From: Peter Staubach <staubach@redhat.com>
Subject: Re: Can we flush directory data when the ctime changes?
Date: Tue, 08 Aug 2006 10:27:23 -0400
Message-ID: <44D89F4B.8080702@redhat.com>
References: <17624.15554.514216.623190@cse.unsw.edu.au>
	<1155045918.5673.26.camel@localhost>
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Cc: Neil Brown <neilb@suse.de>,
	Linux NFS Mailing List <nfs@lists.sourceforge.net>
To: Trond Myklebust <trond.myklebust@fys.uio.no>
In-Reply-To: <1155045918.5673.26.camel@localhost>
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Trond Myklebust wrote:
> On Tue, 2006-08-08 at 17:26 +1000, Neil Brown wrote:
>   
>> Hi,
>>  We have a scenario where readdir in the linux client gets confused by 
>> responses from a Netapp fileserver.
>>
>> What happens is that a readdir collects and caches the directory.
>> Then a subsequent readdir finds the first page is still in the cache
>> but the second page is missing.
>> The nfs client uses a cookie from the first page to request subsequent
>> entries and received a list of entries starting from the beginning of
>> the directory rather than from the point that it was up to.   It seems
>> that the cookies have changed.
>>
>> The GETATTR call that the client makes to validate the cache reports
>> that the mtime hasn't change, *but the ctime has*.
>>     
>
> Growl! If the directory contents change, then the mtime should too. Page
> 22 of RFC1813:
>
>         Mtime is the time when the file data was last modified.  Ctime
>         is the time when the attributes of the file were last changed.
>
> Directory cookies are not file or directory attributes!
>
> In addition, NFSv3 has the cookie verifier mechanism for the server to
> specifically inform the client that the cookies are invalid.
>
> IOW: this really needs to be fixed on the _server_. I'm not happy taking
> new patches that may cause the client GETATTR calls to skyrocket again.

This really does seem like a bug in the NetApp server.  With a change
like this, a simple chmod(2) could cause the client to invalidate its
caches...

       ps

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