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

[Ian Kent <raven@themaw.net>]

Sage Weil wrote:
> Hi Ian,
> 
> Have you had a chance to look at getting autofs4 lookup/revalidate 
> adjusted so that this real_lookup() fix[1] can go in?
> 
> Please let me know if there is anything I can do to help here.  If you're 
> still occupied, I'm happy to spin something up and send it your way... 
> just let me know.

Sorry, I haven't had time to do more on this.
There is also the issue of what to do about removing the autofs module
and renaming autofs4 to autofs, as this will break the autofs module.

I did start contacting people I think would want to know about this but
haven't gone further than an initial mail.

The other thing is that this patch was originally written quite a while
ago and, although it appears to work ok, I'm not sure it's quite what we
need.

Sorry for delaying you.

> 
> thanks-
> sage
> 
> 
> [1] http://marc.info/?l=linux-fsdevel&m=123749395609697&w=2
> 
> 
> On Fri, 3 Apr 2009, Ian Kent wrote:
> 
>> 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
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