From 86ee8ba64daf5e09a71e4c216f81fae8d1c937f3 Mon Sep 17 00:00:00 2001
From: Philippe De Muyter <phdm@macqel.be>
Date: Wed, 27 Feb 2013 17:05:16 -0800
Subject: block/partition/msdos: detect AIX formatted disks even without 55aa

AIX formatted disks do not always have the MSDOS 55aa signature.
This happens e.g. for unbootable AIX disks.

Up to now, such disks were not recognized as AIX disks, because of the
missing 55aa.  Fix that by inverting the two tests.  Let's first
check for the AIX magic strings, and only if that fails check for
the MSDOS magic word.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Cc: Andreas Mohr <andi@lisas.de>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Olaf Hering <olh@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/block/partitions/msdos.c b/block/partitions/msdos.c
index 8752a5d..7681cd2 100644
--- a/block/partitions/msdos.c
+++ b/block/partitions/msdos.c
@@ -455,14 +455,19 @@ int msdos_partition(struct parsed_partitions *state)
 	data = read_part_sector(state, 0, &sect);
 	if (!data)
 		return -1;
-	if (!msdos_magic_present(data + 510)) {
+
+	/*
+	 * Note order! (some AIX disks, e.g. unbootable kind,
+	 * have no MSDOS 55aa)
+	 */
+	if (aix_magic_present(state, data)) {
 		put_dev_sector(sect);
+		strlcat(state->pp_buf, " [AIX]", PAGE_SIZE);
 		return 0;
 	}
 
-	if (aix_magic_present(state, data)) {
+	if (!msdos_magic_present(data + 510)) {
 		put_dev_sector(sect);
-		strlcat(state->pp_buf, " [AIX]", PAGE_SIZE);
 		return 0;
 	}
 
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