linux-ext4 - Re: [Gluster-devel] regressions due to 64-bit ext4 directory cookies

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Message-ID: <5151C33E.2070008@redhat.com>
Date:	Tue, 26 Mar 2013 10:48:14 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Bernd Schubert <bernd.schubert@...m.fraunhofer.de>
CC:	Anand Avati <anand.avati@...il.com>,
	"Theodore Ts'o" <tytso@....edu>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-nfs@...r.kernel.org, linux-ext4@...r.kernel.org,
	gluster-devel@...gnu.org
Subject: Re: [Gluster-devel] regressions due to 64-bit ext4 directory cookies

On 3/26/13 10:23 AM, Bernd Schubert wrote:
> Sorry for my late reply, I had been rather busy.
> 
> On 02/14/2013 01:05 AM, Anand Avati wrote:
>> On Wed, Feb 13, 2013 at 3:44 PM, Theodore Ts'o <tytso@....edu> wrote:
>>>
>>> I suspect this would seriously screw over Gluster, though, and this
>>> wouldn't be a solution for NFSv3, since NFS needs long-lived directory
>>> cookies, and not the short-lived cookies which is all POSIX/SuSv3
>>> guarantees.
>>>
>>
>> Actually this would work just fine with Gluster. Except in the case of
> 
> Would it really work perfectly? What about a server reboot in the middle of a readdir of a client?
> 
>> gluster-NFS, the native client is only acting like a router/proxy of
>> syscalls to the backend system. A directory opened by an application will
>> have a matching directory fd opened on ext4, and readdir from an app will
>> be translated into readdir on the matching fd on ext4. So the
>> app-on-glusterfs and glusterfsd-on-ext4 are essentially "moving in tandem".
>> As long as the offs^H^H^H^H cookies do not overflow in the transformation,
>> Gluster would not have a problem.
>>
>> However Gluster-NFS (and NFS in general, too) will break, as we
>> opendir/closedir potentially on every request.
> 
> We don't have reached a conclusion so far, do we? What about the
> ioctl approach, but a bit differently? Would it work to specify the
> allowed upper bits for ext4 (for example 16 additional bit) and the
> remaining part for gluster? One of the mails had the calculation
> formula:

I did throw together an ioctl patch last week, but I think Anand has a new
approach he's trying out which won't require ext4 code changes.  I'll let
him reply when he has a moment.  :)

-Eric

> final_d_off = (ext4_d_off * MAX_SERVERS) + server_idx
> 
> But what is the value of MAX_SERVERS?
> 
> 
> Cheers,
> Bernd
> 
> 
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