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MDCHAIN(9)		 BSD Kernel Developer's	Manual		    MDCHAIN(9)

NAME
     mdchain, md_initm,	md_done, md_append_record, md_next_record,
     md_get_uint8, md_get_uint16, md_get_uint16be, md_get_uint16le,
     md_get_uint32, md_get_uint32be, md_get_uint32le, md_get_int64,
     md_get_int64be, md_get_int64le, md_get_mem, md_get_mbuf, md_get_uio --
     set of functions to dissect an mbuf chain to various data types

SYNOPSIS
     options LIBMCHAIN
     kldload libmchain

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

     void
     md_initm(struct mdchain *mdp, struct mbuf *m);

     void
     md_done(struct mdchain *mdp);

     void
     md_append_record(struct mdchain *mdp, struct mbuf *top);

     int
     md_next_record(struct mdchain *mdp);

     int
     md_get_uint8(struct mdchain *mdp, uint8_t *x);

     int
     md_get_uint16(struct mdchain *mdp,	uint16_t *x);

     int
     md_get_uint16be(struct mdchain *mdp, uint16_t *x);

     int
     md_get_uint16le(struct mdchain *mdp, uint16_t *x);

     int
     md_get_uint32(struct mdchain *mdp,	uint32_t *x);

     int
     md_get_uint32be(struct mdchain *mdp, uint32_t *x);

     int
     md_get_uint32le(struct mdchain *mdp, uint32_t *x);

     int
     md_get_int64(struct mdchain *mdp, int64_t *x);

     int
     md_get_int64be(struct mdchain *mdp, int64_t *x);

     int
     md_get_int64le(struct mdchain *mdp, int64_t *x);

     int
     md_get_mem(struct mdchain *mdp, caddr_t target, int size, int type);

     int
     md_get_mbuf(struct	mdchain	*mdp, int size,	struct mbuf **m);

     int
     md_get_uio(struct mdchain *mdp, struct uio	*uiop, int size);

DESCRIPTION
     These functions are used to decompose mbuf	chains to various data types.
     The mdchain structure is used as a	working	context	and should be initial-
     ized through a call of the	mb_initm() function.  It has the following
     fields:

     md_top  (struct mbuf *) A pointer to the top of the parsed	mbuf chain.

     md_cur  (struct mbuf *) A pointer to the currently	parsed mbuf.

     md_pas  (int) Offset in the current mbuf.

     The md_done() function disposes of	an mbuf	chain pointed to by the
     mdp-_md_top field and sets	the field to NULL.

     The md_append_record() appends a new mbuf chain using m_nextpkt field to
     form a single linked list of mbuf chains.	If the mdp-_md_top field is
     NULL, then	this function behaves exactly as the md_initm()	function.

     The md_next_record() function extracts the	next mbuf chain	and disposes
     the current one, if any.  For a new mbuf chain it calls the md_initm()
     function.	If there is no data left the function returns ENOENT.

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

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

     MB_MSYSTEM	 Use the bcopy() function.

     MB_MUSER	 Use the copyin(9) function.

     MB_MINLINE	 Use an	"inline" loop which does not call any function.

     If	target is NULL,	an actual copy is not performed	and the	function just
     skips the given number of bytes.

RETURN VALUES
     All int functions return zero if successful, otherwise an error code is
     returned.

     Note: after failure of any	function, an mbuf chain	is left	in the broken
     state and only the	md_done() function can safely be called	to destroy it.

EXAMPLES
     struct mdchain *mdp;
     struct mbuf *m;
     uint16_t length;
     uint8_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);

SEE ALSO
     mbchain(9), mbuf(9)

AUTHORS
     This manual page was written by Boris Popov <bp@FreeBSD.org>.

BSD			       February	28, 2001			   BSD

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | SEE ALSO | AUTHORS

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