Linux System Call-msgget function details

Source: Internet
Author: User
Linux System Call-msgget function details-Linux general technology-Linux programming and kernel information, the following is a detailed description. Function Description:
Gets the ID of the Message Queue associated with a key. There are two scenarios in which a message queue is created:
1. If the key value is IPC_PRIVATE.
2. Alternatively, the key value is not IPC_PRIVATE, and the message queue corresponding to the key does not exist, and IPC_CREAT is specified in the flag.

If a new message queue is created, the msqid_ds data structure associated with it is initialized as follows:
Msg_perm.cuid and msg_perm.uid are valid user IDs of callers;
Msg_perm.cgid and msg_perm.gid are valid user group logos of callers;
Msg_perm.mode: The minimum nine digits are set to the lowest nine digits of msgflg;
Msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime are set to 0;
Msg_ctime is set to the current time;
Msg_qbytes is set to MSGMNB.

# Include
# Include
# Include

Int msgget (key_t key, int msgflg );

Key: The key associated with the message queue.
Msgflg: indicates the establishment and access permissions of message queues.

Return description:
If the message queue is successfully executed, the Message Queue id value is returned. -1 is returned for failure, and errno is set to one of the following values
EACCES: the specified message queue already exists, but the calling process does not have the permission to access it and does not have the CAP_IPC_OWNER permission.
EEXIST: The Message Queue specified by the key already exists, while IPC_CREAT and IPC_EXCL are both specified in msgflg.
ENOENT: The Message Queue specified by the key does not exist. The IPC_CREAT flag is not specified in msgflg.
ENOMEM: A Message Queue needs to be created, but the memory is insufficient.
ENOSPC: A Message Queue needs to be created, but the system limit has been reached.
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