netdevice
===
Linux 提供了一系列的低階(low-level)網路介面，可供開發者使用獲取網路裝置資訊。
我們可以通過syscall ioctl去取用這些資訊[ioctl 原型](https://man7.org/linux/man-pages/man2/ioctl.2.html):
```Clike=
#include <sys/ioctl.h>
int ioctl(int d, int request, ...);
```
可以送出的需求如下[sockios.h](https://github.com/torvalds/linux/blob/master/include/uapi/linux/sockios.h):
```Clike=
/* Routing table calls. */
#define SIOCADDRT 0x890B /* add routing table entry */
#define SIOCDELRT 0x890C /* delete routing table entry */
#define SIOCRTMSG 0x890D /* unused */
/* Socket configuration controls. */
#define SIOCGIFNAME 0x8910 /* get iface name */
#define SIOCSIFLINK 0x8911 /* set iface channel */
#define SIOCGIFCONF 0x8912 /* get iface list */
#define SIOCGIFFLAGS 0x8913 /* get flags */
#define SIOCSIFFLAGS 0x8914 /* set flags */
#define SIOCGIFADDR 0x8915 /* get PA address */
#define SIOCSIFADDR 0x8916 /* set PA address */
#define SIOCGIFDSTADDR 0x8917 /* get remote PA address */
#define SIOCSIFDSTADDR 0x8918 /* set remote PA address */
#define SIOCGIFBRDADDR 0x8919 /* get broadcast PA address */
#define SIOCSIFBRDADDR 0x891a /* set broadcast PA address */
#define SIOCGIFNETMASK 0x891b /* get network PA mask */
#define SIOCSIFNETMASK 0x891c /* set network PA mask */
#define SIOCGIFMETRIC 0x891d /* get metric */
#define SIOCSIFMETRIC 0x891e /* set metric */
#define SIOCGIFMEM 0x891f /* get memory address (BSD) */
#define SIOCSIFMEM 0x8920 /* set memory address (BSD) */
#define SIOCGIFMTU 0x8921 /* get MTU size */
#define SIOCSIFMTU 0x8922 /* set MTU size */
#define SIOCSIFNAME 0x8923 /* set interface name */
#define SIOCSIFHWADDR 0x8924 /* set hardware address */
#define SIOCGIFENCAP 0x8925 /* get/set encapsulations */
#define SIOCSIFENCAP 0x8926
#define SIOCGIFHWADDR 0x8927 /* Get hardware address */
#define SIOCGIFSLAVE 0x8929 /* Driver slaving support */
#define SIOCSIFSLAVE 0x8930
#define SIOCADDMULTI 0x8931 /* Multicast address lists */
#define SIOCDELMULTI 0x8932
#define SIOCGIFINDEX 0x8933 /* name -> if_index mapping */
#define SIOGIFINDEX SIOCGIFINDEX /* misprint compatibility :-) */
#define SIOCSIFPFLAGS 0x8934 /* set/get extended flags set */
#define SIOCGIFPFLAGS 0x8935
#define SIOCDIFADDR 0x8936 /* delete PA address */
#define SIOCSIFHWBROADCAST 0x8937 /* set hardware broadcast addr */
#define SIOCGIFCOUNT 0x8938 /* get number of devices */
#define SIOCGIFBR 0x8940 /* Bridging support */
#define SIOCSIFBR 0x8941 /* Set bridging options */
#define SIOCGIFTXQLEN 0x8942 /* Get the tx queue length */
#define SIOCSIFTXQLEN 0x8943 /* Set the tx queue length */
/* SIOCGIFDIVERT was: 0x8944 Frame diversion support */
/* SIOCSIFDIVERT was: 0x8945 Set frame diversion options */
#define SIOCETHTOOL 0x8946 /* Ethtool interface */
#define SIOCGMIIPHY 0x8947 /* Get address of MII PHY in use. */
#define SIOCGMIIREG 0x8948 /* Read MII PHY register. */
#define SIOCSMIIREG 0x8949 /* Write MII PHY register. */
#define SIOCWANDEV 0x894A /* get/set netdev parameters */
#define SIOCOUTQNSD 0x894B /* output queue size (not sent only) */
#define SIOCGSKNS 0x894C /* get socket network namespace */
/* ARP cache control calls. */
/* 0x8950 - 0x8952 * obsolete calls, don't re-use */
#define SIOCDARP 0x8953 /* delete ARP table entry */
#define SIOCGARP 0x8954 /* get ARP table entry */
#define SIOCSARP 0x8955 /* set ARP table entry */
/* RARP cache control calls. */
#define SIOCDRARP 0x8960 /* delete RARP table entry */
#define SIOCGRARP 0x8961 /* get RARP table entry */
#define SIOCSRARP 0x8962 /* set RARP table entry */
/* Driver configuration calls */
#define SIOCGIFMAP 0x8970 /* Get device parameters */
#define SIOCSIFMAP 0x8971 /* Set device parameters */
/* DLCI configuration calls */
#define SIOCADDDLCI 0x8980 /* Create new DLCI device */
#define SIOCDELDLCI 0x8981 /* Delete DLCI device */
#define SIOCGIFVLAN 0x8982 /* 802.1Q VLAN support */
#define SIOCSIFVLAN 0x8983 /* Set 802.1Q VLAN options */
/* bonding calls */
#define SIOCBONDENSLAVE 0x8990 /* enslave a device to the bond */
#define SIOCBONDRELEASE 0x8991 /* release a slave from the bond*/
#define SIOCBONDSETHWADDR 0x8992 /* set the hw addr of the bond */
#define SIOCBONDSLAVEINFOQUERY 0x8993 /* rtn info about slave state */
#define SIOCBONDINFOQUERY 0x8994 /* rtn info about bond state */
#define SIOCBONDCHANGEACTIVE 0x8995 /* update to a new active slave */
/* bridge calls */
#define SIOCBRADDBR 0x89a0 /* create new bridge device */
#define SIOCBRDELBR 0x89a1 /* remove bridge device */
#define SIOCBRADDIF 0x89a2 /* add interface to bridge */
#define SIOCBRDELIF 0x89a3 /* remove interface from bridge */
/* hardware time stamping: parameters in linux/net_tstamp.h */
#define SIOCSHWTSTAMP 0x89b0 /* set and get config */
#define SIOCGHWTSTAMP 0x89b1 /* get config */
```
---
我們可以開啟一個socket，並透過ioctl獲取網路介面資訊[Linux网络接口操作之ioctl-1_接口参数](https://segmentfault.com/a/1190000005138358)。如下範例，取得所有網路介面卡名稱[pi-router-os-core](https://github.com/sss22213/pi-router-os-core/blob/master/networkinfo/src/netinfo.c)。
```Clike=
/**
* @brief Get all of interface name.
*
* @return true
* @return false
*/
bool netinfo_list_all_interface_name(char (*ary)[IFACE_NAME_LENGTH])
{
int fd = 0;
int ret = 0;
// Create an structure of ifreq for save all of interface name.
struct ifreq ifr[IFACE_MAXIMUN_LENGTH];
// Create an structure of interface conf.
struct ifconf ifc;
// Alloc new memory space to save interface information.
ifc.ifc_len = IFACE_MAXIMUN_LENGTH * sizeof(struct ifreq);
ifc.ifc_buf = (char*)(ifr);
// Create socket connection by IPV4, SOCK_DGRAM.
fd = socket(AF_INET, SOCK_DGRAM, 0);
// Send system call ioctl and argument SIOCGIFCONF.
ret = ioctl(fd, SIOCGIFCONF, (char*)&ifc);
close(fd);
if (ret == -1) {
return false;
}
// The loop will print all of interface name.
for (int iface_idx = 0; iface_idx < ifc.ifc_len / sizeof(struct ifreq); iface_idx++) {
strncpy(ary[iface_idx], ifr[iface_idx].ifr_name, sizeof(char)*IFACE_NAME_LENGTH);
}
return true;
}
```
:::info
[netdevice(7) linux manual](https://man7.org/linux/man-pages/man7/netdevice.7.html)
:::
如上範例，想要取回Interface name，必須透過兩個資料結構，從ioctl取回想要的資訊。
1. Interface conf structure [struct ifconf](https://github.com/torvalds/linux/blob/master/include/uapi/linux/if.h)。
```Clike=
/*
* Structure used in SIOCGIFCONF request.
* Used to retrieve interface configuration
* for machine (useful for programs which
* must know all networks accessible).
*/
/* for compatibility with glibc net/if.h */
struct ifconf {
int ifc_len; /* size of buffer */
union {
char __user *ifcu_buf;
struct ifreq __user *ifcu_req;
} ifc_ifcu;
};
#define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
#define ifc_req ifc_ifcu.ifcu_req /* array of structures */
```
:::info
這個structure只用於SIOCGIFCONF。也就是只負責取得Interface name and IPV4。
:::
2. 給予條件並獲取回傳資訊 [struct ifreq](https://github.com/torvalds/linux/blob/master/include/uapi/linux/if.h)。
```Clike=
/*
* Interface request structure used for socket
* ioctl's. All interface ioctl's must have parameter
* definitions which begin with ifr_name. The
* remainder may be interface specific.
*/
struct ifreq {
#define IFHWADDRLEN 6
union
{
char ifrn_name[IFNAMSIZ]; /* Interface name */
} ifr_ifrn;
union {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
struct sockaddr ifru_netmask;
struct sockaddr ifru_hwaddr;
short ifru_flags;
int ifru_ivalue;
int ifru_mtu;
struct ifmap ifru_map;
char ifru_slave[IFNAMSIZ]; /* Just fits the size */
char ifru_newname[IFNAMSIZ];
void __user * ifru_data;
struct if_settings ifru_settings;
} ifr_ifru;
};
```
* 詳細來看struct ifreq分成兩個區塊。
a. 網路介面卡名稱interface name。
```Clike=
union
{
char ifrn_name[IFNAMSIZ]; /* Interface name */
} ifr_ifrn;
```
b. 網路介面卡的其他資訊。
```Clike=
union {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
struct sockaddr ifru_netmask;
struct sockaddr ifru_hwaddr;
short ifru_flags;
int ifru_ivalue;
int ifru_mtu;
struct ifmap ifru_map;
char ifru_slave[IFNAMSIZ]; /* Just fits the size */
char ifru_newname[IFNAMSIZ];
void __user * ifru_data;
struct if_settings ifru_settings;
} ifr_ifru;
```
依據這個範例，我們可以從struct ifreq獲取interface name和ipv4，也就是ifrn_name和ifru_addr。
ifrn_name位於a部分，ifru_addr位於b部分。
觀察b部分，發現是由union修飾的結構，也就是說這些結構共用一塊相同的記憶體空間。依照不同的需求(例如: SIOCGIFHWADDR)，可以轉型成相對應的結構(ifr_hwaddr)獲取內容。
---
看到以下的範例，將想要查詢的interface放入ifrn_name，並送出ioctl取得netmask。[pi-router-os-core](https://github.com/sss22213/pi-router-os-core/blob/master/networkinfo/src/netinfo.c)
```Clike=
// Get MAC address
struct ifreq ifr;
strncpy(ifr.ifrn_name, "eth0", sizeof(char)*IFNAMSIZ);
ret = ioctl(fd, SIOCGIFHWADDR, &ifr);
if (ret == -1) {
close(fd);
return false;
}
for (int mac_addr_idx = 0; mac_addr_idx < 6 ; mac_addr_idx++) {
sprintf(macaddress + 3 * mac_addr_idx, "%02x:", ifr.ifr_hwaddr.sa_data[mac_addr_idx]);
}
```
將共用記憶體轉成目標結構ifr_hwaddr。
```Clike=
ifr.ifr_hwaddr.sa_data[mac_addr_idx]
```
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