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.\" Copyright (c) 2001 Boris Popov
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.\" $FreeBSD: src/share/man/man9/mdchain.9,v 1.8.22.1.6.1 2010/12/21 17:09:25 kensmith Exp $
.\"
.Dd February 28, 2001
.Dt MDCHAIN 9
.Os
.Sh NAME
.Nm mdchain ,
.Nm md_initm ,
.Nm md_done ,
.Nm md_append_record ,
.Nm md_next_record ,
.Nm md_get_uint8 ,
.Nm md_get_uint16 ,
.Nm md_get_uint16be ,
.Nm md_get_uint16le ,
.Nm md_get_uint32 ,
.Nm md_get_uint32be ,
.Nm md_get_uint32le ,
.Nm md_get_int64 ,
.Nm md_get_int64be ,
.Nm md_get_int64le ,
.Nm md_get_mem ,
.Nm md_get_mbuf ,
.Nm md_get_uio
.Nd "set of functions to dissect an mbuf chain to various data types"
.Sh SYNOPSIS
.Cd options LIBMCHAIN
.Li kldload libmchain
.Pp
.In sys/param.h
.In sys/uio.h
.In sys/mchain.h
.Ft void
.Fn md_initm "struct mdchain *mdp" "struct mbuf *m"
.Ft void
.Fn md_done "struct mdchain *mdp"
.Ft void
.Fn md_append_record "struct mdchain *mdp" "struct mbuf *top"
.Ft int
.Fn md_next_record "struct mdchain *mdp"
.Ft int
.Fn md_get_uint8 "struct mdchain *mdp" "u_int8_t *x"
.Ft int
.Fn md_get_uint16 "struct mdchain *mdp" "u_int16_t *x"
.Ft int
.Fn md_get_uint16be "struct mdchain *mdp" "u_int16_t *x"
.Ft int
.Fn md_get_uint16le "struct mdchain *mdp" "u_int16_t *x"
.Ft int
.Fn md_get_uint32 "struct mdchain *mdp" "u_int32_t *x"
.Ft int
.Fn md_get_uint32be "struct mdchain *mdp" "u_int32_t *x"
.Ft int
.Fn md_get_uint32le "struct mdchain *mdp" "u_int32_t *x"
.Ft int
.Fn md_get_int64 "struct mdchain *mdp" "int64_t *x"
.Ft int
.Fn md_get_int64be "struct mdchain *mdp" "int64_t *x"
.Ft int
.Fn md_get_int64le "struct mdchain *mdp" "int64_t *x"
.Ft int
.Fn md_get_mem "struct mdchain *mdp" "caddr_t target" "int size" "int type"
.Ft int
.Fn md_get_mbuf "struct mdchain *mdp" "int size" "struct mbuf **m"
.Ft int
.Fn md_get_uio "struct mdchain *mdp" "struct uio *uiop" "int size"
.Sh DESCRIPTION
These functions are used to decompose mbuf chains to various data types.
The
.Vt mdchain
structure is used as a working context
and should be initialized through a call of the
.Fn mb_initm
function.
It has the following fields:
.Bl -tag -width "md_top"
.It Va "md_top"
.Pq Vt "struct mbuf *"
A pointer to the top of the parsed mbuf chain.
.It Va md_cur
.Pq Vt "struct mbuf *"
A pointer to the currently parsed mbuf.
.It Va md_pas
.Pq Vt int
Offset in the current mbuf.
.El
.Pp
The
.Fn md_done
function disposes of an mbuf chain pointed to by the
.Fa mdp->md_top
field and sets the field to
.Dv NULL .
.Pp
The
.Fn md_append_record
appends a new mbuf chain using
.Va m_nextpkt
field to form a single linked list of mbuf chains.
If the
.Fa mdp->md_top
field is
.Dv NULL ,
then this function behaves exactly as the
.Fn md_initm
function.
.Pp
The
.Fn md_next_record
function extracts the next mbuf chain and disposes the current one, if any.
For a new mbuf chain it calls the
.Fn md_initm
function.
If there is no data left the function returns
.Er ENOENT .
.Pp
All
.Fn md_get_*
functions perform an actual copy of the data from an mbuf chain.
Functions which have
.Cm le
or
.Cm be
suffixes will perform conversion to the little\- or big\-endian data formats.
.Pp
.Fn md_get_mem
function copies
.Fa size
bytes of data specified by the
.Fa source
argument from an mbuf chain.
The
.Fa type
argument specifies the method used to perform a copy,
and can be one of the following:
.Bl -tag -width ".Dv MB_MINLINE"
.It Dv MB_MSYSTEM
Use the
.Fn bcopy
function.
.It Dv MB_MUSER
Use the
.Xr copyin 9
function.
.It Dv MB_MINLINE
Use an
.Dq inline
loop which does not call any function.
.El
.Pp
If
.Fa target
is
.Dv NULL ,
an actual copy is not performed
and the function just skips the given number of bytes.
.Sh RETURN VALUES
All
.Ft int
functions return zero if successful,
otherwise an error code is returned.
.Pp
.Em Note :
after failure of any function,
an mbuf chain is left in the broken state and only the
.Fn md_done
function can safely be called to destroy it.
.Sh EXAMPLES
.Bd -literal
struct mdchain *mdp;
struct mbuf *m;
u_int16_t length;
u_int8_t byte;

receive(so, &m);
md_initm(mdp, m);
if (md_get_uint8(mdp, &byte) != 0 ||
    md_get_uint16le(mdp, &length) != 0)
	error = EBADRPC;
mb_done(mdp);
.Ed
.Sh SEE ALSO
.Xr mbchain 9 ,
.Xr mbuf 9
.Sh AUTHORS
This manual page was written by
.An Boris Popov Aq bp@FreeBSD.org .