The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: 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 /*
    2  * Copyright (c) 1982, 1986, 1988, 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 3. All advertising materials mentioning features or use of this software
   14  *    must display the following acknowledgement:
   15  *      This product includes software developed by the University of
   16  *      California, Berkeley and its contributors.
   17  * 4. Neither the name of the University nor the names of its contributors
   18  *    may be used to endorse or promote products derived from this software
   19  *    without specific prior written permission.
   20  *
   21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31  * SUCH DAMAGE.
   32  *
   33  *      @(#)uipc_mbuf.c 8.2 (Berkeley) 1/4/94
   34  * $FreeBSD: releng/5.0/sys/kern/uipc_mbuf.c 105194 2002-10-16 01:54:46Z sam $
   35  */
   36 
   37 #include "opt_mac.h"
   38 #include "opt_param.h"
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/kernel.h>
   43 #include <sys/lock.h>
   44 #include <sys/mac.h>
   45 #include <sys/malloc.h>
   46 #include <sys/mbuf.h>
   47 #include <sys/sysctl.h>
   48 #include <sys/domain.h>
   49 #include <sys/protosw.h>
   50 
   51 int     max_linkhdr;
   52 int     max_protohdr;
   53 int     max_hdr;
   54 int     max_datalen;
   55 
   56 /*
   57  * sysctl(8) exported objects
   58  */
   59 SYSCTL_DECL(_kern_ipc);
   60 SYSCTL_INT(_kern_ipc, KIPC_MAX_LINKHDR, max_linkhdr, CTLFLAG_RW,
   61            &max_linkhdr, 0, "");
   62 SYSCTL_INT(_kern_ipc, KIPC_MAX_PROTOHDR, max_protohdr, CTLFLAG_RW,
   63            &max_protohdr, 0, "");
   64 SYSCTL_INT(_kern_ipc, KIPC_MAX_HDR, max_hdr, CTLFLAG_RW, &max_hdr, 0, "");
   65 SYSCTL_INT(_kern_ipc, KIPC_MAX_DATALEN, max_datalen, CTLFLAG_RW,
   66            &max_datalen, 0, "");
   67 
   68 /*
   69  * Copy mbuf pkthdr from "from" to "to".
   70  * "from" must have M_PKTHDR set, and "to" must be empty.
   71  * aux pointer will be moved to "to".
   72  */
   73 void
   74 m_copy_pkthdr(struct mbuf *to, struct mbuf *from)
   75 {
   76 
   77 #if 0
   78         KASSERT(to->m_flags & M_PKTHDR,
   79             ("m_copy_pkthdr() called on non-header"));
   80 #endif
   81 #ifdef MAC
   82         if (to->m_flags & M_PKTHDR)
   83                 mac_destroy_mbuf(to);
   84 #endif
   85         to->m_data = to->m_pktdat;
   86         to->m_flags = from->m_flags & M_COPYFLAGS;
   87         to->m_pkthdr = from->m_pkthdr;
   88 #ifdef MAC
   89         mac_init_mbuf(to, 1);                   /* XXXMAC no way to fail */
   90         mac_create_mbuf_from_mbuf(from, to);
   91 #endif
   92         SLIST_INIT(&from->m_pkthdr.tags);
   93 }
   94 
   95 /*
   96  * Lesser-used path for M_PREPEND:
   97  * allocate new mbuf to prepend to chain,
   98  * copy junk along.
   99  */
  100 struct mbuf *
  101 m_prepend(struct mbuf *m, int len, int how)
  102 {
  103         struct mbuf *mn;
  104 
  105         MGET(mn, how, m->m_type);
  106         if (mn == NULL) {
  107                 m_freem(m);
  108                 return (NULL);
  109         }
  110         if (m->m_flags & M_PKTHDR) {
  111                 M_COPY_PKTHDR(mn, m);
  112 #ifdef MAC
  113                 mac_destroy_mbuf(m);
  114 #endif
  115                 m->m_flags &= ~M_PKTHDR;
  116         }
  117         mn->m_next = m;
  118         m = mn;
  119         if (len < MHLEN)
  120                 MH_ALIGN(m, len);
  121         m->m_len = len;
  122         return (m);
  123 }
  124 
  125 /*
  126  * Make a copy of an mbuf chain starting "off0" bytes from the beginning,
  127  * continuing for "len" bytes.  If len is M_COPYALL, copy to end of mbuf.
  128  * The wait parameter is a choice of M_TRYWAIT/M_DONTWAIT from caller.
  129  * Note that the copy is read-only, because clusters are not copied,
  130  * only their reference counts are incremented.
  131  */
  132 struct mbuf *
  133 m_copym(struct mbuf *m, int off0, int len, int wait)
  134 {
  135         struct mbuf *n, **np;
  136         int off = off0;
  137         struct mbuf *top;
  138         int copyhdr = 0;
  139 
  140         KASSERT(off >= 0, ("m_copym, negative off %d", off));
  141         KASSERT(len >= 0, ("m_copym, negative len %d", len));
  142         if (off == 0 && m->m_flags & M_PKTHDR)
  143                 copyhdr = 1;
  144         while (off > 0) {
  145                 KASSERT(m != NULL, ("m_copym, offset > size of mbuf chain"));
  146                 if (off < m->m_len)
  147                         break;
  148                 off -= m->m_len;
  149                 m = m->m_next;
  150         }
  151         np = &top;
  152         top = 0;
  153         while (len > 0) {
  154                 if (m == NULL) {
  155                         KASSERT(len == M_COPYALL, 
  156                             ("m_copym, length > size of mbuf chain"));
  157                         break;
  158                 }
  159                 MGET(n, wait, m->m_type);
  160                 *np = n;
  161                 if (n == NULL)
  162                         goto nospace;
  163                 if (copyhdr) {
  164                         M_COPY_PKTHDR(n, m);
  165                         if (len == M_COPYALL)
  166                                 n->m_pkthdr.len -= off0;
  167                         else
  168                                 n->m_pkthdr.len = len;
  169                         copyhdr = 0;
  170                 }
  171                 n->m_len = min(len, m->m_len - off);
  172                 if (m->m_flags & M_EXT) {
  173                         n->m_data = m->m_data + off;
  174                         n->m_ext = m->m_ext;
  175                         n->m_flags |= M_EXT;
  176                         MEXT_ADD_REF(m);
  177                 } else
  178                         bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
  179                             (u_int)n->m_len);
  180                 if (len != M_COPYALL)
  181                         len -= n->m_len;
  182                 off = 0;
  183                 m = m->m_next;
  184                 np = &n->m_next;
  185         }
  186         if (top == NULL)
  187                 mbstat.m_mcfail++;      /* XXX: No consistency. */
  188 
  189         return (top);
  190 nospace:
  191         m_freem(top);
  192         mbstat.m_mcfail++;      /* XXX: No consistency. */
  193         return (NULL);
  194 }
  195 
  196 /*
  197  * Copy an entire packet, including header (which must be present).
  198  * An optimization of the common case `m_copym(m, 0, M_COPYALL, how)'.
  199  * Note that the copy is read-only, because clusters are not copied,
  200  * only their reference counts are incremented.
  201  * Preserve alignment of the first mbuf so if the creator has left
  202  * some room at the beginning (e.g. for inserting protocol headers)
  203  * the copies still have the room available.
  204  */
  205 struct mbuf *
  206 m_copypacket(struct mbuf *m, int how)
  207 {
  208         struct mbuf *top, *n, *o;
  209 
  210         MGET(n, how, m->m_type);
  211         top = n;
  212         if (n == NULL)
  213                 goto nospace;
  214 
  215         M_COPY_PKTHDR(n, m);
  216         n->m_len = m->m_len;
  217         if (m->m_flags & M_EXT) {
  218                 n->m_data = m->m_data;
  219                 n->m_ext = m->m_ext;
  220                 n->m_flags |= M_EXT;
  221                 MEXT_ADD_REF(m);
  222         } else {
  223                 n->m_data = n->m_pktdat + (m->m_data - m->m_pktdat );
  224                 bcopy(mtod(m, char *), mtod(n, char *), n->m_len);
  225         }
  226 
  227         m = m->m_next;
  228         while (m) {
  229                 MGET(o, how, m->m_type);
  230                 if (o == NULL)
  231                         goto nospace;
  232 
  233                 n->m_next = o;
  234                 n = n->m_next;
  235 
  236                 n->m_len = m->m_len;
  237                 if (m->m_flags & M_EXT) {
  238                         n->m_data = m->m_data;
  239                         n->m_ext = m->m_ext;
  240                         n->m_flags |= M_EXT;
  241                         MEXT_ADD_REF(m);
  242                 } else {
  243                         bcopy(mtod(m, char *), mtod(n, char *), n->m_len);
  244                 }
  245 
  246                 m = m->m_next;
  247         }
  248         return top;
  249 nospace:
  250         m_freem(top);
  251         mbstat.m_mcfail++;      /* XXX: No consistency. */ 
  252         return (NULL);
  253 }
  254 
  255 /*
  256  * Copy data from an mbuf chain starting "off" bytes from the beginning,
  257  * continuing for "len" bytes, into the indicated buffer.
  258  */
  259 void
  260 m_copydata(const struct mbuf *m, int off, int len, caddr_t cp)
  261 {
  262         u_int count;
  263 
  264         KASSERT(off >= 0, ("m_copydata, negative off %d", off));
  265         KASSERT(len >= 0, ("m_copydata, negative len %d", len));
  266         while (off > 0) {
  267                 KASSERT(m != NULL, ("m_copydata, offset > size of mbuf chain"));
  268                 if (off < m->m_len)
  269                         break;
  270                 off -= m->m_len;
  271                 m = m->m_next;
  272         }
  273         while (len > 0) {
  274                 KASSERT(m != NULL, ("m_copydata, length > size of mbuf chain"));
  275                 count = min(m->m_len - off, len);
  276                 bcopy(mtod(m, caddr_t) + off, cp, count);
  277                 len -= count;
  278                 cp += count;
  279                 off = 0;
  280                 m = m->m_next;
  281         }
  282 }
  283 
  284 /*
  285  * Copy a packet header mbuf chain into a completely new chain, including
  286  * copying any mbuf clusters.  Use this instead of m_copypacket() when
  287  * you need a writable copy of an mbuf chain.
  288  */
  289 struct mbuf *
  290 m_dup(struct mbuf *m, int how)
  291 {
  292         struct mbuf **p, *top = NULL;
  293         int remain, moff, nsize;
  294 
  295         /* Sanity check */
  296         if (m == NULL)
  297                 return (NULL);
  298         KASSERT((m->m_flags & M_PKTHDR) != 0, ("%s: !PKTHDR", __func__));
  299 
  300         /* While there's more data, get a new mbuf, tack it on, and fill it */
  301         remain = m->m_pkthdr.len;
  302         moff = 0;
  303         p = &top;
  304         while (remain > 0 || top == NULL) {     /* allow m->m_pkthdr.len == 0 */
  305                 struct mbuf *n;
  306 
  307                 /* Get the next new mbuf */
  308                 MGET(n, how, m->m_type);
  309                 if (n == NULL)
  310                         goto nospace;
  311                 if (top == NULL) {              /* first one, must be PKTHDR */
  312                         M_COPY_PKTHDR(n, m);
  313                         nsize = MHLEN;
  314                 } else                          /* not the first one */
  315                         nsize = MLEN;
  316                 if (remain >= MINCLSIZE) {
  317                         MCLGET(n, how);
  318                         if ((n->m_flags & M_EXT) == 0) {
  319                                 (void)m_free(n);
  320                                 goto nospace;
  321                         }
  322                         nsize = MCLBYTES;
  323                 }
  324                 n->m_len = 0;
  325 
  326                 /* Link it into the new chain */
  327                 *p = n;
  328                 p = &n->m_next;
  329 
  330                 /* Copy data from original mbuf(s) into new mbuf */
  331                 while (n->m_len < nsize && m != NULL) {
  332                         int chunk = min(nsize - n->m_len, m->m_len - moff);
  333 
  334                         bcopy(m->m_data + moff, n->m_data + n->m_len, chunk);
  335                         moff += chunk;
  336                         n->m_len += chunk;
  337                         remain -= chunk;
  338                         if (moff == m->m_len) {
  339                                 m = m->m_next;
  340                                 moff = 0;
  341                         }
  342                 }
  343 
  344                 /* Check correct total mbuf length */
  345                 KASSERT((remain > 0 && m != NULL) || (remain == 0 && m == NULL),
  346                         ("%s: bogus m_pkthdr.len", __func__));
  347         }
  348         return (top);
  349 
  350 nospace:
  351         m_freem(top);
  352         mbstat.m_mcfail++;      /* XXX: No consistency. */
  353         return (NULL);
  354 }
  355 
  356 /*
  357  * Concatenate mbuf chain n to m.
  358  * Both chains must be of the same type (e.g. MT_DATA).
  359  * Any m_pkthdr is not updated.
  360  */
  361 void
  362 m_cat(struct mbuf *m, struct mbuf *n)
  363 {
  364         while (m->m_next)
  365                 m = m->m_next;
  366         while (n) {
  367                 if (m->m_flags & M_EXT ||
  368                     m->m_data + m->m_len + n->m_len >= &m->m_dat[MLEN]) {
  369                         /* just join the two chains */
  370                         m->m_next = n;
  371                         return;
  372                 }
  373                 /* splat the data from one into the other */
  374                 bcopy(mtod(n, caddr_t), mtod(m, caddr_t) + m->m_len,
  375                     (u_int)n->m_len);
  376                 m->m_len += n->m_len;
  377                 n = m_free(n);
  378         }
  379 }
  380 
  381 void
  382 m_adj(struct mbuf *mp, int req_len)
  383 {
  384         int len = req_len;
  385         struct mbuf *m;
  386         int count;
  387 
  388         if ((m = mp) == NULL)
  389                 return;
  390         if (len >= 0) {
  391                 /*
  392                  * Trim from head.
  393                  */
  394                 while (m != NULL && len > 0) {
  395                         if (m->m_len <= len) {
  396                                 len -= m->m_len;
  397                                 m->m_len = 0;
  398                                 m = m->m_next;
  399                         } else {
  400                                 m->m_len -= len;
  401                                 m->m_data += len;
  402                                 len = 0;
  403                         }
  404                 }
  405                 m = mp;
  406                 if (mp->m_flags & M_PKTHDR)
  407                         m->m_pkthdr.len -= (req_len - len);
  408         } else {
  409                 /*
  410                  * Trim from tail.  Scan the mbuf chain,
  411                  * calculating its length and finding the last mbuf.
  412                  * If the adjustment only affects this mbuf, then just
  413                  * adjust and return.  Otherwise, rescan and truncate
  414                  * after the remaining size.
  415                  */
  416                 len = -len;
  417                 count = 0;
  418                 for (;;) {
  419                         count += m->m_len;
  420                         if (m->m_next == (struct mbuf *)0)
  421                                 break;
  422                         m = m->m_next;
  423                 }
  424                 if (m->m_len >= len) {
  425                         m->m_len -= len;
  426                         if (mp->m_flags & M_PKTHDR)
  427                                 mp->m_pkthdr.len -= len;
  428                         return;
  429                 }
  430                 count -= len;
  431                 if (count < 0)
  432                         count = 0;
  433                 /*
  434                  * Correct length for chain is "count".
  435                  * Find the mbuf with last data, adjust its length,
  436                  * and toss data from remaining mbufs on chain.
  437                  */
  438                 m = mp;
  439                 if (m->m_flags & M_PKTHDR)
  440                         m->m_pkthdr.len = count;
  441                 for (; m; m = m->m_next) {
  442                         if (m->m_len >= count) {
  443                                 m->m_len = count;
  444                                 break;
  445                         }
  446                         count -= m->m_len;
  447                 }
  448                 while (m->m_next)
  449                         (m = m->m_next) ->m_len = 0;
  450         }
  451 }
  452 
  453 /*
  454  * Rearange an mbuf chain so that len bytes are contiguous
  455  * and in the data area of an mbuf (so that mtod and dtom
  456  * will work for a structure of size len).  Returns the resulting
  457  * mbuf chain on success, frees it and returns null on failure.
  458  * If there is room, it will add up to max_protohdr-len extra bytes to the
  459  * contiguous region in an attempt to avoid being called next time.
  460  */
  461 struct mbuf *
  462 m_pullup(struct mbuf *n, int len)
  463 {
  464         struct mbuf *m;
  465         int count;
  466         int space;
  467 
  468         /*
  469          * If first mbuf has no cluster, and has room for len bytes
  470          * without shifting current data, pullup into it,
  471          * otherwise allocate a new mbuf to prepend to the chain.
  472          */
  473         if ((n->m_flags & M_EXT) == 0 &&
  474             n->m_data + len < &n->m_dat[MLEN] && n->m_next) {
  475                 if (n->m_len >= len)
  476                         return (n);
  477                 m = n;
  478                 n = n->m_next;
  479                 len -= m->m_len;
  480         } else {
  481                 if (len > MHLEN)
  482                         goto bad;
  483                 MGET(m, M_DONTWAIT, n->m_type);
  484                 if (m == NULL)
  485                         goto bad;
  486                 m->m_len = 0;
  487                 if (n->m_flags & M_PKTHDR) {
  488                         M_COPY_PKTHDR(m, n);
  489                         n->m_flags &= ~M_PKTHDR;
  490                 }
  491         }
  492         space = &m->m_dat[MLEN] - (m->m_data + m->m_len);
  493         do {
  494                 count = min(min(max(len, max_protohdr), space), n->m_len);
  495                 bcopy(mtod(n, caddr_t), mtod(m, caddr_t) + m->m_len,
  496                   (u_int)count);
  497                 len -= count;
  498                 m->m_len += count;
  499                 n->m_len -= count;
  500                 space -= count;
  501                 if (n->m_len)
  502                         n->m_data += count;
  503                 else
  504                         n = m_free(n);
  505         } while (len > 0 && n);
  506         if (len > 0) {
  507                 (void) m_free(m);
  508                 goto bad;
  509         }
  510         m->m_next = n;
  511         return (m);
  512 bad:
  513         m_freem(n);
  514         mbstat.m_mpfail++;      /* XXX: No consistency. */
  515         return (NULL);
  516 }
  517 
  518 /*
  519  * Partition an mbuf chain in two pieces, returning the tail --
  520  * all but the first len0 bytes.  In case of failure, it returns NULL and
  521  * attempts to restore the chain to its original state.
  522  *
  523  * Note that the resulting mbufs might be read-only, because the new
  524  * mbuf can end up sharing an mbuf cluster with the original mbuf if
  525  * the "breaking point" happens to lie within a cluster mbuf. Use the
  526  * M_WRITABLE() macro to check for this case.
  527  */
  528 struct mbuf *
  529 m_split(struct mbuf *m0, int len0, int wait)
  530 {
  531         struct mbuf *m, *n;
  532         u_int len = len0, remain;
  533 
  534         for (m = m0; m && len > m->m_len; m = m->m_next)
  535                 len -= m->m_len;
  536         if (m == NULL)
  537                 return (NULL);
  538         remain = m->m_len - len;
  539         if (m0->m_flags & M_PKTHDR) {
  540                 MGETHDR(n, wait, m0->m_type);
  541                 if (n == NULL)
  542                         return (NULL);
  543                 n->m_pkthdr.rcvif = m0->m_pkthdr.rcvif;
  544                 n->m_pkthdr.len = m0->m_pkthdr.len - len0;
  545                 m0->m_pkthdr.len = len0;
  546                 if (m->m_flags & M_EXT)
  547                         goto extpacket;
  548                 if (remain > MHLEN) {
  549                         /* m can't be the lead packet */
  550                         MH_ALIGN(n, 0);
  551                         n->m_next = m_split(m, len, wait);
  552                         if (n->m_next == NULL) {
  553                                 (void) m_free(n);
  554                                 return (NULL);
  555                         } else {
  556                                 n->m_len = 0;
  557                                 return (n);
  558                         }
  559                 } else
  560                         MH_ALIGN(n, remain);
  561         } else if (remain == 0) {
  562                 n = m->m_next;
  563                 m->m_next = NULL;
  564                 return (n);
  565         } else {
  566                 MGET(n, wait, m->m_type);
  567                 if (n == NULL)
  568                         return (NULL);
  569                 M_ALIGN(n, remain);
  570         }
  571 extpacket:
  572         if (m->m_flags & M_EXT) {
  573                 n->m_flags |= M_EXT;
  574                 n->m_ext = m->m_ext;
  575                 MEXT_ADD_REF(m);
  576                 n->m_data = m->m_data + len;
  577         } else {
  578                 bcopy(mtod(m, caddr_t) + len, mtod(n, caddr_t), remain);
  579         }
  580         n->m_len = remain;
  581         m->m_len = len;
  582         n->m_next = m->m_next;
  583         m->m_next = NULL;
  584         return (n);
  585 }
  586 /*
  587  * Routine to copy from device local memory into mbufs.
  588  * Note that `off' argument is offset into first mbuf of target chain from
  589  * which to begin copying the data to.
  590  */
  591 struct mbuf *
  592 m_devget(char *buf, int totlen, int off, struct ifnet *ifp,
  593          void (*copy)(char *from, caddr_t to, u_int len))
  594 {
  595         struct mbuf *m;
  596         struct mbuf *top = 0, **mp = &top;
  597         int len;
  598 
  599         if (off < 0 || off > MHLEN)
  600                 return (NULL);
  601 
  602         MGETHDR(m, M_DONTWAIT, MT_DATA);
  603         if (m == NULL)
  604                 return (NULL);
  605         m->m_pkthdr.rcvif = ifp;
  606         m->m_pkthdr.len = totlen;
  607         len = MHLEN;
  608 
  609         while (totlen > 0) {
  610                 if (top) {
  611                         MGET(m, M_DONTWAIT, MT_DATA);
  612                         if (m == NULL) {
  613                                 m_freem(top);
  614                                 return (NULL);
  615                         }
  616                         len = MLEN;
  617                 }
  618                 if (totlen + off >= MINCLSIZE) {
  619                         MCLGET(m, M_DONTWAIT);
  620                         if (m->m_flags & M_EXT)
  621                                 len = MCLBYTES;
  622                 } else {
  623                         /*
  624                          * Place initial small packet/header at end of mbuf.
  625                          */
  626                         if (top == NULL && totlen + off + max_linkhdr <= len) {
  627                                 m->m_data += max_linkhdr;
  628                                 len -= max_linkhdr;
  629                         }
  630                 }
  631                 if (off) {
  632                         m->m_data += off;
  633                         len -= off;
  634                         off = 0;
  635                 }
  636                 m->m_len = len = min(totlen, len);
  637                 if (copy)
  638                         copy(buf, mtod(m, caddr_t), (u_int)len);
  639                 else
  640                         bcopy(buf, mtod(m, caddr_t), (u_int)len);
  641                 buf += len;
  642                 *mp = m;
  643                 mp = &m->m_next;
  644                 totlen -= len;
  645         }
  646         return (top);
  647 }
  648 
  649 /*
  650  * Copy data from a buffer back into the indicated mbuf chain,
  651  * starting "off" bytes from the beginning, extending the mbuf
  652  * chain if necessary.
  653  */
  654 void
  655 m_copyback(struct mbuf *m0, int off, int len, caddr_t cp)
  656 {
  657         int mlen;
  658         struct mbuf *m = m0, *n;
  659         int totlen = 0;
  660 
  661         if (m0 == NULL)
  662                 return;
  663         while (off > (mlen = m->m_len)) {
  664                 off -= mlen;
  665                 totlen += mlen;
  666                 if (m->m_next == NULL) {
  667                         n = m_get_clrd(M_DONTWAIT, m->m_type);
  668                         if (n == NULL)
  669                                 goto out;
  670                         n->m_len = min(MLEN, len + off);
  671                         m->m_next = n;
  672                 }
  673                 m = m->m_next;
  674         }
  675         while (len > 0) {
  676                 mlen = min (m->m_len - off, len);
  677                 bcopy(cp, off + mtod(m, caddr_t), (u_int)mlen);
  678                 cp += mlen;
  679                 len -= mlen;
  680                 mlen += off;
  681                 off = 0;
  682                 totlen += mlen;
  683                 if (len == 0)
  684                         break;
  685                 if (m->m_next == NULL) {
  686                         n = m_get(M_DONTWAIT, m->m_type);
  687                         if (n == NULL)
  688                                 break;
  689                         n->m_len = min(MLEN, len);
  690                         m->m_next = n;
  691                 }
  692                 m = m->m_next;
  693         }
  694 out:    if (((m = m0)->m_flags & M_PKTHDR) && (m->m_pkthdr.len < totlen))
  695                 m->m_pkthdr.len = totlen;
  696 }
  697 
  698 void
  699 m_print(const struct mbuf *m)
  700 {
  701         int len;
  702         const struct mbuf *m2;
  703 
  704         len = m->m_pkthdr.len;
  705         m2 = m;
  706         while (len) {
  707                 printf("%p %*D\n", m2, m2->m_len, (u_char *)m2->m_data, "-");
  708                 len -= m2->m_len;
  709                 m2 = m2->m_next;
  710         }
  711         return;
  712 }
  713 
  714 u_int
  715 m_fixhdr(struct mbuf *m0)
  716 {
  717         u_int len;
  718 
  719         len = m_length(m0, NULL);
  720         m0->m_pkthdr.len = len;
  721         return (len);
  722 }
  723 
  724 u_int
  725 m_length(struct mbuf *m0, struct mbuf **last)
  726 {
  727         struct mbuf *m;
  728         u_int len;
  729 
  730         len = 0;
  731         for (m = m0; m != NULL; m = m->m_next) {
  732                 len += m->m_len;
  733                 if (m->m_next == NULL)
  734                         break;
  735         }
  736         if (last != NULL)
  737                 *last = m;
  738         return (len);
  739 }

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