From c666601a935b94cc0f3310339411b6940de751ba Mon Sep 17 00:00:00 2001
From: Josh Durgin <josh.durgin@dreamhost.com>
Date: Mon, 21 Nov 2011 17:11:12 -0800
Subject: [PATCH] rbd: move snap_rwsem to the device, rename to header_rwsem

A new temporary header is allocated each time the header changes, but
only the changed properties are copied over. We don't need a new
semaphore for each header update.

This addresses http://tracker.newdream.net/issues/2174

Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>
Reviewed-by: Alex Elder <elder@dreamhost.com>
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