On Tue, 25 May 2004, Mike Waychison wrote:

> >
> >
> > The kernel never sees the cache.
> 
> This is further complicated as the kernel may call the readdir operation
> once per directory/map entry.
> 
> > The filesystem itself must be kept up to
> > date. Creating or removing directories during a readdir operation will
> > end in tears without a doubt.
> 
> - ->readdir itself is serialized on the parent inode's i_sem, as are all
> real_lookups (the call that makes the ->lookup callback).

Can be a problem if userspace expects to see the changes as they occur. 
Directory modification seems to cause opendir/readdir calls a bit of a 
problem for large directories. So scandir is needed instead.

> 
> >
> > But the real worry is the frequency with which this happens (as I
> > mentioned above).
> >
> > If we could just come up with a workable heuristic for map refresh we
> > would be OK.
> >
> 
> What is wrong with a cache of map keys in kernelspace? (Other than
> modifying the kernel module being a last resort)

Nothing.

This is, pretty much, the way the autofs v4 internal design is. 
It's probably not a good idea to make wholsale changes within a point 
release as well. 

Of course you are working on a different design for which this does not 
apply.

Mind, I'm likely to use a similar mechinism to fix the direct map and lazy 
mounting of multi-mount map in v4. So thanks for your fresh ideas.

Ian

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