Re: GFS2: Add LED support to GFS2

[Steven Whitehouse]

Hi,

On Wed, 2009-07-22 at 17:15 +0200, Andi Kleen wrote:
> > I did consider adding a feature to filter events on a per superblock
> > basis, but I decided against it in the end, as it seemed to be making
> > things too complicated (how should we specify the superblock? what
> > should the user interface be?).
> 
> Maybe key on mount points? (so passing vfsmnts) 
> 
That might be an issue though... there might be multiple super blocks
for a single mount point I think. We could try specifying devices
instead, but there might be multiple devices for one fs.

We can't hold refs to the vfsmnts since that would prevent umount, so
we'd need to get notified at umount time so that we can clear old
entries from the list. Matching on devices might just resolve this, but
its no good when device numbers are not stable, which would make
configuration a pain across a cluster.

What was a simple patch is rapidly becoming rather complicated :(

> So have some sysfs file where you echo mount points into to enable
> LED activity.
> 
Yes, the real issue is where to put them. I'm not sure if we can add
them into the LED sysfs files which where they probably ought to live.
Richard, what do you think?

> Ok that would be a little clumpsy for a "10 million bind mounts" case,
> but presumably that's very rare and they can still make it work.
> 
> -Andi
> 
I suspect that it will become less rare as time goes on.

So whilst I'd also like a more generic feature, I'm still not entirely
convinced that it would be a better solution yet,

Steve.


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