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Linux系统调用

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<TITLE>Syscall specifications of Linux - msgctl</TITLE>
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<H2><A NAME="SEC74" HREF="syscalls_toc.html#SEC74" tppabs="http://personal.xfol.com/%7erezaie/syscall/syscalls_toc.html#SEC74">msgctl</A></H2>
<P>
<H3>SYNOPSIS</H3>
<P>
<CODE>int msgctl(int <VAR>msqid</VAR>,int <VAR>cmd</VAR>,struct msqid_ds *<VAR>buf</VAR>);</CODE>
<P>
<H3>PARAMETERS</H3>
<P>
<VAR>msqid</VAR>: [in] the message queue to manipulate.
<P>
<VAR>cmd</VAR>: [in] the operation to perform on the message queue.
<P>
<VAR>buf</VAR>: the interpretation of this parameter depends on <VAR>cmd</VAR>.
<P>
<H3>DESCRIPTION</H3>
<P>
Manipulates a message queue. <VAR>cmd</VAR> may be one of:
<P>
<DL COMPACT>
<DT><CODE>IPC_STAT</CODE>
<DD>retreives some information on the queue.
<P>
<DT><CODE>IPC_SET</CODE>
<DD>modify some operating parameters of the queue. <VAR>buf</VAR> points to a
<CODE>msqid_ds</CODE> structure. The only modifiable parameters are:
<CODE>msg_perm.uid</CODE>, <CODE>msg_perm.gid</CODE>, <CODE>msg_perm.mode</CODE> (only
lowest 9 bits) and <CODE>msg_qbytes</CODE>. The calling task uid must be one
of the creator uid or the owner uid of the queue or the superuser uid.
Only the superuser may rise <CODE>msg_qbytes</CODE> beyond the system limit of
<CODE>MSGMNB</CODE>.
<P>
<DT><CODE>IPC_RMID</CODE>
<DD>immediately destroys the message queue and awake all sleaping reader and
writer processes.
</DL>
<P>
<H3>RETURN VALUE</H3>
<P>
On success zero is returned. On error -1 is returned and <CODE>errno</CODE> is
set to one of the following values:
<P>
<UL>
<LI><CODE>EACCESS</CODE>: the caller tried <CODE>IPC_STAT</CODE> but does not have
read permission on the queue.
<LI><CODE>EIDRM</CODE>: the queue is already removed.
<LI><CODE>EINVAL</CODE>: invalid value for <VAR>cmd</VAR> or <VAR>msqid</VAR>.
<LI><CODE>EPERM</CODE>: the taks tried an operation for which it does not
have the necessary privileges. 
<LI><CODE>EFAULT</CODE>.
</UL>
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