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.\" Copyright (c) 2001 Boris Popov
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.\" $FreeBSD: src/share/man/man9/mbchain.9,v 1.7.2.1.6.1 2010/12/21 17:09:25 kensmith Exp $
.\"
.Dd February 20, 2001
.Dt MBCHAIN 9
.Os
.Sh NAME
.Nm mbchain ,
.Nm mb_init ,
.Nm mb_initm ,
.Nm mb_done ,
.Nm mb_detach ,
.Nm mb_fixhdr ,
.Nm mb_reserve ,
.Nm mb_put_uint8 ,
.Nm mb_put_uint16be ,
.Nm mb_put_uint16le ,
.Nm mb_put_uint32be ,
.Nm mb_put_uint32le ,
.Nm mb_put_int64be ,
.Nm mb_put_int64le ,
.Nm mb_put_mem ,
.Nm mb_put_mbuf ,
.Nm mb_put_uio
.Nd "set of functions to build an mbuf chain from 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 int
.Fn mb_init "struct mbchain *mbp"
.Ft void
.Fn mb_initm "struct mbchain *mbp" "struct mbuf *m"
.Ft void
.Fn mb_done "struct mbchain *mbp"
.Ft struct mbuf *
.Fn mb_detach "struct mbchain *mbp"
.Ft int
.Fn mb_fixhdr "struct mbchain *mbp"
.Ft caddr_t
.Fn mb_reserve "struct mbchain *mbp" "int size"
.Ft int
.Fn mb_put_uint8 "struct mbchain *mbp" "u_int8_t x"
.Ft int
.Fn mb_put_uint16be "struct mbchain *mbp" "u_int16_t x"
.Ft int
.Fn mb_put_uint16le "struct mbchain *mbp" "u_int16_t x"
.Ft int
.Fn mb_put_uint32be "struct mbchain *mbp" "u_int32_t x"
.Ft int
.Fn mb_put_uint32le "struct mbchain *mbp" "u_int32_t x"
.Ft int
.Fn mb_put_int64be "struct mbchain *mbp" "int64_t x"
.Ft int
.Fn mb_put_int64le "struct mbchain *mbp" "int64_t x"
.Ft int
.Fn mb_put_mem "struct mbchain *mbp" "c_caddr_t source" "int size" "int type"
.Ft int
.Fn mb_put_mbuf "struct mbchain *mbp" "struct mbuf *m"
.Ft int
.Fn mb_put_uio "struct mbchain *mbp" "struct uio *uiop" "int size"
.Sh DESCRIPTION
These functions are used to compose mbuf chains from various data types.
The
.Vt mbchain
structure is used as a working context and should be initialized with a call
to either
.Fn mb_init
or
.Fn mb_initm .
It has the following fields:
.Bl -tag -width ".Va mb_count"
.It Va "mb_top"
.Pq Vt "struct mbuf *"
A pointer to the top of constructed mbuf chain.
.It Va mb_cur
.Pq Vt "struct mbuf *"
A pointer to the currently filled mbuf.
.It Va mb_mleft
.Pq Vt int
Number of bytes left in the current mbuf.
.It Va mb_count
.Pq Vt int
Total number of bytes placed in the mbuf chain.
.It Va mb_copy
.Pq Vt "mb_copy_t *"
User-defined function to perform a copy into mbuf;
useful if any unusual
data conversion is necessary.
.It Va mb_udata
.Pq Vt "void *"
User-supplied data which can be used in the
.Va mb_copy
function.
.El
.Pp
.Fn mb_done
function disposes an mbuf chain pointed to by
.Fa mbp->mb_top
field and sets
the field to
.Dv NULL .
.Pp
.Fn mb_detach
function returns the value of
.Fa mbp->mb_top
field and sets its value to
.Dv NULL .
.Pp
.Fn mb_fixhdr
recalculates the length of an mbuf chain and updates the
.Va m_pkthdr.len
field of the first mbuf in the chain.
It returns the calculated length.
.Pp
.Fn mb_reserve
ensures that the object of the length specified by the
.Fa size
argument will fit in the current mbuf (mbuf allocation is performed if
necessary), and advances all pointers as if the real data was placed.
Returned
value will point to the beginning of the reserved space.
Note that the size
of the object should not exceed
.Dv MLEN
bytes.
.Pp
All
.Fn mb_put_*
functions perform an actual copy of the data into mbuf chain.
Functions which have
.Cm le
or
.Cm be
suffixes will perform conversion to the little\- or big\-endian data formats.
.Pp
.Fn mb_put_mem
function copies
.Fa size
bytes of data specified by the
.Fa source
argument to 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
.Fn bcopy
function.
.It Dv MB_MUSER
Use
.Xr copyin 9
function.
.It Dv MB_MINLINE
Use an
.Dq inline
loop which does not call any function.
.It Dv MB_MZERO
Do not copy any data, but just fill the destination with zero bytes.
.It Dv MB_MCUSTOM
Call function specified by the
.Fa mbp->mb_copy
field.
.El
.Sh RETURN VALUES
All
.Ft int
functions except
.Fn mb_fixhdr
return zero if successful and an error code otherwise.
.Pp
.Em Note :
after failure of any function, an mbuf chain is left in the broken state,
and only
.Fn mb_done
function can safely be called to destroy it.
.Sh EXAMPLES
.Bd -literal
struct mbchain *mbp;
struct mbuf *m;

mb_init(mbp);
mb_put_uint8(mbp, 33);
mb_put_uint16le(mbp, length);
m = m_copym(mbp->mb_top, 0, M_COPYALL, M_WAIT);
send(m);
mb_done(mbp);
.Ed
.Sh SEE ALSO
.Xr mbuf 9 ,
.Xr mdchain 9
.Sh AUTHORS
This manual page was written by
.An Boris Popov Aq bp@FreeBSD.org .