如何订阅内核callback消息？

是的，这些事件发布在netlink NETLINK_ROUTE套接字上。

下面是一个打印出各种RTMGRP_LINK事件/消息的小例子。 我无法找到任何理智的文档，所以你要么必须经验地进行测试，要么通过netif_carrier_on / netif_carrier_off函数从内核跟踪代码，找出你感兴趣的是哪种类型的netlink消息。

对于网络设备的给定载波指示，我相信IFF_LOWER_UP或/和IFF_UP标志将被设置/清除：

 #include <errno.h> #include <stdio.h> #include <string.h> #include <asm/types.h> #include <asm/types.h> #include <sys/socket.h> #include <linux/netlink.h> #include <linux/if.h> #include <linux/rtnetlink.h> #define ENTRY(x) {x, #x} struct { unsigned flag; const char *name; } ifi_flag_map[] = { ENTRY(IFF_UP), ENTRY(IFF_BROADCAST), ENTRY(IFF_DEBUG), ENTRY(IFF_LOOPBACK), ENTRY(IFF_POINTOPOINT), ENTRY(IFF_NOTRAILERS), ENTRY(IFF_RUNNING), ENTRY(IFF_NOARP), ENTRY(IFF_PROMISC), ENTRY(IFF_ALLMULTI), ENTRY(IFF_MASTER), ENTRY(IFF_SLAVE), ENTRY(IFF_MULTICAST), ENTRY(IFF_PORTSEL), ENTRY(IFF_AUTOMEDIA), ENTRY(IFF_DYNAMIC), ENTRY(IFF_LOWER_UP), ENTRY(IFF_DORMANT), ENTRY(IFF_ECHO), }; struct { unsigned type; const char *name; } nlmrt_type_map[] = { ENTRY(RTM_NEWLINK ), ENTRY(RTM_DELLINK), ENTRY(RTM_GETLINK), ENTRY(RTM_SETLINK), ENTRY(RTM_NEWADDR ), ENTRY(RTM_DELADDR), ENTRY(RTM_GETADDR), ENTRY(RTM_NEWROUTE ), ENTRY(RTM_DELROUTE), ENTRY(RTM_GETROUTE), ENTRY(RTM_NEWNEIGH ), ENTRY(RTM_DELNEIGH), ENTRY(RTM_GETNEIGH), ENTRY(RTM_NEWRULE ), ENTRY(RTM_DELRULE), ENTRY(RTM_GETRULE), ENTRY(RTM_NEWQDISC ), ENTRY(RTM_DELQDISC), ENTRY(RTM_GETQDISC), ENTRY(RTM_NEWTCLASS ), ENTRY(RTM_DELTCLASS), ENTRY(RTM_GETTCLASS), ENTRY(RTM_NEWTFILTER ), ENTRY(RTM_DELTFILTER), ENTRY(RTM_NEWACTION ), ENTRY(RTM_DELACTION), ENTRY(RTM_GETACTION), ENTRY(RTM_NEWPREFIX ), ENTRY(RTM_GETMULTICAST ), ENTRY(RTM_GETANYCAST ), ENTRY(RTM_NEWNEIGHTBL ), ENTRY(RTM_GETNEIGHTBL ), ENTRY(RTM_SETNEIGHTBL), ENTRY(RTM_NEWNDUSEROPT ), ENTRY(RTM_NEWADDRLABEL ), ENTRY(RTM_DELADDRLABEL), ENTRY(RTM_GETADDRLABEL), ENTRY(RTM_GETDCB ), ENTRY(RTM_SETDCB), ENTRY(RTM_NEWNETCONF ), ENTRY(RTM_GETNETCONF ), ENTRY(RTM_NEWMDB ), ENTRY(RTM_DELMDB ), ENTRY(RTM_GETMDB ), }; void print_type(unsigned type) { size_t i; for (i = 0; i < sizeof nlmrt_type_map/sizeof nlmrt_type_map[0]; i++) { if (type == nlmrt_type_map[i].type) { printf("\t\tMsg Type: %s\n", nlmrt_type_map[i].name); return; } } printf("\t\tMsg Type: unknown(%d)\n", type); } void print_flags(unsigned flags, unsigned change) { size_t i; printf("\t\tflags: "); for (i = 0; i < sizeof ifi_flag_map/sizeof ifi_flag_map[0]; i++) { if (flags & ifi_flag_map[i].flag) { if (change & ifi_flag_map[i].flag) { printf("%s(C) ", ifi_flag_map[i].name); } else { printf("%s ", ifi_flag_map[i].name); } } } puts(""); } void read_msg(int fd) { int len; char buf[4096]; struct iovec iov = { buf, sizeof(buf) }; struct sockaddr_nl sa; struct msghdr msg = { (void *)&sa, sizeof(sa), &iov, 1, NULL, 0, 0 }; struct nlmsghdr *nh; len = recvmsg(fd, &msg, 0); if(len == -1) { perror("recvmsg"); return; } for (nh = (struct nlmsghdr *) buf; NLMSG_OK (nh, len); nh = NLMSG_NEXT (nh, len)) { struct ifinfomsg *ifimsg; /* The end of multipart message. */ printf("netlink message: len = %u, type = %u, flags = 0x%X, seq = %u, pid = %u\n", nh->nlmsg_len, nh->nlmsg_type, nh->nlmsg_flags, nh->nlmsg_seq, nh->nlmsg_pid); if (nh->nlmsg_type == NLMSG_DONE) return; if (nh->nlmsg_type == NLMSG_ERROR) { continue; } ifimsg = NLMSG_DATA(nh); printf("\tifi_family = %u, ifi_type = %u, ifi_index = %u, ifi_flags = 0x%X, ifi_change = 0x%X\n", ifimsg->ifi_family , ifimsg->ifi_type , ifimsg->ifi_index , ifimsg->ifi_flags , ifimsg->ifi_change); print_type(nh->nlmsg_type); print_flags(ifimsg->ifi_flags, ifimsg->ifi_change); } } int main(int argc, char *argv[]) { struct sockaddr_nl sa; int fd; memset(&sa, 0, sizeof(sa)); sa.nl_family = AF_NETLINK; sa.nl_groups = RTMGRP_LINK; //sa.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_IFADDR; fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE); if(fd == -1) { perror("socket"); return 1; } if(bind(fd, (struct sockaddr *) &sa, sizeof(sa)) == -1) { perror("bind"); return 1; } for(;;) { read_msg(fd); } return 0; }