1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
|
.\" $OpenBSD: mbuf.9,v 1.118 2018/12/07 08:37:24 claudio Exp $
.\"
.\" Copyright (c) 2001 Jean-Jacques Bernard-Gundol <jjbg@openbsd.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. The name of the author may not be used to endorse or promote products
.\" derived from this software without specific prior written permission
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: December 7 2018 $
.Dt MGET 9
.Os
.Sh NAME
.Nm m_copym ,
.Nm m_free ,
.Nm m_get ,
.Nm MGET ,
.Nm m_getclr ,
.Nm m_gethdr ,
.Nm m_removehdr ,
.Nm m_resethdr ,
.Nm m_calchdrlen ,
.Nm MGETHDR ,
.Nm m_prepend ,
.Nm M_PREPEND ,
.Nm m_pulldown ,
.Nm m_pullup ,
.Nm m_split ,
.Nm m_makespace ,
.Nm m_getptr ,
.Nm m_adj ,
.Nm m_copyback ,
.Nm m_defrag ,
.Nm m_freem ,
.Nm m_freemp ,
.Nm m_purge ,
.Nm m_reclaim ,
.Nm m_copydata ,
.Nm m_cat ,
.Nm m_devget ,
.Nm m_apply ,
.Nm MCLGET ,
.Nm MCLGETI ,
.Nm MEXTADD ,
.Nm m_align ,
.Nm M_READONLY ,
.Nm m_leadingspace ,
.Nm m_trailingspace ,
.Nm mtod ,
.Nm m_dup_pkt ,
.Nm m_dup_pkthdr
.Nd kernel memory management for networking protocols
.Sh SYNOPSIS
.In sys/mbuf.h
.Ft struct mbuf *
.Fn m_copym "struct mbuf *m" "int off" "int len" "int wait"
.Ft struct mbuf *
.Fn m_free "struct mbuf *m"
.Ft struct mbuf *
.Fn m_get "int how" "int type"
.Fn MGET "struct mbuf *m" "int how" "int type"
.Ft struct mbuf *
.Fn m_getclr "int how" "int type"
.Ft void
.Fn m_removehdr "struct mbuf *m"
.Ft void
.Fn m_resethdr "struct mbuf *m"
.Ft void
.Fn m_calchdrlen "struct mbuf *m"
.Ft struct mbuf *
.Fn m_gethdr "int how" "int type"
.Fn MGETHDR "struct mbuf *m" "int how" "int type"
.Ft struct mbuf *
.Fn m_prepend "struct mbuf *m" "int len" "int how"
.Fn M_PREPEND "struct mbuf *m" "int plen" "int how"
.Ft struct mbuf *
.Fn m_pulldown "struct mbuf *m" "int off" "int len" "int *offp"
.Ft struct mbuf *
.Fn m_pullup "struct mbuf *n" "int len"
.Ft struct mbuf *
.Fn m_split "struct mbuf *m0" "int len0" "int wait"
.Ft struct mbuf *
.Fn m_makespace "struct mbuf *m0" "int skip" "int hlen" "int *off"
.Ft struct mbuf *
.Fn m_getptr "struct mbuf *m" "int loc" "int *off"
.Ft void
.Fn m_adj "struct mbuf *mp" "int req_len"
.Ft int
.Fn m_copyback "struct mbuf *m0" "int off" "int len" "const void *cp" "int wait"
.Ft int
.Fn m_defrag "struct mbuf *m" "int wait"
.Ft struct mbuf *
.Fn m_freem "struct mbuf *m"
.Ft struct mbuf *
.Fn m_freemp "struct mbuf **mp"
.Ft void
.Fn m_purge "struct mbuf *m"
.Ft void
.Fn m_reclaim "void"
.Ft void
.Fn m_copydata "struct mbuf *m" "int off" "int len" "caddr_t cp"
.Ft void
.Fn m_cat "struct mbuf *m" "struct mbuf *n"
.Ft struct mbuf *
.Fn m_devget "char *buf" "int totlen" "int off"
.Ft int
.Fn m_apply "struct mbuf *m" "int off" "int len" \
"int (*func)(caddr_t, caddr_t, unsigned int)" "caddr_t fstate"
.Fn MCLGET "struct mbuf *m" "int how"
.Ft struct mbuf *
.Fn MCLGETI "struct mbuf *m" "int how" "struct ifnet *ifp" "int len"
.Fn MEXTADD "struct mbuf *m" "caddr_t buf" "u_int size" "int flags" \
"void (*free)(caddr_t, u_int, void *)" "void *arg"
.Ft void
.Fn m_align "struct mbuf *m" "int len"
.Fn M_READONLY "struct mbuf *m"
.Ft int
.Fn m_leadingspace "struct mbuf *m"
.Ft int
.Fn m_trailingspace "struct mbuf *m"
.Ft struct mbuf *
.Fn m_dup_pkt "struct mbuf *m" "u_int adj" "int how"
.Ft int
.Fn m_dup_pkthdr "struct mbuf *to" "struct mbuf *from" "int how"
.Bd -literal
#define MSIZE 256
#define MLEN (MSIZE - sizeof(struct m_hdr))
#define MHLEN (MLEN - sizeof(struct pkthdr))
#define MAXMCLBYTES (64 * 1024)
#define MINCLSIZE (MHLEN + MLEN + 1)
#define M_MAXCOMPRESS (MHLEN / 2)
#define MCLSHIFT 11
#define MCLBYTES (1 << MCLSHIFT)
#define MCLOFSET (MCLBYTES - 1)
#define mtod(m,t) ((t)((m)->m_data))
struct m_hdr {
struct mbuf *mh_next;
struct mbuf *mh_nextpkt;
caddr_t mh_data;
u_int mh_len;
short mh_type;
u_short mh_flags;
#ifndef __LP64__
u_int mh_pad;
#endif
};
struct pkthdr {
void *ph_cookie;
SLIST_HEAD(, m_tag) ph_tags;
int64_t ph_timestamp;
int len;
u_int16_t ph_tagsset;
u_int16_t ph_flowid;
u_int16_t csum_flags;
u_int16_t ether_vtag;
u_int ph_rtableid;
u_int ph_ifidx;
u_int8_t ph_loopcnt;
struct pkthdr_pf pf;
};
struct pkthdr_pf {
struct pf_state_key *statekey;
struct inpcb *inp;
u_int32_t qid;
u_int16_t tag;
u_int8_t flags;
u_int8_t routed;
u_int8_t prio;
u_int8_t pad[3];
};
struct mbuf_ext {
caddr_t ext_buf;
void *ext_arg;
u_int ext_free_fn;
u_int ext_size;
struct mbuf *ext_nextref;
struct mbuf *ext_prevref;
};
struct mbuf {
struct m_hdr m_hdr;
union {
struct {
struct pkthdr MH_pkthdr;
union {
struct mbuf_ext MH_ext;
char MH_databuf[MHLEN];
} MH_dat;
} MH;
char M_databuf[MLEN];
} M_dat;
};
#define m_next m_hdr.mh_next
#define m_len m_hdr.mh_len
#define m_data m_hdr.mh_data
#define m_type m_hdr.mh_type
#define m_flags m_hdr.mh_flags
#define m_nextpkt m_hdr.mh_nextpkt
#define m_pkthdr M_dat.MH.MH_pkthdr
#define m_ext M_dat.MH.MH_dat.MH_ext
#define m_pktdat M_dat.MH.MH_dat.MH_databuf
#define m_dat M_dat.M_databuf
.Ed
.Sh DESCRIPTION
The
.Nm mbuf
functions provide a way to manage the memory buffers used by the kernel's
networking subsystem.
Several functions and macros are used to allocate and deallocate mbufs,
but also to get, inject, remove, copy, modify, prepend or append data
inside these mbufs.
The size of an
.Nm mbuf
is defined by MSIZE.
.Pp
An
.Nm mbuf
structure is defined as an
.Fa m_hdr
structure followed by a
union.
The header contains the following elements:
.Bl -tag -width foobarmoocow
.It Fa mh_next
A pointer to the next mbuf in the mbuf chain.
.It Fa mh_nextpkt
A pointer to the next mbuf chain (i.e., packet) in the queue.
.It Fa mh_data
Indicates the address of the beginning of data in the mbuf.
.It Fa mh_len
Indicates the amount of data in the mbuf.
.It Fa mh_type
Indicates the type of data contained in the mbuf (see below).
.It Fa mh_flags
Flags (see below).
.El
.Pp
The
.Fa mh_type
variable can take the following values:
.Pp
.Bl -tag -compact -offset indent -width XXXXXXXXXXXXXXXXXX
.It Dv MT_FREE
the mbuf should be on the free list.
.It Dv MT_DATA
the data in the mbuf was dynamically allocated.
.It Dv MT_HEADER
the data contains a packet header.
.It Dv MT_SONAME
the data is a socket name.
.It Dv MT_SOOPTS
the data are socket options.
.It Dv MT_FTABLE
the data is a fragment reassembly header.
.It Dv MT_CONTROL
the mbuf contains extra-data protocol message.
.It Dv MT_OOBDATA
the data consists of out-of-band data.
.El
.Pp
The
.Fa mh_flags
variable can take the following values:
.Pp
.Bl -tag -compact -offset indent -width XXXXXXXXXXXXXXXXXX
.It Dv M_EXT
mbuf has associated external storage.
.It Dv M_PKTHDR
the mbuf is the first that forms a packet.
.It Dv M_EOR
end of record.
.It Dv M_EXTWR
external storage is writable.
.It Dv M_PROTO1
protocol-specific.
.It Dv M_VLANTAG
.Fa m_pkthdr.ether_vtag
variable is valid.
.It Dv M_LOOP
packet has been sent from local machine.
.It Dv M_ACAST
received as IPv6 anycast.
.It Dv M_BCAST
packet sent/received as link-level broadcast.
.It Dv M_MCAST
packet sent/received as link-level multicast.
.It Dv M_CONF
packet was encrypted (ESP-transport).
.It Dv M_AUTH
packet was authenticated (AH or ESP).
.It Dv M_TUNNEL
header was IP-in-IP encapsulated by tunnel mode IPsec.
.It Dv M_ZEROIZE
Zero the data part of the mbufs in the mbuf chain pointed to by
.Nm m_free .
.It Dv M_COMP
header was decompressed.
.It Dv M_LINK0
link layer specific flag.
.El
.Pp
An external cluster is used when the data to hold in the mbuf is
large.
The size of an external cluster is between MCLBYTES and MAXMCLBYTES.
A cluster should be used when the size of the data reach MINCLSIZE
(the minimum size to be held by an external cluster).
.Pp
The combination of the M_EXT and M_PKTHDR flags give four types of
mbuf.
When none of these constants are in use, the mbuf is a "normal"
one, where the data part of the mbuf has the following elements:
.Bl -tag -width foobarmoocow
.It Fa m_dat
buffer holding the data (size MLEN).
.El
.Pp
When only M_PKTHDR is set, the data contained in the mbuf is a packet header.
The data itself is contained in the mbuf (just like the previous case),
but part of the mbuf is used to store a packet header.
The data part has then the following elements:
.Bl -tag -width foobarmoocow
.It Fa m_pkthdr
packet header, containing the length of the data, a pointer to the
interface on which the data was received, checksum information
and list of
.Xr mbuf_tags 9 .
.It Fa m_pktdat
buffer holding the data (size MHLEN).
.El
.Pp
The
.Fa m_pkthdr.csum_flags
variable can take the following values:
.Pp
.Bl -tag -compact -offset indent -width XXXXXXXXXXXXXXXXXX
.It Dv M_IPV4_CSUM_OUT
IPv4 checksum needed.
.It Dv M_TCP_CSUM_OUT
TCP checksum needed.
.It Dv M_UDP_CSUM_OUT
UDP checksum needed.
.It Dv M_ICMP_CSUM_OUT
ICMP/ICMPv6 checksum needed.
.It Dv M_IPV4_CSUM_IN_OK
IPv4 checksum verified.
.It Dv M_IPV4_CSUM_IN_BAD
IPv4 checksum bad.
.It Dv M_TCP_CSUM_IN_OK
TCP checksum verified.
.It Dv M_TCP_CSUM_IN_BAD
TCP checksum bad.
.It Dv M_UDP_CSUM_IN_OK
UDP checksum verified.
.It Dv M_UDP_CSUM_IN_BAD
UDP checksum bad.
.It Dv M_ICMP_CSUM_IN_OK
ICMP/ICMPv6 checksum verified.
.It Dv M_ICMP_CSUM_IN_BAD
ICMP/ICMPv6 checksum bad.
.It Dv M_IPV6_DF_OUT
Do not fragment IPv6 on output.
.El
.Pp
The
.Fa m_pkthdr.flowid
variable can contain a low resolution (15-bit) classification of a
flow or connection that the current mbuf is part of.
If the flowid is valid, it may be used as an alternative to hashing
the packets content to pick between different paths for the traffic.
The following masks can be ORed with the flowid:
.Pp
.Bl -tag -compact -offset indent -width XXXXXXXXXXXXXXXXXX
.It Dv M_FLOWID_VALID
The flow ID has been set.
.It Dv M_FLOWID_MASK
The flow ID.
.El
.Pp
When only M_EXT flag is set, an external storage buffer is being used to
hold the data, which is no longer stored in the mbuf.
The data part of the mbuf has now the following elements:
.Bl -tag -width foobarmoocow
.It Fa m_pkthdr
a packet header, just like the previous case, but it is empty.
No information is stored here.
.It Fa m_ext
a structure containing information about the external storage
buffer.
The information consists of the address of the external buffer,
a pointer to the function used to free the buffer, a pointer to the
arguments of the function, the size of the buffer, the type of the
buffer, and pointers to the previous and next mbufs using this
cluster.
.El
.Pp
When both the M_EXT and M_PKTHDR flags are set, an external storage buffer
is being used to store the data and this data contains a packet header.
The structure used is the same as the previous one except that the
.Fa m_pkthdr
element is not empty, it contains the same information as when
M_PKTHDR is used alone.
.Bl -tag -width Ds
.It Fn m_copym "struct mbuf *m" "int off" "int len" "int wait"
Copy an mbuf chain starting at
.Fa off
bytes from the beginning
and continuing for
.Fa len
bytes.
If
.Fa off
is zero and
.Fa m
has the M_PKTHDR flag set,
the header is copied.
If
.Fa len
is M_COPYALL
the whole mbuf is copied.
The
.Fa wait
parameter can be M_WAIT or
M_DONTWAIT.
It does not copy clusters, it just increases their reference count.
.It Fn m_free "struct mbuf *m"
Free the mbuf pointed to by
.Fa m .
A pointer to the successor of the mbuf,
if it exists, is returned by the function.
If
.Fa m
is a
.Dv NULL
pointer, no action occurs and
.Dv NULL
is returned.
.It Fn m_get "int how" "int type"
Return a pointer to an mbuf of the type specified.
If the
.Fa how
argument is
.Fa M_WAITOK ,
the function may call
.Xr tsleep 9
to await resources.
If
.Fa how
is
.Fa M_DONTWAIT
and resources are not available,
.Fn m_get
returns NULL.
.It Fn MGET "struct mbuf *m" "int how" "int type"
Return a pointer to an mbuf in
.Fa m
of the type specified.
See
.Fn m_get
for a description of
.Fa how .
.It Fn m_getclr "int how" "int type"
Return a pointer to an mbuf of the type specified, and clear the data
area of the mbuf.
See
.Fn m_get
for a description of
.Fa how .
.It Fn m_removehdr "struct mbuf *m"
Convert an mbuf with packet header to one without.
Delete all
.Xr pf 4
data and all tags attached to an
.Fa mbuf .
Keep the data and mbuf chain, clear the packet header.
.It Fn m_resethdr "struct mbuf *m"
Delete all
.Xr pf 4
data and all tags attached to an
.Fa mbuf .
Keep the data and mbuf chain, initialize the packet header.
.It Fn m_calchdrlen "struct mbuf *m"
Set the packet header length to the sum of all length values in the
mbuf chain.
.It Fn m_gethdr "int how" "int type"
Return a pointer to an mbuf of the type specified after initializing
it to contain a packet header.
See
.Fn m_get
for a description of
.Fa how .
.It Fn MGETHDR "struct mbuf *m" "int how" "int type"
Return a pointer to an mbuf of the type specified after initializing
it to contain a packet header.
See
.Fn m_get
for a description of
.Fa how .
.It Fn m_prepend "struct mbuf *m" "int len" "int how"
Prepend space of size
.Fa plen
to the mbuf pointed to by
.Fa m .
If necessary allocate a new mbuf and prepend it to the mbuf chain pointed to by
.Fa m .
If
.Fa m
points to an mbuf with a packet header, it is moved to the new
mbuf that has been prepended.
The return value is a pointer on the new mbuf chain.
If this function fails to allocate a new mbuf,
.Fa m
is freed.
See
.Fn m_get
for a description of
.Fa how .
.It Fn M_PREPEND "struct mbuf *m" "int plen" "int how"
Prepend space of size
.Fa plen
to the mbuf pointed to by
.Fa m .
If a new mbuf must be allocated,
.Fa how
specifies whether to wait or not.
If this function fails to allocate a new mbuf,
.Fa m
is freed.
.It Fn m_pulldown "struct mbuf *m" "int off" "int len" "int *offp"
Ensure that the data in the mbuf chain starting at
.Fa off
and ending at
.Fa off+len
will be put in a continuous memory region.
If memory must be allocated, then it will fail if the
.Fa len
argument is greater than MAXMCLBYTES.
The pointer returned points to an mbuf in the chain and the new offset
for data in this mbuf is
.Fa *offp .
If this function fails,
.Fa m
is freed.
.It Fn m_pullup "struct mbuf *n" "int len"
Ensure that the data in the mbuf chain starting at the beginning of
the chain and ending at
.Fa len
will be put in continuous memory region.
If memory must be allocated, then it will fail if the
.Fa len
argument is greater than MAXMCLBYTES.
If this function fails,
.Fa n
is freed.
.It Fn m_split "struct mbuf *m0" "int len0" "int wait"
Split an mbuf chain in two pieces, returning a pointer to
the tail (which is made of the previous mbuf chain except the first
.Fa len0
bytes).
.It Fn m_makespace "struct mbuf *m0" "int skip" "int hlen" "int *off"
Make space for a continuous memory region of length
.Fa hlen
at
.Fa skip
bytes into the mbuf chain.
On success, the mbuf of the continuous memory is returned
together with an offset
.Fa off
into the mbuf.
On failure, NULL is returned and the mbuf chain may have been modified.
The caller is assumed to always free the chain.
.It Fn m_getptr "struct mbuf *m" "int loc" "int *off"
Returns a pointer to the mbuf containing the data located at
.Fa loc
bytes of the beginning.
The offset in the new mbuf is pointed to by
.Fa off .
.It Fn m_adj "struct mbuf *mp" "int req_len"
Trims
.Fa req_len
bytes of data from the mbuf chain pointed to by
.Fa mp .
If
.Fa req_len
is positive, the data will be trimmed from the head of the mbuf chain
and if it is negative, it will be trimmed from the tail of the mbuf
chain.
.It Fn m_copyback "struct mbuf *m0" "int off" "int len" "caddr_t cp" "int wait"
Copy data from a buffer pointed to by
.Fa cp
back into the mbuf chain pointed to by
.Fa m0
starting at
.Fa off
bytes from the beginning, extending the mbuf chain if
necessary, sleeping for mbufs if
.Fa wait
is
.Fa M_WAIT .
If
.Fa M_NOWAIT
is set and no mbufs are available,
.Fn m_copyback
returns
.Er ENOBUFS .
The mbuf chain must be initialized properly, including setting
.Fa m_len .
.It Fn m_defrag "struct mbuf *m" "int wait"
Defragment the data mbufs referenced by
.Fa m
by replacing the chain with a copy of their contents made into a
single mbuf or cluster.
.Fa wait
specifies whether it can wait or not for the replacement storage.
.Fn m_defrag
returns 0 on success or
.Er ENOBUFS
on failure.
The mbuf pointer
.Fa m
remains in existence and unchanged on failure.
.It Fn m_freem "struct mbuf *m"
Free the mbuf chain pointed to by
.Fa m .
A pointer to the next mbuf in the list linked by m_nextpkt,
if it exists, is returned by the function.
If
.Fa m
is a
.Dv NULL
pointer, no action occurs and
.Dv NULL
is returned.
.It Fn m_freemp "struct mbuf **mp"
Set the input mbuf pointer to
.Dv NULL
and call
.Fn m_freem .
.It Fn m_purge "struct mbuf *m"
Free the list of mbufs linked by m_nextpkt that is pointed to by
.Fa m .
Each mbuf is freed by a call to
.Fn m_freem .
If
.Fa m
is a
.Dv NULL
pointer, no action occurs.
.It Fn m_reclaim "void"
Ask protocols to free unused memory space.
.It Fn m_copydata "struct mbuf *m" "int off" "int len" "caddr_t cp"
Copy data from the mbuf chain pointed to by
.Fa m
starting at
.Fa off
bytes from the beginning and continuing for
.Fa len
bytes into the buffer pointed to by
.Fa cp .
.It Fn m_cat "struct mbuf *m" "struct mbuf *n"
Concatenate the mbuf chain pointed to by
.Fa n
to the mbuf chain pointed to by
.Fa m .
The mbuf chains must be of the same type.
.It Fn m_devget "char *buf" "int totlen" "int off"
Copy
.Fa totlen
bytes of data from device local memory pointed to by
.Fa buf .
The data is copied into an mbuf chain at offset
.Fa off
and a pointer to the head of the chain is returned.
Returns NULL on failure.
.It Fn m_apply "struct mbuf *m" "int off" "int len" \
"int (*func)(caddr_t, caddr_t, unsigned int)" "caddr_t fstate"
Apply the function
.Fa func
to the data in the mbuf chain pointed to by
.Fa m
starting at
.Fa off
bytes from the beginning and continuing for
.Fa len
bytes.
.It Fn mtod "struct mbuf *m" "datatype"
Return a pointer to the data contained in the specified mbuf
.Fa m
cast to
.Fa datatype .
.It Fn MCLGET "struct mbuf *m" "int how"
Allocate and add an mbuf cluster to the mbuf pointed to by
.Fa m .
On success, the flag M_EXT is set in the mbuf.
See
.Fn m_get
for a description of
.Fa how .
.It Fn MCLGETI "struct mbuf *m" "int how" "struct ifnet *ifp" "int len"
If
.Fa m
is NULL, allocate it.
Then allocate and add an mbuf cluster of length
.Fa len
to the mbuf pointed to by
.Fa m .
Returns either the mbuf
.Fa m
that was passed in, or the newly allocated one which was allocated; in
either case the flag M_EXT is set in the mbuf.
See
.Fn m_get
for a description of
.Fa how .
.It Fn MEXTADD "struct mbuf *m" "caddr_t buf" "u_int size" "int flags" \
"void (*free)(caddr_t, u_int, void *)" "void *arg"
Add pre-allocated storage to the mbuf pointed to by
.Fa m .
On success, the flag M_EXT is set in the mbuf, and M_EXTWR is specified in
.Fa flags .
.It Fn m_align "struct mbuf *m" "int len"
Set the
.Fa m_data
pointer of the newly allocated mbuf
.Fa m
to an object of the specified size
.Fa len
at the end of this mbuf data area, longword aligned.
.It Fn M_READONLY "struct mbuf *m"
Check if the data of the mbuf pointed to by
.Fa m
is read-only.
This is true for non-cluster external storage and for clusters that
are being referenced by more than one mbuf.
.It Fn m_leadingspace "struct mbuf *m"
Compute the amount of space available before the current start of data
in the mbuf pointed to by
.Fa m .
If the data of the mbuf pointed to by
.Fa m
is read-only then 0 is returned.
.It Fn m_trailingspace "struct mbuf *m"
Compute the amount of space available after the end of data in the
mbuf pointed to by
.Fa m .
If the data of the mbuf pointed to by
.Fa m
is read-only then 0 is returned.
.It Fn m_dup_pkt "struct mbuf *m" "u_int adj" "int how"
Allocate a new mbuf and storage and copy the packet data and header,
including mbuf tags, from
.Fa m .
The data in the new mbuf will be offset from the start of the storage by
.Fa adj
bytes.
See
.Fn m_get
for a description of
.Fa how .
.It Fn m_dup_pkthdr "struct mbuf *to" "struct mbuf *from" "int how"
Copy mbuf packet header, including mbuf tags, from
.Fa from
to
.Fa to .
See
.Fn m_get
for a description of
.Fa how .
.El
.Sh CODE REFERENCES
The mbuf management functions are implemented in the files
.Pa sys/kern/uipc_mbuf.c
and
.Pa sys/kern/uipc_mbuf2.c .
The function prototypes and the macros are located in
.Pa sys/sys/mbuf.h .
.Sh SEE ALSO
.Xr netstat 1 ,
.Xr mbuf_tags 9 ,
.Xr mutex 9 ,
.Xr spl 9
.Rs
.%A Jun-Ichiro Hagino
.%T "Mbuf issues in 4.4BSD IPv6/IPsec support (experiences from KAME IPv6/IPsec implementation)"
.%B "Proceedings of the Freenix Track: 2000 USENIX Annual Technical Conference"
.%D June 2000
.Re
|