linux-kernel - Re: Revoking filesystems [was Re: Sysfs attributes racing with unregistration]

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Date:	Thu, 5 Jan 2012 07:32:33 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Theodore Ts'o <tytso@....edu>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: Revoking filesystems [was Re: Sysfs attributes racing with
 unregistration]

Hello,

On Thu, Jan 05, 2012 at 10:13:31AM -0500, Alan Stern wrote:
> I don't have a clear idea of what's involved (in particular, how to go
> from a block_device structure to a mounted filesystem).  But the place
> to do it would probably be block/genhd.c:invalidate_partition().  Ted
> can tell you if there's a better alternative.
> 
> > Do you know how hard it is to detect at mount time if a block device
> > might be hot-plugable?  We can always use a mount option here and
> > make userspace figure it out, but being to have a good default would
> > be nice.
> 
> I don't think it's possible to tell if a device is hot-unpluggable.  
> For example, the device itself might not be removable from its parent, 
> but the parent might be hot-unpluggable.  You'll probably have to 
> assume that every device can potentially be unplugged, one way or 
> another.
> 
> Also, even devices that aren't hot-unpluggable can fail.  The end 
> result should be pretty much the same.

Ummm.... I could be missing something but filesystems need to be able
to deal with partial device failures (ie. some block can't be read)
and hot-unplug or handling full failure is a logical extension of
that.  That's how it already works, so I don't really think that is a
particularly good application for the revoke mechanism.

Thanks.

-- 
tejun
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