我正试图了解rtnetlink是如何工作的，所以我开始考虑建立一个小的图书馆，让我自己进入它。
我已经到了发送/接收netlink消息可以正常工作的地步。
现在我正在努力研究如何处理RTM_GETLINK请求的答案。
这是我当前的代码：
#include <errno.h>
#include <linux/if.h>
#include <linux/if_link.h>
#include <linux/rtnetlink.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
int main(void) {
unsigned char buf[65535];
unsigned char mac_buf[6];
int tmp_int;
/*
* a standard request
*/
struct {
struct nlmsghdr __r_nl_msg;
struct ifinfomsg __r_ii_msg;
} req;
int sfd, answer_size, attr_len;
struct nlmsghdr *nl_msg_ptr;
struct ifinfomsg *inf_msg_ptr;
struct rtattr *rta_ptr;
/*
* create a socket
*/
if ((sfd = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE)) < 0) {
fprintf(stderr, "ERROR socket(): %s\n", strerror(errno));
return (sfd);
}
/*
* zero out req
*/
memset(&req, 0, sizeof(req));
/*
* prepare the header
*/
req.__r_nl_msg.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg));
req.__r_nl_msg.nlmsg_flags = NLM_F_REQUEST | NLM_F_MATCH;
req.__r_nl_msg.nlmsg_type = RTM_GETLINK; /* to get iface information */
req.__r_nl_msg.nlmsg_seq = 1; /* start seq */
req.__r_ii_msg.ifi_family = AF_UNSPEC; /* AF_INET6 for IPv6 */
req.__r_ii_msg.ifi_change =
0xffffffff; /* man rtnetlink says this; but why? */
/*
* send out request
*/
if (send(sfd, &req, req.__r_nl_msg.nlmsg_len, 0) < 0) {
fprintf(stderr, "ERROR send(): %s\n", strerror(errno));
close(sfd);
return (-1);
}
/*
* receive the answer/process it
*/
while (1) {
if ((answer_size = recv(sfd, buf, sizeof(buf), 0)) < 0) {
fprintf(stderr, "ERROR recv(): %s\n", strerror(errno));
close(sfd);
return (-1);
}
printf("\n=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=\n");
printf("[INFO] %d bytes received.\n", answer_size);
/*
* go over the nlmsghdr's in this answer
*/
for (nl_msg_ptr = (struct nlmsghdr *)buf;
answer_size > (int)sizeof(*nl_msg_ptr);) {
int len = nl_msg_ptr->nlmsg_len;
printf("[INFO] Message length of '%d' bytes.\n", len);
/*
* check if we should stop here
*/
switch (nl_msg_ptr->nlmsg_type) {
case NLMSG_ERROR:
printf("[ERROR] Message is of tmp_int 'NLMSG_ERROR'.\n");
case NLMSG_DONE:
close(sfd);
return (0);
}
if (!NLMSG_OK(nl_msg_ptr, (unsigned int)answer_size)) {
printf("[ERROR] Received message is NOT ok.\n");
close(sfd);
return (-1);
}
/*
* set pointers to work with
*/
inf_msg_ptr = (struct ifinfomsg *)NLMSG_DATA(nl_msg_ptr);
rta_ptr = (struct rtattr *)IFLA_RTA(inf_msg_ptr);
printf("[INFO] Index is: '%d'.\n", inf_msg_ptr->ifi_index);
printf("[INFO] Iface Type: '%d'\n", inf_msg_ptr->ifi_type); /* ARPHRD_* */
printf("[INFO] Up/Down: '%d'\n", inf_msg_ptr->ifi_flags & IFF_UP);
printf("[INFO] Promisc: '%d'\n", inf_msg_ptr->ifi_flags & IFF_PROMISC);
/*
* process attributes
*/
attr_len = IFLA_PAYLOAD(nl_msg_ptr);
for (; RTA_OK(rta_ptr, attr_len); rta_ptr = RTA_NEXT(rta_ptr, attr_len)) {
switch (rta_ptr->rta_type) {
case IFLA_ADDRESS:
memcpy(mac_buf, RTA_DATA(rta_ptr), 6);
printf("[%d][ADDRRESS] %02x:%02x:%02x:%02x:%02x:%02x\n",
inf_msg_ptr->ifi_index, mac_buf[0], mac_buf[1], mac_buf[2],
mac_buf[3], mac_buf[4], mac_buf[5]);
break;
case IFLA_BROADCAST:
memcpy(mac_buf, RTA_DATA(rta_ptr), 6);
printf("[%d][BROADCAST] %02x:%02x:%02x:%02x:%02x:%02x\n",
inf_msg_ptr->ifi_index, mac_buf[0], mac_buf[1], mac_buf[2],
mac_buf[3], mac_buf[4], mac_buf[5]);
break;
case IFLA_IFNAME:
printf("[%d][IFNAME] %s\n", inf_msg_ptr->ifi_index,
RTA_DATA(rta_ptr));
break;
case IFLA_MTU:
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][MTU] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_LINK: /* ??? */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][LINK] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_QDISC:
printf("[%d][QDISC] %s\n", inf_msg_ptr->ifi_index, RTA_DATA(rta_ptr));
break;
case IFLA_STATS:
printf("[%d][STATS] ...\n", inf_msg_ptr->ifi_index);
break;
case IFLA_COST: /* ??? */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][COST] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_PRIORITY: /* ??? */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][PRIORITY] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_MASTER: /* ??? */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][MASTER] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_WIRELESS: /* ??? */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][WIRELESS] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_PROTINFO: /* ??? */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][PROTINFO] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_TXQLEN:
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][TXQLEN] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_MAP: /* ??? */
printf("[%d][MAP] ...\n", inf_msg_ptr->ifi_index);
break;
case IFLA_WEIGHT: /* ??? */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][WIGHT] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_OPERSTATE: /* operational state; interface can be up but if
nothing is connected its OPERSTATE is down */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][OPERSTATE] %d=", inf_msg_ptr->ifi_index, tmp_int);
switch (tmp_int) {
case IF_OPER_UP:
printf("IF_OPER_UP\n");
break;
case IF_OPER_DORMANT:
printf("IF_OPER_DORMANT\n");
break;
case IF_OPER_LOWERLAYERDOWN:
printf("IF_OPER_LOWERLAYERDOWN\n");
break;
case IF_OPER_DOWN:
printf("IF_OPER_DOWN\n");
break;
case IF_OPER_NOTPRESENT:
printf("IF_OPER_NOTPRESENT\n");
break;
case IF_OPER_TESTING:
printf("IF_OPER_TESTING\n");
break;
case IF_OPER_UNKNOWN:
printf("IF_OPER_UNKNOWN\n");
break;
default:
printf("N/A\n");
break;
};
break;
case IFLA_LINKMODE: /* Mode of the link */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][LINKMODE] %d=", inf_msg_ptr->ifi_index, tmp_int);
if (tmp_int == IF_LINK_MODE_DORMANT) {
printf("IF_LINK_MODE_DORMANT\n");
} else if (tmp_int == IF_LINK_MODE_DEFAULT) {
printf("IF_LINK_MODE_DEFAULT\n");
} else {
printf("UNKNOWN\n");
}
break;
case IFLA_LINKINFO: /* ??? */
printf("[%d][LINKINFO] ... len=%d\n", inf_msg_ptr->ifi_index,
rta_ptr->rta_len);
break;
case IFLA_IFALIAS: /* alias of the interface - outdated since one
interface can have multiple addrs. */
printf("[%d][IFALIAS] %s\n", inf_msg_ptr->ifi_index,
RTA_DATA(rta_ptr));
break;
case IFLA_STATS64: /* stats with 64 bit values */
printf("[%d][STATS64] ...\n", inf_msg_ptr->ifi_index);
break;
case IFLA_GROUP: /* the group to which the interface belongs to ??? */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][GROUP] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_PROMISCUITY: /* if > 0, the interface is in promisc mode */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][PROMISCUITY] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_CARRIER: /* if > 0, the interface has a carrier e.g. is
connected to something (???) */
memcpy(&tmp_int, RTA_DATA(rta_ptr), 4);
printf("[%d][CARRIER] %d\n", inf_msg_ptr->ifi_index, tmp_int);
break;
case IFLA_PAD: /* ??? */
printf("[%d][PAD] len=%d\n", inf_msg_ptr->ifi_index,
rta_ptr->rta_len);
break;
case IFLA_XDP: /* something about packet filtering ... ??? */
printf("[%d][XDP] len=%d\n", inf_msg_ptr->ifi_index,
rta_ptr->rta_len);
break;
case IFLA_EVENT: /* ??? */
printf("[%d][EVENT] len=%d\n", inf_msg_ptr->ifi_index,
rta_ptr->rta_len);
break;
default:
printf("[%d][UNKNOWN] len=%d tmp_int=%d\n", inf_msg_ptr->ifi_index,
rta_ptr->rta_len, rta_ptr->rta_type);
break;
};
}
answer_size -= NLMSG_ALIGN(len);
nl_msg_ptr = (struct nlmsghdr *)((char *)nl_msg_ptr + NLMSG_ALIGN(len));
}
}
return (0);
}
我最大的问题是，我不知道某些属性类型的含义以及它们的形式（char[]、int、unsigned int，…）。
此外，我不知道如何处理“嵌套”属性，如IFLA_LINKINFO。
我有以下问题的属性摘要：
IFLA_LINK, IFLA_COST, IFLA_PRIORITY, IFLA_MASTER, IFLA_WIRELESS, IFLA_PROTINFO, IFLA_MAP, IFLA_WEIGHT, IFLA_LINKINFO, IFLA_AF_SPEC, IFLA_GROUP, IFLA_NUM_RX_QUEUES, IFLA_NUM_TX_QUEUES, IFLA_CARRIER, IFLA_CARRIER_CHANGES, IFLA_PROTO_DOWN, IFLA_GSO_MAX_SEGS, IFLA_GSO_MAX_SIZE, IFLA_PAD, IFLA_CARRIER_UP_COUNT, IFLA_CARRIER_DOWN_COUNT, IFLA_EVENT
... 基本上都是这样。
我使用/usr/include/linux/if_link.h作为属性类型的引用。
在我的任何问题上提供任何帮助都是非常好的！（同时反馈我的代码）--提前谢谢！
最佳答案
捷径是使用libnl：
libnl github
描述于：
libnl docs
在构建库时，可以生成该链接的站点以及api信息。
下载并构建后，会有几个链接讨论这些属性：
libnl/doc/api/lib_2route_2link_8c_source.html
lib/route/link.c