189 lines
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189 lines
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<title>shmat</title>
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<basefont size="3"> <a name="shmat"></a> <a name="tag_03_675"></a><!-- shmat -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_675_01"></a>NAME</h4>
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<blockquote>shmat - XSI shared memory attach operation</blockquote>
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<h4><a name="tag_03_675_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/sys/shm.h.html">sys/shm.h</a>><br>
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<br>
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void *shmat(int</tt> <i>shmid</i><tt>, const void *</tt><i>shmaddr</i><tt>, int</tt> <i>shmflg</i><tt>); <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_675_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>shmat</i>() function operates on XSI shared memory (see the Base Definitions volume of IEEE Std 1003.1-2001, <a
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href="../basedefs/xbd_chap03.html#tag_03_340">Section 3.340, Shared Memory Object</a>). It is unspecified whether this function
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interoperates with the realtime interprocess communication facilities defined in <a href=
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"xsh_chap02_08.html#tag_02_08"><i>Realtime</i></a> .</p>
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<p>The <i>shmat</i>() function attaches the shared memory segment associated with the shared memory identifier specified by
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<i>shmid</i> to the address space of the calling process. The segment is attached at the address specified by one of the following
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criteria:</p>
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<ul>
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<li>
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<p>If <i>shmaddr</i> is a null pointer, the segment is attached at the first available address as selected by the system.</p>
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</li>
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<li>
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<p>If <i>shmaddr</i> is not a null pointer and (<i>shmflg</i> &SHM_RND) is non-zero, the segment is attached at the address
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given by (<i>shmaddr</i> -((<i>uintptr_t</i>)<i>shmaddr</i> %SHMLBA)). The character <tt>'%'</tt> is the C-language remainder
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operator.</p>
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</li>
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<li>
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<p>If <i>shmaddr</i> is not a null pointer and (<i>shmflg</i> &SHM_RND) is 0, the segment is attached at the address given by
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<i>shmaddr</i>.</p>
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</li>
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<li>
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<p>The segment is attached for reading if (<i>shmflg</i> &SHM_RDONLY) is non-zero and the calling process has read permission;
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otherwise, if it is 0 and the calling process has read and write permission, the segment is attached for reading and writing.</p>
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</li>
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</ul>
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</blockquote>
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<h4><a name="tag_03_675_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>shmat</i>() shall increment the value of <i>shm_nattch</i> in the data structure associated with
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the shared memory ID of the attached shared memory segment and return the segment's start address.</p>
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<p>Otherwise, the shared memory segment shall not be attached, <i>shmat</i>() shall return -1, and <i>errno</i> shall be set to
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indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_675_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>shmat</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EACCES]</dt>
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<dd>Operation permission is denied to the calling process; see <a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess
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Communication</i></a> .</dd>
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<dt>[EINVAL]</dt>
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<dd>The value of <i>shmid</i> is not a valid shared memory identifier, the <i>shmaddr</i> is not a null pointer, and the value of
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(<i>shmaddr</i> -((<i>uintptr_t</i>)<i>shmaddr</i> %SHMLBA)) is an illegal address for attaching shared memory; or the
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<i>shmaddr</i> is not a null pointer, (<i>shmflg</i> &SHM_RND) is 0, and the value of <i>shmaddr</i> is an illegal address for
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attaching shared memory.</dd>
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<dt>[EMFILE]</dt>
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<dd>The number of shared memory segments attached to the calling process would exceed the system-imposed limit.</dd>
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<dt>[ENOMEM]</dt>
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<dd>The available data space is not large enough to accommodate the shared memory segment.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_675_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_675_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The POSIX Realtime Extension defines alternative interfaces for interprocess communication. Application developers who need to
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use IPC should design their applications so that modules using the IPC routines described in <a href=
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"xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> can be easily modified to use the alternative
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interfaces.</p>
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</blockquote>
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<h4><a name="tag_03_675_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_675_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_675_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> , <a href=
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"xsh_chap02_08.html#tag_02_08"><i>Realtime</i></a> , <a href="exec.html"><i><a href="../functions/exec.html">exec</a></i>()</a> ,
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<a href="exit.html"><i>exit</i>()</a> , <a href="fork.html"><i>fork</i>()</a> , <a href="shmctl.html"><i>shmctl</i>()</a> , <a
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href="shmdt.html"><i>shmdt</i>()</a> , <a href="shmget.html"><i>shmget</i>()</a> , <a href="shm_open.html"><i>shm_open</i>()</a> ,
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<a href="shm_unlink.html"><i>shm_unlink</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/sys/shm.h.html"><i><sys/shm.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_675_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 2. Derived from Issue 2 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_675_12"></a>Issue 5</h4>
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<blockquote>
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<p>Moved from SHARED MEMORY to BASE.</p>
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<p>The note about use of POSIX Realtime Extension IPC routines has been moved from FUTURE DIRECTIONS to a new APPLICATION USAGE
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section.</p>
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</blockquote>
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<h4><a name="tag_03_675_13"></a>Issue 6</h4>
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<blockquote>
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<p>The Open Group Corrigendum U021/13 is applied.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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