651 lines
16 KiB
Groff
651 lines
16 KiB
Groff
.\" $NetBSD: mbuf.9,v 1.20 2001/12/26 01:07:45 wiz Exp $
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.\"
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.\" Copyright (c) 1997 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This documentation is derived from text contributed to The NetBSD Foundation
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.\" by S.P.Zeidler (aka stargazer).
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd October 3, 1997
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.Dt MBUF 9
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.Os
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.Sh NAME
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.Nm mbuf ,
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.Nm m_get ,
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.Nm m_getclr ,
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.Nm m_gethdr ,
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.Nm m_devget ,
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.Nm m_copym ,
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.Nm m_copypacket ,
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.Nm m_copydata ,
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.Nm m_copyback ,
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.Nm m_cat ,
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.Nm m_dup ,
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.Nm m_prepend ,
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.Nm m_pulldown ,
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.Nm m_pullup ,
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.Nm m_split ,
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.Nm m_adj ,
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.Nm m_free ,
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.Nm m_freem ,
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.Nm mtod ,
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.Nm mtocl ,
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.Nm cltom ,
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.Nm MGET ,
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.Nm MGETHDR ,
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.Nm MEXTMALLOC ,
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.Nm MEXTADD ,
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.Nm MCLGET ,
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.Nm M_COPY_PKTHDR ,
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.Nm M_ALIGN ,
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.Nm MH_ALIGN ,
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.Nm M_LEADINGSPACE ,
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.Nm M_TRAILINGSPACE ,
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.Nm M_PREPEND ,
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.Nm MCHTYPE ,
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.Nm MEXTREMOVE ,
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.Nm MFREE ,
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.Nd "functions and macros for managing memory used by networking code"
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.Sh SYNOPSIS
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.Fd #include <sys/mbuf.h>
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.Ft struct mbuf *
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.Fn m_get "int nowait" "int type"
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.Ft struct mbuf *
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.Fn m_getclr "int nowait" "int type"
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.Ft struct mbuf *
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.Fn m_gethdr "int nowait" "int type"
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.Ft struct mbuf *
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.Fn m_devget "char *buf" "int totlen" "int off0" "struct ifnet *ifp" "void (*copy)(const void *, void *, size_t)"
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.Ft struct mbuf *
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.Fn m_copym "struct mbuf *m" "int off0" "int len" "int wait"
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.Ft struct mbuf *
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.Fn m_copypacket "struct mbuf *m" "int how"
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.Ft void
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.Fn m_copydata "struct mbuf *m" "int off" "int len" "caddr_t cp"
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.Ft void
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.Fn m_copyback "struct mbuf *m0" "int off" "int len" "caddr_t cp"
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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_dup "struct mbuf *m" "int off0" "int len" "int wait"
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.Ft struct mbuf *
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.Fn m_prepend "struct mbuf *m" "int len" "int how"
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.Ft struct mbuf *
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.Fn m_pulldown "struct mbuf *n" "int off" "int len" "int *offp"
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.Ft struct mbuf *
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.Fn m_pullup "struct mbuf *n" "int len"
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.Ft struct mbuf *
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.Fn m_split "struct mbuf *m0" "int len0" "int wait"
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.Ft void
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.Fn m_adj "struct mbuf *mp" "int req_len"
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.Ft struct mbuf *
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.Fn m_free "struct mbuf *m"
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.Ft void
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.Fn m_freem "struct mbuf *m"
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.Ft datatype
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.Fn mtod "struct mbuf *m" "datatype"
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.Ft u_long
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.Fn mtocl "void *datapointer"
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.Ft caddr_t
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.Fn cltom "u_long clusternum"
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.Ft void
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.Fn MGET "struct mbuf *m" "int how" "int type"
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.Ft void
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.Fn MGETHDR "struct mbuf *m" "int how" "int type"
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.Ft void
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.Fn MEXTMALLOC "struct mbuf *m" "int len" "int how"
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.Ft void
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.Fn MEXTADD "struct mbuf *m" "caddr_t buf" "int size" "int type" "void (*free)(caddr_t, u_int, void *)" "void *arg"
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.Ft void
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.Fn MCLGET "struct mbuf *m" "int how"
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.Ft void
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.Fn M_COPY_PKTHDR "struct mbuf *to" "struct mbuf *from"
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.Ft void
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.Fn M_ALIGN "struct mbuf *m" "int len"
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.Ft void
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.Fn MH_ALIGN "struct mbuf *m" "int len"
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.Ft int
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.Fn M_LEADINGSPACE "struct mbuf *m"
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.Ft int
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.Fn M_TRAILINGSPACE "struct mbuf *m"
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.Ft void
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.Fn M_PREPEND "struct mbuf *m" "int plen" "int how"
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.Ft void
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.Fn MCHTYPE "struct mbuf *m" "int type"
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.Ft void
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.Fn MEXTREMOVE "struct mbuf *m"
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.Ft void
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.Fn MFREE "struct mbuf *m" "struct mbuf *n"
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.Sh DESCRIPTION
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The
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.Nm
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functions and macros provide an easy and consistent way to handle
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a networking stack's memory management needs.
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An
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.Nm
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consists of a header and a data area.
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It is of a fixed size,
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.Dv MSIZE
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.Pq defined in Aq Pa machine/param.h ,
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which includes overhead.
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The header contains a pointer to the next
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.Nm
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in the
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.Sq "mbuf chain" ,
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a pointer to the next
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.Sq "mbuf chain" ,
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a pointer to the data area, the amount of data in this mbuf, its type
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and a
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.Dv flags
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field.
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.Pp
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The
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.Dv type
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variable can signify:
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.Bl -tag -compact -offset indent -width "XXXXXXXXXXX"
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.It Dv MT_FREE
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the mbuf should be on the ``free'' list
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.It Dv MT_DATA
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data was dynamically allocated
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.It Dv MT_HEADER
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data is a packet header
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.It Dv MT_SONAME
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data is a socket name
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.It Dv MT_SOOPTS
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data is socket options
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.It Dv MT_FTABLE
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data is the fragment reassembly header
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.It Dv MT_CONTROL
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mbuf contains ancillary \&(protocol control\&) data
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.It Dv MT_OOBDATA
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mbuf contains out-of-band data.
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.El
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.Pp
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The
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.Dv flags
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variable contains information describing the
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.Nm "" ,
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notably:
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.Bl -tag -compact -offset indent -width "XXXXXXXXXXX"
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.It Dv M_EXT
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has external storage
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.It Dv M_PKTHDR
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is start of record
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.It Dv M_EOR
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is end of record
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.It Dv M_CLUSTER
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external storage is a cluster.
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.El
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.Pp
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If an
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.Nm
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designates the start of a record
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.Pq Dv M_PKTHDR ,
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its
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.Dv flags
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field may contain additional information describing the content of
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the record:
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.Bl -tag -compact -offset indent -width "XXXXXXXXXXX"
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.It Dv M_BCAST
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sent/received as link-level broadcast
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.It Dv M_MCAST
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sent/received as link-level multicast
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.It Dv M_LINK0 ,
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.It Dv M_LINK1 ,
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.It Dv M_LINK2
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three link-level specific flags.
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.El
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.Pp
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An
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.Nm
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may add a single
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.Sq "mbuf cluster"
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of
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.Dv MCLBYTES
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bytes
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.Pq also defined in Aq Pa machine/param.h ,
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which has no additional overhead
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and is used instead of the internal data area; this is done when at least
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.Dv MINCLSIZE
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bytes of data must be stored.
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.Pp
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When the
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.Dv M_EXT
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flag is raised for an mbuf,
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the external storage area could be shared among multiple mbufs.
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Be careful when you attempt to overwrite the data content of the mbuf.
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.Bl -tag -width compact
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.It Fn m_get "int nowait" "int type"
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Allocates an mbuf and initializes it to contain internal data.
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The
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.Fa nowait
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parameter is a choice of
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.Dv M_WAIT / M_DONTWAIT
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from caller.
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.Dv M_WAIT
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means the call cannot fail, but may take forever.
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The
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.Fa type
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parameter is an mbuf type.
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.It Fn m_getclr "int nowait" "int type"
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Allocates an mbuf and initializes it to contain internal data, then
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zeros the data area.
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The
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.Fa nowait
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parameter is a choice of
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.Dv M_WAIT / M_DONTWAIT
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from caller.
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The
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.Fa type
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parameter is an mbuf type.
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.It Fn m_gethdr "int nowait" "int type"
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Allocates an mbuf and initializes it to contain a packet header and internal
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data.
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The
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.Fa nowait
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parameter is a choice of
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.Dv M_WAIT / M_DONTWAIT
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from caller.
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The
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.Fa type
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parameter is an mbuf type.
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.It Fn m_devget "char *buf" "int totlen" "int off0" "struct ifnet *ifp" "void (*copy)(const void *, void *, size_t)"
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Copies
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.Fa len
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bytes from device local memory into mbufs using copy routine
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.Fa copy .
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If parameter
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.Fa off
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is non-zero, the packet is supposed to be trailer-encapsulated and
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.Fa off
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bytes plus the type and length fields will be skipped before copying.
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Returns the top of the mbuf chain it created.
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.It Fn m_copym "struct mbuf *m" "int off0" "int len" "int wait"
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Creates a copy of an mbuf chain starting
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.Fa off0
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bytes from the beginning, continuing for
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.Fa len
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bytes. If the
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.Fa len
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requested is
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.Dv M_COPYALL ,
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the complete mbuf chain will be copied.
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The
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.Fa wait
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parameter is a choice of
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.Dv M_WAIT / M_DONTWAIT
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from caller.
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.It Fn m_copypacket "struct mbuf *m" "int how"
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Copies an entire packet, including header (which must be present).
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This function is an optimization of the common case
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.Li m_copym(m, 0, Dv M_COPYALL, Fa how ) .
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.It Fn m_copydata "struct mbuf *m" "int off" "int len" "caddr_t cp"
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Copies
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.Fa len
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bytes data from mbuf chain
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.Fa m
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into the buffer
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.Fa cp ,
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starting
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.Fa off
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bytes from the beginning.
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.It Fn m_copyback "struct mbuf *m0" "int off" "int len" "caddr_t cp"
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Copies
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.Fa len
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bytes data from buffer
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.Fa cp
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back into the mbuf chain
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.Fa m0 ,
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starting
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.Fa off
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bytes from the beginning, extending the mbuf chain if necessary.
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.It Fn m_cat "struct mbuf *m" "struct mbuf *n"
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Concatenates mbuf chain
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.Fa n
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to
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.Fa m .
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Both chains must be of the same type; packet headers will
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.Em not
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be updated if present.
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.It Fn m_dup "struct mbuf *m" "int off0" "int len" "int wait"
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Similarly to
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.Fn m_copym ,
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the function creates a copy of an mbuf chain starting
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.Fa off0
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bytes from the beginning, continuing for
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.Fa len
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bytes.
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While
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.Fn m_copym
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tries to share external storage for mbufs with
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.Dv M_EXT
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flag,
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.Fn m_dup
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will deep-copy the whole data content into new mbuf chain
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and avoids shared external storage.
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.It Fn m_prepend "struct mbuf *m" "int len" "int how"
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Lesser-used path for
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.Fn M_PREPEND :
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allocates new mbuf
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.Fa m
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of size
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.Fa len
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to prepend to the chain, copying junk along.
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The
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.Fa how
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parameter is a choice of
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.Dv M_WAIT / M_DONTWAIT
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from caller.
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.It Fn m_pulldown "struct mbuf *n" "int off" "int len" "int *offp"
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Rearranges an mbuf chain so that
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.Fa len
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bytes from offset
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.Fa off
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are contiguous and in the data area of an mbuf.
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The return value points to an mbuf in the middle of the mbuf chain
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.Fa m .
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If we call the return value
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.Fa n ,
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the contiguous data region is available at
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.Li "mtod(n, caddr_t) + *offp" ,
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or
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.Li "mtod(n, caddr_t)"
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if
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.Fa offp
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is
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.Dv NULL .
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The top of the mbuf chain
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.Fa m ,
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and mbufs up to
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.Fa off ,
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will not be modified.
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On successful return, it is guaranteed that the mbuf pointed to by
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.Fa n
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does not have a shared external storage,
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therefore it is safe to update the contiguous region.
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Returns
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.Dv NULL
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and frees the mbuf chain on failure.
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.Fa len
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must be smaller or equal than
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.Dv MCLBYTES .
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.It Fn m_pullup "struct mbuf *m" "int len"
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Rearranges an mbuf chain so that
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.Fa len
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bytes are contiguous
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and in the data area of an mbuf (so that
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.Fn mtod
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will work for a structure of size
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.Fa len ) .
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Returns the resulting
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mbuf chain on success, frees it and returns
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.Dv NULL
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on failure.
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If there is room, it will add up to
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.Dv max_protohdr
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-
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.Fa len
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extra bytes to the
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contiguous region to possibly avoid being called again.
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.Fa len
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must be smaller or equal than
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.Dv MHLEN .
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.It Fn m_split "struct mbuf *m0" "int len0" "int wait"
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Partitions an mbuf chain in two pieces, returning the tail,
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which is all but the first
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.Fa len0
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bytes. In case of failure, it returns
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.Dv NULL
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and attempts to
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restore the chain to its original state.
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.It Fn m_adj "struct mbuf *mp" "int req_len"
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Shaves off
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.Fa req_len
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bytes from head or tail of the (valid) data area.
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If
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.Fa req_len
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is greater than zero, front bytes are being shaved off, if it's smaller,
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from the back (and if it is zero, the mbuf will stay bearded).
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This function does not move data in any way, but is used to manipulate the
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data area pointer and data length variable of the mbuf in a non-clobbering
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way.
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.It Fn m_free "struct mbuf *m"
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Frees mbuf
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.Fa m .
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.It Fn m_freem "struct mbuf *m"
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Frees the mbuf chain beginning with
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.Fa m .
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This function contains the elementary sanity check for a
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.Dv NULL
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pointer.
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.It Fn mtod "struct mbuf *m" "datatype"
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Returns a pointer to the data contained in the specified mbuf
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.Fa m ,
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type-casted to the specified data type
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.Fa datatype .
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Implemented as a macro.
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.It Fn mtocl "void *datapointer"
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Takes a
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.Fa datapointer
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within an mbuf cluster and returns the cluster index number of the mbuf
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owning the data.
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Avoid this; it may be deprecated in the future.
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Implemented as a macro.
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.It Fn cltom "u_long clusternum"
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Takes an mbuf cluster index number
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.Fa clusternum
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and returns a pointer to the beginning of the cluster.
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Avoid this; it may be deprecated in the future.
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Implemented as a macro.
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.It Fn MGET "struct mbuf *m" "int how" "int type"
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Allocates mbuf
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.Fa m
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and initializes it to contain internal data.
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See
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.Fn m_get .
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Implemented as a macro.
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.It Fn MGETHDR "struct mbuf *m" "int how" "int type"
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Allocates mbuf
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.Fa m
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and initializes it to contain a packet header.
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See
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.Fn m_gethdr .
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Implemented as a macro.
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.It Fn MEXTMALLOC "struct mbuf *m" "int len" "int how"
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Allocates external storage of size
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.Fa len
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for mbuf
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.Fa m .
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The
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.Fa how
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parameter is a choice of
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.Dv M_WAIT / M_DONTWAIT
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from caller.
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The flag
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.Dv M_EXT
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is set upon success.
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Implemented as a macro.
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.It Fn MEXTADD "struct mbuf *m" "caddr_t buf" "int size" "int type" "void (*free)(caddr_t, u_int, void *)" "void *arg"
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Adds pre-allocated external storage
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.Fa buf
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|
to a normal mbuf
|
|
.Fa m ;
|
|
the parameters
|
|
.Fa size ,
|
|
.Fa type ,
|
|
.Fa free
|
|
and
|
|
.Fa arg
|
|
describe the external storage.
|
|
.Fa size
|
|
is the size of the storage,
|
|
.Fa type
|
|
describes its
|
|
.Xr malloc 9
|
|
type,
|
|
.Fa free
|
|
is a free routine (if not the usual one), and
|
|
.Fa arg
|
|
is a possible argument to the free routine.
|
|
The flag
|
|
.Dv M_EXT
|
|
is set upon success.
|
|
Implemented as a macro.
|
|
.It Fn MCLGET "struct mbuf *m" "int how"
|
|
Allocates and adds an mbuf cluster to a normal mbuf
|
|
.Fa m .
|
|
The
|
|
.Fa how
|
|
parameter is a choice of
|
|
.Dv M_WAIT / M_DONTWAIT
|
|
from caller.
|
|
The flag
|
|
.Dv M_EXT
|
|
is set upon success.
|
|
Implemented as a macro.
|
|
.It Fn M_COPY_PKTHDR "struct mbuf *to" "struct mbuf *from"
|
|
Copies the mbuf pkthdr from mbuf
|
|
.Fa from
|
|
to mbuf
|
|
.Fa to .
|
|
.Fa from
|
|
must have the type flag
|
|
.Dv M_PKTHDR
|
|
set, and
|
|
.Fa to
|
|
must be empty.
|
|
Implemented as a macro.
|
|
.It Fn M_ALIGN "struct mbuf *m" "int len"
|
|
Sets the data pointer of a newly allocated mbuf
|
|
.Fa m
|
|
to
|
|
.Fa len
|
|
bytes from the end of the mbuf data area, so that
|
|
.Fa len
|
|
bytes of data written to the mbuf
|
|
.Fa m ,
|
|
starting at the data pointer, will be aligned to the end of the data area.
|
|
Implemented as a macro.
|
|
.It Fn MH_ALIGN "struct mbuf *m" "int len"
|
|
Sets the data pointer of a newly allocated packetheader mbuf
|
|
.Fa m
|
|
to
|
|
.Fa len
|
|
bytes from the end of the mbuf data area, so that
|
|
.Fa len
|
|
bytes of data written to the mbuf
|
|
.Fa m ,
|
|
starting at the data pointer, will be aligned to the end of the data area.
|
|
Implemented as a macro.
|
|
.It Fn M_LEADINGSPACE "struct mbuf *m"
|
|
Returns the amount of space available before the current start of valid
|
|
data in mbuf
|
|
.Fa m .
|
|
Returns 0 if the mbuf data part is shared across multiple mbufs
|
|
.Pq i.e. not writable .
|
|
Implemented as a macro.
|
|
.It Fn M_TRAILINGSPACE "struct mbuf *m"
|
|
Returns the amount of space available after the current end of valid
|
|
data in mbuf
|
|
.Fa m .
|
|
Returns 0 if the mbuf data part is shared across multiple mbufs
|
|
.Pq i.e. not writable .
|
|
Implemented as a macro.
|
|
.It Fn M_PREPEND "struct mbuf *m" "int plen" "int how"
|
|
Prepends space of size
|
|
.Fa plen
|
|
to mbuf
|
|
.Fa m .
|
|
If a new mbuf must be allocated,
|
|
.Fa how
|
|
specifies whether to wait.
|
|
If
|
|
.Fa how
|
|
is
|
|
.Dv M_DONTWAIT
|
|
and allocation fails, the original mbuf chain is freed and
|
|
.Fa m
|
|
is set to
|
|
.Dv NULL .
|
|
Implemented as a macro.
|
|
.It Fn MCHTYPE "struct mbuf *m" "int type"
|
|
Change mbuf
|
|
.Fa m
|
|
to new type
|
|
.Fa type .
|
|
Implemented as a macro.
|
|
.It Fn MEXTREMOVE "struct mbuf *m"
|
|
Removes external storage from mbuf
|
|
.Fa m .
|
|
The flag
|
|
.Dv M_EXT
|
|
is removed.
|
|
Implemented as a macro.
|
|
.It Fn MFREE "struct mbuf *m" "struct mbuf *n"
|
|
Frees a single mbuf
|
|
.Fa m
|
|
and places the successor, if any, in mbuf
|
|
.Fa n .
|
|
Implemented as a macro.
|
|
.El
|
|
.Sh FILES
|
|
The
|
|
.Nm
|
|
management functions are implemented within the file
|
|
.Pa sys/kern/uipc_mbuf.c .
|
|
Function prototypes, and the functions implemented as macros
|
|
are located in
|
|
.Pa sys/sys/mbuf.h .
|
|
Both pathnames are relative to the root of the
|
|
.Nx
|
|
source tree,
|
|
.Pa /usr/src .
|
|
.Sh SEE ALSO
|
|
.Pa /usr/share/doc/smm/18.net ,
|
|
.Xr netstat 1 ,
|
|
.Xr malloc 9
|
|
.Rs
|
|
.%A Jun-ichiro Hagino
|
|
.%T "Mbuf issues in 4.4BSD IPv6/IPsec support (experiences from KAME IPv6/IPsec implemntation)"
|
|
.%B "Proceedings of the freenix track: 2000 USENIX annual technical conference"
|
|
.%D June 2000
|
|
.Re
|
|
.Sh AUTHORS
|
|
The original mbuf data structures were designed by Rob Gurwitz
|
|
when he did the initial TCP/IP implementation at BBN.
|
|
.br
|
|
Further extensions and enhancements were made by Bill Joy, Sam Leffler,
|
|
and Mike Karels at CSRG.
|
|
.br
|
|
Current implementation of external storage by Matt Thomas
|
|
.br
|
|
<matt@3am-software.com> and Jason R. Thorpe <thorpej@NetBSD.ORG>.
|