[openib-general] Some Missing Features from mthca/user MAD access

[Michael S. Tsirkin]

Hello!
Quoting r. Roland Dreier (roland.list at gmail.com) "Re: [openib-general] Some Missing Features from mthca/user MAD access":
> > I wander if sysfs can be used for this somehow.
> 
> Not as we're discussing, because all the file operations are already set by
> the sysfs code.

I know, I was thinking about modifying the f_ops and calling
back to the original. A bit ugly ...

> However, is it so bad to make the existing cap_mask sysfs file writable and
> just say that userspace has to clean up if the SM exits uncleanly?
> 
>  - R.

Yes, I think it is. It involves catching CTRL-C in the application
and other such horror, and it never works 100%.
And what about running to opensms on the same HCA?
I think it is clearly kernel's job to handle synchronisation and do cleanups
when application exits.

After consideration, I think the proper way is add a reference count
and clean is_sm when it falls to 0.
This way runnning two opensms on the same HCA and two different
HCAs in the same subnet behaves the same.

To do this, I think either and ioctl on umad, or
a flag to open to set this bit is not too bad though.

MST