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

[Jason Gunthorpe]

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.

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)

> 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.

Jason