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Message-ID: <20120105153233.GA11934@google.com>
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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