TRAILINGSPACE(m));
                  }
                  mlen = min (m->m_len - off, len);
                  if ((m->m_flags & M_EXTPG) != 0)
                          m_copytounmapped(m, off, mlen, cp);
                  else
                          bcopy(cp, off + mtod(m, caddr_t), (u_int)mlen);
                  cp += mlen;
                  len -= mlen;
                  mlen += off;
                  off = 0;
                  totlen += mlen;
                  if (len == 0)
                          break;
                  if (m->m_next == NULL) {
                          n = m_get(M_NOWAIT, 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;
  }
  
  /*
   * Append the specified data to the indicated mbuf chain,
   * Extend the mbuf chain if the new data does not fit in
   * existing space.
   *
   * Return 1 if able to complete the job; otherwise 0.
   */
  int
  m_append(struct mbuf *m0, int len, c_caddr_t cp)
  {
          struct mbuf *m, *n;
          int remainder, space;
  
          for (m = m0; m->m_next != NULL; m = m->m_next)
                  ;
          remainder = len;
          space = M_TRAILINGSPACE(m);
          if (space > 0) {
                  /*
                   * Copy into available space.
                   */
                  if (space > remainder)
                          space = remainder;
                  bcopy(cp, mtod(m, caddr_t) + m->m_len, space);
                  m->m_len += space;
                  cp += space, remainder -= space;
          }
          while (remainder > 0) {
                  /*
                   * Allocate a new mbuf; could check space
                   * and allocate a cluster instead.
                   */
                  n = m_get(M_NOWAIT, m->m_type);
                  if (n == NULL)
                          break;
                  n->m_len = min(MLEN, remainder);
                  bcopy(cp, mtod(n, caddr_t), n->m_len);
                  cp += n->m_len, remainder -= n->m_len;
                  m->m_next = n;
                  m = n;
          }
          if (m0->m_flags & M_PKTHDR)
                  m0->m_pkthdr.len += len - remainder;
          return (remainder == 0);
  }
  
  static int
  m_apply_extpg_one(struct mbuf *m, int off, int len,
      int (*f)(void *, void *, u_int), void *arg)
  {
          void *p;
          u_int i, count, pgoff, pglen;
          int rval;
  
          KASSERT(PMAP_HAS_DMAP,
              ("m_apply_extpg_one does not support unmapped mbufs"));
          off += mtod(m, vm_offset_t);
          if (off < m->m_epg_hdrlen) {
                  count = min(m->m_epg_hdrlen - off, len);
                  rval = f(arg, m->m_epg_hdr + off, count);
                  if (rval)
                          return (rval);
                  len -= count;
                  off = 0;
          } else
                  off -= m->m_epg_hdrlen;
          pgoff = m->m_epg_1st_off;
          for (i = 0; i < m->m_epg_npgs && len > 0; i++) {
                  pglen = m_epg_pagelen(m, i, pgoff);
                  if (off < pglen) {
                          count = min(pglen - off, len);
                          p = (void *)PHYS_TO_DMAP(m->m_epg_pa[i] + pgoff + off);
                          rval = f(arg, p, count);
                          if (rval)
                                  return (rval);
                          len -= count;
                          off = 0;
                  } else
                          off -= pglen;
                  pgoff = 0;
          }
          if (len > 0) {
                  KASSERT(off < m->m_epg_trllen,
                      ("m_apply_extpg_one: offset beyond trailer"));
                  KASSERT(len <= m->m_epg_trllen - off,
                      ("m_apply_extpg_one: length beyond trailer"));
                  return (f(arg, m->m_epg_trail + off, len));
          }
          return (0);
  }
  
  /* Apply function f to the data in a single mbuf. */
  static int
  m_apply_one(struct mbuf *m, int off, int len,
      int (*f)(void *, void *, u_int), void *arg)
  {
          if ((m->m_flags & M_EXTPG) != 0)
                  return (m_apply_extpg_one(m, off, len, f, arg));
          else
                  return (f(arg, mtod(m, caddr_t) + off, len));
  }
  
  /*
   * Apply function f to the data in an mbuf chain starting "off" bytes from
   * the beginning, continuing for "len" bytes.
   */
  int
  m_apply(struct mbuf *m, int off, int len,
      int (*f)(void *, void *, u_int), void *arg)
  {
          u_int count;
          int rval;
  
          KASSERT(off >= 0, ("m_apply, negative off %d", off));
          KASSERT(len >= 0, ("m_apply, negative len %d", len));
          while (off > 0) {
                  KASSERT(m != NULL, ("m_apply, 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_apply, offset > size of mbuf chain"));
                  count = min(m->m_len - off, len);
                  rval = m_apply_one(m, off, count, f, arg);
                  if (rval)
                          return (rval);
                  len -= count;
                  off = 0;
                  m = m->m_next;
          }
          return (0);
  }
  
  /*
   * Return a pointer to mbuf/offset of location in mbuf chain.
   */
  struct mbuf *
  m_getptr(struct mbuf *m, int loc, int *off)
  {
  
          while (loc >= 0) {
                  /* Normal end of search. */
                  if (m->m_len > loc) {
                          *off = loc;
                          return (m);
                  } else {
                          loc -= m->m_len;
                          if (m->m_next == NULL) {
                                  if (loc == 0) {
                                          /* Point at the end of valid data. */
                                          *off = m->m_len;
                                          return (m);
                                  }
                                  return (NULL);
                          }
                          m = m->m_next;
                  }
          }
          return (NULL);
  }
  
  void
  m_print(const struct mbuf *m, int maxlen)
  {
          int len;
          int pdata;
          const struct mbuf *m2;
  
          if (m == NULL) {
                  printf("mbuf: %p\n", m);
                  return;
          }
  
          if (m->m_flags & M_PKTHDR)
                  len = m->m_pkthdr.len;
          else
                  len = -1;
          m2 = m;
          while (m2 != NULL && (len == -1 || len)) {
                  pdata = m2->m_len;
                  if (maxlen != -1 && pdata > maxlen)
                          pdata = maxlen;
                  printf("mbuf: %p len: %d, next: %p, %b%s", m2, m2->m_len,
                      m2->m_next, m2->m_flags, "\2\20freelist\17skipfw"
                      "\11proto5\10proto4\7proto3\6proto2\5proto1\4rdonly"
                      "\3eor\2pkthdr\1ext", pdata ? "" : "\n");
                  if (pdata)
                          printf(", %*D\n", pdata, (u_char *)m2->m_data, "-");
                  if (len != -1)
                          len -= m2->m_len;
                  m2 = m2->m_next;
          }
          if (len > 0)
                  printf("%d bytes unaccounted for.\n", len);
          return;
  }
  
  u_int
  m_fixhdr(struct mbuf *m0)
  {
          u_int len;
  
          len = m_length(m0, NULL);
          m0->m_pkthdr.len = len;
          return (len);
  }
  
  u_int
  m_length(struct mbuf *m0, struct mbuf **last)
  {
          struct mbuf *m;
          u_int len;
  
          len = 0;
          for (m = m0; m != NULL; m = m->m_next) {
                  len += m->m_len;
                  if (m->m_next == NULL)
                          break;
          }
          if (last != NULL)
                  *last = m;
          return (len);
  }
  
  /*
   * 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.
   */
  struct mbuf *
  m_defrag(struct mbuf *m0, int how)
  {
          struct mbuf *m_new = NULL, *m_final = NULL;
          int progress = 0, length;
  
          MBUF_CHECKSLEEP(how);
          if (!(m0->m_flags & M_PKTHDR))
                  return (m0);
  
          m_fixhdr(m0); /* Needed sanity check */
  
  #ifdef MBUF_STRESS_TEST
          if (m_defragrandomfailures) {
                  int temp = arc4random() & 0xff;
                  if (temp == 0xba)
                          goto nospace;
          }
  #endif
  
          if (m0->m_pkthdr.len > MHLEN)
                  m_final = m_getcl(how, MT_DATA, M_PKTHDR);
          else
                  m_final = m_gethdr(how, MT_DATA);
  
          if (m_final == NULL)
                  goto nospace;
  
          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) {
                          if (length > MLEN)
                                  m_new = m_getcl(how, MT_DATA, 0);
                          else
                                  m_new = m_get(how, MT_DATA);
                          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;
          }
  #ifdef MBUF_STRESS_TEST
          if (m0->m_next == NULL)
                  m_defraguseless++;
  #endif
          m_freem(m0);
          m0 = m_final;
  #ifdef MBUF_STRESS_TEST
          m_defragpackets++;
          m_defragbytes += m0->m_pkthdr.len;
  #endif
          return (m0);
  nospace:
  #ifdef MBUF_STRESS_TEST
          m_defragfailure++;
  #endif
          if (m_final)
                  m_freem(m_final);
          return (NULL);
  }
  
  /*
   * Return the number of fragments an mbuf will use.  This is usually
   * used as a proxy for the number of scatter/gather elements needed by
   * a DMA engine to access an mbuf.  In general mapped mbufs are
   * assumed to be backed by physically contiguous buffers that only
   * need a single fragment.  Unmapped mbufs, on the other hand, can
   * span disjoint physical pages.
   */
  static int
  frags_per_mbuf(struct mbuf *m)
  {
          int frags;
  
          if ((m->m_flags & M_EXTPG) == 0)
                  return (1);
  
          /*
           * The header and trailer are counted as a single fragment
           * each when present.
           *
           * XXX: This overestimates the number of fragments by assuming
           * all the backing physical pages are disjoint.
           */
          frags = 0;
          if (m->m_epg_hdrlen != 0)
                  frags++;
          frags += m->m_epg_npgs;
          if (m->m_epg_trllen != 0)
                  frags++;
  
          return (frags);
  }
  
  /*
   * Defragment an mbuf chain, returning at most maxfrags separate
   * mbufs+clusters.  If this is not possible NULL is returned and
   * the original mbuf chain is left in its present (potentially
   * modified) state.  We use two techniques: collapsing consecutive
   * mbufs and replacing consecutive mbufs by a cluster.
   *
   * NB: this should really be named m_defrag but that name is taken
   */
  struct mbuf *
  m_collapse(struct mbuf *m0, int how, int maxfrags)
  {
          struct mbuf *m, *n, *n2, **prev;
          u_int curfrags;
  
          /*
           * Calculate the current number of frags.
           */
          curfrags = 0;
          for (m = m0; m != NULL; m = m->m_next)
                  curfrags += frags_per_mbuf(m);
          /*
           * First, try to collapse mbufs.  Note that we always collapse
           * towards the front so we don't need to deal with moving the
           * pkthdr.  This may be suboptimal if the first mbuf has much
           * less data than the following.
           */
          m = m0;
  again:
          for (;;) {
                  n = m->m_next;
                  if (n == NULL)
                          break;
                  if (M_WRITABLE(m) &&
                      n->m_len < M_TRAILINGSPACE(m)) {
                          m_copydata(n, 0, n->m_len,
                              mtod(m, char *) + m->m_len);
                          m->m_len += n->m_len;
                          m->m_next = n->m_next;
                          curfrags -= frags_per_mbuf(n);
                          m_free(n);
                          if (curfrags <= maxfrags)
                                  return m0;
                  } else
                          m = n;
          }
          KASSERT(maxfrags > 1,
                  ("maxfrags %u, but normal collapse failed", maxfrags));
          /*
           * Collapse consecutive mbufs to a cluster.
           */
          prev = &m0->m_next;             /* NB: not the first mbuf */
          while ((n = *prev) != NULL) {
                  if ((n2 = n->m_next) != NULL &&
                      n->m_len + n2->m_len < MCLBYTES) {
                          m = m_getcl(how, MT_DATA, 0);
                          if (m == NULL)
                                  goto bad;
                          m_copydata(n, 0,  n->m_len, mtod(m, char *));
                          m_copydata(n2, 0,  n2->m_len,
                              mtod(m, char *) + n->m_len);
                          m->m_len = n->m_len + n2->m_len;
                          m->m_next = n2->m_next;
                          *prev = m;
                          curfrags += 1;  /* For the new cluster */
                          curfrags -= frags_per_mbuf(n);
                          curfrags -= frags_per_mbuf(n2);
                          m_free(n);
                          m_free(n2);
                          if (curfrags <= maxfrags)
                                  return m0;
                          /*
                           * Still not there, try the normal collapse
                           * again before we allocate another cluster.
                           */
                          goto again;
                  }
                  prev = &n->m_next;
          }
          /*
           * No place where we can collapse to a cluster; punt.
           * This can occur if, for example, you request 2 frags
           * but the packet requires that both be clusters (we
           * never reallocate the first mbuf to avoid moving the
           * packet header).
           */
  bad:
          return NULL;
  }
  
  #ifdef MBUF_STRESS_TEST
  
  /*
   * Fragment an mbuf chain.  There's no reason you'd ever want to do
   * this in normal usage, but it's great for stress testing various
   * mbuf consumers.
   *
   * If fragmentation is not possible, the original chain will be
   * returned.
   *
   * Possible length values:
   * 0     no fragmentation will occur
   * > 0  each fragment will be of the specified length
   * -1   each fragment will be the same random value in length
   * -2   each fragment's length will be entirely random
   * (Random values range from 1 to 256)
   */
  struct mbuf *
  m_fragment(struct mbuf *m0, int how, int length)
  {
          struct mbuf *m_first, *m_last;
          int divisor = 255, progress = 0, fraglen;
  
          if (!(m0->m_flags & M_PKTHDR))
                  return (m0);
  
          if (length == 0 || length < -2)
                  return (m0);
          if (length > MCLBYTES)
                  length = MCLBYTES;
          if (length < 0 && divisor > MCLBYTES)
                  divisor = MCLBYTES;
          if (length == -1)
                  length = 1 + (arc4random() % divisor);
          if (length > 0)
                  fraglen = length;
  
          m_fixhdr(m0); /* Needed sanity check */
  
          m_first = m_getcl(how, MT_DATA, M_PKTHDR);
          if (m_first == NULL)
                  goto nospace;
  
          if (m_dup_pkthdr(m_first, m0, how) == 0)
                  goto nospace;
  
          m_last = m_first;
  
          while (progress < m0->m_pkthdr.len) {
                  if (length == -2)
                          fraglen = 1 + (arc4random() % divisor);
                  if (fraglen > m0->m_pkthdr.len - progress)
                          fraglen = m0->m_pkthdr.len - progress;
  
                  if (progress != 0) {
                          struct mbuf *m_new = m_getcl(how, MT_DATA, 0);
                          if (m_new == NULL)
                                  goto nospace;
  
                          m_last->m_next = m_new;
                          m_last = m_new;
                  }
  
                  m_copydata(m0, progress, fraglen, mtod(m_last, caddr_t));
                  progress += fraglen;
                  m_last->m_len = fraglen;
          }
          m_freem(m0);
          m0 = m_first;
          return (m0);
  nospace:
          if (m_first)
                  m_freem(m_first);
          /* Return the original chain on failure */
          return (m0);
  }
  
  #endif
  
  /*
   * Free pages from mbuf_ext_pgs, assuming they were allocated via
   * vm_page_alloc() and aren't associated with any object.  Complement
   * to allocator from m_uiotombuf_nomap().
   */
  void
  mb_free_mext_pgs(struct mbuf *m)
  {
          vm_page_t pg;
  
          M_ASSERTEXTPG(m);
          for (int i = 0; i < m->m_epg_npgs; i++) {
                  pg = PHYS_TO_VM_PAGE(m->m_epg_pa[i]);
                  vm_page_unwire_noq(pg);
                  vm_page_free(pg);
          }
  }
  
  static struct mbuf *
  m_uiotombuf_nomap(struct uio *uio, int how, int len, int maxseg, int flags)
  {
          struct mbuf *m, *mb, *prev;
          vm_page_t pg_array[MBUF_PEXT_MAX_PGS];
          int error, length, i, needed;
          ssize_t total;
          int pflags = malloc2vm_flags(how) | VM_ALLOC_NODUMP | VM_ALLOC_WIRED;
  
          MPASS((flags & M_PKTHDR) == 0);
          MPASS((how & M_ZERO) == 0);
  
          /*
           * len can be zero or an arbitrary large value bound by
           * the total data supplied by the uio.
           */
          if (len > 0)
                  total = MIN(uio->uio_resid, len);
          else
                  total = uio->uio_resid;
  
          if (maxseg == 0)
                  maxseg = MBUF_PEXT_MAX_PGS * PAGE_SIZE;
  
          /*
           * If total is zero, return an empty mbuf.  This can occur
           * for TLS 1.0 connections which send empty fragments as
           * a countermeasure against the known-IV weakness in CBC
           * ciphersuites.
           */
          if (__predict_false(total == 0)) {
                  mb = mb_alloc_ext_pgs(how, mb_free_mext_pgs);
                  if (mb == NULL)
                          return (NULL);
                  mb->m_epg_flags = EPG_FLAG_ANON;
                  return (mb);
          }
  
          /*
           * Allocate the pages
           */
          m = NULL;
          while (total > 0) {
                  mb = mb_alloc_ext_pgs(how, mb_free_mext_pgs);
                  if (mb == NULL)
                          goto failed;
                  if (m == NULL)
                          m = mb;
                  else
                          prev->m_next = mb;
                  prev = mb;
                  mb->m_epg_flags = EPG_FLAG_ANON;
                  needed = length = MIN(maxseg, total);
                  for (i = 0; needed > 0; i++, needed -= PAGE_SIZE) {
  retry_page:
                          pg_array[i] = vm_page_alloc_noobj(pflags);
                          if (pg_array[i] == NULL) {
                                  if (how & M_NOWAIT) {
                                          goto failed;
                                  } else {
                                          vm_wait(NULL);
                                          goto retry_page;
                                  }
                          }
                          mb->m_epg_pa[i] = VM_PAGE_TO_PHYS(pg_array[i]);
                          mb->m_epg_npgs++;
                  }
                  mb->m_epg_last_len = length - PAGE_SIZE * (mb->m_epg_npgs - 1);
                  MBUF_EXT_PGS_ASSERT_SANITY(mb);
                  total -= length;
                  error = uiomove_fromphys(pg_array, 0, length, uio);
                  if (error != 0)
                          goto failed;
                  mb->m_len = length;
                  mb->m_ext.ext_size += PAGE_SIZE * mb->m_epg_npgs;
                  if (flags & M_PKTHDR)
                          m->m_pkthdr.len += length;
          }
          return (m);
  
  failed:
          m_freem(m);
          return (NULL);
  }
  
  /*
   * Copy the contents of uio into a properly sized mbuf chain.
   */
  struct mbuf *
  m_uiotombuf(struct uio *uio, int how, int len, int align, int flags)
  {
          struct mbuf *m, *mb;
          int error, length;
          ssize_t total;
          int progress = 0;
  
          if (flags & M_EXTPG)
                  return (m_uiotombuf_nomap(uio, how, len, align, flags));
  
          /*
           * len can be zero or an arbitrary large value bound by
           * the total data supplied by the uio.
           */
          if (len > 0)
                  total = (uio->uio_resid < len) ? uio->uio_resid : len;
          else
                  total = uio->uio_resid;
  
          /*
           * The smallest unit returned by m_getm2() is a single mbuf
           * with pkthdr.  We can't align past it.
           */
          if (align >= MHLEN)
                  return (NULL);
  
          /*
           * Give us the full allocation or nothing.
           * If len is zero return the smallest empty mbuf.
           */
          m = m_getm2(NULL, max(total + align, 1), how, MT_DATA, flags);
          if (m == NULL)
                  return (NULL);
          m->m_data += align;
  
          /* Fill all mbufs with uio data and update header information. */
          for (mb = m; mb != NULL; mb = mb->m_next) {
                  length = min(M_TRAILINGSPACE(mb), total - progress);
  
                  error = uiomove(mtod(mb, void *), length, uio);
                  if (error) {
                          m_freem(m);
                          return (NULL);
                  }
  
                  mb->m_len = length;
                  progress += length;
                  if (flags & M_PKTHDR) {
                          m->m_pkthdr.len += length;
                          m->m_pkthdr.memlen += MSIZE;
                          if (mb->m_flags & M_EXT)
                                  m->m_pkthdr.memlen += mb->m_ext.ext_size;
                  }
          }
          KASSERT(progress == total, ("%s: progress != total", __func__));
  
          return (m);
  }
  
  /*
   * Copy data to/from an unmapped mbuf into a uio limited by len if set.
   */
  int
  m_unmapped_uiomove(const struct mbuf *m, int m_off, struct uio *uio, int len)
  {
          vm_page_t pg;
          int error, i, off, pglen, pgoff, seglen, segoff;
  
          M_ASSERTEXTPG(m);
          error = 0;
  
          /* Skip over any data removed from the front. */
          off = mtod(m, vm_offset_t);
  
          off += m_off;
          if (m->m_epg_hdrlen != 0) {
                  if (off >= m->m_epg_hdrlen) {
                          off -= m->m_epg_hdrlen;
                  } else {
                          seglen = m->m_epg_hdrlen - off;
                          segoff = off;
                          seglen = min(seglen, len);
                          off = 0;
                          len -= seglen;
                          error = uiomove(__DECONST(void *,
                              &m->m_epg_hdr[segoff]), seglen, uio);
                  }
          }
          pgoff = m->m_epg_1st_off;
          for (i = 0; i < m->m_epg_npgs && error == 0 && len > 0; i++) {
                  pglen = m_epg_pagelen(m, i, pgoff);
                  if (off >= pglen) {
                          off -= pglen;
                          pgoff = 0;
                          continue;
                  }
                  seglen = pglen - off;
                  segoff = pgoff + off;
                  off = 0;
                  seglen = min(seglen, len);
                  len -= seglen;
                  pg = PHYS_TO_VM_PAGE(m->m_epg_pa[i]);
                  error = uiomove_fromphys(&pg, segoff, seglen, uio);
                  pgoff = 0;
          };
          if (len != 0 && error == 0) {
                  KASSERT((off + len) <= m->m_epg_trllen,
                      ("off + len > trail (%d + %d > %d, m_off = %d)", off, len,
                      m->m_epg_trllen, m_off));
                  error = uiomove(__DECONST(void *, &m->m_epg_trail[off]),
                      len, uio);
          }
          return (error);
  }
  
  /*
   * Copy an mbuf chain into a uio limited by len if set.
   */
  int
  m_mbuftouio(struct uio *uio, const struct mbuf *m, int len)
  {
          int error, length, total;
          int progress = 0;
  
          if (len > 0)
                  total = min(uio->uio_resid, len);
          else
                  total = uio->uio_resid;
  
          /* Fill the uio with data from the mbufs. */
          for (; m != NULL; m = m->m_next) {
                  length = min(m->m_len, total - progress);
  
                  if ((m->m_flags & M_EXTPG) != 0)
                          error = m_unmapped_uiomove(m, 0, uio, length);
                  else
                          error = uiomove(mtod(m, void *), length, uio);
                  if (error)
                          return (error);
  
                  progress += length;
          }
  
          return (0);
  }
  
  /*
   * Create a writable copy of the mbuf chain.  While doing this
   * we compact the chain with a goal of producing a chain with
   * at most two mbufs.  The second mbuf in this chain is likely
   * to be a cluster.  The primary purpose of this work is to create
   * a writable packet for encryption, compression, etc.  The
   * secondary goal is to linearize the data so the data can be
   * passed to crypto hardware in the most efficient manner possible.
   */
  struct mbuf *
  m_unshare(struct mbuf *m0, int how)
  {
          struct mbuf *m, *mprev;
          struct mbuf *n, *mfirst, *mlast;
          int len, off;
  
          mprev = NULL;
          for (m = m0; m != NULL; m = mprev->m_next) {
                  /*
                   * Regular mbufs are ignored unless there's a cluster
                   * in front of it that we can use to coalesce.  We do
                   * the latter mainly so later clusters can be coalesced
                   * also w/o having to handle them specially (i.e. convert
                   * mbuf+cluster -> cluster).  This optimization is heavily
                   * influenced by the assumption that we're running over
                   * Ethernet where MCLBYTES is large enough that the max
                   * packet size will permit lots of coalescing into a
                   * single cluster.  This in turn permits efficient
                   * crypto operations, especially when using hardware.
                   */
                  if ((m->m_flags & M_EXT) == 0) {
                          if (mprev && (mprev->m_flags & M_EXT) &&
                              m->m_len <= M_TRAILINGSPACE(mprev)) {
                                  /* XXX: this ignores mbuf types */
                                  memcpy(mtod(mprev, caddr_t) + mprev->m_len,
                                      mtod(m, caddr_t), m->m_len);
                                  mprev->m_len += m->m_len;
                                  mprev->m_next = m->m_next;      /* unlink from chain */
                                  m_free(m);                      /* reclaim mbuf */
                          } else {
                                  mprev = m;
                          }
                          continue;
                  }
                  /*
                   * Writable mbufs are left alone (for now).
                   */
                  if (M_WRITABLE(m)) {
                          mprev = m;
                          continue;
                  }
  
                  /*
                   * Not writable, replace with a copy or coalesce with
                   * the previous mbuf if possible (since we have to copy
                   * it anyway, we try to reduce the number of mbufs and
                   * clusters so that future work is easier).
                   */
                  KASSERT(m->m_flags & M_EXT, ("m_flags 0x%x", m->m_flags));
                  /* NB: we only coalesce into a cluster or larger */
                  if (mprev != NULL && (mprev->m_flags & M_EXT) &&
                      m->m_len <= M_TRAILINGSPACE(mprev)) {
                          /* XXX: this ignores mbuf types */
                          memcpy(mtod(mprev, caddr_t) + mprev->m_len,
                              mtod(m, caddr_t), m->m_len);
                          mprev->m_len += m->m_len;
                          mprev->m_next = m->m_next;      /* unlink from chain */
                          m_free(m);                      /* reclaim mbuf */
                          continue;
                  }
  
                  /*
                   * Allocate new space to hold the copy and copy the data.
                   * We deal with jumbo mbufs (i.e. m_len > MCLBYTES) by
                   * splitting them into clusters.  We could just malloc a
                   * buffer and make it external but too many device drivers
                   * don't know how to break up the non-contiguous memory when
                   * doing DMA.
                   */
                  n = m_getcl(how, m->m_type, m->m_flags & M_COPYFLAGS);
                  if (n == NULL) {
                          m_freem(m0);
                          return (NULL);
                  }
                  if (m->m_flags & M_PKTHDR) {
                          KASSERT(mprev == NULL, ("%s: m0 %p, m %p has M_PKTHDR",
                              __func__, m0, m));
                          m_move_pkthdr(n, m);
                  }
                  len = m->m_len;
                  off = 0;
                  mfirst = n;
                  mlast = NULL;
                  for (;;) {
                          int cc = min(len, MCLBYTES);
                          memcpy(mtod(n, caddr_t), mtod(m, caddr_t) + off, cc);
                          n->m_len = cc;
                          if (mlast != NULL)
                                  mlast->m_next = n;
                          mlast = n;
  #if 0
                          newipsecstat.ips_clcopied++;
  #endif
  
                          len -= cc;
                          if (len <= 0)
                                  break;
                          off += cc;
  
                          n = m_getcl(how, m->m_type, m->m_flags & M_COPYFLAGS);
                          if (n == NULL) {
                                  m_freem(mfirst);
                                  m_freem(m0);
                                  return (NULL);
                          }
                  }
                  n->m_next = m->m_next;
                  if (mprev == NULL)
                          m0 = mfirst;            /* new head of chain */
                  else
                          mprev->m_next = mfirst; /* replace old mbuf */
                  m_free(m);                      /* release old mbuf */
                  mprev = mfirst;
          }
          return (m0);
  }
  
  #ifdef MBUF_PROFILING
  
  #define MP_BUCKETS 32 /* don't just change this as things may overflow.*/
  struct mbufprofile {
          uintmax_t wasted[MP_BUCKETS];
          uintmax_t used[MP_BUCKETS];
          uintmax_t segments[MP_BUCKETS];
  } mbprof;
  
  void
  m_profile(struct mbuf *m)
  {
          int segments = 0;
          int used = 0;
          int wasted = 0;
  
          while (m) {
                  segments++;
                  used += m->m_len;
                  if (m->m_flags & M_EXT) {
                          wasted += MHLEN - sizeof(m->m_ext) +
                              m->m_ext.ext_size - m->m_len;
                  } else {
                          if (m->m_flags & M_PKTHDR)
                                  wasted += MHLEN - m->m_len;
                          else
                                  wasted += MLEN - m->m_len;
                  }
                  m = m->m_next;
          }
          /* be paranoid.. it helps */
          if (segments > MP_BUCKETS - 1)
                  segments = MP_BUCKETS - 1;
          if (used > 100000)
                  used = 100000;
          if (wasted > 100000)
                  wasted = 100000;
          /* store in the appropriate bucket */
          /* don't bother locking. if it's slightly off, so what? */
          mbprof.segments[segments]++;
          mbprof.used[fls(used)]++;
          mbprof.wasted[fls(wasted)]++;
  }
  
  static int
  mbprof_handler(SYSCTL_HANDLER_ARGS)
  {
          char buf[256];
          struct sbuf sb;
          int error;
          uint64_t *p;
  
          sbuf_new_for_sysctl(&sb, buf, sizeof(buf), req);
  
          p = &mbprof.wasted[0];
          sbuf_printf(&sb,
              "wasted:\n"
              "%ju %ju %ju %ju %ju %ju %ju %ju "
              "%ju %ju %ju %ju %ju %ju %ju %ju\n",
              p[0], p[1], p[2], p[3], p[4], p[5], p[6], p[7],
              p[8], p[9], p[10], p[11], p[12], p[13], p[14], p[15]);
  #ifdef BIG_ARRAY
          p = &mbprof.wasted[16];
          sbuf_printf(&sb,
              "%ju %ju %ju %ju %ju %ju %ju %ju "
              "%ju %ju %ju %ju %ju %ju %ju %ju\n",
              p[0], p[1], p[2], p[3], p[4], p[5], p[6], p[7],
              p[8], p[9], p[10], p[11], p[12], p[13], p[14], p[15]);
  #endif
          p = &mbprof.used[0];
          sbuf_printf(&sb,
              "used:\n"
              "%ju %ju %ju %ju %ju %ju %ju %ju "
              "%ju %ju %ju %ju %ju %ju %ju %ju\n",
              p[0], p[1], p[2], p[3], p[4], p[5], p[6], p[7],
              p[8], p[9], p[10], p[11], p[12], p[13], p[14], p[15]);
  #ifdef BIG_ARRAY
          p = &mbprof.used[16];
          sbuf_printf(&sb,
              "%ju %ju %ju %ju %ju %ju %ju %ju "
              "%ju %ju %ju %ju %ju %ju %ju %ju\n",
              p[0], p[1], p[2], p[3], p[4], p[5], p[6], p[7],
              p[8], p[9], p[10], p[11], p[12], p[13], p[14], p[15]);
  #endif
          p = &mbprof.segments[0];
          sbuf_printf(&sb,
              "segments:\n"
              "%ju %ju %ju %ju %ju %ju %ju %ju "
              "%ju %ju %ju %ju %ju %ju %ju %ju\n",
              p[0], p[1], p[2], p[3], p[4], p[5], p[6], p[7],
              p[8], p[9], p[10], p[11], p[12], p[13], p[14], p[15]);
  #ifdef BIG_ARRAY
          p = &mbprof.segments[16];
          sbuf_printf(&sb,
              "%ju %ju %ju %ju %ju %ju %ju %ju "
              "%ju %ju %ju %ju %ju %ju %ju %jju",
              p[0], p[1], p[2], p[3], p[4], p[5], p[6], p[7],
              p[8], p[9], p[10], p[11], p[12], p[13], p[14], p[15]);
  #endif
  
          error = sbuf_finish(&sb);
          sbuf_delete(&sb);
          return (error);
  }
  
  static int
  mbprof_clr_handler(SYSCTL_HANDLER_ARGS)
  {
          int clear, error;
  
          clear = 0;
          error = sysctl_handle_int(oidp, &clear, 0, req);
          if (error || !req->newptr)
                  return (error);
  
          if (clear) {
                  bzero(&mbprof, sizeof(mbprof));
          }
  
          return (error);
  }
  
  SYSCTL_PROC(_kern_ipc, OID_AUTO, mbufprofile,
      CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
      mbprof_handler, "A",
      "mbuf profiling statistics");
  
  SYSCTL_PROC(_kern_ipc, OID_AUTO, mbufprofileclr,
      CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, 0,
      mbprof_clr_handler, "I",
      "clear mbuf profiling statistics");
  #endif

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