Pull device-mapper changes for 3.4 from Alasdair Kergon:

 - Update thin provisioning to support read-only external snapshot
   origins and discards.
 - A new target, dm verity, for device content validation.
 - Mark dm uevent and dm raid as no-longer-experimental.
 - Miscellaneous other fixes and clean-ups.

* tag 'dm-3.4-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/agk/linux-dm: (27 commits)
  dm: add verity target
  dm bufio: prefetch
  dm thin: add pool target flags to control discard
  dm thin: support discards
  dm thin: prepare to support discard
  dm thin: use dm_target_offset
  dm thin: support read only external snapshot origins
  dm thin: relax hard limit on the maximum size of a metadata device
  dm persistent data: remove space map ref_count entries if redundant
  dm thin: commit outstanding data every second
  dm: reject trailing characters in sccanf input
  dm raid: handle failed devices during start up
  dm thin metadata: pass correct space map to dm_sm_root_size
  dm persistent data: remove redundant value_size arg from value_ptr
  dm mpath: detect invalid map_context
  dm: clear bi_end_io on remapping failure
  dm table: simplify call to free_devices
  dm thin: correct comments
  dm raid: no longer experimental
  dm uevent: no longer experimental
  ...