Re: Should exportfs/mountd cope with case-insensitive directory names.

[NeilBrown <neilb@suse.de>]

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On Thu, 3 Apr 2014 13:24:31 -0400 "J. Bruce Fields" <bfields@fieldses.org>
wrote:

> On Thu, Apr 03, 2014 at 01:16:25PM -0400, J. Bruce Fields wrote:
> > In the presence of bind mounts it's definitely possible for two
> > different paths to reach the same directory.
> > 
> > I don't know if that's actually a problem here....
> 
> Without testing: if we've got the same filesystem mounted at /foo/bar
> and /foo/baz, but only export /foo/bar, will this change make that
> export show up at /foo/baz as well?
> 
> (Since we'll now consider /foo/bar and /foo/baz to match where
> previously they didn't?)

Good question.  I should test, but I suspect "yes".  I'm not really happy
about that.

Maybe we could use name_to_handle_at().  That returns the mnt_id
which is different for different bind mounts.
So if the mnt_id and the handle are the same, it is the same directory.  If
not, then not.

I did worry a bit about all the extra stat calls, but as you say: they are
cached so it shouldn't be a big problem.

It would  make sense to stat (or name_to_handle_at) the name from the kernel
just once, then compare the value against everything in the export table.

We could possible store handles in the export table, but then we would need
to check for changes to mountinfo (I think 'poll' can do that) and clear out
the cache whenever a mount changes.

I might play with some code if I find time...

Thanks,
NeilBrown

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