linux-kernel - Re: Sysfs attributes racing with unregistration

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Message-ID: <Pine.LNX.4.44L0.1201041431160.1505-100000@iolanthe.rowland.org>
Date:	Wed, 4 Jan 2012 14:41:12 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	Tejun Heo <tj@...nel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: Sysfs attributes racing with unregistration

On Wed, 4 Jan 2012, Eric W. Biederman wrote:

> > Someone (I think Eric, right?) was trying to generalize the semantics
> > to vfs layer so that severance/revocation capability is generally
> > available.  IIRC, it didn't get through tho.
> 
> Unfortunately I didn't have time to complete the effort of those
> patches.  The approach was not fundamentally rejected but it needed a
> clear and convincing use case as well as some strong scrutiny.  But
> fundamentally finding a way to do that was seen as an interesting,
> if it could be solved without slowing down the existing cases.

Ted Ts'o has been talking about something similar but not the same -- a
way to revoke an entire filesystem.  For example, see commit
7c2e70879fc0949b4220ee61b7c4553f6976a94d (ext4: add ext4-specific
kludge to avoid an oops after the disk disappears).

The use case for that is obvious and widespread: Somebody yanks out a
USB drive without unmounting it first.

Alan Stern

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