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mq_setattr (3)
  • mq_setattr (2) ( FreeBSD man: Системные вызовы )
  • mq_setattr (3) ( Solaris man: Библиотечные вызовы )
  • >> mq_setattr (3) ( Linux man: Библиотечные вызовы )
  • mq_setattr (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.  

    SEE ALSO

    mq_close(3), mq_notify(3), mq_open(3), mq_receive(3), mq_send(3), mq_unlink(3), mq_overview(7)  

    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/.


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    RETURN VALUE
    ERRORS
    CONFORMING TO
    NOTES
    SEE ALSO
    COLOPHON


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