[ofa-general] Re: [PATCH v2 RESEND] rdma_cm: Add debugfs entries to monitor rdma_cm connections

[Moni Shoua]

Jason Gunthorpe wrote:
> On Wed, Jun 24, 2009 at 06:55:43PM +0300, Moni Shoua wrote:
> 
>> I believe that Jason and I still disagree but...
>     
>> Jason suggests that I implement this feature with netlink. This
>> approach might have an advantage but if I understand it right this
>> approach requires a patch also to some user application in order to
>> take advantage of this patch.
> 
> The kernel devs have made it clear that the preferred way to export
> this information is through netlink and/or a file in /proc/net/..
> 
> You never got an answer if /proc/net is truely discouraged or not.
As I remember I got opinions against /proc/net. I'm willing to move the 
virtual files to there if this is acceptable by all. Otherwise I will 
find myself in the same situation.

Roland, Sean - what do you think?

> 
> debugfs is completely useless because it cannot be used for actual
> end-user interrogation and the rules are it should not be used as a
> stable kernel-user interface. (ie is NOT a new dumping ground like
> /proc/ was)
> 
I don't know about that. The only fault of debugfs that I'm aware of is that distros don't mount it by default

>> Also, I think that there is a value for a virtual text file under
>> debugfs to monitor rdma_cm connections easily and without any other
>> special app besides 'cat' (just like in IPoIB).
> 
> If you have the netlink based program there really is no point in
> including something under debugfs. It is just bloat.
> 
>> Finally, this implementation doesn't contradict netlink
>> implementation in the future (and it won't be the first time).
> 
> As I said before, the stack has reached a level of maturity that new
> stuff going in should meaningfully 'move the ball forward' toward a
> mature and complete stack. In the context of state reporting that
> means a stable user interface that programs like lsof, netstat, etc,
> can rely upon.
> 
> Putting something under debugfs clearly does nothing to advance that
> goal.
> 
> Further, there is clearly alot of state information we should be
> exporting to userspace. RDMA-CM stuff is only a tiny portion. netlink
> is the kernel devs answer to all of this.
> 
I just want to emphasize that my goal for now is to supply a simple way to monitor rdma_cm connections, nothing more and nothing less. I don't want it  to depend on special userspace application and in fact, I just want to add a capability like we have in many other modules. This is a feature that we always get request for from customers and developers.