Hello,
I am trying very hard to understand the userspace view of Netlink sockets.
However, my programming is not suffiecient enough to fully understand the man
pages or the source(iproute2/zebra) and work off of that. I have tried many
times but there seems no good documentation or implementation to help me. I
have found this implementation written by someone on LKML 2 years ago,
however the code produces no output. If I can get the code to produce some
and the expected output im sure I can work and understand the code from
there. However, because I did not write this code nor do I fully understand
netlink sockets I am at a loss of what to do. Can someone explain to me if
this code is correct for the 2.6.x series kernel? Furthermore, the author did
not define replybuf nor byes nor netlink_fd so I have guessed as to their
types. Ideally in the future Id like to use netlink to gather interface
information and modify routing tables, however without a solid base to learn
and adapt, I am at a loss.
Any help is appreciated. Thanks.
//File descriptor
int netlink_sk;
ssize_t bytes;
struct nlmsghdr *replybuf;
struct nlmsghdr buffer;
replybuf = &buffer;
//This is the netlink message itself.
struct {
struct nlmsghdr hdr;
struct ifinfomsg info;
} msg;
// This contains the info neccesary to bind the netlink socket
struct sockaddr_nl addr;
// Create and bind the netlink socket
netlink_sk = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
memset(&addr, 0, sizeof(addr));
addr.nl_family = AF_NETLINK;
addr.nl_pid = getpid();
addr.nl_groups = RTMGRP_IPV4_IFADDR;
//Bind it
bind(netlink_sk, (struct sockaddr *)&addr, sizeof(addr));
/* Build the netlink request */
memset(&msg, 0, sizeof(msg));
msg.hdr.nlmsg_len = sizeof(msg);
msg.hdr.nlmsg_type = RTM_GETLINK;
msg.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_MATCH;
msg.hdr.nlmsg_pid = getpid();
msg.hdr.nlmsg_seq = 0;
msg.info.ifi_family = AF_UNSPEC;
msg.info.ifi_type = 0;
msg.info.ifi_index = 0;
msg.info.ifi_change = 0;
/* Send the message */
send(netlink_sk, &msg, msg.hdr.nlmsg_len, 0);
/* Loop, as we might get replies spread over several packets */
while((bytes = recv(netlink_sk,replybuf, sizeof(replybuf), 0))) {
struct nlmsghdr *hdr = (struct nlmsghdr *)replybuf;
if(hdr->nlmsg_type == NLMSG_DONE) {
break;
}
/* Loop over the messages in this packet */
while(bytes) {
int len = hdr->nlmsg_len;
struct ifinfomsg *info = (ifinfomsg *)NLMSG_DATA(hdr);
struct rtattr *rta = IFLA_RTA(info);
len -= NLMSG_LENGTH(sizeof(*info));
/* Loop over the attributes in this message */
while(RTA_OK(rta, len)) {
switch(rta->rta_type) {
case IFLA_IFNAME:
printf("Found device %s - %u\n",
RTA_DATA(rta), info->ifi_index);
break;
}
rta = RTA_NEXT(rta, len);
}
bytes -= hdr->nlmsg_len;
(hdr) += hdr->nlmsg_len;
}
}
----------------------------------------
EB
> All is fine except that I can reliably "oops" it simply by trying to read
> from /proc/apm (e.g. cat /proc/apm).
> oops output and ksymoops-2.3.4 output is attached.
> Is there anything else I can contribute?
The latitude and longtitude of the bios writers current position, and
a ballistic missile.
--Alan Cox 2000-12-08
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