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

       #include <sys/param.h>
       #include <sys/uio.h>
       #include <sys/mchain.h>

       int
       mb_init(struct mbchain *mbp);

       void
       mb_initm(struct mbchain *mbp, struct mbuf *m);

       void
       mb_done(struct mbchain *mbp);

       struct mbuf *
       mb_detach(struct mbchain *mbp);

       int
       mb_fixhdr(struct mbchain *mbp);

       caddr_t
       mb_reserve(struct mbchain *mbp, int size);

       int
       mb_put_uint8(struct mbchain *mbp, uint8_t x);

       int
       mb_put_uint16be(struct mbchain *mbp, uint16_t x);

       int
       mb_put_uint16le(struct mbchain *mbp, uint16_t x);

       int
       mb_put_uint32be(struct mbchain *mbp, uint32_t x);

       int
       mb_put_uint32le(struct mbchain *mbp, uint32_t x);

       int
       mb_put_int64be(struct mbchain *mbp, int64_t x);

       int
       mb_put_int64le(struct mbchain *mbp, int64_t x);

       int
       mb_put_mem(struct mbchain *mbp, c_caddr_t source, int size, int type);

       int
       mb_put_mbuf(struct mbchain *mbp, struct mbuf *m);

       int
       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 mbchain structure is used
       as a working context and should be initialized with a call to either mb_init() or mb_initm().  It has the
       following fields:

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

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

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

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

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

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

       mb_done() function disposes an mbuf chain pointed to by mbp->mb_top field and sets the field to NULL.

       mb_detach() function returns the value of mbp->mb_top field and sets its value to NULL.

       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.

       mb_reserve() ensures that the object of the length specified by the 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  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.

       mb_put_mem() function copies size bytes of data specified by the source argument to an mbuf  chain.   The
       type argument specifies the method used to perform a copy, and can be one of the following:

       MB_MSYSTEM  Use 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 mbp->mb_copy field.

RETURN VALUES

       All int functions except 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 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 Boris Popov <bp@FreeBSD.org>.

Debian                                          February 20, 2001                                     MBCHAIN(9)