MBCHAIN(9) BSD 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, u_int8_t x);
int
mb_put_uint16be(struct mbchain *mbp, u_int16_t x);
int
mb_put_uint16le(struct mbchain *mbp, u_int16_t x);
int
mb_put_uint32be(struct mbchain *mbp, u_int32_t x);
int
mb_put_uint32le(struct mbchain *mbp, u_int32_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 initial‐
ized 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 calcu‐
lated 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 ALSOmbuf(9), mdchain(9)AUTHORS
This manual page was written by Boris Popov ⟨bp@FreeBSD.org⟩.
BSD February 20, 2001 BSD
