Copyright (c) 2001 Boris Popov
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$FreeBSD: releng/10.2/share/man/man9/mbchain.9 231564 2012-02-12 18:29:56Z ed $
.Dd February 20, 2001 .Dt MBCHAIN 9 .Os .Sh NAME .Nm mbchain , .Nm mb_init , .Nm mb_initm , .Nm mb_done , .Nm mb_detach , .Nm mb_fixhdr , .Nm mb_reserve , .Nm mb_put_uint8 , .Nm mb_put_uint16be , .Nm mb_put_uint16le , .Nm mb_put_uint32be , .Nm mb_put_uint32le , .Nm mb_put_int64be , .Nm mb_put_int64le , .Nm mb_put_mem , .Nm mb_put_mbuf , .Nm mb_put_uio .Nd "set of functions to build an mbuf chain from various data types" .Sh SYNOPSIS .Cd options LIBMCHAIN .Li kldload libmchain
p n sys/param.h n sys/uio.h n 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" .Sh 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: l -tag -width ".Va mb_count" t Va "mb_top"
q Vt "struct mbuf *" A pointer to the top of constructed mbuf chain. t Va mb_cur
q Vt "struct mbuf *" A pointer to the currently filled mbuf. t Va mb_mleft
q Vt int Number of bytes left in the current mbuf. t Va mb_count
q Vt int Total number of bytes placed in the mbuf chain. t Va mb_copy
q Vt "mb_copy_t *" User-defined function to perform a copy into mbuf; useful if any unusual data conversion is necessary. t Va mb_udata
q Vt "void *" User-supplied data which can be used in the .Va mb_copy function. .El
p .Fn mb_done function disposes an mbuf chain pointed to by .Fa mbp->mb_top field and sets the field to .Dv NULL .
p .Fn mb_detach function returns the value of .Fa mbp->mb_top field and sets its value to .Dv NULL .
p .Fn mb_fixhdr recalculates the length of an mbuf chain and updates the .Va m_pkthdr.len field of the first mbuf in the chain. It returns the calculated length.
p .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 .Dv MLEN bytes.
p All .Fn mb_put_* functions perform an actual copy of the data into mbuf chain. Functions which have .Cm le or .Cm be suffixes will perform conversion to the little- or big-endian data formats.
p .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: l -tag -width ".Dv MB_MINLINE" t Dv MB_MSYSTEM Use .Fn bcopy function. t Dv MB_MUSER Use .Xr copyin 9 function. t Dv MB_MINLINE Use an .Dq inline loop which does not call any function. t Dv MB_MZERO Do not copy any data, but just fill the destination with zero bytes. t Dv MB_MCUSTOM Call function specified by the .Fa mbp->mb_copy field. .El .Sh RETURN VALUES All .Ft int functions except .Fn mb_fixhdr return zero if successful and an error code otherwise.
p .Em 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. .Sh EXAMPLES d -literal 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); .Ed .Sh SEE ALSO .Xr mbuf 9 , .Xr mdchain 9 .Sh AUTHORS This manual page was written by .An Boris Popov Aq bp@FreeBSD.org .