msgctl(2) [opensolaris man page]
msgctl(2) System Calls msgctl(2) NAME
msgctl - message control operations SYNOPSIS
#include <sys/msg.h> int msgctl(int msqid, int cmd, struct msqid_ds *buf); DESCRIPTION
The msgctl() function provides a variety of message control operations as specified by cmd. The following cmds 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). 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 /* access permission bits only */ msg_qbytes This command can be executed only by a process that has either the {PRIV_IPC_OWNER} privilege or an effective user ID equal to the value of msg_perm.cuid or msg_perm.uid in the data structure associated with msqid. Only a process with the {PRIV_SYS_IPC_CONFIG} privilege can raise the value of msg_qbytes. IPC_RMID Remove the message queue identifier specified by msqid from the system and destroy the message queue and data structure associ- ated with it. This cmd can only be executed by a process that has an effective user ID either with appropriate privileges asserted in the effective set or equal to the value of msg_perm.cuid or msg_perm.uid in the data structure associated with msqid. The buf argument is ignored. RETURN VALUES
Upon successful completion, msgctl() returns 0. Otherwise, it returns -1 and sets errno to indicate the error. ERRORS
The msgctl() function will fail if: EACCES The cmd argument is IPC_STAT and operation permission is denied to the calling process (see Intro(2)). EFAULT The buf argument points to an illegal address. EINVAL The msqid argument is not a valid message queue identifier; or the cmd argument is not a valid command or is IPC_SET and msg_perm.uid or msg_perm.gid is not valid. EOVERFLOW The cmd argument is IPC_STAT and uid or gid is too large to be stored in the structure pointed to by buf. EPERM The cmd argument is IPC_RMID or IPC_SET, the {PRIV_SYS_IPC_OWNER} privilege is not asserted in the effective set of the call- ing process, and is not equal to the value of msg_perm.cuid or msg_perm.uid in the data structure associated with msqid. The cmd argument is IPC_SET, an attempt is being made to increase to the value of msg_qbytes, and the {PRIV_SYS_IPC_CONFIG} privilege is not asserted in the effective set of the calling process. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
Intro(2), msgget(2), msgrcv(2), msgsnd(2), attributes(5), privileges(5), standards(5) SunOS 5.11 22 Mar 2004 msgctl(2)
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msgctl(2) System Calls Manual msgctl(2) NAME
msgctl - Performs message control operations SYNOPSIS
#include <sys/msg.h> int msgctl( int msqid, int cmd, struct msqid_ds *buf); Application developers may want to specify #include statements for <sys/types.h> and <sys/ipc.h> before the one for <sys/msg.h> if programs are being developed for multiple platforms. The additional #include statements are not required on Tru64 UNIX systems or by ISO or X/Open standards, but may be required on other vendors' systems that conform to these standards. STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: msgctl(): XSH5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. PARAMETERS
Specifies the message queue ID. Specifies the type of command. The possible commands and the operations they perform are as follows: Queries the message queue ID by copying the contents of its associated data structure into the buf structure. The process must have manda- tory read access to the message queue with respect to all access control policies. Sets the message queue ID by copying values found in the buf structure into corresponding fields in the msqid_ds structure associated with the message queue ID. This operation is restricted. The effective user ID of the calling process must be equal to that of superuser or equal to the value of msg_perm.uid or msg_perm.cuid in the associated msqid_ds structure. Only superuser can raise the value of msg_qbytes. Removes the message queue ID and deallocates its associated msqid_ds structure. This operation is restricted. The effective user ID of the calling process must be equal to that of supe- ruser or equal to the value of msg_perm.uid or msg_perm.cuid in the associated msqid_ds structure. Points to a msqid_ds structure. This structure is used only with the IPC_STAT and IPC_SET commands. With IPC_STAT, the results of the query are copied to this structure. With IPC_SET, the values in this structure are used to set the corresponding fields in the msqid_ds structure associated with the message queue ID. In either case, the calling process must have allocated the structure before making the call. DESCRIPTION
The msgctl() function allows a process to query or set the contents of the msqid_ds structure associated with the specified message queue ID. It also allows a process to remove the message queue ID and its associated msqid_ds structure. The cmd value determines which opera- tion is performed. The IPC_SET command uses the user-supplied contents of the buf structure to set the following members of the msqid_ds structure associated with the message queue ID: The owner's user ID. The owner's group ID. The access modes for the queue. Only the low-order nine bits are set. The maximum number of bytes on the queue. The time of the last msgctl() operation that changed the structure. RETURN VALUES
Upon successful completion, msgctl( returns a value of 0 (zero). Otherwise, a value of -1 is returned and errno is set to indicate the error. ERRORS
The msgctl() function sets errno to the specified values for the following conditions: The cmd parameter is IPC_STAT, but the calling process does not have read permission. [Tru64 UNIX] The cmd parameter is IPC_STAT or IPC_SET, and an error occurred in accessing the buf structure. The msqid parameter is not a valid message queue ID, or the cmd parameter is not a valid command. The cmd parameter is equal to either IPC_RMID or IPC_SET, and the calling process does not have appropriate privilege. The cmd parameter is equal to IPC_SET, and an attempt is being made to increase the value of the msg_qbytes parameter when the calling process does not have the superuser privilege. RELATED INFORMATION
Functions: msgget(2), msgrcv(2), msgsnd(2) Data Structures: msqid_ds(4) Standards: standards(5) delim off msgctl(2)