【学习随手记】POSIX消息队列执行报Permission denied的问题。

最近学习UNIX环境网络编程POSIX消息队列的时候发现一个问题，在mq_open的时候总会报Permission denied的错误。

查看mq_overview后才得以解决。

mq_overview原文描述如下：

Mounting the message queue file system
       On Linux, message queues are created in a virtual file system.   (Other
       implementations  may  also  provide such a feature, but the details are
       likely to differ.)  This file system can be mounted (by the  superuser)
       using the following commands:

           # mkdir /dev/mqueue
           # mount -t mqueue none /dev/mqueue

       The sticky bit is automatically enabled on the mount directory.

       After  the file system has been mounted, the message queues on the sys‐
       tem can be viewed and manipulated using the commands usually  used  for
       files (e.g., ls(1) and rm(1)).

创建MQ的代码如下：

#include <unpipc.h>

int
main(int argc, char **argv)
{
    int c, flags;
    mqd_t mqd;

    flags = O_RDWR | O_CREAT;

    while ((c = Getopt(argc, argv, "e")) != -1)
    {
        switch (c) 
        {
        case 'e':
            flags |= O_EXCL;
            break;
        }
    }

    if (optind != argc - 1)
        err_quit("usage: mqcreate [-e] <name>");

    mqd = Mq_open(argv[optind], flags, 0777, NULL);
    Mq_close(mqd);

    exit(0);
}