Re: POSIX message queues

[Manfred Spraul]

Krzysztof Benedyczak wrote:

> Hello
>
> For quite a long time there are two implementations of posix mqueues
> around. I think it is time to decide at least if both of them have
> chances of beeing applied to official kernel. So I would
> like to know if Peter Waechtler's implementations is considered superior
> or there is possible some discussion and further work on our
> implementation is worthwhile.
>  
Could you try to merge your work? Or at least: look at each others work. 
For example Krzysiek/Michal's implementation has wake-one semantics, 
which is IMHO a requirement.

Krzysiek: What is MQ_IOC_CLOSE? It looks like a stale ioctl. Please 
remove such code from the patch.

The last time I looked at your patch I noticed a race between creation and setting queue attributes. Did you fix that?


> There are a lot of differencies but if the most important one is use of
> ioctl vs syscalls it can be changed (in fact our implementation loong time
> ago used syscalls).
>  
I personally prefer syscalls, but that's just my personal preference. 
For example the notification info is a structure, and printing it to a 
text stream and then parsing it back again is just odd. And I don't see 
how you can fix the O_CREAT+unusual mq_maxmsg races.
Why do you check against MQ_MAXMSG in user space? That's wrong. The 
kernel will reject too large limits, probably depending on 
/proc/sys/kern/ configuration. Checking in user space doesn't gain 
anything, except that you loose the ability for runtime changes.
Please reuse the load_msg/store_msg functions instead of a 
kmalloc(arg.msg_len, GFP_KERNEL) + copy_from_user. kmalloc(16384) is not 
reliable - it needs a continuous block of 16 kB, and after a long 
runtime, the memory is so fragmented that such memory may not exist. 
This is a known problem for x86_64: They would prefer to have 16 kB 
blocks for the stack, but this results in errors during stress testing.
proc_write_max_queues: off-by-one error. tmp[16] ='\0' overwrites the stack.
Is is necessary that the filesystem is visible to user space? What about 
chroot environments, or environments with per-user mount points. I don't 
like the dependence on /proc/mounts.

> In another words: is our implementation in the position
> of NGPT or better? ;-)
>  
Do you know if Ulrich Drepper has looked at your user space libraries? 
Your code must end up in glibc, and he's the maintainer.

--
   Manfred

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