mq_setattr.2 (2010 09)

mq_setattr(2) mq_setattr(2)

NAME

mq_setattr - set the blocking status of a message queue associated with a descriptor

SYNOPSIS

#include <sys/mqueue.h>

int mq_setattr(mqd_t mqdes,

const struct mq_attr *mqstat,

struct mq_attr *omqstat,

);

DESCRIPTION

The mq_setattr() system call changes the blocking status of a message queue associated with the

descriptor, mqdes. The blocking status that is modiﬁed is per message queue descriptor and another

open descriptor for the same message queue can have a different blocking status.

The argument mqstat , points to an

mq_attr

structure that speciﬁes the blocking status desired. More

speciﬁcally, if the

O_NONBLOCK bit in the mq_ﬂags ﬁeld of the

mq_attr structure is set, the descriptor

is marked as non-blocking. Otherwise it is marked as blocking.

If omstat is non-NULL,

mq_setattr() will store in the

mq_attr structure referenced by omqstat, the

previous message queue attributes and the queue blocking status associated with this mqdes. The values

returned are the same as would be returned by a call to

mq_getattr().

To use this function, link in the realtime library by specifying

-lrt on the compiler or linker command

line.

RETURN VALUE

mq_setattr() returns the following values:

0 Successful completion.

-1 Failure. errno is set to indicate the error.

ERRORS

mq_setattr() fails, errno is set to one of the following values:

[EBADF] mqdes is not a valid message queue descriptor.

[EINVAL] mqstat does not point to a valid

mq_attr structure, or omqstat is non-NULL and

does not point to a valid

mq_attr structure.

[ENOSYS]

mq_setattr() is not supported by the implementation.