xsh_chap02_10.html

posix标准英文,html格式

<p class="tent"><b>int</b></p>
</td>
<td align="left">
<p class="tent">Non-zero requests reuse of local addresses in <a href="../functions/bind.html"><i>bind</i>()</a>
(protocol-specific).</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">SO_SNDBUF</p>
</td>
<td align="left">
<p class="tent"><b>int</b></p>
</td>
<td align="left">
<p class="tent">Size of send buffer (in bytes).</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">SO_SNDLOWAT</p>
</td>
<td align="left">
<p class="tent"><b>int</b></p>
</td>
<td align="left">
<p class="tent">Minimum amount of data to send for output operations (in bytes).</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">SO_SNDTIMEO</p>
</td>
<td align="left">
<p class="tent"><b>struct timeval</b></p>
</td>
<td align="left">
<p class="tent">Timeout value for a socket send operation.</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">SO_TYPE</p>
</td>
<td align="left">
<p class="tent"><b>int</b></p>
</td>
<td align="left">
<p class="tent">Identify socket type ( <a href="../functions/getsockopt.html"><i>getsockopt</i>()</a> only).</p>
</td>
</tr>
</table>
</center>

<p>The SO_BROADCAST option requests permission to send broadcast datagrams on the socket. Support for SO_BROADCAST is
protocol-specific. The default for SO_BROADCAST is that the ability to send broadcast datagrams on a socket is disabled.</p>

<p>The SO_DEBUG option enables debugging in the underlying protocol modules. This can be useful for tracing the behavior of the
underlying protocol modules during normal system operation. The semantics of the debug reports are implementation-defined. The
default value for SO_DEBUG is for debugging to be turned off.</p>

<p>The SO_DONTROUTE option requests that outgoing messages bypass the standard routing facilities. The destination must be on a
directly-connected network, and messages are directed to the appropriate network interface according to the destination address. It
is protocol-specific whether this option has any effect and how the outgoing network interface is chosen. Support for this option
with each protocol is implementation-defined.</p>

<p>The SO_ERROR option is used only on <a href="../functions/getsockopt.html"><i>getsockopt</i>()</a>. When this option is
specified, <a href="../functions/getsockopt.html"><i>getsockopt</i>()</a> shall return any pending error on the socket and clear
the error status. It shall return a value of 0 if there is no pending error. SO_ERROR may be used to check for asynchronous errors
on connected connectionless-mode sockets or for other types of asynchronous errors. SO_ERROR has no default value.</p>

<p>The SO_KEEPALIVE option enables the periodic transmission of messages on a connected socket. The behavior of this option is
protocol-specific. The default value for SO_KEEPALIVE is zero, specifying that this capability is turned off.</p>

<p>The SO_LINGER option controls the action of the interface when unsent messages are queued on a socket and a <a href=
"../functions/close.html"><i>close</i>()</a> is performed. The details of this option are protocol-specific. The default value for
SO_LINGER is zero, or off, for the <i>l_onoff</i> element of the option value and zero seconds for the linger time specified by the
<i>l_linger</i> element.</p>

<p>The SO_OOBINLINE option is valid only on protocols that support out-of-band data. The SO_OOBINLINE option requests that
out-of-band data be placed in the normal data input queue as received; it is then accessible using the <a href=
"../functions/read.html"><i>read</i>()</a> or <a href="../functions/recv.html"><i>recv</i>()</a> functions without the MSG_OOB flag
set. The default for SO_OOBINLINE is off; that is, for out-of-band data not to be placed in the normal data input queue.</p>

<p>The SO_RCVBUF option requests that the buffer space allocated for receive operations on this socket be set to the value, in
bytes, of the option value. Applications may wish to increase buffer size for high volume connections, or may decrease buffer size
to limit the possible backlog of incoming data. The default value for the SO_RCVBUF option value is implementation-defined, and may
vary by protocol.</p>

<p>The maximum value for the option for a socket may be obtained by the use of the <a href=
"../functions/fpathconf.html"><i>fpathconf</i>()</a> function, using the value _PC_SOCK_MAXBUF.</p>

<p>The SO_RCVLOWAT option sets the minimum number of bytes to process for socket input operations. In general, receive calls block
until any (non-zero) amount of data is received, then return the smaller of the amount available or the amount requested. The
default value for SO_RCVLOWAT is 1, and does not affect the general case. If SO_RCVLOWAT is set to a larger value, blocking receive
calls normally wait until they have received the smaller of the low water mark value or the requested amount. Receive calls may
still return less than the low water mark if an error occurs, a signal is caught, or the type of data next in the receive queue is
different from that returned (for example, out-of-band data). As mentioned previously, the default value for SO_RCVLOWAT is 1 byte.
It is implementation-defined whether the SO_RCVLOWAT option can be set.</p>

<p>The SO_RCVTIMEO option is an option to set a timeout value for input operations. It accepts a <b>timeval</b> structure with the
number of seconds and microseconds specifying the limit on how long to wait for an input operation to complete. If a receive
operation has blocked for this much time without receiving additional data, it shall return with a partial count or <i>errno</i>
shall be set to [EWOULDBLOCK] if no data were received. The default for this option is the value zero, which indicates that a
receive operation will not time out. It is implementation-defined whether the SO_RCVTIMEO option can be set.</p>

<p>The SO_REUSEADDR option indicates that the rules used in validating addresses supplied in a <a href=
"../functions/bind.html"><i>bind</i>()</a> should allow reuse of local addresses. Operation of this option is protocol-specific.
The default value for SO_REUSEADDR is off; that is, reuse of local addresses is not permitted.</p>

<p>The SO_SNDBUF option requests that the buffer space allocated for send operations on this socket be set to the value, in bytes,
of the option value. The default value for the SO_SNDBUF option value is implementation-defined, and may vary by protocol. The
maximum value for the option for a socket may be obtained by the use of the <a href=
"../functions/fpathconf.html"><i>fpathconf</i>()</a> function, using the value _PC_SOCK_MAXBUF.</p>

<p>The SO_SNDLOWAT option sets the minimum number of bytes to process for socket output operations. Most output operations process
all of the data supplied by the call, delivering data to the protocol for transmission and blocking as necessary for flow control.
Non-blocking output operations process as much data as permitted subject to flow control without blocking, but process no data if
flow control does not allow the smaller of the send low water mark value or the entire request to be processed. A <a href=
"../functions/select.html"><i>select</i>()</a> operation testing the ability to write to a socket shall return true only if the
send low water mark could be processed. The default value for SO_SNDLOWAT is implementation-defined and protocol-specific. It is
implementation-defined whether the SO_SNDLOWAT option can be set.</p>

<p>The SO_SNDTIMEO option is an option to set a timeout value for the amount of time that an output function shall block because
flow control prevents data from being sent. As noted in <a href="#tagtcjh_2">Socket-Level Options</a> , the option value is a
<b>timeval</b> structure with the number of seconds and microseconds specifying the limit on how long to wait for an output
operation to complete. If a send operation has blocked for this much time, it shall return with a partial count or <i>errno</i> set
to [EWOULDBLOCK] if no data were sent. The default for this option is the value zero, which indicates that a send operation will
not time out. It is implementation-defined whether the SO_SNDTIMEO option can be set.</p>

<p>The SO_TYPE option is used only on <a href="../functions/getsockopt.html"><i>getsockopt</i>()</a>. When this option is
specified, <a href="../functions/getsockopt.html"><i>getsockopt</i>()</a> shall return the type of the socket (for example,
SOCK_STREAM). This option is useful to servers that inherit sockets on start-up. SO_TYPE has no default value.</p>

<h4><a name="tag_02_10_17">  2.10.17 </a>Use of Sockets for Local UNIX Connections</h4>

<p>Support for UNIX domain sockets is mandatory.</p>

<p>UNIX domain sockets provide process-to-process communication in a single system.</p>

<h5><a name="tag_02_10_17_01"></a>Headers</h5>

<p>The symbolic constant AF_UNIX defined in the <a href="../basedefs/sys/socket.h.html"><i>&lt;sys/socket.h&gt;</i></a> header is
used to identify the UNIX domain address family. The <a href="../basedefs/sys/un.h.html"><i>&lt;sys/un.h&gt;</i></a> header
contains other definitions used in connection with UNIX domain sockets. See the Base Definitions volume of
IEEE&nbsp;Std&nbsp;1003.1-2001, <a href="../basedefs/xbd_chap13.html#tag_13">Chapter 13, Headers</a>.</p>

<p>The <b>sockaddr_storage</b> structure defined in <a href="../basedefs/sys/socket.h.html"><i>&lt;sys/socket.h&gt;</i></a> shall
be large enough to accommodate a <b>sockaddr_un</b> structure (see the <a href=
"../basedefs/sys/un.h.html"><i>&lt;sys/un.h&gt;</i></a> header defined in the Base Definitions volume of
IEEE&nbsp;Std&nbsp;1003.1-2001, <a href="../basedefs/xbd_chap13.html#tag_13">Chapter 13, Headers</a>) and shall be aligned at an
appropriate boundary so that pointers to it can be cast as pointers to <b>sockaddr_un</b> structures and used to access the fields
of those structures without alignment problems. When a <b>sockaddr_storage</b> structure is cast as a <b>sockaddr_un</b> structure,
the <i>ss_family</i> field maps onto the <i>sun_family</i> field.</p>

<h4><a name="tag_02_10_18">  2.10.18 </a>Use of Sockets over Internet Protocols</h4>

<p>When a socket is created in the Internet family with a protocol value of zero, the implementation shall use the protocol listed
below for the type of socket created.</p>

<dl compact>
<dt>SOCK_STREAM</dt>

<dd>IPPROTO_TCP.</dd>

<dt>SOCK_DGRAM</dt>

<dd>IPPROTO_UDP.</dd>

<dt>SOCK_RAW</dt>

<dd><sup>[<a href="javascript:open_code('RS')">RS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
IPPROTO_RAW. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>SOCK_SEQPACKET</dt>

<dd>Unspecified.</dd>
</dl>

<p><sup>[<a href="javascript:open_code('RS')">RS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> A
raw interface to IP is available by creating an Internet socket of type SOCK_RAW. The default protocol for type SOCK_RAW shall be
identified in the IP header with the value IPPROTO_RAW. Applications should not use the default protocol when creating a socket
with type SOCK_RAW, but should identify a specific protocol by value. The ICMP control protocol is accessible from a raw socket by
specifying a value of IPPROTO_ICMP for protocol. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>

<h4><a name="tag_02_10_19">  2.10.19 </a>Use of Sockets over Internet Protocols Based on IPv4</h4>

<p>Support for sockets over Internet protocols based on IPv4 is mandatory.</p>

<h5><a name="tag_02_10_19_01"></a>Headers</h5>

<p>The symbolic constant AF_INET defined in the <a href="../basedefs/sys/socket.h.html"><i>&lt;sys/socket.h&gt;</i></a> header is
used to identify the IPv4 Internet address family. The <a href="../basedefs/netinet/in.h.html"><i>&lt;netinet/in.h&gt;</i></a>
header contains other definitions used in connection with IPv4 Internet sockets. See the Base Definitions volume of
IEEE&nbsp;Std&nbsp;1003.1-2001, <a href="../basedefs/xbd_chap13.html#tag_13">Chapter 13, Headers</a>.</p>

<p>The <b>sockaddr_storage</b> structure defined in <a href="../basedefs/sys/socket.h.html"><i>&lt;sys/socket.h&gt;</i></a> shall
be large enough to accommodate a <b>sockaddr_in</b> structure (see the <a href=
"../basedefs/netinet/in.h.html"><i>&lt;netinet/in.h&gt;</i></a> header defined in the Base Definitions volume of
IEEE&nbsp;Std&nbsp;1003.1-2001, <a href="../basedefs/xbd_chap13.html#tag_13">Chapter 13, Headers</a>) and shall be aligned at an
appropriate boundary so that pointers to it can be cast as pointers to <b>sockaddr_in</b> structures and used to access the fields
of those structures without alignment problems. When a <b>sockaddr_storage</b> structure is cast as a <b>sockaddr_in</b> structure,
the <i>ss_family</i> field maps onto the <i>sin_family</i> field.</p>

<h4><a name="tag_02_10_20">  2.10.20 </a>Use of Sockets over Internet Protocols Based on IPv6</h4>

<p><sup>[<a href="javascript:open_code('IP6')">IP6</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
This section describes extensions to support sockets over Internet protocols based on IPv6. This functionality is dependent on
support of the IPV6 option (and the rest of this section is not further marked for this option). <img src="../images/opt-end.gif"
alt="[Option End]" border="0"></p>

<p>To enable smooth transition from IPv4 to IPv6, the features defined in this section may, in certain circumstances, also be used
in connection with IPv4; see <a href="#tag_02_10_20_02">Compatibility with IPv4</a>.</p>

<h5><a name="tag_02_10_20_01"></a>Addressing</h5>

<p>IPv6 overcomes the addressing limitations of previous versions by using 128-bit addresses instead of 32-bit addresses. The IPv6
address architecture is described in RFC&nbsp;2373.</p>

<p>There are three kinds of IPv6 address:</p>