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msgctl

SYNOPSIS

int msgctl(int msqid,int cmd,struct msqid_ds *buf);

PARAMETERS

msqid: [in] the message queue to manipulate.

cmd: [in] the operation to perform on the message queue.

buf: the interpretation of this parameter depends on cmd.

DESCRIPTION

Manipulates a message queue. cmd may be one of:

IPC_STAT

retreives some information on the queue.

IPC_SET

modify some operating parameters of the queue. buf points to a msqid_ds structure. The only modifiable parameters are: msg_perm.uid, msg_perm.gid, msg_perm.mode (only lowest 9 bits) and msg_qbytes. 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 msg_qbytes beyond the system limit of MSGMNB.

IPC_RMID

immediately destroys the message queue and awake all sleaping reader and writer processes.

RETURN VALUE

On success zero is returned. On error -1 is returned and errno is set to one of the following values:

• EACCESS: the caller tried IPC_STAT but does not have read permission on the queue.
• EIDRM: the queue is already removed.
• EINVAL: invalid value for cmd or msqid.
• EPERM: the taks tried an operation for which it does not have the necessary privileges.
• EFAULT.

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