ceph/ceph-client — pull request #3 by idryomov (2013-12-13 16:01:05+00:00)
Title: 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