linux-ext4 - Re: regressions due to 64-bit ext4 directory cookies

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Message-ID: <20130213134033.GF14195@fieldses.org>
Date:	Wed, 13 Feb 2013 08:40:33 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	linux-ext4@...r.kernel.org, sandeen@...hat.com,
	Theodore Ts'o <tytso@....edu>,
	Bernd Schubert <bernd.schubert@...m.fraunhofer.de>,
	gluster-devel@...gnu.org
Subject: Re: regressions due to 64-bit ext4 directory cookies

On Tue, Feb 12, 2013 at 10:56:36PM -0800, Andreas Dilger wrote:
> On 2013-02-12, at 12:28 PM, J. Bruce Fields wrote:
> > 06effdbb49af5f6c "nfsd: vfs_llseek() with 32 or 64 bit offsets (hashes)"
> > and previous patches solved problems with hash collisions in large
> > directories by using 64- instead of 32- bit directory hashes in some
> > cases.  But it caused problems for users who assume directory offsets
> > are "small".  Two cases we've run across:
> > 
> > 	- older NFS clients: 64-bit cookies cause applications on
> >           many older clients to fail.
> > 	- gluster: gluster assumed that it could take the top bits of
> > 	  the offset for its own use.
> > 
> > In both cases we could argue we're in the right: the nfs protocol
> > defines cookies to be 64 bits, so clients should be prepared to handle them (remapping to smaller integers if necessary to placate 
> > applications using older system interfaces).
> 
> There appears to already be support for handling this for NFSv2
> clients, so it should be possible to have an NFS server mount
> option to set this for all clients:
> 
>         /* NFSv2 only supports 32 bit cookies */
>         if (rqstp->rq_vers > 2)
>                 may_flags |= NFSD_MAY_64BIT_COOKIE;
> 
> Alternately, this might be detected on a per-client basis by
> whitelist or blacklist if there is some way for the server to
> identify the client?

No, there isn't.

--b.
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