Re: [RFC][PATCH] Posix Message Queues

[Alan Cox]

On Llu, 2003-07-14 at 21:16, Manfred Spraul wrote:
> Hi Michal,
> 
> You've implemented mq_open() in user space by combining open()+ioctl() 
> syscalls. I think it's racy:
> 
> What if two processes call
> {
>     fd = mq_open("dummy",O_CREAT,0777,{.mq_maxmsg=10000});
>     mq_send = mq_send(fd,buf,10000,0);
> }
> 
> I think setting the queue options and creating a new queue must be 
> atomic, i.e. we need a new syscall.

O_EXCL lets you know if you are the real creator. That means you can
create it 000, fix it up, fchmod it and go