The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/uipc_mbuf.c

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    1 /*      $NetBSD: uipc_mbuf.c,v 1.92.6.3 2006/09/08 12:06:51 ghen Exp $  */
    2 
    3 /*-
    4  * Copyright (c) 1999, 2001 The NetBSD Foundation, Inc.
    5  * All rights reserved.
    6  *
    7  * This code is derived from software contributed to The NetBSD Foundation
    8  * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
    9  * NASA Ames Research Center.
   10  *
   11  * Redistribution and use in source and binary forms, with or without
   12  * modification, are permitted provided that the following conditions
   13  * are met:
   14  * 1. Redistributions of source code must retain the above copyright
   15  *    notice, this list of conditions and the following disclaimer.
   16  * 2. Redistributions in binary form must reproduce the above copyright
   17  *    notice, this list of conditions and the following disclaimer in the
   18  *    documentation and/or other materials provided with the distribution.
   19  * 3. All advertising materials mentioning features or use of this software
   20  *    must display the following acknowledgement:
   21  *      This product includes software developed by the NetBSD
   22  *      Foundation, Inc. and its contributors.
   23  * 4. Neither the name of The NetBSD Foundation nor the names of its
   24  *    contributors may be used to endorse or promote products derived
   25  *    from this software without specific prior written permission.
   26  *
   27  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   28  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   29  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   30  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   31  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   32  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   33  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   34  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   35  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   36  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   37  * POSSIBILITY OF SUCH DAMAGE.
   38  */
   39 
   40 /*
   41  * Copyright (c) 1982, 1986, 1988, 1991, 1993
   42  *      The Regents of the University of California.  All rights reserved.
   43  *
   44  * Redistribution and use in source and binary forms, with or without
   45  * modification, are permitted provided that the following conditions
   46  * are met:
   47  * 1. Redistributions of source code must retain the above copyright
   48  *    notice, this list of conditions and the following disclaimer.
   49  * 2. Redistributions in binary form must reproduce the above copyright
   50  *    notice, this list of conditions and the following disclaimer in the
   51  *    documentation and/or other materials provided with the distribution.
   52  * 3. Neither the name of the University nor the names of its contributors
   53  *    may be used to endorse or promote products derived from this software
   54  *    without specific prior written permission.
   55  *
   56  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   57  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   58  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   59  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   60  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   61  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   62  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   63  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   64  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   65  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   66  * SUCH DAMAGE.
   67  *
   68  *      @(#)uipc_mbuf.c 8.4 (Berkeley) 2/14/95
   69  */
   70 
   71 #include <sys/cdefs.h>
   72 __KERNEL_RCSID(0, "$NetBSD: uipc_mbuf.c,v 1.92.6.3 2006/09/08 12:06:51 ghen Exp $");
   73 
   74 #include "opt_mbuftrace.h"
   75 
   76 #include <sys/param.h>
   77 #include <sys/systm.h>
   78 #include <sys/proc.h>
   79 #include <sys/malloc.h>
   80 #define MBTYPES
   81 #include <sys/mbuf.h>
   82 #include <sys/kernel.h>
   83 #include <sys/syslog.h>
   84 #include <sys/domain.h>
   85 #include <sys/protosw.h>
   86 #include <sys/pool.h>
   87 #include <sys/socket.h>
   88 #include <sys/sysctl.h>
   89 
   90 #include <net/if.h>
   91 
   92 #include <uvm/uvm.h>
   93 
   94 
   95 struct  pool mbpool;            /* mbuf pool */
   96 struct  pool mclpool;           /* mbuf cluster pool */
   97 
   98 struct pool_cache mbpool_cache;
   99 struct pool_cache mclpool_cache;
  100 
  101 struct mbstat mbstat;
  102 int     max_linkhdr;
  103 int     max_protohdr;
  104 int     max_hdr;
  105 int     max_datalen;
  106 
  107 static int mb_ctor(void *, void *, int);
  108 
  109 void    *mclpool_alloc(struct pool *, int);
  110 void    mclpool_release(struct pool *, void *);
  111 
  112 struct pool_allocator mclpool_allocator = {
  113         mclpool_alloc, mclpool_release, 0,
  114 };
  115 
  116 static struct mbuf *m_copym0(struct mbuf *, int, int, int, int);
  117 static struct mbuf *m_split0(struct mbuf *, int, int, int);
  118 static int m_copyback0(struct mbuf **, int, int, const void *, int, int);
  119 
  120 /* flags for m_copyback0 */
  121 #define M_COPYBACK0_COPYBACK    0x0001  /* copyback from cp */
  122 #define M_COPYBACK0_PRESERVE    0x0002  /* preserve original data */
  123 #define M_COPYBACK0_COW         0x0004  /* do copy-on-write */
  124 #define M_COPYBACK0_EXTEND      0x0008  /* extend chain */
  125 
  126 const char mclpool_warnmsg[] =
  127     "WARNING: mclpool limit reached; increase NMBCLUSTERS";
  128 
  129 MALLOC_DEFINE(M_MBUF, "mbuf", "mbuf");
  130 
  131 #ifdef MBUFTRACE
  132 struct mownerhead mowners = LIST_HEAD_INITIALIZER(mowners);
  133 struct mowner unknown_mowners[] = {
  134         { "unknown", "free" },
  135         { "unknown", "data" },
  136         { "unknown", "header" },
  137         { "unknown", "soname" },
  138         { "unknown", "soopts" },
  139         { "unknown", "ftable" },
  140         { "unknown", "control" },
  141         { "unknown", "oobdata" },
  142 };
  143 struct mowner revoked_mowner = { "revoked", "" };
  144 #endif
  145 
  146 /*
  147  * Initialize the mbuf allocator.
  148  */
  149 void
  150 mbinit(void)
  151 {
  152 
  153         KASSERT(sizeof(struct _m_ext) <= MHLEN);
  154         KASSERT(sizeof(struct mbuf) == MSIZE);
  155 
  156         pool_init(&mbpool, msize, 0, 0, 0, "mbpl", NULL);
  157         pool_init(&mclpool, mclbytes, 0, 0, 0, "mclpl", &mclpool_allocator);
  158 
  159         pool_set_drain_hook(&mbpool, m_reclaim, NULL);
  160         pool_set_drain_hook(&mclpool, m_reclaim, NULL);
  161 
  162         pool_cache_init(&mbpool_cache, &mbpool, mb_ctor, NULL, NULL);
  163         pool_cache_init(&mclpool_cache, &mclpool, NULL, NULL, NULL);
  164 
  165         /*
  166          * Set the hard limit on the mclpool to the number of
  167          * mbuf clusters the kernel is to support.  Log the limit
  168          * reached message max once a minute.
  169          */
  170         pool_sethardlimit(&mclpool, nmbclusters, mclpool_warnmsg, 60);
  171 
  172         /*
  173          * Set a low water mark for both mbufs and clusters.  This should
  174          * help ensure that they can be allocated in a memory starvation
  175          * situation.  This is important for e.g. diskless systems which
  176          * must allocate mbufs in order for the pagedaemon to clean pages.
  177          */
  178         pool_setlowat(&mbpool, mblowat);
  179         pool_setlowat(&mclpool, mcllowat);
  180 
  181 #ifdef MBUFTRACE
  182         {
  183                 /*
  184                  * Attach the unknown mowners.
  185                  */
  186                 int i;
  187                 MOWNER_ATTACH(&revoked_mowner);
  188                 for (i = sizeof(unknown_mowners)/sizeof(unknown_mowners[0]);
  189                      i-- > 0; )
  190                         MOWNER_ATTACH(&unknown_mowners[i]);
  191         }
  192 #endif
  193 }
  194 
  195 /*
  196  * sysctl helper routine for the kern.mbuf subtree.  nmbclusters may
  197  * or may not be writable, and mblowat and mcllowat need range
  198  * checking and pool tweaking after being reset.
  199  */
  200 static int
  201 sysctl_kern_mbuf(SYSCTLFN_ARGS)
  202 {
  203         int error, newval;
  204         struct sysctlnode node;
  205 
  206         node = *rnode;
  207         node.sysctl_data = &newval;
  208         switch (rnode->sysctl_num) {
  209         case MBUF_NMBCLUSTERS:
  210                 if (mb_map != NULL) {
  211                         node.sysctl_flags &= ~CTLFLAG_READWRITE;
  212                         node.sysctl_flags |= CTLFLAG_READONLY;
  213                 }
  214                 /* FALLTHROUGH */
  215         case MBUF_MBLOWAT:
  216         case MBUF_MCLLOWAT:
  217                 newval = *(int*)rnode->sysctl_data;
  218                 break;
  219         default:
  220                 return (EOPNOTSUPP);
  221         }
  222 
  223         error = sysctl_lookup(SYSCTLFN_CALL(&node));
  224         if (error || newp == NULL)
  225                 return (error);
  226         if (newval < 0)
  227                 return (EINVAL);
  228 
  229         switch (node.sysctl_num) {
  230         case MBUF_NMBCLUSTERS:
  231                 if (newval < nmbclusters)
  232                         return (EINVAL);
  233                 nmbclusters = newval;
  234                 pool_sethardlimit(&mclpool, nmbclusters, mclpool_warnmsg, 60);
  235                 break;
  236         case MBUF_MBLOWAT:
  237                 mblowat = newval;
  238                 pool_setlowat(&mbpool, mblowat);
  239                 break;
  240         case MBUF_MCLLOWAT:
  241                 mcllowat = newval;
  242                 pool_setlowat(&mclpool, mcllowat);
  243                 break;
  244         }
  245 
  246         return (0);
  247 }
  248 
  249 #ifdef MBUFTRACE
  250 static int
  251 sysctl_kern_mbuf_mowners(SYSCTLFN_ARGS)
  252 {
  253         struct mowner *mo;
  254         size_t len = 0;
  255         int error = 0;
  256 
  257         if (namelen != 0)
  258                 return (EINVAL);
  259         if (newp != NULL)
  260                 return (EPERM);
  261 
  262         LIST_FOREACH(mo, &mowners, mo_link) {
  263                 if (oldp != NULL) {
  264                         if (*oldlenp - len < sizeof(*mo)) {
  265                                 error = ENOMEM;
  266                                 break;
  267                         }
  268                         error = copyout(mo, (caddr_t) oldp + len,
  269                                         sizeof(*mo));
  270                         if (error)
  271                                 break;
  272                 }
  273                 len += sizeof(*mo);
  274         }
  275 
  276         if (error == 0)
  277                 *oldlenp = len;
  278 
  279         return (error);
  280 }
  281 #endif /* MBUFTRACE */
  282 
  283 SYSCTL_SETUP(sysctl_kern_mbuf_setup, "sysctl kern.mbuf subtree setup")
  284 {
  285 
  286         sysctl_createv(clog, 0, NULL, NULL,
  287                        CTLFLAG_PERMANENT,
  288                        CTLTYPE_NODE, "kern", NULL,
  289                        NULL, 0, NULL, 0,
  290                        CTL_KERN, CTL_EOL);
  291         sysctl_createv(clog, 0, NULL, NULL,
  292                        CTLFLAG_PERMANENT,
  293                        CTLTYPE_NODE, "mbuf",
  294                        SYSCTL_DESCR("mbuf control variables"),
  295                        NULL, 0, NULL, 0,
  296                        CTL_KERN, KERN_MBUF, CTL_EOL);
  297 
  298         sysctl_createv(clog, 0, NULL, NULL,
  299                        CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
  300                        CTLTYPE_INT, "msize",
  301                        SYSCTL_DESCR("mbuf base size"),
  302                        NULL, msize, NULL, 0,
  303                        CTL_KERN, KERN_MBUF, MBUF_MSIZE, CTL_EOL);
  304         sysctl_createv(clog, 0, NULL, NULL,
  305                        CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
  306                        CTLTYPE_INT, "mclbytes",
  307                        SYSCTL_DESCR("mbuf cluster size"),
  308                        NULL, mclbytes, NULL, 0,
  309                        CTL_KERN, KERN_MBUF, MBUF_MCLBYTES, CTL_EOL);
  310         sysctl_createv(clog, 0, NULL, NULL,
  311                        CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
  312                        CTLTYPE_INT, "nmbclusters",
  313                        SYSCTL_DESCR("Limit on the number of mbuf clusters"),
  314                        sysctl_kern_mbuf, 0, &nmbclusters, 0,
  315                        CTL_KERN, KERN_MBUF, MBUF_NMBCLUSTERS, CTL_EOL);
  316         sysctl_createv(clog, 0, NULL, NULL,
  317                        CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
  318                        CTLTYPE_INT, "mblowat",
  319                        SYSCTL_DESCR("mbuf low water mark"),
  320                        sysctl_kern_mbuf, 0, &mblowat, 0,
  321                        CTL_KERN, KERN_MBUF, MBUF_MBLOWAT, CTL_EOL);
  322         sysctl_createv(clog, 0, NULL, NULL,
  323                        CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
  324                        CTLTYPE_INT, "mcllowat",
  325                        SYSCTL_DESCR("mbuf cluster low water mark"),
  326                        sysctl_kern_mbuf, 0, &mcllowat, 0,
  327                        CTL_KERN, KERN_MBUF, MBUF_MCLLOWAT, CTL_EOL);
  328         sysctl_createv(clog, 0, NULL, NULL,
  329                        CTLFLAG_PERMANENT,
  330                        CTLTYPE_STRUCT, "stats",
  331                        SYSCTL_DESCR("mbuf allocation statistics"),
  332                        NULL, 0, &mbstat, sizeof(mbstat),
  333                        CTL_KERN, KERN_MBUF, MBUF_STATS, CTL_EOL);
  334 #ifdef MBUFTRACE
  335         sysctl_createv(clog, 0, NULL, NULL,
  336                        CTLFLAG_PERMANENT,
  337                        CTLTYPE_STRUCT, "mowners",
  338                        SYSCTL_DESCR("Information about mbuf owners"),
  339                        sysctl_kern_mbuf_mowners, 0, NULL, 0,
  340                        CTL_KERN, KERN_MBUF, MBUF_MOWNERS, CTL_EOL);
  341 #endif /* MBUFTRACE */
  342 }
  343 
  344 void *
  345 mclpool_alloc(struct pool *pp, int flags)
  346 {
  347         boolean_t waitok = (flags & PR_WAITOK) ? TRUE : FALSE;
  348 
  349         return ((void *)uvm_km_alloc_poolpage1(mb_map, NULL, waitok));
  350 }
  351 
  352 void
  353 mclpool_release(struct pool *pp, void *v)
  354 {
  355 
  356         uvm_km_free_poolpage1(mb_map, (vaddr_t)v);
  357 }
  358 
  359 /*ARGSUSED*/
  360 static int
  361 mb_ctor(void *arg, void *object, int flags)
  362 {
  363         struct mbuf *m = object;
  364 
  365 #ifdef POOL_VTOPHYS
  366         m->m_paddr = POOL_VTOPHYS(m);
  367 #else
  368         m->m_paddr = M_PADDR_INVALID;
  369 #endif
  370         return (0);
  371 }
  372 
  373 void
  374 m_reclaim(void *arg, int flags)
  375 {
  376         struct domain *dp;
  377         const struct protosw *pr;
  378         struct ifnet *ifp;
  379         int s = splvm();
  380 
  381         DOMAIN_FOREACH(dp) {
  382                 for (pr = dp->dom_protosw;
  383                      pr < dp->dom_protoswNPROTOSW; pr++)
  384                         if (pr->pr_drain)
  385                                 (*pr->pr_drain)();
  386         }
  387         IFNET_FOREACH(ifp) {
  388                 if (ifp->if_drain)
  389                         (*ifp->if_drain)(ifp);
  390         }
  391         splx(s);
  392         mbstat.m_drain++;
  393 }
  394 
  395 /*
  396  * Space allocation routines.
  397  * These are also available as macros
  398  * for critical paths.
  399  */
  400 struct mbuf *
  401 m_get(int nowait, int type)
  402 {
  403         struct mbuf *m;
  404 
  405         MGET(m, nowait, type);
  406         return (m);
  407 }
  408 
  409 struct mbuf *
  410 m_gethdr(int nowait, int type)
  411 {
  412         struct mbuf *m;
  413 
  414         MGETHDR(m, nowait, type);
  415         return (m);
  416 }
  417 
  418 struct mbuf *
  419 m_getclr(int nowait, int type)
  420 {
  421         struct mbuf *m;
  422 
  423         MGET(m, nowait, type);
  424         if (m == 0)
  425                 return (NULL);
  426         memset(mtod(m, caddr_t), 0, MLEN);
  427         return (m);
  428 }
  429 
  430 void
  431 m_clget(struct mbuf *m, int nowait)
  432 {
  433 
  434         MCLGET(m, nowait);
  435 }
  436 
  437 struct mbuf *
  438 m_free(struct mbuf *m)
  439 {
  440         struct mbuf *n;
  441 
  442         MFREE(m, n);
  443         return (n);
  444 }
  445 
  446 void
  447 m_freem(struct mbuf *m)
  448 {
  449         struct mbuf *n;
  450 
  451         if (m == NULL)
  452                 return;
  453         do {
  454                 MFREE(m, n);
  455                 m = n;
  456         } while (m);
  457 }
  458 
  459 #ifdef MBUFTRACE
  460 /*
  461  * Walk a chain of mbufs, claiming ownership of each mbuf in the chain.
  462  */
  463 void
  464 m_claimm(struct mbuf *m, struct mowner *mo)
  465 {
  466 
  467         for (; m != NULL; m = m->m_next)
  468                 MCLAIM(m, mo);
  469 }
  470 #endif
  471 
  472 /*
  473  * Mbuffer utility routines.
  474  */
  475 
  476 /*
  477  * Lesser-used path for M_PREPEND:
  478  * allocate new mbuf to prepend to chain,
  479  * copy junk along.
  480  */
  481 struct mbuf *
  482 m_prepend(struct mbuf *m, int len, int how)
  483 {
  484         struct mbuf *mn;
  485 
  486         MGET(mn, how, m->m_type);
  487         if (mn == (struct mbuf *)NULL) {
  488                 m_freem(m);
  489                 return ((struct mbuf *)NULL);
  490         }
  491         if (m->m_flags & M_PKTHDR) {
  492                 M_COPY_PKTHDR(mn, m);
  493                 m_tag_delete_chain(m, NULL);
  494                 m->m_flags &= ~M_PKTHDR;
  495         } else {
  496                 MCLAIM(mn, m->m_owner);
  497         }
  498         mn->m_next = m;
  499         m = mn;
  500         if (len < MHLEN)
  501                 MH_ALIGN(m, len);
  502         m->m_len = len;
  503         return (m);
  504 }
  505 
  506 /*
  507  * Make a copy of an mbuf chain starting "off0" bytes from the beginning,
  508  * continuing for "len" bytes.  If len is M_COPYALL, copy to end of mbuf.
  509  * The wait parameter is a choice of M_WAIT/M_DONTWAIT from caller.
  510  */
  511 int MCFail;
  512 
  513 struct mbuf *
  514 m_copym(struct mbuf *m, int off0, int len, int wait)
  515 {
  516 
  517         return m_copym0(m, off0, len, wait, 0); /* shallow copy on M_EXT */
  518 }
  519 
  520 struct mbuf *
  521 m_dup(struct mbuf *m, int off0, int len, int wait)
  522 {
  523 
  524         return m_copym0(m, off0, len, wait, 1); /* deep copy */
  525 }
  526 
  527 static struct mbuf *
  528 m_copym0(struct mbuf *m, int off0, int len, int wait, int deep)
  529 {
  530         struct mbuf *n, **np;
  531         int off = off0;
  532         struct mbuf *top;
  533         int copyhdr = 0;
  534 
  535         if (off < 0 || len < 0)
  536                 panic("m_copym: off %d, len %d", off, len);
  537         if (off == 0 && m->m_flags & M_PKTHDR)
  538                 copyhdr = 1;
  539         while (off > 0) {
  540                 if (m == 0)
  541                         panic("m_copym: m == 0, off %d", off);
  542                 if (off < m->m_len)
  543                         break;
  544                 off -= m->m_len;
  545                 m = m->m_next;
  546         }
  547         np = &top;
  548         top = 0;
  549         while (len > 0) {
  550                 if (m == 0) {
  551                         if (len != M_COPYALL)
  552                                 panic("m_copym: m == 0, len %d [!COPYALL]",
  553                                     len);
  554                         break;
  555                 }
  556                 MGET(n, wait, m->m_type);
  557                 *np = n;
  558                 if (n == 0)
  559                         goto nospace;
  560                 MCLAIM(n, m->m_owner);
  561                 if (copyhdr) {
  562                         M_COPY_PKTHDR(n, m);
  563                         if (len == M_COPYALL)
  564                                 n->m_pkthdr.len -= off0;
  565                         else
  566                                 n->m_pkthdr.len = len;
  567                         copyhdr = 0;
  568                 }
  569                 n->m_len = min(len, m->m_len - off);
  570                 if (m->m_flags & M_EXT) {
  571                         if (!deep) {
  572                                 n->m_data = m->m_data + off;
  573                                 n->m_ext = m->m_ext;
  574                                 MCLADDREFERENCE(m, n);
  575                         } else {
  576                                 /*
  577                                  * we are unsure about the way m was allocated.
  578                                  * copy into multiple MCLBYTES cluster mbufs.
  579                                  */
  580                                 MCLGET(n, wait);
  581                                 n->m_len = 0;
  582                                 n->m_len = M_TRAILINGSPACE(n);
  583                                 n->m_len = min(n->m_len, len);
  584                                 n->m_len = min(n->m_len, m->m_len - off);
  585                                 memcpy(mtod(n, caddr_t), mtod(m, caddr_t) + off,
  586                                     (unsigned)n->m_len);
  587                         }
  588                 } else
  589                         memcpy(mtod(n, caddr_t), mtod(m, caddr_t)+off,
  590                             (unsigned)n->m_len);
  591                 if (len != M_COPYALL)
  592                         len -= n->m_len;
  593                 off += n->m_len;
  594 #ifdef DIAGNOSTIC
  595                 if (off > m->m_len)
  596                         panic("m_copym0 overrun");
  597 #endif
  598                 if (off == m->m_len) {
  599                         m = m->m_next;
  600                         off = 0;
  601                 }
  602                 np = &n->m_next;
  603         }
  604         if (top == 0)
  605                 MCFail++;
  606         return (top);
  607 nospace:
  608         m_freem(top);
  609         MCFail++;
  610         return (NULL);
  611 }
  612 
  613 /*
  614  * Copy an entire packet, including header (which must be present).
  615  * An optimization of the common case `m_copym(m, 0, M_COPYALL, how)'.
  616  */
  617 struct mbuf *
  618 m_copypacket(struct mbuf *m, int how)
  619 {
  620         struct mbuf *top, *n, *o;
  621 
  622         MGET(n, how, m->m_type);
  623         top = n;
  624         if (!n)
  625                 goto nospace;
  626 
  627         MCLAIM(n, m->m_owner);
  628         M_COPY_PKTHDR(n, m);
  629         n->m_len = m->m_len;
  630         if (m->m_flags & M_EXT) {
  631                 n->m_data = m->m_data;
  632                 n->m_ext = m->m_ext;
  633                 MCLADDREFERENCE(m, n);
  634         } else {
  635                 memcpy(mtod(n, char *), mtod(m, char *), n->m_len);
  636         }
  637 
  638         m = m->m_next;
  639         while (m) {
  640                 MGET(o, how, m->m_type);
  641                 if (!o)
  642                         goto nospace;
  643 
  644                 MCLAIM(o, m->m_owner);
  645                 n->m_next = o;
  646                 n = n->m_next;
  647 
  648                 n->m_len = m->m_len;
  649                 if (m->m_flags & M_EXT) {
  650                         n->m_data = m->m_data;
  651                         n->m_ext = m->m_ext;
  652                         MCLADDREFERENCE(m, n);
  653                 } else {
  654                         memcpy(mtod(n, char *), mtod(m, char *), n->m_len);
  655                 }
  656 
  657                 m = m->m_next;
  658         }
  659         return top;
  660 nospace:
  661         m_freem(top);
  662         MCFail++;
  663         return NULL;
  664 }
  665 
  666 /*
  667  * Copy data from an mbuf chain starting "off" bytes from the beginning,
  668  * continuing for "len" bytes, into the indicated buffer.
  669  */
  670 void
  671 m_copydata(struct mbuf *m, int off, int len, void *vp)
  672 {
  673         unsigned count;
  674         char *cp = vp;
  675 
  676         if (off < 0 || len < 0)
  677                 panic("m_copydata: off %d, len %d", off, len);
  678         while (off > 0) {
  679                 if (m == 0)
  680                         panic("m_copydata: m == 0, off %d", off);
  681                 if (off < m->m_len)
  682                         break;
  683                 off -= m->m_len;
  684                 m = m->m_next;
  685         }
  686         while (len > 0) {
  687                 if (m == 0)
  688                         panic("m_copydata: m == 0, len %d", len);
  689                 count = min(m->m_len - off, len);
  690                 memcpy(cp, mtod(m, caddr_t) + off, count);
  691                 len -= count;
  692                 cp += count;
  693                 off = 0;
  694                 m = m->m_next;
  695         }
  696 }
  697 
  698 /*
  699  * Concatenate mbuf chain n to m.
  700  * n might be copied into m (when n->m_len is small), therefore data portion of
  701  * n could be copied into an mbuf of different mbuf type.
  702  * Any m_pkthdr is not updated.
  703  */
  704 void
  705 m_cat(struct mbuf *m, struct mbuf *n)
  706 {
  707 
  708         while (m->m_next)
  709                 m = m->m_next;
  710         while (n) {
  711                 if (M_READONLY(m) || n->m_len > M_TRAILINGSPACE(m)) {
  712                         /* just join the two chains */
  713                         m->m_next = n;
  714                         return;
  715                 }
  716                 /* splat the data from one into the other */
  717                 memcpy(mtod(m, caddr_t) + m->m_len, mtod(n, caddr_t),
  718                     (u_int)n->m_len);
  719                 m->m_len += n->m_len;
  720                 n = m_free(n);
  721         }
  722 }
  723 
  724 void
  725 m_adj(struct mbuf *mp, int req_len)
  726 {
  727         int len = req_len;
  728         struct mbuf *m;
  729         int count;
  730 
  731         if ((m = mp) == NULL)
  732                 return;
  733         if (len >= 0) {
  734                 /*
  735                  * Trim from head.
  736                  */
  737                 while (m != NULL && len > 0) {
  738                         if (m->m_len <= len) {
  739                                 len -= m->m_len;
  740                                 m->m_len = 0;
  741                                 m = m->m_next;
  742                         } else {
  743                                 m->m_len -= len;
  744                                 m->m_data += len;
  745                                 len = 0;
  746                         }
  747                 }
  748                 m = mp;
  749                 if (mp->m_flags & M_PKTHDR)
  750                         m->m_pkthdr.len -= (req_len - len);
  751         } else {
  752                 /*
  753                  * Trim from tail.  Scan the mbuf chain,
  754                  * calculating its length and finding the last mbuf.
  755                  * If the adjustment only affects this mbuf, then just
  756                  * adjust and return.  Otherwise, rescan and truncate
  757                  * after the remaining size.
  758                  */
  759                 len = -len;
  760                 count = 0;
  761                 for (;;) {
  762                         count += m->m_len;
  763                         if (m->m_next == (struct mbuf *)0)
  764                                 break;
  765                         m = m->m_next;
  766                 }
  767                 if (m->m_len >= len) {
  768                         m->m_len -= len;
  769                         if (mp->m_flags & M_PKTHDR)
  770                                 mp->m_pkthdr.len -= len;
  771                         return;
  772                 }
  773                 count -= len;
  774                 if (count < 0)
  775                         count = 0;
  776                 /*
  777                  * Correct length for chain is "count".
  778                  * Find the mbuf with last data, adjust its length,
  779                  * and toss data from remaining mbufs on chain.
  780                  */
  781                 m = mp;
  782                 if (m->m_flags & M_PKTHDR)
  783                         m->m_pkthdr.len = count;
  784                 for (; m; m = m->m_next) {
  785                         if (m->m_len >= count) {
  786                                 m->m_len = count;
  787                                 break;
  788                         }
  789                         count -= m->m_len;
  790                 }
  791                 while (m->m_next)
  792                         (m = m->m_next) ->m_len = 0;
  793         }
  794 }
  795 
  796 /*
  797  * Rearange an mbuf chain so that len bytes are contiguous
  798  * and in the data area of an mbuf (so that mtod and dtom
  799  * will work for a structure of size len).  Returns the resulting
  800  * mbuf chain on success, frees it and returns null on failure.
  801  * If there is room, it will add up to max_protohdr-len extra bytes to the
  802  * contiguous region in an attempt to avoid being called next time.
  803  */
  804 int MPFail;
  805 
  806 struct mbuf *
  807 m_pullup(struct mbuf *n, int len)
  808 {
  809         struct mbuf *m;
  810         int count;
  811         int space;
  812 
  813         /*
  814          * If first mbuf has no cluster, and has room for len bytes
  815          * without shifting current data, pullup into it,
  816          * otherwise allocate a new mbuf to prepend to the chain.
  817          */
  818         if ((n->m_flags & M_EXT) == 0 &&
  819             n->m_data + len < &n->m_dat[MLEN] && n->m_next) {
  820                 if (n->m_len >= len)
  821                         return (n);
  822                 m = n;
  823                 n = n->m_next;
  824                 len -= m->m_len;
  825         } else {
  826                 if (len > MHLEN)
  827                         goto bad;
  828                 MGET(m, M_DONTWAIT, n->m_type);
  829                 if (m == 0)
  830                         goto bad;
  831                 MCLAIM(m, n->m_owner);
  832                 m->m_len = 0;
  833                 if (n->m_flags & M_PKTHDR) {
  834                         M_COPY_PKTHDR(m, n);
  835                         m_tag_delete_chain(n, NULL);
  836                         n->m_flags &= ~M_PKTHDR;
  837                 }
  838         }
  839         space = &m->m_dat[MLEN] - (m->m_data + m->m_len);
  840         do {
  841                 count = min(min(max(len, max_protohdr), space), n->m_len);
  842                 memcpy(mtod(m, caddr_t) + m->m_len, mtod(n, caddr_t),
  843                   (unsigned)count);
  844                 len -= count;
  845                 m->m_len += count;
  846                 n->m_len -= count;
  847                 space -= count;
  848                 if (n->m_len)
  849                         n->m_data += count;
  850                 else
  851                         n = m_free(n);
  852         } while (len > 0 && n);
  853         if (len > 0) {
  854                 (void) m_free(m);
  855                 goto bad;
  856         }
  857         m->m_next = n;
  858         return (m);
  859 bad:
  860         m_freem(n);
  861         MPFail++;
  862         return (NULL);
  863 }
  864 
  865 /*
  866  * Like m_pullup(), except a new mbuf is always allocated, and we allow
  867  * the amount of empty space before the data in the new mbuf to be specified
  868  * (in the event that the caller expects to prepend later).
  869  */
  870 int MSFail;
  871 
  872 struct mbuf *
  873 m_copyup(struct mbuf *n, int len, int dstoff)
  874 {
  875         struct mbuf *m;
  876         int count, space;
  877 
  878         if (len > (MHLEN - dstoff))
  879                 goto bad;
  880         MGET(m, M_DONTWAIT, n->m_type);
  881         if (m == NULL)
  882                 goto bad;
  883         MCLAIM(m, n->m_owner);
  884         m->m_len = 0;
  885         if (n->m_flags & M_PKTHDR) {
  886                 M_COPY_PKTHDR(m, n);
  887                 m_tag_delete_chain(n, NULL);
  888                 n->m_flags &= ~M_PKTHDR;
  889         }
  890         m->m_data += dstoff;
  891         space = &m->m_dat[MLEN] - (m->m_data + m->m_len);
  892         do {
  893                 count = min(min(max(len, max_protohdr), space), n->m_len);
  894                 memcpy(mtod(m, caddr_t) + m->m_len, mtod(n, caddr_t),
  895                     (unsigned)count);
  896                 len -= count;
  897                 m->m_len += count;
  898                 n->m_len -= count;
  899                 space -= count;
  900                 if (n->m_len)
  901                         n->m_data += count;
  902                 else
  903                         n = m_free(n);
  904         } while (len > 0 && n);
  905         if (len > 0) {
  906                 (void) m_free(m);
  907                 goto bad;
  908         }
  909         m->m_next = n;
  910         return (m);
  911  bad:
  912         m_freem(n);
  913         MSFail++;
  914         return (NULL);
  915 }
  916 
  917 /*
  918  * Partition an mbuf chain in two pieces, returning the tail --
  919  * all but the first len0 bytes.  In case of failure, it returns NULL and
  920  * attempts to restore the chain to its original state.
  921  */
  922 struct mbuf *
  923 m_split(struct mbuf *m0, int len0, int wait)
  924 {
  925 
  926         return m_split0(m0, len0, wait, 1);
  927 }
  928 
  929 static struct mbuf *
  930 m_split0(struct mbuf *m0, int len0, int wait, int copyhdr)
  931 {
  932         struct mbuf *m, *n;
  933         unsigned len = len0, remain, len_save;
  934 
  935         for (m = m0; m && len > m->m_len; m = m->m_next)
  936                 len -= m->m_len;
  937         if (m == 0)
  938                 return (NULL);
  939         remain = m->m_len - len;
  940         if (copyhdr && (m0->m_flags & M_PKTHDR)) {
  941                 MGETHDR(n, wait, m0->m_type);
  942                 if (n == 0)
  943                         return (NULL);
  944                 MCLAIM(n, m0->m_owner);
  945                 n->m_pkthdr.rcvif = m0->m_pkthdr.rcvif;
  946                 n->m_pkthdr.len = m0->m_pkthdr.len - len0;
  947                 len_save = m0->m_pkthdr.len;
  948                 m0->m_pkthdr.len = len0;
  949                 if (m->m_flags & M_EXT)
  950                         goto extpacket;
  951                 if (remain > MHLEN) {
  952                         /* m can't be the lead packet */
  953                         MH_ALIGN(n, 0);
  954                         n->m_next = m_split(m, len, wait);
  955                         if (n->m_next == 0) {
  956                                 (void) m_free(n);
  957                                 m0->m_pkthdr.len = len_save;
  958                                 return (NULL);
  959                         } else
  960                                 return (n);
  961                 } else
  962                         MH_ALIGN(n, remain);
  963         } else if (remain == 0) {
  964                 n = m->m_next;
  965                 m->m_next = 0;
  966                 return (n);
  967         } else {
  968                 MGET(n, wait, m->m_type);
  969                 if (n == 0)
  970                         return (NULL);
  971                 MCLAIM(n, m->m_owner);
  972                 M_ALIGN(n, remain);
  973         }
  974 extpacket:
  975         if (m->m_flags & M_EXT) {
  976                 n->m_ext = m->m_ext;
  977                 MCLADDREFERENCE(m, n);
  978                 n->m_data = m->m_data + len;
  979         } else {
  980                 memcpy(mtod(n, caddr_t), mtod(m, caddr_t) + len, remain);
  981         }
  982         n->m_len = remain;
  983         m->m_len = len;
  984         n->m_next = m->m_next;
  985         m->m_next = 0;
  986         return (n);
  987 }
  988 /*
  989  * Routine to copy from device local memory into mbufs.
  990  */
  991 struct mbuf *
  992 m_devget(char *buf, int totlen, int off0, struct ifnet *ifp,
  993     void (*copy)(const void *from, void *to, size_t len))
  994 {
  995         struct mbuf *m;
  996         struct mbuf *top = 0, **mp = &top;
  997         int off = off0, len;
  998         char *cp;
  999         char *epkt;
 1000 
 1001         cp = buf;
 1002         epkt = cp + totlen;
 1003         if (off) {
 1004                 /*
 1005                  * If 'off' is non-zero, packet is trailer-encapsulated,
 1006                  * so we have to skip the type and length fields.
 1007                  */
 1008                 cp += off + 2 * sizeof(u_int16_t);
 1009                 totlen -= 2 * sizeof(u_int16_t);
 1010         }
 1011         MGETHDR(m, M_DONTWAIT, MT_DATA);
 1012         if (m == 0)
 1013                 return (NULL);
 1014         m->m_pkthdr.rcvif = ifp;
 1015         m->m_pkthdr.len = totlen;
 1016         m->m_len = MHLEN;
 1017 
 1018         while (totlen > 0) {
 1019                 if (top) {
 1020                         MGET(m, M_DONTWAIT, MT_DATA);
 1021                         if (m == 0) {
 1022                                 m_freem(top);
 1023                                 return (NULL);
 1024                         }
 1025                         m->m_len = MLEN;
 1026                 }
 1027                 len = min(totlen, epkt - cp);
 1028                 if (len >= MINCLSIZE) {
 1029                         MCLGET(m, M_DONTWAIT);
 1030                         if ((m->m_flags & M_EXT) == 0) {
 1031                                 m_free(m);
 1032                                 m_freem(top);
 1033                                 return (NULL);
 1034                         }
 1035                         m->m_len = len = min(len, MCLBYTES);
 1036                 } else {
 1037                         /*
 1038                          * Place initial small packet/header at end of mbuf.
 1039                          */
 1040                         if (len < m->m_len) {
 1041                                 if (top == 0 && len + max_linkhdr <= m->m_len)
 1042                                         m->m_data += max_linkhdr;
 1043                                 m->m_len = len;
 1044                         } else
 1045                                 len = m->m_len;
 1046                 }
 1047                 if (copy)
 1048                         copy(cp, mtod(m, caddr_t), (size_t)len);
 1049                 else
 1050                         memcpy(mtod(m, caddr_t), cp, (size_t)len);
 1051                 cp += len;
 1052                 *mp = m;
 1053                 mp = &m->m_next;
 1054                 totlen -= len;
 1055                 if (cp == epkt)
 1056                         cp = buf;
 1057         }
 1058         return (top);
 1059 }
 1060 
 1061 /*
 1062  * Copy data from a buffer back into the indicated mbuf chain,
 1063  * starting "off" bytes from the beginning, extending the mbuf
 1064  * chain if necessary.
 1065  */
 1066 void
 1067 m_copyback(struct mbuf *m0, int off, int len, const void *cp)
 1068 {
 1069 #if defined(DEBUG)
 1070         struct mbuf *origm = m0;
 1071         int error;
 1072 #endif /* defined(DEBUG) */
 1073 
 1074         if (m0 == NULL)
 1075                 return;
 1076 
 1077 #if defined(DEBUG)
 1078         error =
 1079 #endif /* defined(DEBUG) */
 1080         m_copyback0(&m0, off, len, cp,
 1081             M_COPYBACK0_COPYBACK|M_COPYBACK0_EXTEND, M_DONTWAIT);
 1082 
 1083 #if defined(DEBUG)
 1084         if (error != 0 || (m0 != NULL && origm != m0))
 1085                 panic("m_copyback");
 1086 #endif /* defined(DEBUG) */
 1087 }
 1088 
 1089 struct mbuf *
 1090 m_copyback_cow(struct mbuf *m0, int off, int len, const void *cp, int how)
 1091 {
 1092         int error;
 1093 
 1094         /* don't support chain expansion */
 1095         KDASSERT(off + len <= m_length(m0));
 1096 
 1097         error = m_copyback0(&m0, off, len, cp,
 1098             M_COPYBACK0_COPYBACK|M_COPYBACK0_COW, how);
 1099         if (error) {
 1100                 /*
 1101                  * no way to recover from partial success.
 1102                  * just free the chain.
 1103                  */
 1104                 m_freem(m0);
 1105                 return NULL;
 1106         }
 1107         return m0;
 1108 }
 1109 
 1110 /*
 1111  * m_makewritable: ensure the specified range writable.
 1112  */
 1113 int
 1114 m_makewritable(struct mbuf **mp, int off, int len, int how)
 1115 {
 1116         int error;
 1117 #if defined(DEBUG)
 1118         struct mbuf *n;
 1119         int origlen, reslen;
 1120 
 1121         origlen = m_length(*mp);
 1122 #endif /* defined(DEBUG) */
 1123 
 1124 #if 0 /* M_COPYALL is large enough */
 1125         if (len == M_COPYALL)
 1126                 len = m_length(*mp) - off; /* XXX */
 1127 #endif
 1128 
 1129         error = m_copyback0(mp, off, len, NULL,
 1130             M_COPYBACK0_PRESERVE|M_COPYBACK0_COW, how);
 1131 
 1132 #if defined(DEBUG)
 1133         reslen = 0;
 1134         for (n = *mp; n; n = n->m_next)
 1135                 reslen += n->m_len;
 1136         if (origlen != reslen)
 1137                 panic("m_makewritable: length changed");
 1138         if (((*mp)->m_flags & M_PKTHDR) != 0 && reslen != (*mp)->m_pkthdr.len)
 1139                 panic("m_makewritable: inconsist");
 1140 #endif /* defined(DEBUG) */
 1141 
 1142         return error;
 1143 }
 1144 
 1145 int
 1146 m_copyback0(struct mbuf **mp0, int off, int len, const void *vp, int flags,
 1147     int how)
 1148 {
 1149         int mlen;
 1150         struct mbuf *m, *n;
 1151         struct mbuf **mp;
 1152         int totlen = 0;
 1153         const char *cp = vp;
 1154 
 1155         KASSERT(mp0 != NULL);
 1156         KASSERT(*mp0 != NULL);
 1157         KASSERT((flags & M_COPYBACK0_PRESERVE) == 0 || cp == NULL);
 1158         KASSERT((flags & M_COPYBACK0_COPYBACK) == 0 || cp != NULL);
 1159 
 1160         mp = mp0;
 1161         m = *mp;
 1162         while (off > (mlen = m->m_len)) {
 1163                 off -= mlen;
 1164                 totlen += mlen;
 1165                 if (m->m_next == 0) {
 1166                         if ((flags & M_COPYBACK0_EXTEND) == 0)
 1167                                 goto out;
 1168                         n = m_getclr(how, m->m_type);
 1169                         if (n == 0)
 1170                                 goto out;
 1171                         n->m_len = min(MLEN, len + off);
 1172                         m->m_next = n;
 1173                 }
 1174                 mp = &m->m_next;
 1175                 m = m->m_next;
 1176         }
 1177         while (len > 0) {
 1178                 mlen = m->m_len - off;
 1179                 if (mlen != 0 && M_READONLY(m)) {
 1180                         char *datap;
 1181                         int eatlen;
 1182 
 1183                         /*
 1184                          * this mbuf is read-only.
 1185                          * allocate a new writable mbuf and try again.
 1186                          */
 1187 
 1188 #if defined(DIAGNOSTIC)
 1189                         if ((flags & M_COPYBACK0_COW) == 0)
 1190                                 panic("m_copyback0: read-only");
 1191 #endif /* defined(DIAGNOSTIC) */
 1192 
 1193                         /*
 1194                          * if we're going to write into the middle of
 1195                          * a mbuf, split it first.
 1196                          */
 1197                         if (off > 0 && len < mlen) {
 1198                                 n = m_split0(m, off, how, 0);
 1199                                 if (n == NULL)
 1200                                         goto enobufs;
 1201                                 m->m_next = n;
 1202                                 mp = &m->m_next;
 1203                                 m = n;
 1204                                 off = 0;
 1205                                 continue;
 1206                         }
 1207 
 1208                         /*
 1209                          * XXX TODO coalesce into the trailingspace of
 1210                          * the previous mbuf when possible.
 1211                          */
 1212 
 1213                         /*
 1214                          * allocate a new mbuf.  copy packet header if needed.
 1215                          */
 1216                         MGET(n, how, m->m_type);
 1217                         if (n == NULL)
 1218                                 goto enobufs;
 1219                         MCLAIM(n, m->m_owner);
 1220                         if (off == 0 && (m->m_flags & M_PKTHDR) != 0) {
 1221                                 /* XXX M_MOVE_PKTHDR */
 1222                                 M_COPY_PKTHDR(n, m);
 1223                                 n->m_len = MHLEN;
 1224                         } else {
 1225                                 if (len >= MINCLSIZE)
 1226                                         MCLGET(n, M_DONTWAIT);
 1227                                 n->m_len =
 1228                                     (n->m_flags & M_EXT) ? MCLBYTES : MLEN;
 1229                         }
 1230                         if (n->m_len > len)
 1231                                 n->m_len = len;
 1232 
 1233                         /*
 1234                          * free the region which has been overwritten.
 1235                          * copying data from old mbufs if requested.
 1236                          */
 1237                         if (flags & M_COPYBACK0_PRESERVE)
 1238                                 datap = mtod(n, char *);
 1239                         else
 1240                                 datap = NULL;
 1241                         eatlen = n->m_len;
 1242                         KDASSERT(off == 0 || eatlen >= mlen);
 1243                         if (off > 0) {
 1244                                 KDASSERT(len >= mlen);
 1245                                 m->m_len = off;
 1246                                 m->m_next = n;
 1247                                 if (datap) {
 1248                                         m_copydata(m, off, mlen, datap);
 1249                                         datap += mlen;
 1250                                 }
 1251                                 eatlen -= mlen;
 1252                                 mp = &m->m_next;
 1253                                 m = m->m_next;
 1254                         }
 1255                         while (m != NULL && M_READONLY(m) &&
 1256                             n->m_type == m->m_type && eatlen > 0) {
 1257                                 mlen = min(eatlen, m->m_len);
 1258                                 if (datap) {
 1259                                         m_copydata(m, 0, mlen, datap);
 1260                                         datap += mlen;
 1261                                 }
 1262                                 m->m_data += mlen;
 1263                                 m->m_len -= mlen;
 1264                                 eatlen -= mlen;
 1265                                 if (m->m_len == 0)
 1266                                         *mp = m = m_free(m);
 1267                         }
 1268                         if (eatlen > 0)
 1269                                 n->m_len -= eatlen;
 1270                         n->m_next = m;
 1271                         *mp = m = n;
 1272                         continue;
 1273                 }
 1274                 mlen = min(mlen, len);
 1275                 if (flags & M_COPYBACK0_COPYBACK) {
 1276                         memcpy(mtod(m, caddr_t) + off, cp, (unsigned)mlen);
 1277                         cp += mlen;
 1278                 }
 1279                 len -= mlen;
 1280                 mlen += off;
 1281                 off = 0;
 1282                 totlen += mlen;
 1283                 if (len == 0)
 1284                         break;
 1285                 if (m->m_next == 0) {
 1286                         if ((flags & M_COPYBACK0_EXTEND) == 0)
 1287                                 goto out;
 1288                         n = m_get(how, m->m_type);
 1289                         if (n == 0)
 1290                                 break;
 1291                         n->m_len = min(MLEN, len);
 1292                         m->m_next = n;
 1293                 }
 1294                 mp = &m->m_next;
 1295                 m = m->m_next;
 1296         }
 1297 out:    if (((m = *mp0)->m_flags & M_PKTHDR) && (m->m_pkthdr.len < totlen))
 1298                 m->m_pkthdr.len = totlen;
 1299 
 1300         return 0;
 1301 
 1302 enobufs:
 1303         return ENOBUFS;
 1304 }
 1305 
 1306 /*
 1307  * Apply function f to the data in an mbuf chain starting "off" bytes from the
 1308  * beginning, continuing for "len" bytes.
 1309  */
 1310 int
 1311 m_apply(struct mbuf *m, int off, int len,
 1312     int (*f)(void *, caddr_t, unsigned int), void *arg)
 1313 {
 1314         unsigned int count;
 1315         int rval;
 1316 
 1317         KASSERT(len >= 0);
 1318         KASSERT(off >= 0);
 1319 
 1320         while (off > 0) {
 1321                 KASSERT(m != NULL);
 1322                 if (off < m->m_len)
 1323                         break;
 1324                 off -= m->m_len;
 1325                 m = m->m_next;
 1326         }
 1327         while (len > 0) {
 1328                 KASSERT(m != NULL);
 1329                 count = min(m->m_len - off, len);
 1330 
 1331                 rval = (*f)(arg, mtod(m, caddr_t) + off, count);
 1332                 if (rval)
 1333                         return (rval);
 1334 
 1335                 len -= count;
 1336                 off = 0;
 1337                 m = m->m_next;
 1338         }
 1339 
 1340         return (0);
 1341 }
 1342 
 1343 /*
 1344  * Return a pointer to mbuf/offset of location in mbuf chain.
 1345  */
 1346 struct mbuf *
 1347 m_getptr(struct mbuf *m, int loc, int *off)
 1348 {
 1349 
 1350         while (loc >= 0) {
 1351                 /* Normal end of search */
 1352                 if (m->m_len > loc) {
 1353                         *off = loc;
 1354                         return (m);
 1355                 } else {
 1356                         loc -= m->m_len;
 1357 
 1358                         if (m->m_next == NULL) {
 1359                                 if (loc == 0) {
 1360                                         /* Point at the end of valid data */
 1361                                         *off = m->m_len;
 1362                                         return (m);
 1363                                 } else
 1364                                         return (NULL);
 1365                         } else
 1366                                 m = m->m_next;
 1367                 }
 1368         }
 1369 
 1370         return (NULL);
 1371 }

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