From 3ff5588d3f8afad65ded52ac0e4191462fe034cb Mon Sep 17 00:00:00 2001
From: Alan Stern <stern@rowland.harvard.edu>
Date: Tue, 7 Sep 2010 11:44:01 -0400
Subject: [PATCH] [SCSI] sd: improve logic and efficiecy of media-change
 detection

This patch (as1415) improves the formerly incomprehensible logic in
sd_media_changed() (the current code refers to "changed" as a state,
whereas in fact it is a relation between two states).  It also adds a
big comment so that everyone can understand what is really going on.

The patch also improves efficiency by not reporting a media change
when no medium was ever present.  If no medium was present the last
time we checked and there's still no medium, it's not necessary to
tell the caller that a change occurred.  Doing so merely causes the
caller to attempt to revalidate a non-existent disk, which is a waste
of time.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>
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