Re: Can we flush directory data when the ctime changes?

[Peter Staubach <staubach@redhat.com>]

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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