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MSGCTL
!!!MSGCTL
NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
NOTES
CONFORMING TO
SEE ALSO
----
!!NAME


msgctl - message control operations
!!SYNOPSIS


__# include
____int msgctl ( int__ ''msqid''__, int__ ''cmd''__, struct msqid_ds *__''buf'' __)__
!!DESCRIPTION


The function performs the control operation specified by
''cmd'' on the message queue with identifier
''msqid''. Legal values for ''cmd'' are:


__IPC_STAT__


Copy info from the message queue data structure into the
structure pointed to by ''buf''. The user must have read
access privileges on the message queue.


__IPC_SET__


Write the values of some members of the __msqid_ds__
structure pointed to by ''buf'' to the message queue data
structure, updating also its __msg_ctime__ member.
Considered members from the user supplied __struct
msqid_ds__ pointed to by ''buf'' are


__     msg_perm.uid
msg_perm.gid
msg_perm.mode__  /* only lowest 9-bits */
__     msg_qbytes
__The calling process effective user-ID must be one among super-user, creator or owner of the message queue. Only the super-user can raise the __msg_qbytes__ value beyond the system parameter __MSGMNB__.


__IPC_RMID__


Remove immediately the message queue and its data structures
awakening all waiting reader and writer processes (with an
error return and __errno__ set to __EIDRM__). The
calling process effective user-ID must be one among
super-user, creator or owner of the message
queue.
!!RETURN VALUE


If successful, the return value will be __0__, otherwise
__-1__ with __errno__ indicating the
error.
!!ERRORS


For a failing return, __errno__ will be set to one among
the following values:


__EACCES__


The argument ''cmd'' is equal to __IPC_STAT__ but the
calling process has no read access permissions on the
message queue ''msqid''.


__EFAULT__


The argument ''cmd'' has value __IPC_SET__ or
__IPC_STAT__ but the address pointed to by ''buf''
isn't accessible.


__EIDRM__


The message queue was removed.


__EINVAL__


Invalid value for ''cmd'' or ''msqid''.


__EPERM__


The argument ''cmd'' has value __IPC_SET__ or
__IPC_RMID__ but the calling process effective user-ID
has insufficient privileges to execute the command. Note
this is also the case of a non super-user process trying to
increase the __msg_qbytes__ value beyond the value
specified by the system parameter
__MSGMNB__.
!!NOTES


The __IPC_INFO__, __MSG_STAT__ and __MSG_INFO__
control calls are used by the ipcs(8) program to
provide information on allocated resources. In the future
these can be modified as needed or moved to a proc file
system interface.


Various fields in a ''struct msqid_ds'' were shorts under
Linux 2.2 and have become longs under Linux 2.4. To take
advantage of this, a recompilation under glibc-2.1.91 or
later should suffice. (The kernel distinguishes old and new
calls by a IPC_64 flag in ''cmd''.)
!!CONFORMING TO


SVr4, SVID. SVID does not document the EIDRM error
condition.
!!SEE ALSO


ipc(5), msgget(2), msgsnd(2),
msgrcv(2)
----

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Version 1, saved on Tuesday, June 4, 2002 12:23:43 am by "perry"

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