[PATCH] ratelimit printk messages from the audit system

[Eric Paris]

On Thu, 2008-01-24 at 13:08 -0500, Paul Moore wrote:
> On Thursday 24 January 2008 1:01:12 pm Eric Paris wrote:
> > On Thu, 2008-01-24 at 12:52 -0500, Paul Moore wrote:
> > > On Wednesday 23 January 2008 5:06:53 pm Linda Knippers wrote:
> > > > Eric Paris wrote:
> > > > > On Wed, 2008-01-23 at 16:05 -0500, Linda Knippers wrote:
> > > > >> This is unrelated to your patch but I think it would be nice
> > > > >> if audit_lost represented the number of audit messages lost
> > > > >> since the last time the message came out or the last time an
> > > > >> audit record came out. Today its a cumulative count since the
> > > > >> system was booted.  Is it too much overhead to zero it?
> > > > >
> > > > > Shouldn't be too much overhead, we are already on a
> > > > > slow/unlikely path. What's the benefit though?  Just don't want
> > > > > to have to do a subtraction?
> > > >
> > > > Well that, plus if the system is up for a long time (which we
> > > > hope) and the message is infrequent (which we also hope), then it
> > > > could take me a while to find the previous message in order to do
> > > > the subtraction.
> > > >
> > > > > If we are dropping the 'we lost some messages' message 0'ing
> > > > > the counter at that time would be a bad idea, certainly not
> > > > > unsolvable, but I don't see what it buys us.
> > > >
> > > > I wouldn't want to lose the message, just make it more useful. 
> > > > And if we zero it we don't have to worry about it wrapping.  As
> > > > it is now, its really just the count since the last time it
> > > > wrapped.
> > >
> > > I like Linda's idea of zero'ing the lost message counter once we
> > > are able to start sending messages again for all the reasons listed
> > > above. I haven't looked at the audit message sending code, but we
> > > are only talking about adding an extra conditional in the common
> > > case and in the worst case a conditional and an assignment. 
> > > Granted they are atomic ops, but everyone keeps telling me that
> > > atomic ops are pretty quick on almost all of the platforms that
> > > Linux supports ...
> >
> > Delivery of audit lost messages is through printk/syslog.  Assuming
> > we can assure it gets out of printk when we reset the counter we
> > can't assure that it made it to syslog.  That means we could lose
> > that message and have no record of it at all, nor any chance that in
> > the future it would get recorded that it was lost either.
> 
> That sort of begs the question - why do we even bother printing the 
> audit record lost message?
> 
>  :)

Hey its best effort what can I say.  At least without reseting the
counter we could realize one of them didn't make it sometime later.  Not
worth much I admit   :)
-Eric