MBCHAIN(9)             FreeBSD Kernel Developer's Manual            MBCHAIN(9)

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>.

FreeBSD 13.1-RELEASE-p6        February 20, 2001       FreeBSD 13.1-RELEASE-p6