mirror of https://github.com/mkerrisk/man-pages
128 lines
3.3 KiB
Groff
128 lines
3.3 KiB
Groff
.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
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.\"
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.\" %%%LICENSE_START(VERBATIM_ONE_PARA)
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.\" Permission is granted to distribute possibly modified copies
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.\" of this page provided the header is included verbatim,
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.\" and in case of nontrivial modification author and date
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.\" of the modification is added to the header.
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.\" %%%LICENSE_END
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.\"
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.\" $Id: rtnetlink.3,v 1.2 1999/05/18 10:35:10 freitag Exp $
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.\"
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.TH RTNETLINK 3 2020-11-01 "GNU" "Linux Programmer's Manual"
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.SH NAME
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rtnetlink \- macros to manipulate rtnetlink messages
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.SH SYNOPSIS
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.B #include <asm/types.h>
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.br
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.B #include <linux/netlink.h>
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.br
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.B #include <linux/rtnetlink.h>
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.br
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.B #include <sys/socket.h>
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.PP
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.BI "rtnetlink_socket = socket(AF_NETLINK, int " socket_type \
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", NETLINK_ROUTE);"
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.PP
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.BI "int RTA_OK(struct rtattr *" rta ", int " rtabuflen );
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.PP
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.BI "void *RTA_DATA(struct rtattr *" rta );
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.PP
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.BI "unsigned int RTA_PAYLOAD(struct rtattr *" rta );
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.PP
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.BI "struct rtattr *RTA_NEXT(struct rtattr *" rta \
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", unsigned int " rtabuflen );
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.PP
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.BI "unsigned int RTA_LENGTH(unsigned int " length );
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.PP
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.BI "unsigned int RTA_SPACE(unsigned int "length );
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.SH DESCRIPTION
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All
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.BR rtnetlink (7)
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messages consist of a
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.BR netlink (7)
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message header and appended attributes.
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The attributes should be manipulated only using the macros provided here.
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.PP
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.BI RTA_OK( rta ", " attrlen )
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returns true if
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.I rta
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points to a valid routing attribute;
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.I attrlen
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is the running length of the attribute buffer.
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When not true then you must assume there are no more attributes in the
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message, even if
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.I attrlen
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is nonzero.
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.PP
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.BI RTA_DATA( rta )
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returns a pointer to the start of this attribute's data.
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.PP
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.BI RTA_PAYLOAD( rta )
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returns the length of this attribute's data.
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.PP
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.BI RTA_NEXT( rta ", " attrlen )
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gets the next attribute after
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.IR rta .
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Calling this macro will update
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.IR attrlen .
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You should use
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.B RTA_OK
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to check the validity of the returned pointer.
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.PP
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.BI RTA_LENGTH( len )
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returns the length which is required for
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.I len
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bytes of data plus the header.
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.PP
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.BI RTA_SPACE( len )
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returns the amount of space which will be needed in a message with
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.I len
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bytes of data.
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.SH CONFORMING TO
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These macros are nonstandard Linux extensions.
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.SH BUGS
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This manual page is incomplete.
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.SH EXAMPLES
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.\" FIXME . ? would be better to use libnetlink in the EXAMPLE code here
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Creating a rtnetlink message to set the MTU of a device:
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.PP
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.in +4n
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.EX
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#include <linux/rtnetlink.h>
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\&...
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struct {
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struct nlmsghdr nh;
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struct ifinfomsg if;
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char attrbuf[512];
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} req;
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struct rtattr *rta;
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unsigned int mtu = 1000;
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int rtnetlink_sk = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
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memset(&req, 0, sizeof(req));
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req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(req.if));
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req.nh.nlmsg_flags = NLM_F_REQUEST;
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req.nh.nlmsg_type = RTM_NEWLINK;
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req.if.ifi_family = AF_UNSPEC;
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req.if.ifi_index = INTERFACE_INDEX;
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req.if.ifi_change = 0xffffffff; /* ??? */
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rta = (struct rtattr *)(((char *) &req) +
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NLMSG_ALIGN(req.nh.nlmsg_len));
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rta\->rta_type = IFLA_MTU;
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rta\->rta_len = RTA_LENGTH(sizeof(mtu));
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req.nh.nlmsg_len = NLMSG_ALIGN(req.nh.nlmsg_len) +
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RTA_LENGTH(sizeof(mtu));
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memcpy(RTA_DATA(rta), &mtu, sizeof(mtu));
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send(rtnetlink_sk, &req, req.nh.nlmsg_len, 0);
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.EE
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.in
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.SH SEE ALSO
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.BR netlink (3),
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.BR netlink (7),
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.BR rtnetlink (7)
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