Re: [Xenomai] rtdm: minimal patch for sys_rtdm_recvmsg

[Jan Kiszka <jan.kiszka@web.de>]

On 2013-06-17 11:53, Manuel Huber wrote:
>> Please post patches inline, makes reviewing easier. The explanatory
>> part, like above, can be put after the "---" so that it won't show up in
>> the commit log.
> Oh, sorry; I forgot to send it plain-text...
> 
>> Let's just only copy back what can change, msg_flags and msg_controllen,
>> just like the kernel does.
> I have already implemented a version that does that, but then I looked at
> rt_udp_recvmsg implementation (stack/ipv4/udp/udp.c) and saw that it also
> sets msg_namelen field. This member will never be used in RTnet source
> code, so I think it should be copied back to the user...
> I mean it seems a little useless, because the user has to know the structur
> anyway; I'm not sure if code really relies on this behaviour....
> 
> So if it's necessary to write back the msg_namelen field, I would need 3
> __xn_put_user calls. I just though it looks ugly and probably does worse
> then a single __xn_copy_to_user call.
> 
> Do you think it's necessary to write back msg_namelen? Because otherwise
> I would definitely prefer using __xn_put_user twice.
> 

I think you stumbled over one of the very old and broken edges of RTnet.
It really makes no sense to copy namelen back. Rather, RTnet should
check msg_namelen before blindly copying the address into the msg_name
buffer.

Jan


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