linux-kernel - Re: [PATCH] nfs-util: Add cache_flush in mountd UMNT procedure.

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Message-ID: <20120711140944.GB11432@fieldses.org>
Date:	Wed, 11 Jul 2012 10:09:44 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	SteveD@...hat.com, Trond.Myklebust@...app.com,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	Vivek Trivedi <vtrivedi018@...il.com>
Subject: Re: [PATCH] nfs-util: Add cache_flush in mountd UMNT procedure.

On Wed, Jul 11, 2012 at 01:10:53PM +0900, Namjae Jeon wrote:
> 2012/7/10, J. Bruce Fields <bfields@...ldses.org>:
> > On Sat, Jul 07, 2012 at 11:17:39PM -0400, Namjae Jeon wrote:
> >> For removing storage device - user needs to safely un-mount the device
> >> and then eject. But if 'EBUSY' occurs in umount then it will create
> >> confusion for the user as it will mean some I/O is in progress - and
> >> won't allow user to safely ejecting device.
> >
> Hi James.
> > The one drawback is that recovering from the cache flushes might be a
> > little expensive if you have a lot of exports in use.
> Good point. I will look for more there is the method flush only mount entry.

I don't think there's a good way to flush only one entry.

Also, this isn't going to help for NFSv4 since a v4 client won't do an
unmount call.

> > I'm curious, since you said this was for a usb disk: are users expected
> > to just unplug it (in which case--is it read only?) or do they have some
> > way of unmounting before they pull the plug?
> Users expected to unplug it on both read only and read/write.
> And there is no way that system be prepared to know about the
> intelligence when the user is going to unplug.
> if the user really want to detach the device safely. There is an
> option like the desktop PC - where, we can say - umount/eject the
> device. There is a proper user interface for safe removal.
> but they can not unplug safely if usb device is mounted with nfs
> because of this issue.

Ideal might be to get some way to notify nfsd when the device
diseappears or the filesystem wants to unmount.  I don't know how to do
that.

--b.
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