linux-kernel - Re: NFS Bug in 2.6.23 ? SOLUTION ?

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Date:	Mon, 19 Nov 2007 08:41:13 +0100
From:	Gianluca Alberici <gianluca@...networks.biz>
To:	Trond Myklebust <trond.myklebust@....uio.no>
CC:	linux-kernel@...r.kernel.org
Subject: Re: NFS Bug in 2.6.23 ? SOLUTION ?

Trond Myklebust wrote:

>On Sun, 2007-11-18 at 19:44 +0100, Gianluca Alberici wrote:
>  
>
>>Trond,
>>
>>The problem is in nfs_mountpoint_timeout. After this time 
>>dentry_delete(/,4) removes the mountpoint, then it is very difficult to 
>>automount (at least with CFSD), one has got to try 2 or three times 
>>cd'ing into the mount point. Applications wont ever had the chance to 
>>autoremount (ENOTDIR).
>>    
>>
>
>Sounds like CFSD has a bug w.r.t. what fsid it returns to the client.
>
>  
>
Very likely...and im sure its not the one...unfortunately CFSD has not 
been mantained for a very long time (i think 2001)
but in the end up to 2.6.20 has done its job very well...

>>I have some questions:
>>
>>- nfs_mountpoint_timeout seems to be set in sysctl.c even if nfsv4 is 
>>not. Is this correct ? I've read somewhere that it was introduced for v4.
>>    
>>
>
>Wrong. It applies to all mountpoint crossing. If the server tells us
>that the fsid has changed, then we create a new mountpoint.
>
>  
>
>>- Why this sysctl is not registered in my 2.6.20 kernel where it should 
>>be registered ?
>>    
>>
>
>Prior to 2.6.21-rc5, we had a bug in register_nfs_fs() whereby it failed
>to register the sysctl table unless you enabled NFSv4.
>
>  
>
>>- Why this parameter has not a 'disabled' value (i mean kind of -1) ?
>>    
>>
>
>Why should it? 
>
For backwards compatilbility ? Couldn't be useful to have the chance to 
make NFS client act
exactly as it always did, at least as an option, to talk to 'ancient NFS 
servers' ?

Or at least have the chance to set this timeout to infinity ?

Many thanks for your time, best regards,

Gianluca

>The current behaviour is quite correct. If you cross a
>mountpoint, then you should remount in order to ensure that the inode
>numbers remain unique per-filesystem.
>  
>
>We know that some ancient NFS servers had problems returning the correct
>fsid in readdirplus replies, so 2.6.22 adds support to disable
>readdirplus calls via a 'nordirplus' mount option. I guess you could try
>that...
>
>Trond
>
>-
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