uipc_mbuf.c revision 15689
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 * $Id: uipc_mbuf.c,v 1.19 1996/05/06 17:18:12 phk Exp $
35 */
36
37#include <sys/param.h>
38#include <sys/systm.h>
39#include <sys/proc.h>
40#include <sys/malloc.h>
41#define MBTYPES
42#include <sys/mbuf.h>
43#include <sys/kernel.h>
44#include <sys/syslog.h>
45#include <sys/domain.h>
46#include <sys/protosw.h>
47
48#include <vm/vm.h>
49#include <vm/vm_param.h>
50#include <vm/vm_kern.h>
51#include <vm/vm_extern.h>
52
53static void mbinit __P((void *));
54SYSINIT(mbuf, SI_SUB_MBUF, SI_ORDER_FIRST, mbinit, NULL)
55
56struct mbuf *mbutl;
57char	*mclrefcnt;
58struct mbstat mbstat;
59struct mbuf *mmbfree;
60union mcluster *mclfree;
61int	max_linkhdr;
62int	max_protohdr;
63int	max_hdr;
64int	max_datalen;
65
66static void	m_reclaim __P((void));
67
68/* ARGSUSED*/
69static void
70mbinit(dummy)
71	void *dummy;
72{
73	int s;
74
75#define NMB_INIT	16
76#if MCLBYTES < 4096
77#define NCL_INIT	(4096/MCLBYTES)
78#else
79#define NCL_INIT	1
80#endif
81
82	mmbfree = NULL; mclfree = NULL;
83	s = splimp();
84	if (m_mballoc(NMB_INIT, M_DONTWAIT) == 0)
85		goto bad;
86	if (m_clalloc(NCL_INIT, M_DONTWAIT) == 0)
87		goto bad;
88	splx(s);
89	return;
90bad:
91	panic("mbinit");
92}
93
94/*
95 * Allocate at least nmb mbufs and place on mbuf free list.
96 * Must be called at splimp.
97 */
98/* ARGSUSED */
99int
100m_mballoc(nmb, nowait)
101	register int nmb;
102	int nowait;
103{
104	register caddr_t p;
105	register int i;
106	int nbytes;
107
108	/* Once we run out of map space, it will be impossible to get
109	 * any more (nothing is ever freed back to the map) (XXX which
110	 * is dumb). (however you are not dead as m_reclaim might
111	 * still be able to free a substantial amount of space).
112	 */
113	if (mb_map_full)
114		return (0);
115
116	nbytes = round_page(nmb * MSIZE);
117	p = (caddr_t)kmem_malloc(mb_map, nbytes, nowait ? M_NOWAIT : M_WAITOK);
118	/*
119	 * Either the map is now full, or this is nowait and there
120	 * are no pages left.
121	 */
122	if (p == NULL)
123		return (0);
124
125	nmb = nbytes / MSIZE;
126	for (i = 0; i < nmb; i++) {
127		((struct mbuf *)p)->m_next = mmbfree;
128		mmbfree = (struct mbuf *)p;
129		p += MSIZE;
130	}
131	mbstat.m_mbufs += nmb;
132	return (1);
133}
134
135/*
136 * Allocate some number of mbuf clusters
137 * and place on cluster free list.
138 * Must be called at splimp.
139 */
140/* ARGSUSED */
141int
142m_clalloc(ncl, nowait)
143	register int ncl;
144	int nowait;
145{
146	register caddr_t p;
147	register int i;
148	int npg;
149
150	/*
151	 * Once we run out of map space, it will be impossible
152	 * to get any more (nothing is ever freed back to the
153	 * map).
154	 */
155	if (mb_map_full)
156		return (0);
157
158	npg = ncl;
159	p = (caddr_t)kmem_malloc(mb_map, ctob(npg),
160				 nowait ? M_NOWAIT : M_WAITOK);
161	/*
162	 * Either the map is now full, or this is nowait and there
163	 * are no pages left.
164	 */
165	if (p == NULL)
166		return (0);
167
168	ncl = ncl * PAGE_SIZE / MCLBYTES;
169	for (i = 0; i < ncl; i++) {
170		((union mcluster *)p)->mcl_next = mclfree;
171		mclfree = (union mcluster *)p;
172		p += MCLBYTES;
173		mbstat.m_clfree++;
174	}
175	mbstat.m_clusters += ncl;
176	return (1);
177}
178
179/*
180 * When MGET failes, ask protocols to free space when short of memory,
181 * then re-attempt to allocate an mbuf.
182 */
183struct mbuf *
184m_retry(i, t)
185	int i, t;
186{
187	register struct mbuf *m;
188
189	m_reclaim();
190#define m_retry(i, t)	(struct mbuf *)0
191	MGET(m, i, t);
192#undef m_retry
193	if (m != NULL)
194		mbstat.m_wait++;
195	else
196		mbstat.m_drops++;
197	return (m);
198}
199
200/*
201 * As above; retry an MGETHDR.
202 */
203struct mbuf *
204m_retryhdr(i, t)
205	int i, t;
206{
207	register struct mbuf *m;
208
209	m_reclaim();
210#define m_retryhdr(i, t) (struct mbuf *)0
211	MGETHDR(m, i, t);
212#undef m_retryhdr
213	if (m != NULL)
214		mbstat.m_wait++;
215	else
216		mbstat.m_drops++;
217	return (m);
218}
219
220static void
221m_reclaim()
222{
223	register struct domain *dp;
224	register struct protosw *pr;
225	int s = splimp();
226
227	for (dp = domains; dp; dp = dp->dom_next)
228		for (pr = dp->dom_protosw; pr < dp->dom_protoswNPROTOSW; pr++)
229			if (pr->pr_drain)
230				(*pr->pr_drain)();
231	splx(s);
232	mbstat.m_drain++;
233}
234
235/*
236 * Space allocation routines.
237 * These are also available as macros
238 * for critical paths.
239 */
240struct mbuf *
241m_get(nowait, type)
242	int nowait, type;
243{
244	register struct mbuf *m;
245
246	MGET(m, nowait, type);
247	return (m);
248}
249
250struct mbuf *
251m_gethdr(nowait, type)
252	int nowait, type;
253{
254	register struct mbuf *m;
255
256	MGETHDR(m, nowait, type);
257	return (m);
258}
259
260struct mbuf *
261m_getclr(nowait, type)
262	int nowait, type;
263{
264	register struct mbuf *m;
265
266	MGET(m, nowait, type);
267	if (m == 0)
268		return (0);
269	bzero(mtod(m, caddr_t), MLEN);
270	return (m);
271}
272
273struct mbuf *
274m_free(m)
275	struct mbuf *m;
276{
277	register struct mbuf *n;
278
279	MFREE(m, n);
280	return (n);
281}
282
283void
284m_freem(m)
285	register struct mbuf *m;
286{
287	register struct mbuf *n;
288
289	if (m == NULL)
290		return;
291	do {
292		MFREE(m, n);
293		m = n;
294	} while (m);
295}
296
297/*
298 * Mbuffer utility routines.
299 */
300
301/*
302 * Lesser-used path for M_PREPEND:
303 * allocate new mbuf to prepend to chain,
304 * copy junk along.
305 */
306struct mbuf *
307m_prepend(m, len, how)
308	register struct mbuf *m;
309	int len, how;
310{
311	struct mbuf *mn;
312
313	MGET(mn, how, m->m_type);
314	if (mn == (struct mbuf *)NULL) {
315		m_freem(m);
316		return ((struct mbuf *)NULL);
317	}
318	if (m->m_flags & M_PKTHDR) {
319		M_COPY_PKTHDR(mn, m);
320		m->m_flags &= ~M_PKTHDR;
321	}
322	mn->m_next = m;
323	m = mn;
324	if (len < MHLEN)
325		MH_ALIGN(m, len);
326	m->m_len = len;
327	return (m);
328}
329
330/*
331 * Make a copy of an mbuf chain starting "off0" bytes from the beginning,
332 * continuing for "len" bytes.  If len is M_COPYALL, copy to end of mbuf.
333 * The wait parameter is a choice of M_WAIT/M_DONTWAIT from caller.
334 */
335static int MCFail;
336
337struct mbuf *
338m_copym(m, off0, len, wait)
339	register struct mbuf *m;
340	int off0, wait;
341	register int len;
342{
343	register struct mbuf *n, **np;
344	register int off = off0;
345	struct mbuf *top;
346	int copyhdr = 0;
347
348	if (off < 0 || len < 0)
349		panic("m_copym");
350	if (off == 0 && m->m_flags & M_PKTHDR)
351		copyhdr = 1;
352	while (off > 0) {
353		if (m == 0)
354			panic("m_copym");
355		if (off < m->m_len)
356			break;
357		off -= m->m_len;
358		m = m->m_next;
359	}
360	np = &top;
361	top = 0;
362	while (len > 0) {
363		if (m == 0) {
364			if (len != M_COPYALL)
365				panic("m_copym");
366			break;
367		}
368		MGET(n, wait, m->m_type);
369		*np = n;
370		if (n == 0)
371			goto nospace;
372		if (copyhdr) {
373			M_COPY_PKTHDR(n, m);
374			if (len == M_COPYALL)
375				n->m_pkthdr.len -= off0;
376			else
377				n->m_pkthdr.len = len;
378			copyhdr = 0;
379		}
380		n->m_len = min(len, m->m_len - off);
381		if (m->m_flags & M_EXT) {
382			n->m_data = m->m_data + off;
383			mclrefcnt[mtocl(m->m_ext.ext_buf)]++;
384			n->m_ext = m->m_ext;
385			n->m_flags |= M_EXT;
386		} else
387			bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
388			    (unsigned)n->m_len);
389		if (len != M_COPYALL)
390			len -= n->m_len;
391		off = 0;
392		m = m->m_next;
393		np = &n->m_next;
394	}
395	if (top == 0)
396		MCFail++;
397	return (top);
398nospace:
399	m_freem(top);
400	MCFail++;
401	return (0);
402}
403
404/*
405 * Copy an entire packet, including header (which must be present).
406 * An optimization of the common case `m_copym(m, 0, M_COPYALL, how)'.
407 */
408struct mbuf *
409m_copypacket(m, how)
410	struct mbuf *m;
411	int how;
412{
413	struct mbuf *top, *n, *o;
414
415	MGET(n, how, m->m_type);
416	top = n;
417	if (!n)
418		goto nospace;
419
420	M_COPY_PKTHDR(n, m);
421	n->m_len = m->m_len;
422	if (m->m_flags & M_EXT) {
423		n->m_data = m->m_data;
424		mclrefcnt[mtocl(m->m_ext.ext_buf)]++;
425		n->m_ext = m->m_ext;
426		n->m_flags |= M_EXT;
427	} else {
428		bcopy(mtod(m, char *), mtod(n, char *), n->m_len);
429	}
430
431	m = m->m_next;
432	while (m) {
433		MGET(o, how, m->m_type);
434		if (!o)
435			goto nospace;
436
437		n->m_next = o;
438		n = n->m_next;
439
440		n->m_len = m->m_len;
441		if (m->m_flags & M_EXT) {
442			n->m_data = m->m_data;
443			mclrefcnt[mtocl(m->m_ext.ext_buf)]++;
444			n->m_ext = m->m_ext;
445			n->m_flags |= M_EXT;
446		} else {
447			bcopy(mtod(m, char *), mtod(n, char *), n->m_len);
448		}
449
450		m = m->m_next;
451	}
452	return top;
453nospace:
454	m_freem(top);
455	MCFail++;
456	return 0;
457}
458
459/*
460 * Copy data from an mbuf chain starting "off" bytes from the beginning,
461 * continuing for "len" bytes, into the indicated buffer.
462 */
463void
464m_copydata(m, off, len, cp)
465	register struct mbuf *m;
466	register int off;
467	register int len;
468	caddr_t cp;
469{
470	register unsigned count;
471
472	if (off < 0 || len < 0)
473		panic("m_copydata");
474	while (off > 0) {
475		if (m == 0)
476			panic("m_copydata");
477		if (off < m->m_len)
478			break;
479		off -= m->m_len;
480		m = m->m_next;
481	}
482	while (len > 0) {
483		if (m == 0)
484			panic("m_copydata");
485		count = min(m->m_len - off, len);
486		bcopy(mtod(m, caddr_t) + off, cp, count);
487		len -= count;
488		cp += count;
489		off = 0;
490		m = m->m_next;
491	}
492}
493
494/*
495 * Concatenate mbuf chain n to m.
496 * Both chains must be of the same type (e.g. MT_DATA).
497 * Any m_pkthdr is not updated.
498 */
499void
500m_cat(m, n)
501	register struct mbuf *m, *n;
502{
503	while (m->m_next)
504		m = m->m_next;
505	while (n) {
506		if (m->m_flags & M_EXT ||
507		    m->m_data + m->m_len + n->m_len >= &m->m_dat[MLEN]) {
508			/* just join the two chains */
509			m->m_next = n;
510			return;
511		}
512		/* splat the data from one into the other */
513		bcopy(mtod(n, caddr_t), mtod(m, caddr_t) + m->m_len,
514		    (u_int)n->m_len);
515		m->m_len += n->m_len;
516		n = m_free(n);
517	}
518}
519
520void
521m_adj(mp, req_len)
522	struct mbuf *mp;
523	int req_len;
524{
525	register int len = req_len;
526	register struct mbuf *m;
527	register count;
528
529	if ((m = mp) == NULL)
530		return;
531	if (len >= 0) {
532		/*
533		 * Trim from head.
534		 */
535		while (m != NULL && len > 0) {
536			if (m->m_len <= len) {
537				len -= m->m_len;
538				m->m_len = 0;
539				m = m->m_next;
540			} else {
541				m->m_len -= len;
542				m->m_data += len;
543				len = 0;
544			}
545		}
546		m = mp;
547		if (mp->m_flags & M_PKTHDR)
548			m->m_pkthdr.len -= (req_len - len);
549	} else {
550		/*
551		 * Trim from tail.  Scan the mbuf chain,
552		 * calculating its length and finding the last mbuf.
553		 * If the adjustment only affects this mbuf, then just
554		 * adjust and return.  Otherwise, rescan and truncate
555		 * after the remaining size.
556		 */
557		len = -len;
558		count = 0;
559		for (;;) {
560			count += m->m_len;
561			if (m->m_next == (struct mbuf *)0)
562				break;
563			m = m->m_next;
564		}
565		if (m->m_len >= len) {
566			m->m_len -= len;
567			if (mp->m_flags & M_PKTHDR)
568				mp->m_pkthdr.len -= len;
569			return;
570		}
571		count -= len;
572		if (count < 0)
573			count = 0;
574		/*
575		 * Correct length for chain is "count".
576		 * Find the mbuf with last data, adjust its length,
577		 * and toss data from remaining mbufs on chain.
578		 */
579		m = mp;
580		if (m->m_flags & M_PKTHDR)
581			m->m_pkthdr.len = count;
582		for (; m; m = m->m_next) {
583			if (m->m_len >= count) {
584				m->m_len = count;
585				break;
586			}
587			count -= m->m_len;
588		}
589		while (m->m_next)
590			(m = m->m_next) ->m_len = 0;
591	}
592}
593
594/*
595 * Rearange an mbuf chain so that len bytes are contiguous
596 * and in the data area of an mbuf (so that mtod and dtom
597 * will work for a structure of size len).  Returns the resulting
598 * mbuf chain on success, frees it and returns null on failure.
599 * If there is room, it will add up to max_protohdr-len extra bytes to the
600 * contiguous region in an attempt to avoid being called next time.
601 */
602static int MPFail;
603
604struct mbuf *
605m_pullup(n, len)
606	register struct mbuf *n;
607	int len;
608{
609	register struct mbuf *m;
610	register int count;
611	int space;
612
613	/*
614	 * If first mbuf has no cluster, and has room for len bytes
615	 * without shifting current data, pullup into it,
616	 * otherwise allocate a new mbuf to prepend to the chain.
617	 */
618	if ((n->m_flags & M_EXT) == 0 &&
619	    n->m_data + len < &n->m_dat[MLEN] && n->m_next) {
620		if (n->m_len >= len)
621			return (n);
622		m = n;
623		n = n->m_next;
624		len -= m->m_len;
625	} else {
626		if (len > MHLEN)
627			goto bad;
628		MGET(m, M_DONTWAIT, n->m_type);
629		if (m == 0)
630			goto bad;
631		m->m_len = 0;
632		if (n->m_flags & M_PKTHDR) {
633			M_COPY_PKTHDR(m, n);
634			n->m_flags &= ~M_PKTHDR;
635		}
636	}
637	space = &m->m_dat[MLEN] - (m->m_data + m->m_len);
638	do {
639		count = min(min(max(len, max_protohdr), space), n->m_len);
640		bcopy(mtod(n, caddr_t), mtod(m, caddr_t) + m->m_len,
641		  (unsigned)count);
642		len -= count;
643		m->m_len += count;
644		n->m_len -= count;
645		space -= count;
646		if (n->m_len)
647			n->m_data += count;
648		else
649			n = m_free(n);
650	} while (len > 0 && n);
651	if (len > 0) {
652		(void) m_free(m);
653		goto bad;
654	}
655	m->m_next = n;
656	return (m);
657bad:
658	m_freem(n);
659	MPFail++;
660	return (0);
661}
662
663/*
664 * Partition an mbuf chain in two pieces, returning the tail --
665 * all but the first len0 bytes.  In case of failure, it returns NULL and
666 * attempts to restore the chain to its original state.
667 */
668struct mbuf *
669m_split(m0, len0, wait)
670	register struct mbuf *m0;
671	int len0, wait;
672{
673	register struct mbuf *m, *n;
674	unsigned len = len0, remain;
675
676	for (m = m0; m && len > m->m_len; m = m->m_next)
677		len -= m->m_len;
678	if (m == 0)
679		return (0);
680	remain = m->m_len - len;
681	if (m0->m_flags & M_PKTHDR) {
682		MGETHDR(n, wait, m0->m_type);
683		if (n == 0)
684			return (0);
685		n->m_pkthdr.rcvif = m0->m_pkthdr.rcvif;
686		n->m_pkthdr.len = m0->m_pkthdr.len - len0;
687		m0->m_pkthdr.len = len0;
688		if (m->m_flags & M_EXT)
689			goto extpacket;
690		if (remain > MHLEN) {
691			/* m can't be the lead packet */
692			MH_ALIGN(n, 0);
693			n->m_next = m_split(m, len, wait);
694			if (n->m_next == 0) {
695				(void) m_free(n);
696				return (0);
697			} else
698				return (n);
699		} else
700			MH_ALIGN(n, remain);
701	} else if (remain == 0) {
702		n = m->m_next;
703		m->m_next = 0;
704		return (n);
705	} else {
706		MGET(n, wait, m->m_type);
707		if (n == 0)
708			return (0);
709		M_ALIGN(n, remain);
710	}
711extpacket:
712	if (m->m_flags & M_EXT) {
713		n->m_flags |= M_EXT;
714		n->m_ext = m->m_ext;
715		mclrefcnt[mtocl(m->m_ext.ext_buf)]++;
716		m->m_ext.ext_size = 0; /* For Accounting XXXXXX danger */
717		n->m_data = m->m_data + len;
718	} else {
719		bcopy(mtod(m, caddr_t) + len, mtod(n, caddr_t), remain);
720	}
721	n->m_len = remain;
722	m->m_len = len;
723	n->m_next = m->m_next;
724	m->m_next = 0;
725	return (n);
726}
727/*
728 * Routine to copy from device local memory into mbufs.
729 */
730struct mbuf *
731m_devget(buf, totlen, off0, ifp, copy)
732	char *buf;
733	int totlen, off0;
734	struct ifnet *ifp;
735	void (*copy) __P((char *from, caddr_t to, u_int len));
736{
737	register struct mbuf *m;
738	struct mbuf *top = 0, **mp = &top;
739	register int off = off0, len;
740	register char *cp;
741	char *epkt;
742
743	cp = buf;
744	epkt = cp + totlen;
745	if (off) {
746		cp += off + 2 * sizeof(u_short);
747		totlen -= 2 * sizeof(u_short);
748	}
749	MGETHDR(m, M_DONTWAIT, MT_DATA);
750	if (m == 0)
751		return (0);
752	m->m_pkthdr.rcvif = ifp;
753	m->m_pkthdr.len = totlen;
754	m->m_len = MHLEN;
755
756	while (totlen > 0) {
757		if (top) {
758			MGET(m, M_DONTWAIT, MT_DATA);
759			if (m == 0) {
760				m_freem(top);
761				return (0);
762			}
763			m->m_len = MLEN;
764		}
765		len = min(totlen, epkt - cp);
766		if (len >= MINCLSIZE) {
767			MCLGET(m, M_DONTWAIT);
768			if (m->m_flags & M_EXT)
769				m->m_len = len = min(len, MCLBYTES);
770			else
771				len = m->m_len;
772		} else {
773			/*
774			 * Place initial small packet/header at end of mbuf.
775			 */
776			if (len < m->m_len) {
777				if (top == 0 && len + max_linkhdr <= m->m_len)
778					m->m_data += max_linkhdr;
779				m->m_len = len;
780			} else
781				len = m->m_len;
782		}
783		if (copy)
784			copy(cp, mtod(m, caddr_t), (unsigned)len);
785		else
786			bcopy(cp, mtod(m, caddr_t), (unsigned)len);
787		cp += len;
788		*mp = m;
789		mp = &m->m_next;
790		totlen -= len;
791		if (cp == epkt)
792			cp = buf;
793	}
794	return (top);
795}
796
797/*
798 * Copy data from a buffer back into the indicated mbuf chain,
799 * starting "off" bytes from the beginning, extending the mbuf
800 * chain if necessary.
801 */
802void
803m_copyback(m0, off, len, cp)
804	struct	mbuf *m0;
805	register int off;
806	register int len;
807	caddr_t cp;
808{
809	register int mlen;
810	register struct mbuf *m = m0, *n;
811	int totlen = 0;
812
813	if (m0 == 0)
814		return;
815	while (off > (mlen = m->m_len)) {
816		off -= mlen;
817		totlen += mlen;
818		if (m->m_next == 0) {
819			n = m_getclr(M_DONTWAIT, m->m_type);
820			if (n == 0)
821				goto out;
822			n->m_len = min(MLEN, len + off);
823			m->m_next = n;
824		}
825		m = m->m_next;
826	}
827	while (len > 0) {
828		mlen = min (m->m_len - off, len);
829		bcopy(cp, off + mtod(m, caddr_t), (unsigned)mlen);
830		cp += mlen;
831		len -= mlen;
832		mlen += off;
833		off = 0;
834		totlen += mlen;
835		if (len == 0)
836			break;
837		if (m->m_next == 0) {
838			n = m_get(M_DONTWAIT, m->m_type);
839			if (n == 0)
840				break;
841			n->m_len = min(MLEN, len);
842			m->m_next = n;
843		}
844		m = m->m_next;
845	}
846out:	if (((m = m0)->m_flags & M_PKTHDR) && (m->m_pkthdr.len < totlen))
847		m->m_pkthdr.len = totlen;
848}
849