在Windows下面，我們可以看到360或者是qq安全衛士的“安全球”，上面顯示實時的網速情況。那麼在Linux裡面如何獲取網卡的實時網速？其實原理很簡單，讀取需要獲取網速的網卡在某段時間dT內流量的變化dL，那麼實時網速就出來了,Speed = dL / dt。
Linux在ifaddrs.h中提供了函數：
/* Create a linked list of `struct ifaddrs' structures, one for each
network interface on the host machine. If successful, store the
list in *IFAP and return 0. On errors, return -1 and set `errno'.
The storage returned in *IFAP is allocated dynamically and can
only be properly freed by passing it to `freeifaddrs'. */
extern int getifaddrs (struct ifaddrs **__ifap) __THROW;
/* Reclaim the storage allocated by a previous `getifaddrs' call. */
extern void freeifaddrs (struct ifaddrs *__ifa) __THROW;
系統會創建一個包含本機所有網卡信息鏈表，然後我們就可以在這個鏈表裡面獲取我們想要的信息。
/* The `getifaddrs' function generates a linked list of these structures.
Each element of the list describes one network interface. */
struct ifaddrs
{
struct ifaddrs *ifa_next; /* Pointer to the next structure. */
char *ifa_name; /* Name of this network interface. */
unsigned int ifa_flags; /* Flags as from SIOCGIFFLAGS ioctl. */
struct sockaddr *ifa_addr; /* Network address of this interface. */
struct sockaddr *ifa_netmask; /* Netmask of this interface. */
union
{
/* At most one of the following two is valid. If the IFF_BROADCAST
bit is set in `ifa_flags', then `ifa_broadaddr' is valid. If the
IFF_POINTOPOINT bit is set, then `ifa_dstaddr' is valid.
It is never the case that both these bits are set at once. */
struct sockaddr *ifu_broadaddr; /* Broadcast address of this interface. */
struct sockaddr *ifu_dstaddr; /* Point-to-point destination address. */
} ifa_ifu;
/* These very same macros are defined by <net/if.h> for `struct ifaddr'.
So if they are defined already, the existing definitions will be fine. */
# ifndef ifa_broadaddr
# define ifa_broadaddr ifa_ifu.ifu_broadaddr
# endif
# ifndef ifa_dstaddr
# define ifa_dstaddr ifa_ifu.ifu_dstaddr
# endif
void *ifa_data; /* Address-specific data (may be unused). */
};
另外這個鏈表我們是可以提前用ioctl來篩選的，可以通過ifa_name和ifa_flags來確定ifa_ifu裡面到底選用那個union。不過這次我們是來測量實時網速的，不必要關心這個。
我們需要關心的是ifa_data這個項，關於這個項我百度了很多，一直沒有發現他到底應該屬於哪個結構體的。
後來無意在 http://www.linuxidc.com/Linux/2014-11/109289.htm 發現有類似的，但是我找不到頭文件在那，所以後來干脆我直接把他放到我的頭文件裡面；
struct if_data{
/* generic interface information */
u_char ifi_type; /* ethernet, tokenring, etc */
u_char ifi_addrlen; /* media address length */
u_char ifi_hdrlen; /* media header length */
u_long ifi_mtu; /* maximum transmission unit */
u_long ifi_metric; /* routing metric (external only) */
u_long ifi_baudrate; /* linespeed */
/* volatile statistics */
u_long ifi_ipackets; /* packets received on interface */
u_long ifi_ierrors; /* input errors on interface */
u_long ifi_opackets; /* packets sent on interface */
u_long ifi_oerrors; /* output errors on interface */
u_long ifi_collisions; /* collisions on csma interfaces */
u_long ifi_ibytes; /* total number of octets received */
u_long ifi_obytes; /* total number of octets sent */
u_long ifi_imcasts; /* packets received via multicast */
u_long ifi_omcasts; /* packets sent via multicast */
u_long ifi_iqdrops; /* dropped on input, this interface */
u_long ifi_noproto; /* destined for unsupported protocol */
struct timeval ifi_lastchange;/* last updated */
};
剛剛開始我就打印了ifi_iobytes,ifi_obytes這兩個項，不管我怎麼下載和上次文件，這兩個量都是0。糾結了我半天，我就直接把所有變量都打印出來，發現ifi_mtu,ifi_metric,ifi_baudrate跟ifconfig eth0輸出的數據很像。
[15:12 @ ~/program/netspeed]$ ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:22:15:67:F8:16
inet addr:210.42.158.204 Bcast:210.42.158.255 Mask:255.255.255.0
inet6 addr: fe80::222:15ff:fe67:f816/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:917978 errors:0 dropped:0 overruns:0 frame:0
TX packets:1132894 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:132866544 (126.7 MiB) TX bytes:1250785627 (1.1 GiB)
Interrupt:29 Base address:0x4000
慢慢的我知道了規律，struct ifaddrs裡面的ifa_data前四個字（32位）以此是發送數據包數，接收數據包數，發送字節數，接收字節數。
我就重新調整了struct if_data的結構體，由於後面的數據全為0，我就保留了4項：
struct if_data
{
/* generic interface information */
u_long ifi_opackets; /* packets sent on interface */
u_long ifi_ipackets; /* packets received on interface */
u_long ifi_obytes; /* total number of octets sent */
u_long ifi_ibytes; /* total number of octets received */
};
測試OK。
[15:17 @ ~/program/netspeed]$ ./netspeed
Get eth0 Speed [OK]
eth0: Up Speed: 1.671066 MB/s || Down Speed: 0.036335 MB/s
附上我已經封裝好的代碼：
int get_if_dbytes(struct if_info* ndev)
{
assert(ndev);
struct ifaddrs *ifa_list = NULL;
struct ifaddrs *ifa = NULL;
struct if_data *ifd = NULL;
int ret = 0;
ret = getifaddrs(&ifa_list);
if(ret < 0) {
perror("Get Interface Address Fail:");
goto end;
}
for(ifa=ifa_list; ifa; ifa=ifa->ifa_next){
if(!(ifa->ifa_flags & IFF_UP) && !(ifa->ifa_flags & IFF_RUNNING))
continue;
if(ifa->ifa_data == 0)
continue;
ret = strcmp(ifa->ifa_name,ndev->ifi_name);
if(ret == 0){
ifd = (struct if_data *)ifa->ifa_data;
ndev->ifi_ibytes = ifd->ifi_ibytes;
ndev->ifi_obytes = ifd->ifi_obytes;
break;
}
}
freeifaddrs(ifa_list);
end:
return (ret ? -1 : 0);
}
int get_if_speed(struct if_speed *ndev)
{
assert(ndev);
struct if_info *p1=NULL,*p2=NULL;
p1 = (struct if_info *)malloc(sizeof(struct if_info));
p2 = (struct if_info *)malloc(sizeof(struct if_info));
bzero(p1,sizeof(struct if_info));
bzero(p2,sizeof(struct if_info));
strncpy(p1->ifi_name,ndev->ifs_name,strlen(ndev->ifs_name));
strncpy(p2->ifi_name,ndev->ifs_name,strlen(ndev->ifs_name));
int ret = 0;
ret = get_if_dbytes(p1);
if(ret < 0) goto end;
usleep(ndev->ifs_us);
ret = get_if_dbytes(p2);
if(ret < 0) goto end;
ndev->ifs_ispeed = p2->ifi_ibytes - p1->ifi_ibytes;
ndev->ifs_ospeed = p2->ifi_obytes - p1->ifi_obytes;
end:
free(p1);
free(p2);
return 0;
}
頭文件：
#ifndef __TSPEED_H__
#define __TSPEED_H__
#ifdef __cplusplus
extern "C"
{
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <error.h>
/* For "open" function */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
struct if_data
{
/* generic interface information */
u_long ifi_opackets; /* packets sent on interface */
u_long ifi_ipackets; /* packets received on interface */
u_long ifi_obytes; /* total number of octets sent */
u_long ifi_ibytes; /* total number of octets received */
};
struct if_info
{
char ifi_name[16];
unsigned long ifi_ibytes;
unsigned long ifi_obytes;
};
struct if_speed
{
char ifs_name[16];
unsigned long ifs_ispeed;
unsigned long ifs_ospeed;
unsigned long ifs_us;
};
extern int get_if_dbytes(struct if_info *ndev);
extern int get_if_speed(struct if_speed *ndev);
#ifdef __cplusplus
}
#endif
#endif
測試代碼：
int main (int argc, char **argv)
{
struct if_speed ndev;
int ret = 0;
bzero(&ndev,sizeof(ndev));
sprintf(ndev.ifs_name,"eth0");
ndev.ifs_us = 100000;
printf("Get %s Speed");
ret = get_if_speed(&ndev);
if(ret < 0)
printf("\t\t\t[Fail]\n");
else
printf("\t\t\t[OK]\n");
float ispeed ,ospeed;
while(1){
ispeed = ndev.ifs_ispeed * 1.0/(ndev.ifs_us/1000 * 0.001);
ospeed = ndev.ifs_ospeed * 1.0/(ndev.ifs_us/1000 * 0.001);
printf("%s: Up Speed: %f MB/s || Down Speed: %f MB/s \r",
ndev.ifs_name,ispeed/(1024.0*1024.0),ospeed/(1024.0*1024.0));
get_if_speed(&ndev);
}
return 0;
} /* ----- End of main() ----- */
可能你有更好的獲取網速的辦法，求留言指點！