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 8752a5d265653a5a743c333c9c99bb259aca554b..7681cd295ab8e61e9350e52ae3e5fdaaeff119c2 100644 (file)
--- 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;
        }