ifconfig 源码, MAC地址分类

源码地址：http://www.tazenda.demon.co.uk/phil/net-tools/

 

$ strace -e socket,ioctl ifconfig eth0 

socket(PF_FILE, SOCK_DGRAM, 0)          = 3 
socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 4 
socket(PF_INET6, SOCK_DGRAM, IPPROTO_IP) = 5 
ioctl(5, SIOCGIFFLAGS, {ifr_name="eth0", ifr_flags=IFF_UP|IFF_BROADCAST|IFF_RUNNING|IFF_MULTICAST}) = 0 
ioctl(5, SIOCGIFHWADDR, {ifr_name="eth0", ifr_hwaddr=00:19:21:10:41:ef}) = 0 
ioctl(5, SIOCGIFMETRIC, {ifr_name="eth0", ifr_metric=0}) = 0 
ioctl(5, SIOCGIFMTU, {ifr_name="eth0", ifr_mtu=1500}) = 0 
ioctl(5, SIOCGIFMAP, {ifr_name="eth0", ifr_map={mem_start=0, mem_end=0, base_addr=0, irq=20, dma=0, port=0}}) = 0 
ioctl(5, SIOCGIFMAP, {ifr_name="eth0", ifr_map={mem_start=0, mem_end=0, base_addr=0, irq=20, dma=0, port=0}}) = 0 
ioctl(5, SIOCGIFTXQLEN, {ifr_name="eth0", ifr_qlen=1000}) = 0 
ioctl(4, SIOCGIFADDR, {ifr_name="eth0", ifr_addr={AF_INET, inet_addr("10.67.7.119")}}) = 0 
ioctl(4, SIOCGIFDSTADDR, {ifr_name="eth0", ifr_dstaddr={AF_INET, inet_addr("10.67.7.119")}}) = 0 
ioctl(4, SIOCGIFBRDADDR, {ifr_name="eth0", ifr_broadaddr={AF_INET, inet_addr("10.67.7.255")}}) = 0 
ioctl(4, SIOCGIFNETMASK, {ifr_name="eth0", ifr_netmask={AF_INET, inet_addr("255.255.255.0")}}) = 0 

实际上ifconfig命令就是通过socket ioctl 拿到网卡的信息，诸如ip地址，MAC MTU 之类的 

MAC地址解析-广播地址、组播地址和单播地址的特征

紫梦芊 发表于: 三月 16th, 2011 | 阅读: | 评论数: (0)

MAC地址分成三类，分别是广播地址、组播地址和单播地址。首先，FF：FF：FF：FF：FF：FF毫无疑问是广播地址。每个网卡出厂时被分配唯一一个单播地址，头24位是设备制造厂商的编号，由IEEE(电气与电子工程师协会)分配，后24位是设备厂商为网卡制定的唯一编号。例如08：00：20：0A：8C：6D是单播地址的例子，其中08：00：20是著名的CPU厂商AMD的编号。单播地址的特征是头8位的最低位为0，于是单播地址共有47位的地址空间。
另一类地址就是组播地址。MAC组播地址的特征是头8位的最低位是1，于是MAC组播地址空间相当巨大——除去全1的47位地址空间。例如01：80：C2：00：00：00是一个组播地址，表示802.1d网桥多播组。网桥就是使用这个地址，相互之间交换配置信息，运行分布式生成树算法，消除网络拓扑结构中的环路。

IP层也有单播、组播和广播的概念。MAC组播地址中的01：00：5E：00：00：00到01：00：5E：7F：FF：FF共计23位对应于IP组播地址。给定一个IP组播地址，将其低23位与01：00：5E：00：00：00的低位取“与”运算，即可的到一个 MAC组播地址。但IP组播地址有28位地址空间，对应的MAC组播地址却只有23位，这样每32个IP组播地址被映射到同一MAC地址上。
MAC组播地址空间远远大于IP组播地址空间。如果网络层仅有IP协议，那么完全能将IP组播地址一对一地映射到MAC组播地址！但MAC地址是一个数据链路层的概念，其上层的网络层远远不只有IP。

用ifconfig修改mac地址：

用ifconfig eth3 hw ether F1:AC:6F:B8:C2:BF 设置mac地址时，会检查它的类型，如果是广播或组播地址或全0的MAC，就会判断它无效，并提示：

SIOCSIFHWADDR: Cannot assign requested address信息。

Cannot assign requested address是由strerror 函数打印出来的信息。

errno 是错误代码，在 errno.h头文件中；
perror是错误输出函数，输出格式为：msg:errno对应的错误信息(加上一个换行符)；
strerror 是通过参数 errnum （就是errno），返回对应的错误信息。它的提示信息见：http://www.freebsd.org/cgi/cvsweb.cgi/src/lib/libc/gen/errlst.c?rev=1.8.12.1;content-type=text%2Fplain中介绍，如：

const char *const sys_errlist[] = {"Undefined error: 0",/*  0 - ENOERROR */"Operation not permitted",/*  1 - EPERM */"No such file or directory",/*  2 - ENOENT */"No such process",/*  3 - ESRCH */"Interrupted system call",/*  4 - EINTR */"Input/output error",/*  5 - EIO */"Device not configured",/*  6 - ENXIO */"Argument list too long",/*  7 - E2BIG */"Exec format error",/*  8 - ENOEXEC */"Bad file descriptor",/*  9 - EBADF */"No child processes",/* 10 - ECHILD */"Resource deadlock avoided",/* 11 - EDEADLK */"Cannot allocate memory",/* 12 - ENOMEM */"Permission denied",/* 13 - EACCES */"Bad address",/* 14 - EFAULT */"Block device required",/* 15 - ENOTBLK */"Device busy",/* 16 - EBUSY */"File exists",/* 17 - EEXIST */"Cross-device link",/* 18 - EXDEV */"Operation not supported by device",/* 19 - ENODEV */"Not a directory",/* 20 - ENOTDIR */"Is a directory",/* 21 - EISDIR */"Invalid argument",/* 22 - EINVAL */"Too many open files in system",/* 23 - ENFILE */"Too many open files",/* 24 - EMFILE */"Inappropriate ioctl for device",/* 25 - ENOTTY */"Text file busy",/* 26 - ETXTBSY */"File too large",/* 27 - EFBIG */"No space left on device",/* 28 - ENOSPC */"Illegal seek",/* 29 - ESPIPE */"Read-only file system",/* 30 - EROFS */"Too many links",/* 31 - EMLINK */"Broken pipe",/* 32 - EPIPE *//* math software */"Numerical argument out of domain",/* 33 - EDOM */"Result too large",/* 34 - ERANGE *//* non-blocking and interrupt i/o */"Resource temporarily unavailable",/* 35 - EAGAIN *//* 35 - EWOULDBLOCK */"Operation now in progress",/* 36 - EINPROGRESS */"Operation already in progress",/* 37 - EALREADY *//* ipc/network software -- argument errors */"Socket operation on non-socket",/* 38 - ENOTSOCK */"Destination address required",/* 39 - EDESTADDRREQ */"Message too long",/* 40 - EMSGSIZE */"Protocol wrong type for socket",/* 41 - EPROTOTYPE */"Protocol not available",/* 42 - ENOPROTOOPT */"Protocol not supported",/* 43 - EPROTONOSUPPORT */"Socket type not supported",/* 44 - ESOCKTNOSUPPORT */"Operation not supported",/* 45 - EOPNOTSUPP */"Protocol family not supported",/* 46 - EPFNOSUPPORT *//* 47 - EAFNOSUPPORT */"Address family not supported by protocol family","Address already in use",/* 48 - EADDRINUSE */"Can't assign requested address",/* 49 - EADDRNOTAVAIL */ ->就是上面例子中的提示/* ipc/network software -- operational errors */"Network is down",/* 50 - ENETDOWN */"Network is unreachable",/* 51 - ENETUNREACH */"Network dropped connection on reset",/* 52 - ENETRESET */"Software caused connection abort",/* 53 - ECONNABORTED */"Connection reset by peer",/* 54 - ECONNRESET */"No buffer space available",/* 55 - ENOBUFS */"Socket is already connected",/* 56 - EISCONN */"Socket is not connected",/* 57 - ENOTCONN */"Can't send after socket shutdown",/* 58 - ESHUTDOWN */"Too many references: can't splice",/* 59 - ETOOMANYREFS */"Operation timed out",/* 60 - ETIMEDOUT */"Connection refused",/* 61 - ECONNREFUSED */"Too many levels of symbolic links",/* 62 - ELOOP */"File name too long",/* 63 - ENAMETOOLONG *//* should be rearranged */"Host is down",/* 64 - EHOSTDOWN */"No route to host",/* 65 - EHOSTUNREACH */"Directory not empty",/* 66 - ENOTEMPTY *//* quotas & mush */"Too many processes",/* 67 - EPROCLIM */"Too many users",/* 68 - EUSERS */"Disc quota exceeded",/* 69 - EDQUOT *//* Network File System */"Stale NFS file handle",/* 70 - ESTALE */"Too many levels of remote in path",/* 71 - EREMOTE */"RPC struct is bad",/* 72 - EBADRPC */"RPC version wrong",/* 73 - ERPCMISMATCH */"RPC prog. not avail",/* 74 - EPROGUNAVAIL */"Program version wrong",/* 75 - EPROGMISMATCH */"Bad procedure for program",/* 76 - EPROCUNAVAIL */"No locks available",/* 77 - ENOLCK */"Function not implemented",/* 78 - ENOSYS */"Inappropriate file type or format",/* 79 - EFTYPE */"Authentication error",/* 80 - EAUTH */"Need authenticator",/* 81 - ENEEDAUTH */"Identifier removed",/* 82 - EIDRM */"No message of desired type",/* 83 - ENOMSG */"Value too large to be stored in data type", /* 84 - EOVERFLOW */"Operation canceled",/* 85 - ECANCELED */"Illegal byte sequence",/* 86 - EILSEQ */"Attribute not found",/* 87 - ENOATTR *//* General */"Programming error",/* 88 - EDOOFUS */"Bad message",/* 89 - EBADMSG */"Multihop attempted",/* 90 - EMULTIHOP */"Link has been severed",/* 91 - ENOLINK */"Protocol error",/* 92 - EPROTO */};const int sys_nerr = sizeof(sys_errlist) / sizeof(sys_errlist[0]);

在linux系统中，它的定义在 include/asm-generic/errno.h中