【Linux环境编程】获取网卡的实时网速

在windows以下。我们能够看到360或者是qq安全卫士的“安全球”。上面显示实时的网速情况。那么在linux里面怎样获取网卡的实时网速？事实上原理非常easy，读取须要获取网速的网卡在某段时间dT内流量的变化dL，那么实时网速就出来了,Speed = dL / dt。

linux在ifaddrs.h中提供了函数：

/* 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;

系统会创建一个包括本机全部网卡信息链表，然后我们就能够在这个链表里面获取我们想要的信息。

/* 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).  */
};

另外这个链表我们是能够提前用ioctl来筛选的，能够通过ifa_name和ifa_flags来确定ifa_ifu里面究竟选用那个union。只是这次我们是来測量实时网速的，不必要关心这个。

我们须要关心的是ifa_data这个项。关于这个项我百度了非常多。一直没有发现他究竟应该属于哪个结构体的。

后来无意在http://blog.chinaunix.net/uid-22832715-id-292763.html发现有相似的，可是我找不到头文件在那。所以后来干脆我直接把他放到我的头文件中面；

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 */
};

刚刚開始我就打印了ifi_iobytes,ifi_obytes这两个项，无论我怎么下载和上次文件，这两个量都是0。

纠结了我半天。我就直接把全部变量都打印出来。发现ifi_mtu,ifi_metric,ifi_baudrate跟ifconfig eth0输出的数据非常像。

[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 

慢慢的我知道了规律，struct ifaddrs里面的ifa_data前四个字（32位）以此是发送数据包数。接收数据包数，发送字节数，接收字节数。

我就又一次调整了struct if_data的结构体，因为后面的数据全为0，我就保留了4项：

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 */
};  

測试OK。

[15:17 @ ~/program/netspeed]$ ./netspeed 
Get eth0 Speed                  [OK]
eth0: Up Speed: 1.671066 MB/s || Down Speed: 0.036335 MB/s 

附上我已经封装好的代码：

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;
}

头文件：

#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

測试代码：

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("			[Fail]
");
    else
        printf("			[OK]
");
    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                   
",
                ndev.ifs_name,ispeed/(1024.0*1024.0),ospeed/(1024.0*1024.0));

        get_if_speed(&ndev);
    }


    return 0;
} /* ----- End of main() ----- */

可能你有更好的获取网速的办法，求留言指点！