Technical Reference: Kernel and Subsystems, Volume 1

kmsgget Kernel Service

Purpose

Obtains a message queue identifier.

Syntax

#include <sys/types.h>
#include <sys/errno.h>
#include <sys/stat.h>
#include <sys/ipc.h>
#include <sys/msg.h>

int kmsgget ( key, msgflg, msqid) key_t key; int msgflg; int *msqid;

Parameters

key	Specifies either a value of IPC_PRIVATE or an IPC key constructed by the ftok subroutine (or a similar algorithm).
msgflg	Specifies that the msgflg parameter is constructed by logically ORing one or more of these values: IPC_CREAT Creates the data structure if it does not already exist. IPC_EXCL Causes the kmsgget kernel service to fail if IPC_CREAT is also set and the data structure already exists. S_IRUSR Permits the process that owns the data structure to read it. S_IWUSR Permits the process that owns the data structure to modify it. S_IRGRP Permits the process group associated with the data structure to read it. S_IWGRP Permits the process group associated with the data structure to modify it. S_IROTH Permits others to read the data structure. S_IWOTH Permits others to modify the data structure. The values that begin with S_I... are defined in the /usr/include/sys/stat.h file. They are a subset of the access permissions that apply to files.
msqid	A reference parameter where a valid message-queue ID is returned if the kmsgget kernel service is successful.

Description

The kmsgget kernel service returns the message-queue identifier specified by the msqid parameter associated with the specified key parameter value. The kmsgget kernel service provides the same functions for user-mode processes in kernel mode as the msgget subroutine performs for kernel processes or user-mode processes in user mode. The kmsgget service can be called by a user-mode process in kernel mode or by a kernel process. A kernel process can also call the msgget subroutine to provide the same function.

Execution Environment

The kmsgget kernel service can be called from the process environment only.

Return Values

0	Indicates successful completion. The msqid parameter is set to a valid message-queue identifier.

If the kmsgget kernel service fails, the msqid parameter is not valid and the return code is one of these four values:

EACCES	Indicates that a message queue ID exists for the key parameter but operation permission as specified by the msgflg parameter cannot be granted.
ENOENT	Indicates that a message queue ID does not exist for the key parameter and the IPC_CREAT command is not set.
ENOSPC	Indicates that a message queue ID is to be created but the system-imposed limit on the maximum number of allowed message queue IDs systemwide will be exceeded.
EEXIST	Indicates that a message queue ID exists for the value specified by the key parameter, and both the IPC_CREAT and IPC_EXCL commands are set.

Related Information

The msgget subroutine.

Message Queue Kernel Services and Understanding System Call Execution in AIX 5L Version 5.2 Kernel Extensions and Device Support Programming Concepts.