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.Dd November 29, 2005
.Dt MQ_SETATTR 2
.Os
.Sh NAME
.Nm mq_setattr
.Nd "set message queue attributes (REALTIME)"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In mqueue.h
.Ft int
.Fo mq_setattr
.Fa "mqd_t mqdes"
.Fa "struct mq_attr *restrict mqstat"
.Fa "struct mq_attr *restrict omqstat"
.Fc
.Sh DESCRIPTION
The
.Fn mq_setattr
system call sets attributes associated with the open message queue description
referenced by the message queue descriptor specified by
.Fa mqdes .
The message queue attributes corresponding to the following members defined
in the
.Vt mq_attr
structure will be set to the specified values upon successful completion of
.Fn mq_setattr :
.Bl -tag -width ".Va mq_flags"
.It Va mq_flags
The value of this member is zero or
.Dv O_NONBLOCK .
.El
.Pp
The values of the
.Va mq_maxmsg , mq_msgsize ,
and
.Va mq_curmsgs
members of the
.Vt mq_attr
structure are ignored by
.Fn mq_setattr .
.Sh RETURN VALUES
Upon successful completion, the function returns a value of zero and the
attributes of the message queue will have been changed as specified.
.Pp
Otherwise, the message queue attributes are unchanged, and the function
returns a value of \-1 and sets the global variable
.Va errno
to indicate the error.
.Sh ERRORS
The
.Fn mq_setattr
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa mqdes
argument is not a valid message queue descriptor.
.El
.Sh SEE ALSO
.Xr mq_open 2 ,
.Xr mq_send 2 ,
.Xr mq_timedsend 2
.Sh STANDARDS
The
.Fn mq_setattr
system call conforms to
.St -p1003.1-2004 .
.Sh HISTORY
Support for
.Tn POSIX
message queues first appeared in
.Fx 7.0 .