[PATCH] bug fix: improve DOS partition table recognition

[Colin Watson]

* libparted/labels/dos.c (msdos_probe): Make Parted's partition-table
recognition code use the same technique that is used by the Linux
kernel and by util-linux's fdisk.  I.e., accept it whenever all four
boot indicators are 0 or 0x80, rather than using the FAT file system-
recognizing heuristic.
More analysis here:
  http://thread.gmane.org/gmane.comp.gnu.parted.devel/2142/focus=3D2154
Reported by David Bala=C5=BEic here:
  https://bugs.launchpad.net/ubuntu/+source/parted/+bug/232175
  http://thread.gmane.org/gmane.comp.gnu.parted.devel/2142
---
 libparted/labels/dos.c |   16 +++++++++-------
 1 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/libparted/labels/dos.c b/libparted/labels/dos.c
index e513a05..81d8600 100644
--- a/libparted/labels/dos.c
+++ b/libparted/labels/dos.c
@@ -192,14 +192,16 @@ msdos_probe (const PedDevice *dev)
 	if (PED_LE16_TO_CPU (part_table->magic) !=3D MSDOS_MAGIC)
 		goto probe_fail;

-	/* if this is a FAT fs, fail here.  Note that the Smart Boot Manager
-	 * Loader (SBML) signature indicates a partition table, not a file
-	 * system.
+	/* If this is a FAT fs, fail here.  Checking for the FAT signature
+	 * has some false positives; instead, do what the Linux kernel does
+	 * and ensure that each partition has a boot indicator that is
+	 * either 0 or 0x80.
 	 */
-	if ((!strncmp (part_table->boot_code + 0x36, "FAT", 3)
-	    && strncmp (part_table->boot_code + 0x40, "SBML", 4) !=3D 0)
-	    || !strncmp (part_table->boot_code + 0x52, "FAT", 3))
-		goto probe_fail;
+	for (i =3D 0; i < 4; i++) {
+		if (part_table->partitions[i].boot_ind !=3D 0
+		    && part_table->partitions[i].boot_ind !=3D 0x80)
+			goto probe_fail;
+	}

 	/* If this is a GPT disk, fail here */
 	for (i =3D 0; i < 4; i++) {
--
1.5.6.rc0.30.g51263