[PATCH] block/partition/msdos: detect AIX formatted disks even without 55aa

[PATCH] block/partition/msdos: detect AIX formatted disks even without 55aa

[Philippe De Muyter]

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>
---
 block/partitions/msdos.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/partitions/msdos.c b/block/partitions/msdos.c
index 8752a5d..4b31ed7 100644
--- a/block/partitions/msdos.c
+++ b/block/partitions/msdos.c
@@ -455,14 +455,15 @@ int msdos_partition(struct parsed_partitions *state)
 	data = read_part_sector(state, 0, &sect);
 	if (!data)
 		return -1;
-	if (!msdos_magic_present(data + 510)) {
+
+	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;
 	}
 
-- 
1.7.1

Re: [PATCH] block/partition/msdos: detect AIX formatted disks even without 55aa

[Andreas Mohr]

Hi,

IMHO that patch would better have a small but important one-liner comment
(one cannot rely on people always making use of SCM history functionality,
thereby this would be at risk of getting reversed accidentally eventually).

E.g.

/* Note order! (some AIX disks, e.g. unbootable kind, have no MSDOS 55aa) */

	if (aix_magic_present(state, data)) {
.
.
.


Apart from that: nice compat catch!

HTH,

Andreas Mohr

-- 
GNU/Linux. It's not the software that's free, it's you.

[PATCH v2] block/partition/msdos: detect AIX formatted disks even without 55aa

[Philippe De Muyter]

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>
---
 block/partitions/msdos.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

v2: add a comment to avoid accidental removal of the tests order
    (suggested by Andreas Mohr <andi@lisas.de>)

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;
 	}
 
-- 
1.7.1