rbd: enable extended devt in single-major mode
If single-major device number allocation scheme is turned on, instead
of reserving 256 minors per device, which imposes a limit of 4096
images mapped at once, reserve 16 minors per device and enable extended
devt feature. This results in a theoretical limit of 65536 images
mapped at once, and still allows to have more than 15 partititions:
partitions starting with 16th are mapped under major 259 (Block
Extended Major):
$ rbd showmapped
id pool image snap device
0 rbd b5 - /dev/rbd0 # no partitions
1 rbd b2 - /dev/rbd1 # 40 partitions
2 rbd b3 - /dev/rbd2 # 2 partitions
$ cat /proc/partitions
251 0 1024 rbd0
251 16 1024 rbd1
251 17 0 rbd1p1
251 18 0 rbd1p2
...
251 30 0 rbd1p14
251 31 0 rbd1p15
259 0 0 rbd1p16
259 1 0 rbd1p17
...
259 23 0 rbd1p39
259 24 0 rbd1p40
251 32 1024 rbd2
251 33 0 rbd2p1
251 34 0 rbd2p2
(major 251 was assigned dynamically at module load time)
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index e5ddcb5..11ae4c1 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -91,7 +91,8 @@
#define RBD_DRV_NAME "rbd"
-#define RBD_PART_SHIFT 8
+#define RBD_MINORS_PER_MAJOR 256
+#define RBD_SINGLE_MAJOR_PART_SHIFT 4
#define RBD_SNAP_DEV_NAME_PREFIX "snap_"
#define RBD_MAX_SNAP_NAME_LEN \
@@ -415,12 +416,12 @@
static int rbd_dev_id_to_minor(int dev_id)
{
- return dev_id << RBD_PART_SHIFT;
+ return dev_id << RBD_SINGLE_MAJOR_PART_SHIFT;
}
static int minor_to_rbd_dev_id(int minor)
{
- return minor >> RBD_PART_SHIFT;
+ return minor >> RBD_SINGLE_MAJOR_PART_SHIFT;
}
static BUS_ATTR(add, S_IWUSR, NULL, rbd_add);
@@ -3434,7 +3435,9 @@
u64 segment_size;
/* create gendisk info */
- disk = alloc_disk(1 << RBD_PART_SHIFT);
+ disk = alloc_disk(single_major ?
+ (1 << RBD_SINGLE_MAJOR_PART_SHIFT) :
+ RBD_MINORS_PER_MAJOR);
if (!disk)
return -ENOMEM;
@@ -3442,6 +3445,8 @@
rbd_dev->dev_id);
disk->major = rbd_dev->major;
disk->first_minor = rbd_dev->minor;
+ if (single_major)
+ disk->flags |= GENHD_FL_EXT_DEVT;
disk->fops = &rbd_bd_ops;
disk->private_data = rbd_dev;
