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.\" This manpage copyright 1998 by Andi Kleen. Subject to the GPL.
.\" Based on the original comments from Alexey Kuznetsov
.\" $Id: netlink.3,v 1.1 1999/05/14 17:17:24 freitag Exp $
.TH NETLINK 3 1999-05-14 "Linux Man Page" "Linux Programmer's Manual"
.SH NAME
netlink \- Netlink macros
.SH SYNOPSIS
.nf
.\" FIXME what will glibc 2.1 use here?
.B #include <asm/types.h>
.br
.B #include <linux/netlink.h>
.br
.BI "int NLMSG_ALIGN(size_t " len );
.br
.BI "int NLMSG_LENGTH(size_t " len );
.br
.BI "int NLMSG_SPACE(size_t " len );
.br
.BI "void *NLMSG_DATA(struct nlmsghdr *" nlh );
.br
.BI "struct nlmsghdr *NLMSG_NEXT(struct nlmsghdr *" nlh ", int " len );
.br
.BI "int NLMSG_OK(struct nlmsghdr *" nlh ", int " len );
.br
.BI "int NLMSG_PAYLOAD(struct nlmsghdr *" nlh ", int " len );
.fi
.SH DESCRIPTION
.I <linux/netlink.h>
defines several standard macros to access or create a netlink datagram.
They are similar in spirit to the macros defined in
.BR cmsg (3)
for auxiliary data.
The buffer passed to and from a netlink socket should
be only accessed using these macros.
.TP
NLMSG_ALIGN
Round the length of a netlink message up to align it properly.
.TP
NLMSG_LENGTH
Gets the payload length as argument and returns the aligned length to store
in the
.B nlmsg_len
field of the
.IR nlmsghdr .
.TP
NLMSG_SPACE
Return the number of bytes a netlink message with payload of the passed length
would occupy.
.TP
NLMSG_DATA
Return a pointer to the payload associated with the passed
.IR nlmsghdr .
.TP
.\" FIXME this is bizarre, maybe the interface should be fixed.
NLMSG_NEXT
Get the next
.I nlmsghdr
in a multipart message.
The caller must check if the current nlmsghdr didn't have the NLMSG_DONE
set \(em this function doesn't return NULL on end.
The length parameter is an lvalue containing the remaining length
of the message buffer.
This macro decrements it by the length of the message header.
.TP
NLMSG_OK
Return true if the netlink message is not truncated and ok to parse.
.TP
NLMSG_PAYLOAD
Return the length of the payload associated with the
.IR nlmsghdr .
.SH NOTES
It is often better to use netlink via
.B libnetlink
than via the low level kernel interface.
.SH "SEE ALSO"
.BR netlink (7)
.PP
and ftp://ftp.inr.ac.ru/ip-routing/iproute2* for libnetlink
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