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>

4 files changed, 8 insertions, 6 deletions

diff --git a/block/genhd.c b/block/genhd.c
index 5cb51c55f6d8..2429ecbbd97d 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -536,7 +536,7 @@ void register_disk(struct gendisk *disk)
         disk->slave_dir = kobject_create_and_add("slaves", &ddev->kobj);
 
         /* No minors to use for partitions */
-        if (!disk_partitionable(disk))
+        if (!disk_part_scan_enabled(disk))
                 goto exit;
 
         /* No such device (e.g., media were just removed) */
@@ -841,7 +841,7 @@ static int show_partition(struct seq_file *seqf, void *v)
         char buf[BDEVNAME_SIZE];
 
         /* Don't show non-partitionable removeable devices or empty devices */
-        if (!get_capacity(sgp) || (!disk_partitionable(sgp) &&
+        if (!get_capacity(sgp) || (!disk_max_parts(sgp) &&
                                    (sgp->flags & GENHD_FL_REMOVABLE)))
                 return 0;
         if (sgp->flags & GENHD_FL_SUPPRESS_PARTITION_INFO)
diff --git a/block/ioctl.c b/block/ioctl.c
index 1124cd297263..5c74efc01903 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -101,7 +101,7 @@ static int blkdev_reread_part(struct block_device *bdev)
         struct gendisk *disk = bdev->bd_disk;
         int res;
 
-        if (!disk_partitionable(disk) || bdev != bdev->bd_contains)
+        if (!disk_part_scan_enabled(disk) || bdev != bdev->bd_contains)
                 return -EINVAL;
         if (!capable(CAP_SYS_ADMIN))
                 return -EACCES;
diff --git a/fs/block_dev.c b/fs/block_dev.c
index ff77262e887c..0bed0d4588dd 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -971,7 +971,7 @@ static void flush_disk(struct block_device *bdev, bool kill_dirty)
 
         if (!bdev->bd_disk)
                 return;
-        if (disk_partitionable(bdev->bd_disk))
+        if (disk_part_scan_enabled(bdev->bd_disk))
                 bdev->bd_invalidated = 1;
 }
 
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)