MSGCTL(2) DOMAIN/IX Reference Manual (SYS5) MSGCTL(2)
NAME
msgctl - message control operations
USAGE
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
int msgctl (msqid, cmd, buf)
int msqid, cmd;
struct msqid_ds *buf;
DESCRIPTION
Msgctl provides a message control operations. Each opera-
tion is specified as a command cmd. The following commands
are available:
IPC_STAT Place the current value of each member of the
data structure associated with msqid into the
structure pointed to by buf. The contents of
this structure are defined in intro(2).
{READ}
IPC_SET Set the value of the following members of the
data structure associated with msqid to the
corresponding value found in the structure
pointed to by buf:
msg_perm.uid
msg_perm.gid
msg_perm.mode /* only low 9 bits */
msg_qbytes
This cmd can only be executed by a process
that has an effective user ID equal to either
that of super user or to the value of
msg_perm.uid in the data structure associated
with msqid. Only super user can raise the
value of msg_qbytes.
IPC_RMID Remove the message queue identifier specified
by msqid from the system and destroy the mes-
sage queue and data structure associated with
it. This cmd can only be executed by a pro-
cess that has an effective user ID equal to
either that of super user or to the value of
msg_perm.uid in the data structure associated
with msqid.
RETURN VALUE
Upon successful completion, msgctl returns a value of zero.
Otherwise, a value of -1 returns and errno is set to indi-
cate the error.
Printed 5/10/85 MSGCTL-1
MSGCTL(2) DOMAIN/IX Reference Manual (SYS5) MSGCTL(2)
ERRORS
Msgctl will fail if one or more of the following is true:
[EINVAL] Msqid is not a valid message queue identif-
ier.
[EINVAL] Cmd is not a valid command.
[EACCES] Cmd is equal to IPC_STAT and {READ} operation
permission is denied to the calling process
(see intro(2)).
[EPERM] Cmd is equal to IPC_RMID or IPC_SET. The
effective user ID of the calling process is
not equal to that of super user and it is not
equal to the value of msg_perm.uid in the
data structure associated with msqid.
[EPERM] Cmd is equal to IPC_SET, an attempt is being
made to increase to the value of msg_qbytes,
and the effective user ID of the calling pro-
cess is not equal to that of super user.
[EFAULT] Buf points to an illegal address.
RELATED INFORMATION
msgget(2), msgop(2)
MSGCTL-2 Printed 5/10/85