2000-10-26 23:15:47 +00:00
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.\" Copyright (c) 2000 FreeBSD Inc.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL [your name] OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd October 17, 2000
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.Dt MBUF 9
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.Os
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.\"
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.Sh NAME
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.Nm mbuf
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.Nd "memory management in the kernel IPC subsystem"
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.\"
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.Sh SYNOPSIS
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2001-02-15 11:47:31 +00:00
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.Fd #include <sys/param.h>
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2000-10-26 23:15:47 +00:00
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.Fd #include <sys/mbuf.h>
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.\"
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2000-11-01 23:02:19 +00:00
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.Ss Mbuf allocation macros
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2000-10-26 23:15:47 +00:00
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.Fn MGET "struct mbuf *mbuf" "int how" "short type"
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.Fn MGETHDR "struct mbuf *mbuf" "int how" "short type"
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.Fn MCLGET "struct mbuf *mbuf" "int how"
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2000-11-01 23:02:19 +00:00
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.Fo MEXTADD
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.Fa "struct mbuf *mbuf"
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.Fa "caddr_t buf"
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.Fa "u_int size"
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.Fa "void (*free)(void *opt_args)"
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.Fa "void *opt_args"
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2000-11-21 22:29:31 +00:00
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.Fa "short flags"
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.Fa "int type"
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2000-11-01 23:02:19 +00:00
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.Fc
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.Fn MEXTFREE "struct mbuf *mbuf"
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.Fn MEXT_ADD_REF "struct mbuf *mbuf"
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.Fn MEXT_REM_REF "struct mbuf *mbuf"
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.Fn MFREE "struct mbuf *mbuf" "struct mbuf *successor"
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.\"
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.Ss Mbuf utility macros
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.Fn mtod "struct mbuf *mbuf" "any type"
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.Fn MEXT_IS_REF "struct mbuf *mbuf"
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.Fn M_COPY_PKTHDR "struct mbuf *to" "struct mbuf *from"
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.Fn M_ALIGN "struct mbuf *mbuf" "u_int len"
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.Fn MH_ALIGN "struct mbuf *mbuf" "u_int len"
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.Fn M_LEADINGSPACE "struct mbuf *mbuf"
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.Fn M_TRAILINGSPACE "struct mbuf *mbuf"
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.Fn M_PREPEND "struct mbuf *mbuf" "int len" "int how"
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.Fn MCHTYPE "struct mbuf *mbuf" "u_int type"
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.Fn M_WRITABLE "struct mbuf *mbuf"
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.\"
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2000-11-01 23:02:19 +00:00
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.Ss Mbuf allocation functions
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2000-10-26 23:15:47 +00:00
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.Ft struct mbuf *
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.Fn m_get "int how" "int type"
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.Ft struct mbuf *
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2001-02-16 03:23:04 +00:00
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.Fn m_getm "struct mbuf *orig" "int len" "int how" "int type"
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.Ft struct mbuf *
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.Fn m_getclr "int how" "int type"
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.Ft struct mbuf *
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.Fn m_gethdr "int how" "int type"
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2000-11-01 23:02:19 +00:00
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.Ft struct mbuf *
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.Fn m_free "struct mbuf *mbuf"
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2000-10-26 23:15:47 +00:00
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.Ft void
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.Fn m_freem "struct mbuf *mbuf"
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2000-11-01 23:02:19 +00:00
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.\"
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.Ss Mbuf utility functions
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2000-10-26 23:15:47 +00:00
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.Ft void
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.Fn m_adj "struct mbuf *mbuf" "int len"
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.Ft struct mbuf *
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.Fn m_prepend "struct mbuf *mbuf" "int len" "int how"
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.Ft struct mbuf *
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.Fn m_pullup "struct mbuf *mbuf" "int len"
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.Ft struct mbuf *
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.Fn m_copym "struct mbuf *mbuf" "int offset" "int len" "int how"
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.Ft struct mbuf *
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.Fn m_copypacket "struct mbuf *mbuf" "int how"
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.Ft struct mbuf *
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.Fn m_dup "struct mbuf *mbuf" "int how"
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.Ft void
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.Fn m_copydata "struct mbuf *mbuf" "int offset" "int len" "caddr_t buf"
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.Ft void
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.Fn m_copyback "struct mbuf *mbuf" "int offset" "int len" "caddr_t buf"
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.Ft struct mbuf *
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.Fo m_devget
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.Fa "char *buf"
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.Fa "int len"
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.Fa "int offset"
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.Fa "struct ifnet *ifp"
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.Fa "void (*copy)(char *from, caddr_t to, u_int len)"
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.Fc
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.Ft void
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.Fn m_cat "struct mbuf *m" "struct mbuf *n"
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.Ft struct mbuf *
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.Fn m_split "struct mbuf *mbuf" "int len" "int how"
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.\"
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.Sh DESCRIPTION
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2000-11-01 23:02:19 +00:00
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An mbuf is a basic unit of memory management in the kernel IPC subsystem.
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2000-11-10 10:08:34 +00:00
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Network packets and socket buffers are stored in mbufs.
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A network packet may span multiple mbufs arranged into a chain
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.Pq linked list ,
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which allows adding or trimming
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network headers with little overhead.
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2000-10-26 23:15:47 +00:00
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.Pp
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2000-11-01 23:02:19 +00:00
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While a developer should not bother with mbuf internals without serious
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reason in order to avoid incompatibilities with future changes, it
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2000-11-01 23:02:19 +00:00
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is useful to understand the mbuf's general structure.
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.Pp
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An mbuf consists of a variable-sized header and a small internal
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buffer for data.
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The mbuf's total size,
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.Dv MSIZE ,
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2000-10-26 23:15:47 +00:00
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is a machine-dependent constant defined in
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.Pa machine/param.h .
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The mbuf header includes:
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.Pp
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.Bl -tag -width "m_nextpkt" -compact -offset indent
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.It Fa m_next
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a pointer to the next buffer in the chain
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.It Fa m_nextpkt
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a pointer to the next chain in the queue
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.It Fa m_data
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a pointer to the data
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.It Fa m_len
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the length of the data
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.It Fa m_type
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the type of data
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2000-10-26 23:15:47 +00:00
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.It Fa m_flags
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the mbuf flags
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.El
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.Pp
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The mbuf flag bits are defined as follows:
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.Bd -literal
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/* mbuf flags */
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#define M_EXT 0x0001 /* has associated external storage */
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#define M_PKTHDR 0x0002 /* start of record */
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#define M_EOR 0x0004 /* end of record */
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#define M_RDONLY 0x0008 /* associated data marked read-only */
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#define M_PROTO1 0x0010 /* protocol-specific */
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#define M_PROTO2 0x0020 /* protocol-specific */
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#define M_PROTO3 0x0040 /* protocol-specific */
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#define M_PROTO4 0x0080 /* protocol-specific */
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#define M_PROTO5 0x0100 /* protocol-specific */
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/* mbuf pkthdr flags, also in m_flags */
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#define M_BCAST 0x0200 /* send/received as link-level broadcast */
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#define M_MCAST 0x0400 /* send/received as link-level multicast */
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#define M_FRAG 0x0800 /* packet is fragment of larger packet */
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#define M_FIRSTFRAG 0x1000 /* packet is first fragment */
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#define M_LASTFRAG 0x2000 /* packet is last fragment */
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2000-10-26 23:15:47 +00:00
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.Ed
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.Pp
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The available mbuf types are defined as follows:
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.Bd -literal
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/* mbuf types */
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#define MT_FREE 0 /* should be on free list */
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#define MT_DATA 1 /* dynamic (data) allocation */
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#define MT_HEADER 2 /* packet header */
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#define MT_SONAME 8 /* socket name */
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#define MT_FTABLE 11 /* fragment reassembly header */
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#define MT_CONTROL 14 /* extra-data protocol message */
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#define MT_OOBDATA 15 /* expedited data */
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.Ed
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.Pp
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If the
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.Dv M_PKTHDR
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flag is set, a
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.Li struct pkthdr m_pkthdr
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is added to the mbuf header.
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It contains a pointer to the interface
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the packet has been received from
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.Pq Fa struct ifnet *rcvif ,
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and the total packet length
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.Pq Fa int len .
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.Pp
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2000-11-10 10:08:34 +00:00
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If small enough, data is stored in the mbuf's internal data buffer.
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If the data is sufficiently large, another mbuf may be added to the chain,
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or external storage may be associated with the mbuf.
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.Dv MHLEN
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bytes of data can fit into an mbuf with the
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.Dv M_PKTHDR
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flag set,
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.Dv MLEN
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bytes can otherwise.
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.Pp
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If external storage is being associated with an mbuf, the
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.Dv m_ext
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header is added at the cost of losing the internal data buffer.
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It includes a pointer to external storage, the size of the storage,
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a pointer to a function used for freeing the storage,
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a pointer to an optional argument that can be passed to the function,
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and a pointer to a reference counter.
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An mbuf using external storage has the
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2000-10-26 23:15:47 +00:00
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.Dv M_EXT
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flag set.
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.Pp
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2000-11-01 23:02:19 +00:00
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The system supplies a macro for allocating the desired external storage
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buffer,
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.Dv MEXTADD .
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.Pp
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The allocation and management of the reference counter is handled by the
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subsystem.
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The developer can check whether the reference count for the
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given mbuf's external storage is greater than 1 with the
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.Dv MEXT_IS_REF
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macro.
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Similarly, the developer can directly add and remove references,
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if absolutely necessary, with the use of the
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.Dv MEXT_ADD_REF
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and
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.Dv MEXT_REM_REF
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macros.
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.Pp
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The system also supplies a default type of external storage buffer called an
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.Dq mbuf cluster .
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Mbuf clusters can be allocated and configured with the use of the
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.Dv MCLGET
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macro.
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Each cluster is
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.Dv MCLBYTES
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in size, where MCLBYTES is a machine-dependent constant.
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The system defines an advisory macro
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.Dv MINCLSIZE ,
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which is the smallest amount of data to put into a cluster.
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It's equal to the sum of
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.Dv MLEN
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and
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.Dv MHLEN .
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It is typically preferable to store data into an mbuf's data region, if size
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permits, as opposed to allocating a separate mbuf cluster to hold the same
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data.
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2000-10-26 23:15:47 +00:00
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.\"
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.Ss Macros and Functions
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2000-11-01 23:02:19 +00:00
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There are numerous predefined macros and functions that provide the
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developer with common utilities.
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.\"
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.Bl -ohang -offset indent
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.It Fn mtod mbuf type
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Convert an mbuf pointer to a data pointer.
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The macro expands to the data pointer cast to the pointer of the specified type.
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.Sy Note :
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It is advisable to ensure that there is enough contiguous data in the mbuf.
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2000-10-26 23:15:47 +00:00
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See
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.Fn m_pullup
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for details.
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.It Fn MGET mbuf how type
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Allocate an mbuf and initialize it to contain internal data.
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.Fa mbuf
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will point to the allocated mbuf on success, or be set to
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.Dv NULL
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on failure.
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The
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.Fa how
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argument is to be set to
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2000-12-24 03:08:17 +00:00
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.Dv M_TRYWAIT
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or
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.Dv M_DONTWAIT .
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It specifies whether the caller is willing to block if necessary.
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If
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.Fa how
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is set to
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.Dv M_TRYWAIT ,
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a failed allocation will result in the caller being put
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to sleep for a designated
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kern.ipc.mbuf_wait
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.Po
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.Xr sysctl 8
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tunable
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.Pc
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number of ticks.
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A number of other mbuf-related
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functions and macros have the same argument because they may
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at some point need to allocate new mbufs.
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.It Fn MGETHDR mbuf how type
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Allocate an mbuf and initialize it to contain a packet header
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and internal data.
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|
|
See
|
2000-10-26 23:15:47 +00:00
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.Fn MGET
|
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|
|
for details.
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|
.It Fn MCLGET mbuf how
|
2000-11-10 10:08:34 +00:00
|
|
|
Allocate and attach an mbuf cluster to an mbuf.
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|
If the macro fails, the
|
2000-10-26 23:15:47 +00:00
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|
.Dv M_EXT
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flag won't be set in the mbuf.
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.It Fn M_PREPEND mbuf len how
|
2000-11-01 23:02:19 +00:00
|
|
|
This macro operates on an mbuf chain.
|
2000-10-26 23:15:47 +00:00
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|
|
It is an optimized wrapper for
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|
|
|
.Fn m_prepend
|
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|
that can make use of possible empty space before data
|
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|
|
.Pq "e.g. left after trimming of a link-layer header" .
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|
The new chain pointer or
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|
.Dv NULL
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|
is in
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.Fa mbuf
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after the call.
|
2000-11-21 22:29:31 +00:00
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|
.It Fn M_WRITABLE mbuf
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|
This macro will evaluate true if the mbuf is not marked
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.Dv M_RDONLY
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and if either the mbuf does not contain external storage or,
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|
if it does,
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|
|
then if the reference count of the storage is not greater than 1.
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|
The
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|
|
.Dv M_RDONLY
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flag can be set in the mbuf's
|
2001-02-01 16:38:02 +00:00
|
|
|
.Dv m_flags .
|
2000-11-21 22:29:31 +00:00
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|
|
This can be achieved during setup of the external storage,
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|
by passing the
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|
.Dv M_RDONLY
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|
bit as a
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.Ar flags
|
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argument to the
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|
|
.Fn MEXTADD
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macro, or can be directly set in individual mbufs.
|
2000-10-26 23:15:47 +00:00
|
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|
.El
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|
|
.Pp
|
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|
|
The functions are:
|
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|
|
.Bl -ohang -offset indent
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.It Fn m_get how type
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|
A function version of
|
2000-11-01 23:02:19 +00:00
|
|
|
.Fn MGET
|
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|
|
for non-critical paths.
|
2001-02-16 03:23:04 +00:00
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|
.It Fn m_getm orig len how type
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|
|
Allocate
|
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|
.Ar len
|
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|
|
bytes worth of mbufs and mbuf clusters if necessary and append the resulting
|
|
|
|
allocated chain to the
|
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|
.Ar orig
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|
|
mbuf chain, if it is non-NULL.
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If the allocation fails at any point,
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|
|
free whatever was allocated and return NULL.
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|
If
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|
.Ar orig
|
|
|
|
is non-NULL,
|
|
|
|
it will not be freed.
|
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|
|
It is possible to use
|
|
|
|
.Fn m_getm
|
|
|
|
to either append
|
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|
|
.Ar len
|
|
|
|
bytes to an existing mbuf or mbuf chain
|
|
|
|
(for example, one which may be sitting in a pre-allocated ring)
|
|
|
|
or to simply perform an all-or-nothing mbuf and mbuf cluster allocation.
|
2000-10-26 23:15:47 +00:00
|
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|
.It Fn m_gethdr how type
|
|
|
|
A function version of
|
2000-11-01 23:02:19 +00:00
|
|
|
.Fn MGETHDR
|
|
|
|
for non-critical paths.
|
2000-10-26 23:15:47 +00:00
|
|
|
.It Fn m_getclr how type
|
2000-11-01 23:02:19 +00:00
|
|
|
Allocate an mbuf and zero out the data region.
|
2000-10-26 23:15:47 +00:00
|
|
|
.El
|
|
|
|
.Pp
|
|
|
|
The functions below operate on mbuf chains.
|
|
|
|
.Bl -ohang -offset indent
|
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|
|
.It Fn m_freem mbuf
|
|
|
|
Free an entire mbuf chain, including any external
|
|
|
|
storage.
|
|
|
|
.\"
|
|
|
|
.It Fn m_adj mbuf len
|
|
|
|
Trim
|
|
|
|
.Fa len
|
2000-11-10 10:22:49 +00:00
|
|
|
bytes from the head of an mbuf chain if
|
2000-10-26 23:15:47 +00:00
|
|
|
.Fa len
|
|
|
|
is positive, from the tail otherwise.
|
|
|
|
.\"
|
|
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|
.It Fn m_prepend mbuf len how
|
|
|
|
Allocate a new mbuf and prepend it to the chain, handle
|
|
|
|
.Dv M_PKTHDR
|
|
|
|
properly.
|
|
|
|
.Sy Note :
|
|
|
|
It doesn't allocate any clusters, so
|
|
|
|
.Fa len
|
|
|
|
must be less than
|
|
|
|
.Dv MLEN
|
|
|
|
or
|
|
|
|
.Dv MHLEN ,
|
|
|
|
depending on the
|
2001-02-01 16:38:02 +00:00
|
|
|
.Dv M_PKTHDR
|
|
|
|
flag setting.
|
2000-10-26 23:15:47 +00:00
|
|
|
.\"
|
|
|
|
.It Fn m_pullup mbuf len
|
|
|
|
Arrange that the first
|
|
|
|
.Fa len
|
2000-11-10 10:22:49 +00:00
|
|
|
bytes of an mbuf chain are contiguous and lay in the data area of
|
2000-10-26 23:15:47 +00:00
|
|
|
.Fa mbuf ,
|
|
|
|
so they are accessible with
|
|
|
|
.Fn mtod mbuf type .
|
|
|
|
Return the new chain on success,
|
|
|
|
.Dv NULL
|
|
|
|
on failure
|
|
|
|
.Pq the chain is freed in this case .
|
|
|
|
.Sy Note :
|
|
|
|
It doesn't allocate any clusters, so
|
|
|
|
.Fa len
|
|
|
|
must be less than
|
|
|
|
.Dv MHLEN .
|
|
|
|
.\"
|
|
|
|
.It Fn m_copym mbuf offset len how
|
|
|
|
Make a copy of an mbuf chain starting
|
|
|
|
.Fa offset
|
|
|
|
bytes from the beginning, continuing for
|
|
|
|
.Fa len
|
2000-11-10 10:08:34 +00:00
|
|
|
bytes.
|
|
|
|
If
|
2000-10-26 23:15:47 +00:00
|
|
|
.Fa len
|
|
|
|
is
|
|
|
|
.Dv M_COPYALL ,
|
|
|
|
copy to the end of the mbuf chain.
|
|
|
|
.Sy Note :
|
|
|
|
The copy is read-only, because clusters are not
|
|
|
|
copied, only their reference counts are incremented.
|
|
|
|
.\"
|
|
|
|
.It Fn m_copypacket mbuf how
|
|
|
|
Copy an entire packet including header, which must be present.
|
|
|
|
This is an optimized version of the common case
|
|
|
|
.Fn m_copym mbuf 0 M_COPYALL how .
|
|
|
|
.Sy Note :
|
|
|
|
the copy is read-only, because clusters are not
|
|
|
|
copied, only their reference counts are incremented.
|
|
|
|
.\"
|
|
|
|
.It Fn m_dup mbuf how
|
|
|
|
Copy a packet header mbuf chain into a completely new chain, including
|
2000-11-10 10:08:34 +00:00
|
|
|
copying any mbuf clusters.
|
|
|
|
Use this instead of
|
2000-10-26 23:15:47 +00:00
|
|
|
.Fn m_copypacket
|
|
|
|
when you need a writable copy of an mbuf chain.
|
|
|
|
.\"
|
|
|
|
.It Fn m_copydata mbuf offset len buf
|
2000-11-10 10:22:49 +00:00
|
|
|
Copy data from an mbuf chain starting
|
2000-10-26 23:15:47 +00:00
|
|
|
.Fa off
|
|
|
|
bytes from the beginning, continuing for
|
|
|
|
.Fa len
|
|
|
|
bytes, into the indicated buffer
|
|
|
|
.Fa buf .
|
|
|
|
.\"
|
|
|
|
.It Fn m_copyback mbuf offset len buf
|
|
|
|
Copy
|
|
|
|
.Fa len
|
|
|
|
bytes from the buffer
|
|
|
|
.Fa buf
|
|
|
|
back into the indicated mbuf chain,
|
|
|
|
starting at
|
|
|
|
.Fa offset
|
|
|
|
bytes from the beginning of the chain, extending the mbuf chain if necessary.
|
|
|
|
.Sy Note :
|
2000-11-10 10:08:34 +00:00
|
|
|
It doesn't allocate any clusters, just adds mbufs to the chain.
|
|
|
|
It's safe to set
|
2000-10-26 23:15:47 +00:00
|
|
|
.Fa offset
|
|
|
|
beyond the current chain end: zeroed mbufs will be allocated to fill the
|
|
|
|
space.
|
|
|
|
.\"
|
|
|
|
.It Fn m_devget buf len offset ifp copy
|
|
|
|
Copy data from a device local memory pointed to by
|
|
|
|
.Fa buf
|
2000-11-10 10:22:49 +00:00
|
|
|
to an mbuf chain.
|
2000-11-10 10:08:34 +00:00
|
|
|
The copy is done using a specified copy routine
|
2000-10-26 23:15:47 +00:00
|
|
|
.Fa copy ,
|
|
|
|
or
|
|
|
|
.Fn bcopy
|
|
|
|
if
|
|
|
|
.Fa copy
|
|
|
|
is
|
|
|
|
.Dv NULL .
|
|
|
|
.\"
|
|
|
|
.It Fn m_cat m n
|
|
|
|
Concatenate
|
|
|
|
.Fa n
|
|
|
|
to
|
|
|
|
.Fa m .
|
|
|
|
Both chains must be of the same type.
|
|
|
|
.Fa N
|
|
|
|
is still valid after the function returned.
|
|
|
|
.Sy Note :
|
|
|
|
It does not handle
|
|
|
|
.Dv M_PKTHDR
|
|
|
|
and friends.
|
|
|
|
.\"
|
|
|
|
.It Fn m_split mbuf len how
|
|
|
|
Partition an mbuf chain in two pieces, returning the tail:
|
|
|
|
all but the first
|
|
|
|
.Fa len
|
2000-11-10 10:08:34 +00:00
|
|
|
bytes.
|
|
|
|
In case of failure, it returns
|
2000-10-26 23:15:47 +00:00
|
|
|
.Dv NULL
|
|
|
|
and attempts to restore the chain to its original state.
|
2000-12-29 09:18:45 +00:00
|
|
|
.El
|
2000-10-26 23:15:47 +00:00
|
|
|
.Sh RETURN VALUES
|
|
|
|
See above.
|
|
|
|
.Sh HISTORY
|
|
|
|
.\" Please correct me if I'm wrong
|
2000-11-10 10:08:34 +00:00
|
|
|
Mbufs appeared in an early version of BSD.
|
|
|
|
Besides for being used for network packets, they were used
|
2000-11-01 23:02:19 +00:00
|
|
|
to store various dynamic structures, such as routing table
|
|
|
|
entries, interface addresses, protocol control blocks, etc.
|
2000-10-26 23:15:47 +00:00
|
|
|
.Sh AUTHORS
|
2000-11-01 23:02:19 +00:00
|
|
|
The original mbuf(9) man page was written by Yar Tikhiy.
|