linux-kernel - Re: [RFC PATCH] nfs: Add NFS3PROC

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Message-ID: <CAKYAXd9-ubxP8iQqTWTG-34Vb_yrDU=9f9hsiRk4go_=QDfxmg@mail.gmail.com>
Date:	Tue, 26 Jun 2012 20:57:30 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	Fields James <bfields@...ldses.org>
Cc:	"Myklebust, Trond" <Trond.Myklebust@...app.com>,
	Morton Andrew <akpm@...ux-foundation.org>,
	Harrosh Boaz <bharrosh@...asas.com>,
	"<linux-nfs@...r.kernel.org>" <linux-nfs@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Vivek Trivedi <t.vivek@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: Re: [RFC PATCH] nfs: Add NFS3PROC_UMOUNT procedure.

2012/6/26, Fields James <bfields@...ldses.org>:
> On Tue, Jun 26, 2012 at 02:51:52PM +0900, Namjae Jeon wrote:
>> 2012/6/25, Fields James <bfields@...ldses.org>:
>> > On Sun, Jun 24, 2012 at 02:12:49PM +0900, Namjae Jeon wrote:
>> >> 2012/6/24, Fields James <bfields@...ldses.org>:
>> >> > On Sat, Jun 23, 2012 at 11:57:10AM -0400, Fields James wrote:
>> >> >> On Sat, Jun 23, 2012 at 03:52:20PM +0000, Myklebust, Trond wrote:
>> >> >> > The other objection is that NFSv3 already has a way to do this
>> >> >> > via
>> >> >> > the
>> >> >> > MOUNT protocol. We already call MOUNTPROC3_UMNT/MOUNTPROC_UMNT on
>> >> >> > unmount of a filesystem.
>> >> >> >
>> >> >> > The problem with this approach is that if the NFS client crashes
>> >> >> > before
>> >> >> > it can call this function, then the server never gets notified.
>> >> >> > That
>> >> >> > is
>> >> >> > a problem that your patch has too...
>> >> >>
>> >> >> Yes.  Could you instead work on describing *exactly* what the
>> >> >> original
>> >> >> problem was that prompted this?
>> >> >
>> >> > ("You" here meaning Namjae Jeon, of course).
>> >> >
>> >> > And note here we've all read the changelog, that's not what I'm
>> >> > asking
>> >> > for.
>> >> >
>> >> > I want to know the details of *your* specific case.  "I have X
>> >> > clients
>> >> > that I use for Y, periodically I want to unmount the exported
>> >> > filesystem
>> >> > to do Z, I tried doing W but it didn't work...".
>> >> As you remember, We discussed this
>> >> issue(http://www.spinics.net/lists/linux-nfs/msg29997.html) with you
>> >> before. you guided me to use exportfs -f call on nfs server.
>> >> It is hard to use this method on our system
>> >
>> > Why is it hard?
>> Two target are connected by only nfs.. we can't manually hand exportfs
>> -f..
>
> So how can you call umount?
I am currently checking two approaches.
1. Add flush cache code in current MOUNTPROC3_UMNT/MOUNTPROC_UMNT.
 -> I heard from Trond that there already are
MOUNTPROC3_UMNT/MOUNTPROC_UMNT. So I will try to fix this issue on
current protocols without many changes. It is not specification
violation.
2. Check your suggestion.
-> I think that your suggestion is very good. it will cover device
unplug case(automount will try to umount about unplugged device) and
current busy umount issue.
If I have one concern, It need to change VFS code. I need your review
and Ack to commit if I post this patch.

Thanks.
>
> --b.
>
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