block: implement CONFIG_DEBUG_BLOCK_EXT_DEVT

Extended devt introduces non-contiguos device numbers.  This patch
implements a debug option which forces most devt allocations to be
from the extended area and spreads them out.  This is enabled by
default if DEBUG_KERNEL is set and achieves...

1. Detects code paths in kernel or userland which expect predetermined
   consecutive device numbers.

2. When something goes wrong, avoid corruption as adding to the minor
   of earlier partition won't lead to the wrong but valid device.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index d1bb0e1d2d28..280d231a86ed 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -87,7 +87,13 @@ MODULE_ALIAS_SCSI_DEVICE(TYPE_MOD);
 MODULE_ALIAS_SCSI_DEVICE(TYPE_RBC);
 
 #define SD_PARTS        64
+
+#if !defined(CONFIG_DEBUG_BLOCK_EXT_DEVT)
 #define SD_MINORS       16
+#else
+#define SD_MINORS       1
+#endif
+
 #define SD_EXT_MINORS   (SD_PARTS - SD_MINORS)
 
 static int  sd_revalidate_disk(struct gendisk *);