msgctl.2

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)msgctl.2	8.1	9/11/90
.TH msgctl 2
.SH Name
msgctl \- message control operations
.SH Syntax
.nf
#include <\fIsys/types.h\fP>
#include <\fIsys/ipc.h\fP>
#include <\fIsys/msg.h\fP>
.PP
int msgctl (\fImsqid, cmd, buf\fP)
int \fImsqid, cmd\fP;
struct \fImsqid_ds, buf\fP;
.fi
.SH Description
.NXR "msgctl system call"
.NXR "msgctl system call" "msgget system call"
.NXR "msgctl system call" "msgsnd system call"
.NXR "message" "control operations"
The
.PN msgctl
system call
provides message control operations as specified by
.I cmd.
The following
.I cmds
are available:
.TP 15
IPC_STAT
Place the current value of each member
of the data structure associated with
.I msqid
into the structure pointed to by
.I buf.
The contents of this structure are defined in 
.MS intro 2 .
.TP 15
IPC_SET
Set the value of the following members of the data structure
associated with
.I msqid
to the corresponding value found in the structure
pointed to by
.IR buf :
.EX
msg_perm.uid
msg_perm.gid
msg_perm.mode	/* only low 9 bits */
msg_qbytes
.EE
.PP
This
.I cmd
can be executed only by a process that has an effective user ID
that is equal to superuser or the value of either
.I msg_perm.uid
or
.I msg_perm.cuid
in the data structure associated with
.IR msqid.
Only the superuser can raise the value of
.IR msg_qbytes.
.RE
.TP 15
IPC_RMID
Remove the message queue identifier specified by
.I msqid
from the system and destroy the message queue
and data structure associated with it. This command can only be executed
by a process that has an effective
user ID equal to either that of the superuser or to the value of
.I msg_perm.uid
in the data structure associated with
.IR msquid.
.SH Return Values
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned and
.I errno
is set to indicate the error.
.SH Diagnostics
The
.PN msgctl
system call
fails under the following conditions:
.TP 15
[EINVAL]
The
.I msqid
is not a valid message queue identifier.
.TP 15
[EINVAL]
The
.I cmd
is not a valid command.
.TP 15
[EACCES]
The
.I cmd
is equal to IPC_STAT
and read operation permission is denied to
the calling process.  For further information, see 
.MS intro 2 .
.TP 15
[EPERM]
The
.I cmd
is equal to IPC_RMID
or IPC_SET
and the effective user ID of the
calling process is not equal to that of
the superuser or to the value of
.I msg_perm.uid
in the data structure associated with
.IR msqid.
.TP 15
[EPERM]
The
.I cmd
is equal to IPC_SET,
an attempt is being made to increase to the
value of
.IR msg_qbytes,
and the effective user ID of the calling process is
not equal to that of superuser.
.TP 15
[EFAULT]
The
.I buf
points to an illegal address.
.SH See Also
msgget(2), msgop(2)