block: add GENHD_FL_NO_PART_SCAN

There are cases where suppressing partition scan is useful - e.g. for
lo devices and pseudo SATA devices which advertise to be a disk but
get upset on partition scan (some port multiplier control devices show
such behavior).

This patch adds GENHD_FL_NO_PART_SCAN which suppresses partition scan
regardless of the number of possible partitions.  disk_partitionable()
is renamed to disk_part_scan_enabled() as suppressing partition scan
doesn't imply the device can't be partitioned using
BLKPG_ADD/DEL_PARTITION calls from userland.  show_partition() now
directly tests disk_max_parts() to maintain backward-compatibility.

-v2: Updated to make it clear that only partition scan is suppressed
     not partitioning itself as suggested by Kay Sievers.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 02fa4697a0e5..6d18f3531f18 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -128,6 +128,7 @@ struct hd_struct {
 #define GENHD_FL_EXT_DEVT                       64 /* allow extended devt */
 #define GENHD_FL_NATIVE_CAPACITY                128
 #define GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE     256
+#define GENHD_FL_NO_PART_SCAN                   512
 
 enum {
         DISK_EVENT_MEDIA_CHANGE                 = 1 << 0, /* media changed */
@@ -234,9 +235,10 @@ static inline int disk_max_parts(struct gendisk *disk)
         return disk->minors;
 }
 
-static inline bool disk_partitionable(struct gendisk *disk)
+static inline bool disk_part_scan_enabled(struct gendisk *disk)
 {
-        return disk_max_parts(disk) > 1;
+        return disk_max_parts(disk) > 1 &&
+                !(disk->flags & GENHD_FL_NO_PART_SCAN);
 }
 
 static inline dev_t disk_devt(struct gendisk *disk)