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

Table 1. Parameters
Item	Description
`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 that is 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

Table 2. Return Values
Item	Description
`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:

Item	Description
`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 that is specified by the `key` parameter, and both the `IPC_CREAT` and `IPC_EXCL` commands are set.