mb_fixhdr (9)

Leading comments

Copyright (c) 2001 Boris Popov

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 ...

(The comments found at the beginning of the groff file "man9/mb_fixhdr.9freebsd".)

NAME

mbchain mb_init mb_initm mb_done mb_detach mb_fixhdr mb_reserve mb_put_uint8 mb_put_uint16be mb_put_uint16le mb_put_uint32be mb_put_uint32le mb_put_int64be mb_put_int64le mb_put_mem mb_put_mbuf mb_put_uio - set of functions to build an mbuf chain from various data types

SYNOPSIS

options LIBMCHAIN kldload libmchain

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 uint8_t x Ft int Fn mb_put_uint16be struct mbchain *mbp uint16_t x Ft int Fn mb_put_uint16le struct mbchain *mbp uint16_t x Ft int Fn mb_put_uint32be struct mbchain *mbp uint32_t x Ft int Fn mb_put_uint32le struct mbchain *mbp uint32_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

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:

mb_top

(Vt struct mbuf * ) A pointer to the top of constructed mbuf chain.

mb_cur

(Vt struct mbuf * ) A pointer to the currently filled mbuf.

mb_mleft

(Vt int ) Number of bytes left in the current mbuf.

mb_count

(Vt int ) Total number of bytes placed in the mbuf chain.

mb_copy

(Vt mb_copy_t * ) User-defined function to perform a copy into mbuf; useful if any unusual data conversion is necessary.

mb_udata

(Vt void * ) User-supplied data which can be used in the mb_copy function.

Fn mb_done function disposes an mbuf chain pointed to by Fa mbp->mb_top field and sets the field to NULL

Fn mb_detach function returns the value of Fa mbp->mb_top field and sets its value to NULL

Fn mb_fixhdr recalculates the length of an mbuf chain and updates the m_pkthdr.len field of the first mbuf in the chain. It returns the calculated length.

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 MLEN bytes.

All Fn mb_put_* functions perform an actual copy of the data into mbuf chain. Functions which have le or be suffixes will perform conversion to the little- or big-endian data formats.

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:

MB_MSYSTEM

Use Fn bcopy function.

MB_MUSER

Use copyin(9) function.

MB_MINLINE

Use an ``inline'' loop which does not call any function.

MB_MZERO

Do not copy any data, but just fill the destination with zero bytes.

MB_MCUSTOM

Call function specified by the Fa mbp->mb_copy field.

RETURN VALUES

All Ft int functions except Fn mb_fixhdr return zero if successful and an error code otherwise.

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.

EXAMPLES

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);

SEE ALSO

mbuf(9), mdchain(9)

AUTHORS

This manual page was written by An Boris Popov Aq bp@FreeBSD.org .