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<td width="68%" background="DDl_back2.jpg" height="44"><big><big><font face="黑体"><p align="center">               ● UNIX网络编程                       (BM: clown)                </font></big></big></td></tr>
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<tr><td width="100%" colspan="2" height="100" align="center" valign="top"><br><p align="center">[<a href="index.htm">回到开始</a>][<a href="17.htm">上一层</a>][<a href="37.htm">下一篇</a>]
<hr><p align="left"><small>发信人: cloudsky (晓舟·轩辕明月), 信区: Linux <br>

标  题: 网络socket编程(5) <br>

发信站: 武汉白云黄鹤站 (Mon Feb  8 20:21:54 1999) , 站内信件 <br>

10. man setsockopt <br>

int getsockopt(int s, int level, int optname, char *optval, int *optlen); <br>

int setsockopt(int s, int level, int optname, const char *optval, int optlen <br>

); <br>

当操作socket选项的时候，选项所在层以及选项名必须被指定。 <br>

为了操作socket层选项，level参数应该是SOL_SOCKET。 <br>

其它层的level参数是协议号。例如，为了指明一个选项由 <br>

TCP协议解释，可以用getprotobyname()函数得到TCP协议号。 <br>

getsockopt调用若失败，*optval == 0 <br>

optname不经解释地传递给适当的协议模块去解释。<sys/socket.h>中定义了socket-le <br>

vel <br>

上的选项。绝大多数socket-level选项的optval是个整数。对于setsockopt()，为了en <br>

able <br>

一个布尔型选项，参数optval应该是一个非零值，反之零值将disable这个选项。 <br>

SO_LINGER       uses a struct linger parameter that specifies the <br>

desired state of the option and  the  linger  interval  (see <br>

below).  struct linger is defined in <sys/socket.h>.  struct <br>

linger contains the following members: <br>

l_onoff   on = 1/off = 0 <br>

l_linger  linger time, in seconds <br>



下列选项是socket-level上的 <br>

SO_DEBUG     enable/disable recording of debugging information <br>

SO_REUSEADDR enable/disable local address reuse <br>

SO_KEEPALIVE enable/disable keep connections alive <br>

SO_DONTROUTE enable/disable routing bypass for outgoing messages <br>

SO_LINGER        linger on close if data is present <br>

SO_BROADCAST enable/disable     permission to transmit broadcast messages <br>

SO_OOBINLINE enable/disable reception of out-of-band data in band <br>

SO_SNDBUF    set buffer size for output <br>

SO_RCVBUF    set buffer size for input <br>

SO_TYPE      get the type of the socket(get only) <br>

SO_ERROR     get and clear error on  the  socket(get only) <br>

SO_KEEPALIVE enables the periodic transmission of messages on a connected so <br>

cket <br>

. <br>

If the connected party fails to respond to these messages, the connection is <br>

  <br>

considered broken and processes using the socket are notified using a SIGPIP <br>

E si <br>

gnal. <br>

SO_DONTROUTE indicates that outgoing messages should bypass the standard rou <br>

ting <br>

ting <br>

facilities. Instead, messages are directed to the appropriate network interf <br>

ace <br>

according to the network  portion of the destination address. <br>

SO_LINGER controls      the action taken when unsent messages are <br>

queued  on       a  socket  and  a close(2) is performed.  If the <br>

socket promises reliable delivery of data and  SO_LINGER  is <br>

set,  the       system  will  block  the  process  on the close() <br>

attempt until it is able to transmit the data  or       until  it <br>

decides  it  is unable to deliver the information (a timeout <br>

period, termed the      linger interval, is specified in the set- <br>

sockopt()       call  when SO_LINGER is requested).  If SO_LINGER <br>

is      disabled and a close() is issued, the system will process <br>

the  close() in a manner that allows the process to continue <br>

as      quickly as possible. <br>

The option      SO_BROADCAST requests permission to  send  broad- <br>

cast  datagrams  on the socket. <br>

对于那些支持带外数据的协议，选项SO_OOBINLINE要求把带外数据放在 <br>

普通数据输入队列里，此时可用不带MSG_OOB标志的recv读取这些带外数据。 <br>

SO_SNDBUF and SO_RCVBUF are options that adjust  the  normal <br>

buffer sizes allocated for      output and input buffers, respec- <br>

tively.  The buffer size may be  increased       for  high-volume <br>

connections  or may be decreased to limit the possible back- <br>



log of incoming data.  The      Internet protocols place an abso- <br>

lute  limit  of  64  Kbytes  on these values for UDP and TCP <br>

sockets. <br>

Finally, SO_TYPE and SO_ERROR are       options  used  only  with <br>

getsockopt().   SO_TYPE  returns the type of the socket (for <br>

example,  SOCK_STREAM).   It  is  useful  for  servers  that <br>

inherit  sockets  on  startup.  SO_ERROR returns any pending <br>

error on the socket and clears the      error status.  It may  be <br>

used  to check for      asynchronous errors on connected datagram <br>

sockets or      for other asynchronous errors. <br>

getsockopt成功则返回0，否则返回-1，errno包含了更详细的信息。 <br>

/usr/include/netinet/in.h中有如下定义 <br>

/* <br>

 * Options for use with [gs]etsockopt at the IP level. <br>

 */ <br>

#define IP_OPTIONS      1       /* set/get IP per-packet options   */ <br>

#define IP_HDRINCL      2       /* int; header is included with data (raw) * <br>

/ <br>

#define IP_TOS          3       /* int; IP type of service and precedence */ <br>

  <br>

#define IP_TTL          4       /* int; IP time to live */ <br>

#define IP_RECVOPTS     5       /* bool; receive all IP options w/datagram * <br>



/ <br>

#define IP_RECVRETOPTS  6       /* bool; receive IP options for response */ <br>

#define IP_RECVDSTADDR  7       /* bool; receive IP dst addr w/datagram */ <br>

#define IP_RETOPTS      8       /* ip_opts; set/get IP per-packet options */ <br>

  <br>

#define IP_MULTICAST_IF         0x10    /* set/get IP multicast interface  * <br>

/ <br>

#define IP_MULTICAST_TTL        0x11    /* set/get IP multicast timetolive * <br>

/ <br>

#define IP_MULTICAST_LOOP       0x12    /* set/get IP multicast loopback   * <br>

/ <br>

#define IP_ADD_MEMBERSHIP       0x13    /* add  an IP group membership     * <br>

/ <br>

#define IP_DROP_MEMBERSHIP      0x14    /* drop an IP group membership     * <br>

/ <br>

#define IP_DEFAULT_MULTICAST_TTL  1     /* normally limit m'casts to 1 hop * <br>

/ <br>

#define IP_DEFAULT_MULTICAST_LOOP 1     /* normally hear sends if a member * <br>

/ <br>

-- <br>

            我问飘逝的风：来迟了？ <br>

            风感慨：是的，他们已经宣战。 <br>



            我问苏醒的大地：还有希望么？ <br>

            大地揉了揉眼睛：还有，还有无数代的少年。 <br>

            我问长空中的英魂：你们相信？ <br>

            英魂带着笑意离去：相信，希望还在。 <br>

</small><hr>
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