libnl基本使用方法
- 一、参考文档
- 二、netlink简介
- 三、nlmsghdr
- 四、netlink group
- 五、Netlink分层模型及消息格式
- 六、Install libnl-3-dev
- 七、编译应用程序
- 八、Linux Driver
- Netlink Library (libnl)
- Understanding And Programming With Netlink Sockets
- https://github.com/ZengjfOS/RaspberryPi/tree/hotplug
- Linux libnl 编程
netlink是基于socket，并且是内核和用户进程都创建各自的socket，这样双方都使用基于socket的收发缓冲队列，这一点最大的好处是内核和用户进程都可以发起向对方发送消息，准确的说用户进程和内核进程(内核在系统中事实上也可以看做一个进程，其进程tgid为0)都可以是消息的发送者。
netlink作为套接字的一种，也遵循socket标准接口，其sockaddr的结构体实现包括：协议族(AF_NETLINK)、进程tgid、组播组
Netlink sockets are connectionless, and operate in much the same way UDP2 sockets do.
LLCP: Logical Link Control Protocol
Netlink协议通常是基于消息的，消息则通常是由Netlink消息头部（struct nlmsghdr）加上有效载荷组成。虽然有效载荷可以由任何数据组成，但是它通常的格式是一 个固定大小的协议相关头部后面紧跟一系列的属性。
- 总长度（32 位）：消息包括 netlink 消息头部在内的总字节数
- 消息类型（16 位）：消息类型指明了消息的有效载荷的类型。netlink 协议定义了多个标准的消息类型。每个协 议簇都可能定义了额外的消息类型。
- 消息标志（16 位）：消息标志可以用来更改消息类型的行为。
- 序列号（32 位）：序列号的使用是可选的，它可以用来引用前一条消息。比如一条错误消息中可以引用导致错 误的那条请求消息。
- 端口号：端口号指明了这条消息需要发往哪个对等节点。如果没有指定端口号，那么这条消息会被投 递给同一个协议簇中第一个匹配的内核端套接字。
Each socket can subscribe to any number of multicast groups of the netlink protocol it is connected to. The socket will then receive a copy of each message sent to any of the groups. Multicast groups are commonly used to implement event notifications.
这里理解netlink中的group的时候可以直接理解成协议分支，目前最多32种。例如NETLINK_ROUTE是其中一种netlink协议，但是该协议有多个group，可以认为事件分类，作为开发者可能只关心整个协议中的一部分事务(group)，同样，并不是说一个socket client只能订阅、加入一个group，实际上是可以加入32种的任意几个，他是通过32bit(4 byte)来保存的；
如下是个人理解关系:
@startsalt
* PF_NETLINK The Netlink Address Family
* NETLINK_ROUTE Protocol
* RTNLGRP_LINK Group
@endsalt参考文档：Netlink分层模型及消息格式
<----- NLMSG_HDRLEN -----> <-------- RTM_PAYOAD(rtm) --->
<RTA_PAYLOAD(r)>
+------------------+- - -+---------------+- - -+--------------+--------+ - -+
| Netlink Header | Pad | Family Header | Pad | Attributes | rtattr | Pad|
| struct nlmsghdr | | struct rtmsg | | stuct rtattr | data | |
+------------------+- - -+---------------+- - -+--------------+--------+ - -+
^ ^ ^ ^ ^
nlh | | | |
NLMSG_DATA(nlh) --------^ | | |
RTM_RTA(rtm)-----------------------------------^ | |
RTA_DATA(rta)-------------------------------------------------^ |
RTA_NEXT(rta)---------------------------------------------------------------^- sudo apt-get install libnl-3-dev
- 获取头文件以及库名：pkg-config --cflags --libs libnl-3.0 libnl-genl-3.0
- -I/usr/include/libnl3 -lnl-genl-3 -lnl-3
- 参考文档：Linux libnl 编程
- 编译：
gcc link-list.c $(pkg-config --cflags --libs libnl-3.0 libnl-genl-3.0)
/*
* List all network interfaces
*/
#include <stdio.h> //printf, perror
#include <stdlib.h> //exit
#include <netlink/netlink.h>
#include <netlink/genl/genl.h>
static int print_link(struct nl_msg * msg, void * arg)
{
// get nlmsghdr from nl_msg
struct nlmsghdr * h = nlmsg_hdr(msg);
// Return a pointer to the payload associated with the passed nlmsghdr，These messages contain an ifinfomsg structure followed by a series of rtattr structures.
struct ifinfomsg * iface = NLMSG_DATA(h);
// route attrs first pointer
struct rtattr * attr = IFLA_RTA(iface);
// route message playload
int remaining = RTM_PAYLOAD(h);
for (; RTA_OK(attr, remaining); attr = RTA_NEXT(attr, remaining))
{
switch (attr->rta_type)
{
case IFLA_IFNAME:
printf("Interface %d : %s\n", iface->ifi_index, (char *)RTA_DATA(attr));
break;
default:
break;
}
}
return NL_OK;
}
void die(char * s)
{
perror(s);
exit(1);
}
int main(void)
{
struct nl_sock * s = nl_socket_alloc();
if (s == NULL) {
die("nl_socket_alloc");
}
if (nl_connect(s, NETLINK_ROUTE) < 0) {
nl_socket_free(s);
die("nl_connet");
}
/**
* General form of address family dependent message.
* struct rtgenmsg {
* unsigned char rtgen_family;
* };
**/
struct rtgenmsg rt_hdr = { .rtgen_family = AF_NETLINK, };
/**
* Construct and transmit a Netlink message.
* Parameters:
* sk: Netlink socket (required)
* type: Netlink message type (required)
* flags: Netlink message flags (optional)
* buf: Data buffer (optional)
* size: Size of data buffer (optional)
*/
if (nl_send_simple(s, RTM_GETLINK, NLM_F_REQUEST|NLM_F_DUMP, &rt_hdr, sizeof(rt_hdr)) < 0) {
nl_socket_free(s);
die("nl_send_simple");
}
//Retrieve the kernel's answer.
nl_socket_modify_cb(s, NL_CB_VALID, NL_CB_CUSTOM, print_link, NULL);
nl_recvmsgs_default(s);
nl_socket_free(s);
return 0;
}- AF == Address Family
- PF == Protocol Family
Message Format:
<--- nlmsg_total_size(payload) --->
<-- nlmsg_msg_size(payload) ->
+----------+- - -+-------------+- - -+-------- - -
| nlmsghdr | Pad | Payload | Pad | nlmsghdr
+----------+- - -+-------------+- - -+-------- - -
nlmsg_data(nlh)---^ ^
nlmsg_next(nlh)-----------------------+
Payload Format:
<---------------------- nlmsg_len(nlh) --------------------->
<------ hdrlen ------> <- nlmsg_attrlen(nlh, hdrlen) ->
+----------------------+- - -+--------------------------------+
| Family Header | Pad | Attributes |
+----------------------+- - -+--------------------------------+
nlmsg_attrdata(nlh, hdrlen)---^
#define TEST_DATA_LEN 16
#define TEST_DATA "netlink send test" /* 仅作为示例，内核NETLINK_ROUTE套接字无法解析 */
struct sockaddr_nl nladdr;
struct msghdr msg;
struct nlmsghdr *nlhdr;
struct iovec iov;
/* 填充目的地址结构 */
memset(&nladdr, 0, sizeof(nladdr));
nladdr.nl_family = AF_NETLINK;
nladdr.nl_pid = 0; /* 地址为内核 */
nladdr.nl_groups = 0; /* 单播 */
/* 填充netlink消息头 */
nlhdr = (struct nlmsghdr *)malloc(NLMSG_SPACE(TEST_DATA_LEN));
nlhdr->nlmsg_len = NLMSG_LENGTH(TEST_DATA_LEN);
nlhdr->nlmsg_flags = NLM_F_REQUEST;
nlhdr->nlmsg_pid = get_pid(); /* 当前套接字所绑定的ID号（此处为本进程的PID） */
nlhdr->nlmsg_seq = 0;
/* 填充netlink消息实际载荷 */
strcpy(NLMSG_DATA(nlhdr), TEST_DATA);
iov.iov_base = (void *)nlhdr;
iov.iov_len = nlhdr->nlmsg_len;
/* 填充数据消息结构 */
memset(&msg, 0, sizeof(msg));
msg.msg_name = (void *)&(nladdr);
msg.msg_namelen = sizeof(nladdr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
/* 发送netlink消息 */
sendmsg (sock, &msg, 0); /* sock 为NETLINK_ROUTE类型套接字 */https://github.com/ZengjfOS/RaspberryPi/tree/netlink
- grep netlink_kernel_create * -R
crypto/crypto_user.c: crypto_nlsk = netlink_kernel_create(&init_net, NETLINK_CRYPTO, &cfg); drivers/power/supply/mediatek/battery/mtk_battery.c: gm.daemo_nl_sk = netlink_kernel_create(&init_net, NETLINK_FGD, &cfg); drivers/staging/gdm724x/netlink_k.c: sock = netlink_kernel_create(&init_net, unit, &cfg); drivers/infiniband/core/netlink.c: nls = netlink_kernel_create(&init_net, NETLINK_RDMA, &cfg); drivers/input/fingerprint/goodix/gf_spi_tee.c: netlink_kernel_create(&init_net, GF_NETLINK_ROUTE, &cfg); drivers/connector/connector.c: dev->nls = netlink_kernel_create(&init_net, NETLINK_CONNECTOR, &cfg); drivers/scsi/scsi_netlink.c: scsi_nl_sock = netlink_kernel_create(&init_net, NETLINK_SCSITRANSPORT, drivers/scsi/scsi_transport_iscsi.c: nls = netlink_kernel_create(&init_net, NETLINK_ISCSI, &cfg); drivers/misc/mediatek/thermal/common/coolers/mtk_ta.c: daemo_nl_sk = netlink_kernel_create(&init_net, NETLINK_TAD, &cfg); drivers/misc/mediatek/usb11/musbfsh_icusb.c: netlink_kernel_create(&init_net, NETLINK_USERSOCK, &nl_cfg); drivers/misc/mediatek/sysenv/mtk_sysenv.c: netlink_sock = netlink_kernel_create(&init_net, NETLINK_USERSOCK, NULL); kernel/audit.c: aunet->nlsk = netlink_kernel_create(net, NETLINK_AUDIT, &cfg); lib/kobject_uevent.c: ue_sk->sk = netlink_kernel_create(net, NETLINK_KOBJECT_UEVENT, &cfg); net/core/rtnetlink.c: sk = netlink_kernel_create(net, NETLINK_ROUTE, &cfg); net/core/sock_diag.c: net->diag_nlsk = netlink_kernel_create(net, NETLINK_SOCK_DIAG, &cfg); net/decnet/netfilter/dn_rtmsg.c: dnrmg = netlink_kernel_create(&init_net, NETLINK_DNRTMSG, &cfg); net/netlink/genetlink.c: net->genl_sock = netlink_kernel_create(net, NETLINK_GENERIC, &cfg); net/netfilter/nfnetlink.c: nfnl = netlink_kernel_create(net, NETLINK_NETFILTER, &cfg); net/netfilter/xt_quota2.c: nflognl = netlink_kernel_create(&init_net, NETLINK_NFLOG, NULL); net/ipv4/fib_frontend.c: sk = netlink_kernel_create(net, NETLINK_FIB_LOOKUP, &cfg); net/xfrm/xfrm_user.c: nlsk = netlink_kernel_create(net, NETLINK_XFRM, &cfg); security/selinux/netlink.c: selnl = netlink_kernel_create(&init_net, NETLINK_SELINUX, &cfg);