Re: [PATCH 1/2] vfs: make real_lookup do dentry revalidation with i_mutex held

[Ian Kent <raven@themaw.net>]

Sage Weil wrote:
>> Latest here works OK.
>>
>> I haven't finished checking yet but it looks like the patch below works 
>> OK. I started with a 2.6.29 build with your two patches but it was a 
>> little broken so I fell back to a Fedora 2.6.27 based kernel without the
>> two revalidate pacthes to debug it. So I still need to test the result 
>> against 2.6.29 again. I also don't have any real way to test for the three 
>> process race we discussed where the revalidate isn't followed by a 
>> ->lookup() but with both of your patches applied that shouldn't be a 
>> problem (as we discussed).
>>
>> I've not run checkpatch.pl against the patch either at this stage.
> 
> That's good news...

I'm still working on this too.
I have some pressing work so it may be a while before I'm totally happy
with the patch. Didn't you say you were expecting a 2.6.31 time frame
for this?

>  
>> There is a further issue and that is regarding the autofs module.
>>
>> I can't see updating autofs for this being practical (although I haven't 
>> actually looked yet). I suspect quite a bit of work would be needed. The 
>> fact is that autofs isn't used much any more and it really should be 
>> replaced with the autofs4 module at some point. But that's a fairly tricky 
>> exercise and will likely cause some user space breakage. It will require 
>> an updated module-init-tools to add "alais autofs4 autofs" for modprobe 
>> backward compatibility and will break for any explicit checks for the 
>> presence of the "autofs4" module.
> 
> Hmm.  Well, I assume autofs needs to work properly before this gets 
> changed, though, right?  Should I see what I can do with it?  I took a 
> quick look, and I don't think it will take too much to make it behave.  
> It looks like the main thing is to make the lookup call to try_fill_dentry 
> return any existing dentry in place of the one the vfs provides.

Yes, or be replaced by what is currently the autofs4 module. The autofs
v2 communication protocol surely can't be being used any more and the
autofs4 module supports versions 3, 4 and 5. In fact I received a mail
from HPA recently suggesting he supports doing this.

I had a quick look as well. I think you'll find it isn't quite as simple
as that. I'll have a closer look as soon as I get a chance.


Ian