Проект OpenNet: MAN mq_getattr (3) Библиотечные вызовы (FreeBSD и Linux)

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mq_getattr (3)

mq_getattr (2) ( FreeBSD man: Системные вызовы )

mq_getattr (3) ( Solaris man: Библиотечные вызовы )

>> mq_getattr (3) ( Linux man: Библиотечные вызовы )

mq_getattr (3) ( POSIX man: Библиотечные вызовы )

NAME

mq_getattr, mq_setattr - get/set message queue attributes

SYNOPSIS

#include <mqueue.h>

mqd_t mq_getattr(mqd_t mqdes, struct mq_attr *attr);

mqd_t mq_setattr(mqd_t mqdes, struct mq_attr *newattr,
                 struct mq_attr *oldattr);

Link with -lrt.

DESCRIPTION

mq_getattr() and mq_setattr() respectively retrieve and modify attributes of the message queue referred to by the descriptor mqdes.

mq_getattr() returns an mq_attr structure in the buffer pointed by attr. This structure is defined as:


struct mq_attr {
    long mq_flags;       /* Flags: 0 or O_NONBLOCK */
    long mq_maxmsg;      /* Max. # of messages on queue */
    long mq_msgsize;     /* Max. message size (bytes) */
    long mq_curmsgs;     /* # of messages currently in queue */
};

The mq_flags field contains flags associated with the open message queue description. This field is initialized when the queue is created by mq_open(3). The only flag that can appear in this field is O_NONBLOCK.

The mq_maxmsg and mq_msgsize fields are set when the message queue is created by mq_open(3). The mq_maxmsg field is an upper limit on the number of messages that may be placed on the queue using mq_send(3). The mq_msgsize field is an upper limit on the size of messages that may be placed on the queue. Both of these fields must have a value greater than zero. Two /proc files that place ceilings on the values for these fields are described in mq_open(3).

The mq_curmsgs field returns the number of messages currently held in the queue.

mq_setattr() sets message queue attributes using information supplied in the mq_attr structure pointed to by newattr. The only attribute that can be modified is the setting of the O_NONBLOCK flag in mq_flags. The other fields in newattr are ignored. If the oldattr field is not NULL, then the buffer that it points to is used to return an mq_attr structure that contains the same information that is returned by mq_getattr().

RETURN VALUE

On success mq_getattr() and mq_setattr() return 0; on error, -1 is returned, with errno set to indicate the error.

ERRORS

EBADF: The descriptor specified in mqdes is invalid.
EINVAL: newattr->mq_flags contained set bits other than O_NONBLOCK.

CONFORMING TO

POSIX.1-2001.

NOTES

On Linux, mq_getattr() and mq_setattr() are library functions layered on top of the mq_getsetattr(2) system call.

COLOPHON

This page is part of release 3.14 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.