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From: Neil Brown <neilb@cse.unsw.edu.au>
To: Florian Weimer <fw@deneb.enyo.de>
Date: Wed, 7 Aug 2002 20:40:21 +1000
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Message-ID: <15696.63765.38094.618742@notabene.cse.unsw.edu.au>
Cc: linux-kernel@vger.kernel.org, gam3@acm.org
Subject: Re: Problems with NFS exports
In-Reply-To: message from Florian Weimer on Wednesday August 7
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On Wednesday August 7, fw@deneb.enyo.de wrote:
> Florian Weimer <fw@deneb.enyo.de> writes:
> 
> > I'm seeing weired errors with nfsctl():
> >
> > This works:
> >
> > nfsservctl(NFSCTL_EXPORT, "deneb.enyo.de", "/mnt/storage/2/backup/deneb/tmp", makedev(3, 66), ino 167772288, uid 65534, gid 65534) = 0
> >
> > But a subsequent call fails:
> >
> > nfsservctl(NFSCTL_EXPORT, "deneb.enyo.de", "/mnt/storage/2/backup/deneb", makedev(3, 66), ino 150995072, uid 65534, gid 65534) = -1 EINVAL (Invalid argument)
> >
> > I don't understand what makes the difference (the inode values are
> > correct).  This is kernel 2.4.18 with XFS support, and the directory
> > resides on an XFS file system.
> >
> > Any ideas?
> 
> (Full quote because of additional recipeint.)
> 
> It appears that a directory tree can only be exported once.  Is this
> intentional?  If yes, the following patch should be applied (to
> linux/fs/nfsd/export.c), so that the return value is more meaningful:

Probably better documentation in exports.5 would be just as useful.
And "BUSY" probably isn't correct ....
The rule is that you cannot export a directory and an ancestor of that
directory in the same filesystem.
/a/1 and /a/2 can both be exported, but not /a and /a/1.

Reason:  exporting "/a" means exporting that directoring and all
descendants of it in the same filesystem.
If you export /a with different flags than /a/1 it is ambiguous.

And personally, I doubt that there are very many situations where it
makes sense.

It would be possible to dis-ambiguate the ambiguity but it wouldn't be
very clean, and I really am not sure that it is worth the effort.

NeilBrown


> 
> --- export.c	2002/08/07 09:22:11	1.1
> +++ export.c	2002/08/07 09:22:28
> @@ -219,6 +219,7 @@
>  		goto finish;
>  	}
>  
> +	err = -EBUSY;
>  	if ((parent = exp_child(clp, dev, nd.dentry)) != NULL) {
>  		dprintk("exp_export: export not valid (Rule 3).\n");
>  		goto finish;
> 
> 
> After this change, the userspace tools can issue are more meaningful
> error message for this case.
> -
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