From: Alex Elder <elder@inktank.com>
Date: Fri, 16 Nov 2012 15:29:16 +0000 (-0600)
Subject: rbd: do not allow remove of mounted-on image
X-Git-Tag: v3.8-rc1~21^2~12
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=42382b709bd1d143b9f0fa93e0a3a1f2f4210707;p=pandora-kernel.git

rbd: do not allow remove of mounted-on image

There is no check in rbd_remove() to see if anybody holds open the
image being removed.  That's not cool.

Add a simple open count that goes up and down with opens and closes
(releases) of the device, and don't allow an rbd image to be removed
if the count is non-zero.

Protect the updates of the open count value with ctl_mutex to ensure
the underlying rbd device doesn't get removed while concurrently
being opened.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
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